Internet DRAFT - draft-irtf-icnrg-ccnxmessages
draft-irtf-icnrg-ccnxmessages
ICNRG M. Mosko
Internet-Draft PARC, Inc.
Intended status: Experimental I. Solis
Expires: July 28, 2019 LinkedIn
C. Wood
University of California Irvine
January 24, 2019
CCNx Messages in TLV Format
draft-irtf-icnrg-ccnxmessages-09
Abstract
This document specifies the encoding of CCNx messages in a TLV packet
format, including the TLV types used by each message element and the
encoding of each value. The semantics of CCNx messages follow the
encoding-independent CCNx Semantics specification.
This document is a product of the Information Centric Networking
research group (ICNRG).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on July 28, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Type-Length-Value (TLV) Packets . . . . . . . . . . . . . . . 5
3.1. Overall packet format . . . . . . . . . . . . . . . . . . 6
3.2. Fixed Headers . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Interest Fixed Header . . . . . . . . . . . . . . . . 8
3.2.1.1. Interest HopLimit . . . . . . . . . . . . . . . . 9
3.2.2. Content Object Fixed Header . . . . . . . . . . . . . 9
3.2.3. InterestReturn Fixed Header . . . . . . . . . . . . . 9
3.2.3.1. InterestReturn HopLimit . . . . . . . . . . . . . 10
3.2.3.2. InterestReturn Flags . . . . . . . . . . . . . . 10
3.2.3.3. Return Code . . . . . . . . . . . . . . . . . . . 10
3.3. Global Formats . . . . . . . . . . . . . . . . . . . . . 10
3.3.1. Pad . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.2. Organization Specific TLVs . . . . . . . . . . . . . 11
3.3.3. Hash Format . . . . . . . . . . . . . . . . . . . . . 11
3.3.4. Link . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4. Hop-by-hop TLV headers . . . . . . . . . . . . . . . . . 13
3.4.1. Interest Lifetime . . . . . . . . . . . . . . . . . . 14
3.4.2. Recommended Cache Time . . . . . . . . . . . . . . . 14
3.4.3. Message Hash . . . . . . . . . . . . . . . . . . . . 15
3.5. Top-Level Types . . . . . . . . . . . . . . . . . . . . . 16
3.6. CCNx Message . . . . . . . . . . . . . . . . . . . . . . 16
3.6.1. Name . . . . . . . . . . . . . . . . . . . . . . . . 17
3.6.1.1. Name Segments . . . . . . . . . . . . . . . . . . 18
3.6.1.2. Interest Payload ID . . . . . . . . . . . . . . . 19
3.6.2. Message TLVs . . . . . . . . . . . . . . . . . . . . 20
3.6.2.1. Interest Message TLVs . . . . . . . . . . . . . . 20
3.6.2.2. Content Object Message TLVs . . . . . . . . . . . 21
3.6.3. Payload . . . . . . . . . . . . . . . . . . . . . . . 23
3.6.4. Validation . . . . . . . . . . . . . . . . . . . . . 23
3.6.4.1. Validation Algorithm . . . . . . . . . . . . . . 23
3.6.4.2. Validation Payload . . . . . . . . . . . . . . . 29
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
4.1. Packet Type Registry . . . . . . . . . . . . . . . . . . 30
4.2. Interest Return Code Registry . . . . . . . . . . . . . . 30
4.3. Hop-by-Hop Type Registry . . . . . . . . . . . . . . . . 31
4.4. Top-Level Type Registry . . . . . . . . . . . . . . . . . 32
4.5. Name Segment Type Registry . . . . . . . . . . . . . . . 33
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4.6. Message Type Registry . . . . . . . . . . . . . . . . . . 34
4.7. Payload Type Registry . . . . . . . . . . . . . . . . . . 35
4.8. Validation Algorithm Type Registry . . . . . . . . . . . 36
4.9. Validation Dependent Data Type Registry . . . . . . . . . 37
4.10. Hash Function Type Registry . . . . . . . . . . . . . . . 39
5. Security Considerations . . . . . . . . . . . . . . . . . . . 40
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.1. Normative References . . . . . . . . . . . . . . . . . . 43
6.2. Informative References . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction
This document specifies a Type-Length-Value (TLV) packet format and
the TLV type and value encodings for CCNx messages. A full
description of the CCNx network protocol, providing an encoding-free
description of CCNx messages and message elements, may be found in
[CCNSemantics]. CCNx is a network protocol that uses a hierarchical
name to forward requests and to match responses to requests. It does
not use endpoint addresses, such as Internet Protocol. Restrictions
in a request can limit the response by the public key of the
response's signer or the cryptographic hash of the response. Every
CCNx forwarder along the path does the name matching and restriction
checking. The CCNx protocol fits within the broader framework of
Information Centric Networking (ICN) protocols [RFC7927].
This document describes a TLV scheme using a fixed 2-byte T and a
fixed 2-byte L field. The rational for this choice is described in
Section 5. Briefly, this choice avoids multiple encodings of the
same value (aliases) and reduces the work of a validator to ensure
compliance. Unlike some uses of TLV in networking, the each network
hop must evaluate the encoding, so even small validation latencies at
each hop could add up to a large overall forwarding delay. For very
small packets or low throughput links, where the extra bytes may
become a concern, one may use a TLV compression protocol, for example
[compress] and [CCNxz].
This document specifies:
o The TLV packet format.
o The overall packet format for CCNx messages.
o The TLV types used by CCNx messages.
o The encoding of values for each type.
o Top level types that exist at the outermost containment.
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o Interest TLVs that exist within Interest containment.
o Content Object TLVs that exist within Content Object containment.
This document is supplemented by this document:
o Message semantics: see [CCNSemantics] for the protocol operation
regarding Interest and Content Object, including the Interest
Return protocol.
o URI notation: see [CCNxURI] for the CCNx URI notation.
The type values in Section 4 represent the values in common usage
today. These values may change pending IANA assignments. All type
values are relative to their parent containers. For example, each
level of a nested TLV structure might define a "type = 1" with a
completely different meaning. In the following, we use the symbolic
names defined in that section.
Packets are represented as 32-bit wide words using ASCII art. Due to
the nested levels of TLV encoding and the presence of optional fields
and variable sizes, there is no concise way to represent all
possibilities. We use the convention that ASCII art fields enclosed
by vertical bars "|" represent exact bit widths. Fields with a
forward slash "/" are variable bit widths, which we typically pad out
to word alignment for picture readability.
The document represents the consensus of the ICN RG. It is the first
ICN protocol from the RG, created from the early CCNx protocol [nnc]
with significant revision and input from the ICN community and RG
members. The draft has received critical reading by several members
of the ICN community and the RG. The authors and RG chairs approve
of the contents. The document is sponsored under the IRTF and is not
issued by the IETF and is not an IETF standard. This is an
experimental protocol and may not be suitable for any specific
application and the specification may change in the future.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Definitions
o Name: A hierarchically structured variable length identifier. It
is an ordered list of path segments, which are variable length
octet strings. In human-readable form, it is represented in URI
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format as ccnx:/path/part. There is no host or query string. See
[CCNxURI] for complete details.
o Interest: A message requesting a Content Object with a matching
Name and other optional selectors to choose from multiple objects
with the same Name. Any Content Object with a Name and attributes
that matches the Name and optional selectors of the Interest is
said to satisfy the Interest.
o Content Object: A data object sent in response to an Interest
request. It has an optional Name and a content payload that are
bound together via cryptographic means.
3. Type-Length-Value (TLV) Packets
We use 16-bit Type and 16-bit Length fields to encode TLV based
packets. This provides 64K different possible types and value field
lengths of up to 64KiB. With 64K possible types at each level of TLV
encoding, there should be sufficient space for basic protocol types,
while also allowing ample room for experimentation, application use,
vendor extensions, and growth. This encoding does not allow for
jumbo packets beyond 64 KiB total length. If used on a media that
allows for jumbo frames, we suggest defining a media adapation
envelope that allows for multiple smaller frames.
There are several global TLV definitions that we reserve at all
hierarchical contexts. The TLV types in the range 0x1000 - 0x1FFF
are reserved for experimental use. The TLV type T_ORG is also
reserved for vendor extensions ( see Section 3.3.2). The TLV type
T_PAD is used to optionally pad a field out to some desired
alignment.
+--------+-------------------------+--------------------------------+
| Abbrev | Name | Description |
+--------+-------------------------+--------------------------------+
| T_ORG | Vendor Specific | Information specific to a |
| | Information (Section | vendor implementation (see |
| | 3.3.2) | below). |
| | | |
| T_PAD | Padding (Section 3.3.1) | Adds padding to a field (see |
| | | below). |
| | | |
| n/a | Experimental | Experimental use. |
+--------+-------------------------+--------------------------------+
Table 1: Reserved TLV Types
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1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Type | Length |
+---------------+---------------+---------------+---------------+
The Length field contains the length of the Value field in octets.
It does not include the length of the Type and Length fields. The
length MAY be zero.
TLV structures are nestable, allowing the Value field of one TLV
structure to contain additional TLV structures. The enclosing TLV
structure is called the container of the enclosed TLV.
Type values are context-dependent. Within a TLV container, one may
re-use previous type values for new context-dependent purposes.
3.1. Overall packet format
Each packet includes the 8 byte fixed header, described below,
followed by a set of TLV fields. These fields are optional hop-by-
hop headers and the Packet Payload.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| PacketType specific fields | HeaderLength |
+---------------+---------------+---------------+---------------+
/ Optional Hop-by-hop header TLVs /
+---------------+---------------+---------------+---------------+
/ PacketPayload TLVs /
+---------------+---------------+---------------+---------------+
The packet payload is a TLV encoding of the CCNx message, followed by
optional Validation TLVs.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| CCNx Message TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+---------------+
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This document describes the Version "1" TLV encoding.
After discarding the fixed and hop-by-hop headers the remaining
PacketPayload should be a valid protocol message. Therefore, the
PacketPayload always begins with 4 bytes of type-length that
specifies the protocol message (whether it is an Interest, Content
Object, or other message type) and its total length. The embedding
of a self-sufficient protocol data unit inside the fixed and hop-by-
hop headers allows a network stack to discard the headers and operate
only on the embedded message. It also de-couples the PacketType
field -- which specifies how to forward the packet -- from the
PacketPayload.
The range of bytes protected by the Validation includes the CCNx
Message and the ValidationAlgorithm.
The ContentObjectHash begins with the CCNx Message and ends at the
tail of the packet.
3.2. Fixed Headers
CCNx messages begin with an 8 byte fixed header (non-TLV format).
The HeaderLength field represents the combined length of the Fixed
and Hop-by-hop headers. The PacketLength field represents the entire
Packet length from the first byte of Version to the last byte of the
packet.
A specific PacketType may assign meaning to the "PacketType specific
fields," which are otherwise reserved. For the three defined
PacketTypes (Interest, ContentObject, and InterestReturn), we define
those values in this document.
The PacketPayload of a CCNx packet is the protocol message itself.
The Content Object Hash is computed over the PacketPayload only,
excluding the fixed and hop-by-hop headers as those might change from
hop to hop. Signed information or Similarity Hashes should not
include any of the fixed or hop-by-hop headers. The PacketPayload
should be self-sufficient in the event that the fixed and hop-by-hop
headers are removed.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| PacketType specific fields | HeaderLength |
+---------------+---------------+---------------+---------------+
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o Version: defines the version of the packet.
o HeaderLength: The length of the fixed header (8 bytes) and hop-by-
hop headers. The minimum value MUST be "8".
o PacketType: describes forwarder actions to take on the packet.
o PacketLength: Total octets of packet including all headers (fixed
header plus hop-by-hop headers) and protocol message.
o PacketType Specific Fields: specific PacketTypes define the use of
these bits.
The PacketType field indicates how the forwarder should process the
packet. A Request Packet (Interest) has PacketType PT_INTEREST, a
Response (Content Object) has PacketType PT_CONTENT, and an
InterestReturn has PacketType PT_RETURN.
HeaderLength is the number of octets from the start of the packet
(Version) to the end of the hop-by-hop headers. PacketLength is the
number of octets from the start of the packet to the end of the
packet. Both lengths have a minimum value of 8 (the fixed header
itself).
The PacketType specific fields are reserved bits whose use depends on
the PacketType. They are used for network-level signaling.
3.2.1. Interest Fixed Header
If the PacketType is PT_INTEREST, it indicates that the PacketPayload
should be processed as an Interest message. For this type of packet,
the Fixed Header includes a field for a HopLimit as well as Reserved
and Flags fields. The Reserved field MUST be set to 0 in an Interest
- this field will be set to a return code in the case of an Interest
Return. There are currently no Flags defined, so this field MUST be
set to 0.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PT_INTEREST | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | Reserved | Flags | HeaderLength |
+---------------+---------------+---------------+---------------+
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3.2.1.1. Interest HopLimit
For an Interest message, the HopLimit is a counter that is
decremented with each hop. It limits the distance an Interest may
travel on the network. The node originating the Interest MAY put in
any value - up to the maximum of 255. Each node that receives an
Interest with a HopLimit decrements the value upon reception. If the
value is 0 after the decrement, the Interest MUST NOT be forwarded
off the node.
It is an error to receive an Interest with a 0 hop-limit from a
remote node.
3.2.2. Content Object Fixed Header
If the PacketType is PT_CONTENT, it indicates that the PacketPayload
should be processed as a Content Object message. A Content Object
defines a Flags field, however there are currently no flags defined,
so the Flags field must be set to 0.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PT_CONTENT | PacketLength |
+---------------+---------------+---------------+---------------+
| Reserved | Flags | HeaderLength |
+---------------+---------------+---------------+---------------+
3.2.3. InterestReturn Fixed Header
If the PacketType is PT_RETURN, it indicates that the PacketPayload
should be processed as a returned Interest message. The only
difference between this InterestReturn message and the original
Interest is that the PacketType is changed to PT_RETURN and a
ReturnCode is is put into the ReturnCode field. All other fields are
unchanged from the Interest packet. The purpose of this encoding is
to prevent packet length changes so no additional bytes are needed to
return an Interest to the previous hop. See [CCNSemantics] for a
protocol description of this packet type.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PT_RETURN | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode | Flags | HeaderLength |
+---------------+---------------+---------------+---------------+
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3.2.3.1. InterestReturn HopLimit
This is the original Interest's HopLimit, as received. It is the
value before being decremented at the current node (i.e. the received
value).
3.2.3.2. InterestReturn Flags
These are the original Flags as set in the Interest.
3.2.3.3. Return Code
The numeric value assigned to the return types is defined below.
This value is set by the node creating the Interest Return.
A return code of "0" MUST NOT be used, as it indicates that the
returning system did not modify the Return Code field.
+-------------------------------------+-----------------------------+
| Type | Return Type |
+-------------------------------------+-----------------------------+
| T_RETURN_NO_ROUTE | No Route |
| | |
| T_RETURN_LIMIT_EXCEEDED | Hop Limit Exceeded |
| | |
| T_RETURN_NO_RESOURCES | No Resources |
| | |
| T_RETURN_PATH_ERROR | Path Error |
| | |
| T_RETURN_PROHIBITED | Prohibited |
| | |
| T_RETURN_CONGESTED | Congested |
| | |
| T_RETURN_MTU_TOO_LARGE | MTU too large |
| | |
| T_RETURN_UNSUPPORTED_HASH_RESTRICTI | Unsupported ContentObjectHa |
| ON | shRestriction |
| | |
| T_RETURN_MALFORMED_INTEREST | Malformed Interest |
+-------------------------------------+-----------------------------+
Table 2: Return Codes
3.3. Global Formats
This section defines global formats that may be nested within other
TLVs.
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3.3.1. Pad
The pad type may be used by protocols that prefer word-aligned data.
The size of the word may be defined by the protocol. Padding 4-byte
words, for example, would use a 1-byte, 2-byte, and 3-byte Length.
Padding 8-byte words would use a (0, 1, 2, 3, 5, 6, 7)-byte Length.
One MUST NOT pad inside a Name. Apart from that, a pad MAY be
inserted after any other TLV in the CCNx Message or in the Validation
Dependent Data In the remainder of this document, we will not show
optional pad TLVs.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PAD | Length |
+---------------+---------------+---------------+---------------+
/ variable length pad MUST be zeros /
+---------------+---------------+---------------+---------------+
3.3.2. Organization Specific TLVs
Organization specific TLVs (also known as Vendor TLVs) MUST use the
T_ORG type. The Length field is the length of the organization
specific information plus 3. The Value begins with the 3 byte
organization number derived from the last three digits of the IANA
Private Enterprise Numbers [EpriseNumbers], followed by the
organization specific information.
A T_ORG MAY be used as a path segment in a Name, in which case it is
a regular path segment and is part of the regular name matching.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_ORG | Length (3+value length) |
+---------------+---------------+---------------+---------------+
| PEN[0] | PEN[1] | PEN[2] | /
+---------------+---------------+---------------+ +
/ Vendor Specific Value /
+---------------+---------------+---------------+---------------+
3.3.3. Hash Format
Hash values are used in several fields throughout a packet. This TLV
encoding is commonly embedded inside those fields to specify the
specific hash function used and it's value. Note that the reserved
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TLV types are also reserved here for user-defined experimental
functions.
The LENGTH field of the hash value MUST be less than or equal to the
hash function length. If the LENGTH is less than the full length, it
is taken as the left LENGTH bytes of the hash function output. Only
specified truncations are allowed, not arbitrary truncations.
This nested format is used because it allows binary comparison of
hash values for certain fields without a router needing to understand
a new hash function. For example, the KeyIdRestriction is bit-wise
compared between an Interest's KeyIdRestriction field and a
ContentObject's KeyId field. This format means the outer field
values do not change with differing hash functions so a router can
still identify those fields and do a binary comparison of the hash
TLV without need to understand the specific hash used. An
alternative approach, such as using T_KEYID_SHA512-256, would require
each router keep an up-to-date parser and supporting user-defined
hash functions here would explode the parsing state-space.
A CCNx entity MUST support the hash type T_SHA-256. An entity MAY
support the remaining hash types.
+-----------+------------------------+
| Abbrev | Lengths (octets) |
+-----------+------------------------+
| T_SHA-256 | 32 |
| | |
| T_SHA-512 | 64, 32 |
| | |
| n/a | Experimental TLV types |
+-----------+------------------------+
Table 3: CCNx Hash Functions
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_FOO | 36 |
+---------------+---------------+---------------+---------------+
| T_SHA512 | 32 |
+---------------+---------------+---------------+---------------+
/ 32-byte hash value /
+---------------+---------------+---------------+---------------+
Example nesting inside type T_FOO
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3.3.4. Link
A Link is the tuple: {Name, [KeyIdRestr], [ContentObjectHashRestr]}.
It is a general encoding that is used in both the payload of a
Content Object with PayloadType = "Link" and in the KeyLink field in
a KeyLocator. A Link is essentially the body of an Interest.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
/ Mandatory CCNx Name /
+---------------+---------------+-------------------------------+
/ Optional KeyIdRestriction /
+---------------------------------------------------------------+
/ Optional ContentObjectHashRestriction /
+---------------------------------------------------------------+
3.4. Hop-by-hop TLV headers
Hop-by-hop TLV headers are unordered and meaning MUST NOT be attached
to their ordering. Three hop-by-hop headers are described in this
document:
+-------------+-------------------+---------------------------------+
| Abbrev | Name | Description |
+-------------+-------------------+---------------------------------+
| T_INTLIFE | Interest Lifetime | The time an Interest should |
| | (Section 3.4.1) | stay pending at an intermediate |
| | | node. |
| | | |
| T_CACHETIME | Recommended Cache | The Recommended Cache Time for |
| | Time (Section | Content Objects. |
| | 3.4.2) | |
| | | |
| T_MSGHASH | Message Hash | The hash of the CCNx Message to |
| | (Section 3.4.3) | end of packet using Section |
| | | 3.3.3 format. |
+-------------+-------------------+---------------------------------+
Table 4: Hop-by-hop Header Types
Additional hop-by-hop headers are defined in higher level
specifications such as the fragmentation specification.
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3.4.1. Interest Lifetime
The Interest Lifetime is the time that an Interest should stay
pending at an intermediate node. It is expressed in milliseconds as
an unsigned, network byte order integer.
A value of 0 (encoded as 1 byte %x00) indicates the Interest does not
elicit a Content Object response. It should still be forwarded, but
no reply is expected and a forwarder could skip creating a PIT entry.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_INTLIFE | Length |
+---------------+---------------+---------------+---------------+
/ /
/ Lifetime (length octets) /
/ /
+---------------+---------------+---------------+---------------+
3.4.2. Recommended Cache Time
The Recommended Cache Time (RCT) is a measure of the useful lifetime
of a Content Object as assigned by a content producer or upstream
node. It serves as a guideline to the Content Store cache in
determining how long to keep the Content Object. It is a
recommendation only and may be ignored by the cache. This is in
contrast to the ExpiryTime (described in Section 3.6.2.2.2) which
takes precedence over the RCT and must be obeyed.
Because the Recommended Cache Time is an optional hop-by-hop header
and not a part of the signed message, a content producer may re-issue
a previously signed Content Object with an updated RCT without
needing to re-sign the message. There is little ill effect from an
attacker changing the RCT as the RCT serves as a guideline only.
The Recommended Cache Time (a millisecond timestamp) is a network
byte ordered unsigned integer of the number of milliseconds since the
epoch in UTC of when the payload expires. It is a 64-bit field.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_CACHETIME | 8 |
+---------------+---------------+---------------+---------------+
/ /
/ Recommended Cache Time /
/ /
+---------------+---------------+---------------+---------------+
3.4.3. Message Hash
Within a trusted domain, an operator may calculate the message hash
at a border device and insert that value into the hop-by-hop headers
of a message. An egress device should remove the value. This
permits intermediate devices within that trusted domain to match
against a ContentObjectHashRestriction without calculating it at
every hop.
The message hash is a cryptographic hash from the start of the CCNx
Message to the end of the packet. It is used to match against the
ContentObjectHashRestriction (Section 3.6.2.1.2). The Message Hash
may be of longer length than an Interest's restriction, in which case
the device should use the left bytes of the Message Hash to check
against the Interest's value.
The Message Hash may only carry one hash type and there may only be
one Message Hash header.
The Message Hash header is unprotected, so this header is only of
practical use within a trusted domain, such as an operator's
autonomous system.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_MSGHASH | (length + 4) |
+---------------+---------------+---------------+---------------+
| (hash type) | length |
+---------------+---------------+---------------+---------------+
/ hash value /
+---------------+---------------+---------------+---------------+
Message Hash Header
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3.5. Top-Level Types
The top-level TLV types listed below exist at the outermost level of
a CCNx protocol message.
+----------------------+-------------------+------------------------+
| Abbrev | Name | Description |
+----------------------+-------------------+------------------------+
| T_INTEREST | Interest (Section | An Interest |
| | 3.6) | MessageType. |
| | | |
| T_OBJECT | Content Object | A Content Object |
| | (Section 3.6) | MessageType |
| | | |
| T_VALIDATION_ALG | Validation | The method of message |
| | Algorithm | verification such as |
| | (Section 3.6.4.1) | Message Integrity |
| | | Check (MIC), a Message |
| | | Authentication Code |
| | | (MAC), or a |
| | | cryptographic |
| | | signature. |
| | | |
| T_VALIDATION_PAYLOAD | Validation | The validation output, |
| | Payload (Section | such as the CRC32C |
| | 3.6.4.2) | code or the RSA |
| | | signature. |
+----------------------+-------------------+------------------------+
Table 5: CCNx Top Level Types
3.6. CCNx Message
This is the format for the CCNx protocol message itself. The CCNx
message is the portion of the packet between the hop-by-hop headers
and the Validation TLVs. The figure below is an expansion of the
"CCNx Message TLV" depicted in the beginning of Section 3. The CCNx
message begins with MessageType and runs through the optional
Payload. The same general format is used for both Interest and
Content Object messages which are differentiated by the MessageType
field. The first enclosed TLV of a CCNx Message is always the Name
TLV. This is followed by an optional Message TLVs and an optional
Payload TLV.
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| MessageType | MessageLength |
+---------------+---------------+---------------+---------------+
| Name TLV (Type = T_NAME) |
+---------------+---------------+---------------+---------------+
/ Optional Message TLVs (Various Types) /
+---------------+---------------+---------------+---------------+
/ Optional Payload TLV (Type = T_PAYLOAD) /
+---------------+---------------+---------------+---------------+
+-----------+-----------------+-------------------------------------+
| Abbrev | Name | Description |
+-----------+-----------------+-------------------------------------+
| T_NAME | Name (Section | The CCNx Name requested in an |
| | 3.6.1) | Interest or published in a Content |
| | | Object. |
| | | |
| T_PAYLOAD | Payload | The message payload. |
| | (Section 3.6.3) | |
+-----------+-----------------+-------------------------------------+
Table 6: CCNx Message Types
3.6.1. Name
A Name is a TLV encoded sequence of segments. The table below lists
the type values appropriate for these Name segments. A Name MUST NOT
include PAD TLVs.
As described in CCNx Semantics [CCNSemantics], using the CCNx URI
[CCNxURI] notation, a T_NAME with 0 length corresponds to ccnx:/ (the
default route) and is distinct from a name with one zero length
segment, such as ccnx:/NAME=. In the TLV encoding, ccnx:/
corresponds to T_NAME with 0 length, while ccnx:/NAME= corresponds to
T_NAME with 4 length and T_NAMESEGMENT with 0 length.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs /
+---------------+---------------+---------------+---------------+
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+---------------+-------------------+-------------------------------+
| Symbolic Name | Name | Description |
+---------------+-------------------+-------------------------------+
| T_NAMESEGMENT | Name segment | A generic name Segment. |
| | (Section 3.6.1.1) | |
| | | |
| T_IPID | Interest Payload | An identifier that represents |
| | ID (Section | the Interest Payload field. |
| | 3.6.1.2) | As an example, the Payload ID |
| | | might be a hash of the |
| | | Interest Payload. This |
| | | provides a way to |
| | | differentiate between |
| | | Interests based on their |
| | | payloads without having to |
| | | parse all the bytes of the |
| | | payload itself; instead using |
| | | only this Payload ID Name |
| | | segment. |
| | | |
| T_APP:00 - | Application | Application-specific payload |
| T_APP:4096 | Components | in a name segment. An |
| | (Section 3.6.1.1) | application may apply its own |
| | | semantics to the 4096 |
| | | reserved types. |
+---------------+-------------------+-------------------------------+
Table 7: CCNx Name Types
3.6.1.1. Name Segments
4096 special application payload name segments are allocated. These
have application semantics applied to them. A good convention is to
put the application's identity in the name prior to using these name
segments.
For example, a name like "ccnx:/foo/bar/hi" would be encoded as:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| (T_NAME) | %x14 (20) |
+---------------+---------------+---------------+---------------+
| (T_NAME_SEGMENT) | %x03 (3) |
+---------------+---------------+---------------+---------------+
| f o o |(T_NAME_SEGMENT)
+---------------+---------------+---------------+---------------+
| | %x03 (3) | b |
+---------------+---------------+---------------+---------------+
| a r | (T_NAME_SEGMENT) |
+---------------+---------------+---------------+---------------+
| %x02 (2) | h | i |
+---------------+---------------+---------------+---------------+
3.6.1.2. Interest Payload ID
The InterestPayloadID is a name segment created by the origin of an
Interest to represent the Interest Payload. This allows the proper
multiplexing of Interests based on their name if they have different
payloads. A common representation is to use a hash of the Interest
Payload as the InterestPayloadID.
As part of the TLV 'value', the InterestPayloadID contains a one
identifier of method used to create the InterestPayloadID followed by
a variable length octet string. An implementation is not required to
implement any of the methods to receive an Interest; the
InterestPayloadID may be treated only as an opaque octet string for
purposes of multiplexing Interests with different payloads. Only a
device creating an InterestPayloadID name segment or a device
verifying such a segment need to implement the algorithms.
It uses the Section 3.3.3 encoding of hash values.
In normal operations, we recommend displaying the InterestPayloadID
as an opaque octet string in a CCNx URI, as this is the common
denominator for implementation parsing.
The InterestPayloadID, even if it is a hash, should not convey any
security context. If a system requires confirmation that a specific
entity created the InterestPayload, it should use a cryptographic
signature on the Interest via the ValidationAlgorithm and
ValidationPayload or use its own methods inside the Interest Payload.
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3.6.2. Message TLVs
Each message type (Interest or Content Object) is associated with a
set of optional Message TLVs. Additional specification documents may
extend the types associated with each.
3.6.2.1. Interest Message TLVs
There are two Message TLVs currently associated with an Interest
message: the KeyIdRestriction selector and the ContentObjectHashRestr
selector are used to narrow the universe of acceptable Content
Objects that would satisfy the Interest.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| MessageType | MessageLength |
+---------------+---------------+---------------+---------------+
| Name TLV |
+---------------+---------------+---------------+---------------+
/ Optional KeyIdRestriction TLV /
+---------------------------------------------------------------+
/ Optional ContentObjectHashRestriction TLV /
+---------------------------------------------------------------+
+----------------+------------------------------+-------------------+
| Abbrev | Name | Description |
+----------------+------------------------------+-------------------+
| T_KEYIDRESTR | KeyIdRestriction (Section | A Section 3.3.3 |
| | 3.6.2.1.1) | representation of |
| | | the KeyId |
| | | |
| T_OBJHASHRESTR | ContentObjectHashRestriction | A Section 3.3.3 |
| | (Section 3.6.2.1.2) | representation of |
| | | the hash of the |
| | | specific Content |
| | | Object that would |
| | | satisfy the |
| | | Interest. |
+----------------+------------------------------+-------------------+
Table 8: CCNx Interest Message TLV Types
3.6.2.1.1. KeyIdRestriction
An Interest MAY include a KeyIdRestriction selector. This ensures
that only Content Objects with matching KeyIds will satisfy the
Interest. See Section 3.6.4.1.4.1 for the format of a KeyId.
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3.6.2.1.2. ContentObjectHashRestriction
An Interest MAY contain a ContentObjectHashRestriction selector.
This is the hash of the Content Object - the self-certifying name
restriction that must be verified in the network, if an Interest
carried this restriction. It is calculated from the beginning of the
CCNx Message to the end of the packet. The LENGTH MUST be from one
of the allowed values for that hash (see Section 3.3.3).
The ContentObjectHashRestriction SHOULD be of type T_SHA-256 and of
length 32 bytes.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_OBJHASHRESTR | LENGTH+4 |
+---------------+---------------+---------------+---------------+
| <hash type> | LENGTH |
+---------------+---------------+---------------+---------------+
/ LENGTH octets of hash /
+---------------+---------------+---------------+---------------+
3.6.2.2. Content Object Message TLVs
The following message TLVs are currently defined for Content Objects:
PayloadType (optional) and ExpiryTime (optional).
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| MessageType | MessageLength |
+---------------+---------------+---------------+---------------+
| Name TLV |
+---------------+---------------+---------------+---------------+
/ Optional PayloadType TLV /
+---------------------------------------------------------------+
/ Optional ExpiryTime TLV /
+---------------------------------------------------------------+
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+-------------+---------------------+-------------------------------+
| Abbrev | Name | Description |
+-------------+---------------------+-------------------------------+
| T_PAYLDTYPE | PayloadType | Indicates the type of Payload |
| | (Section 3.6.2.2.1) | contents. |
| | | |
| T_EXPIRY | ExpiryTime (Section | The time at which the Payload |
| | 3.6.2.2.2) | expires, as expressed in the |
| | | number of milliseconds since |
| | | the epoch in UTC. If |
| | | missing, Content Object may |
| | | be used as long as desired. |
+-------------+---------------------+-------------------------------+
Table 9: CCNx Content Object Message TLV Types
3.6.2.2.1. PayloadType
The PayloadType is a network byte order integer representing the
general type of the Payload TLV.
o T_PAYLOADTYPE_DATA: Data (possibly encrypted)
o T_PAYLOADTYPE_KEY: Key
o T_PAYLOADTYPE_LINK: Link
The Data type indicate that the Payload of the ContentObject is
opaque application bytes. The Key type indicates that the Payload is
a DER encoded public key. The Link type indicates that the Payload
is one or more Link (Section 3.3.4). If this field is missing, a
"Data" type is assumed.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PAYLDTYPE | Length |
+---------------+---------------+---------------+---------------+
| PayloadType /
+---------------+
3.6.2.2.2. ExpiryTime
The ExpiryTime is the time at which the Payload expires, as expressed
by a timestamp containing the number of milliseconds since the epoch
in UTC. It is a network byte order unsigned integer in a 64-bit
field. A cache or end system should not respond with a Content
Object past its ExpiryTime. Routers forwarding a Content Object do
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not need to check the ExpiryTime. If the ExpiryTime field is
missing, the Content Object has no expressed expiration and a cache
or end system may use the Content Object for as long as desired.
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+---------------+---------------+---------------+---------------+
| T_EXPIRY | 8 |
+---------------+---------------+---------------+---------------+
/ ExpiryTime /
/ /
+---------------+---------------+---------------+---------------+
3.6.3. Payload
The Payload TLV contains the content of the packet. It MAY be of
zero length. If a packet does not have any payload, this field MAY
be omitted, rather than carrying a zero length.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PAYLOAD | Length |
+---------------+---------------+---------------+---------------+
/ Payload Contents /
+---------------+---------------+---------------+---------------+
3.6.4. Validation
Both Interests and Content Objects have the option to include
information about how to validate the CCNx message. This information
is contained in two TLVs: the ValidationAlgorithm TLV and the
ValidationPayload TLV. The ValidationAlgorithm TLV specifies the
mechanism to be used to verify the CCNx message. Examples include
verification with a Message Integrity Check (MIC), a Message
Authentication Code (MAC), or a cryptographic signature. The
ValidationPayload TLV contains the validation output, such as the
CRC32C code or the RSA signature.
An Interest would most likely only use a MIC type of validation - a
crc, checksum, or digest.
3.6.4.1. Validation Algorithm
The ValidationAlgorithm is a set of nested TLVs containing all of the
information needed to verify the message. The outermost container
has type = T_VALIDATION_ALG. The first nested TLV defines the
specific type of validation to be performed on the message. The type
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is identified with the "ValidationType" as shown in the figure below
and elaborated in the table below. Nested within that container are
the TLVs for any ValidationType dependent data, for example a Key Id,
Key Locator etc.
Complete examples of several types may be found in Section 3.6.4.1.5
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | ValidationAlgLength |
+---------------+---------------+---------------+---------------+
| ValidationType | Length |
+---------------+---------------+---------------+---------------+
/ ValidationType dependent data /
+---------------+---------------+---------------+---------------+
+---------------+---------------------+-----------------------------+
| Abbrev | Name | Description |
+---------------+---------------------+-----------------------------+
| T_CRC32C | CRC32C (Section | Castagnoli CRC32 (iSCSI, |
| | 3.6.4.1.1) | ext4, etc.), with normal |
| | | form polynomial 0x1EDC6F41. |
| | | |
| T_HMAC-SHA256 | HMAC-SHA256 | HMAC (RFC 2104) using |
| | (Section 3.6.4.1.2) | SHA256 hash. |
| | | |
| T_RSA-SHA256 | RSA-SHA256 (Section | RSA public key signature |
| | 3.6.4.1.3) | using SHA256 digest. |
| | | |
| EC-SECP-256K1 | SECP-256K1 (Section | Elliptic Curve signature |
| | 3.6.4.1.3) | with SECP-256K1 parameters |
| | | (see [ECC]). |
| | | |
| EC-SECP-384R1 | SECP-384R1 (Section | Elliptic Curve signature |
| | 3.6.4.1.3) | with SECP-384R1 parameters |
| | | (see [ECC]). |
+---------------+---------------------+-----------------------------+
Table 10: CCNx Validation Types
3.6.4.1.1. Message Integrity Checks
MICs do not require additional data in order to perform the
verification. An example is CRC32C that has a "0" length value.
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3.6.4.1.2. Message Authentication Checks
MACs are useful for communication between two trusting parties who
have already shared private keys. Examples include an RSA signature
of a SHA256 digest or others. They rely on a KeyId. Some MACs might
use more than a KeyId, but those would be defined in the future.
3.6.4.1.3. Signature
Signature type Validators specify a digest mechanism and a signing
algorithm to verify the message. Examples include RSA signature og a
SHA256 digest, an Elliptic Curve signature with SECP-256K1
parameters, etc. These Validators require a KeyId and a mechanism
for locating the publishers public key (a KeyLocator) - optionally a
PublicKey or Certificate or KeyLink.
3.6.4.1.4. Validation Dependent Data
Different Validation Algorithms require access to different pieces of
data contained in the ValidationAlgorithm TLV. As described above,
Key Ids, Key Locators, Public Keys, Certificates, Links and Key Names
all play a role in different Validation Algorithms. Any number of
Validation Dependent Data containers can be present in a Validation
Algorithm TLV.
Following is a table of CCNx ValidationType dependent data types:
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+-------------+-----------------------+-----------------------------+
| Abbrev | Name | Description |
+-------------+-----------------------+-----------------------------+
| T_KEYID | SignerKeyId (Section | An identifier of the shared |
| | 3.6.4.1.4.1) | secret or public key |
| | | associated with a MAC or |
| | | Signature. |
| | | |
| T_PUBLICKEY | Public Key (Section | DER encoded public key. |
| | 3.6.4.1.4.2) | |
| | | |
| T_CERT | Certificate (Section | DER encoded X509 |
| | 3.6.4.1.4.3) | certificate. |
| | | |
| T_KEYLINK | KeyLink (Section | A CCNx Link object. |
| | 3.6.4.1.4.4) | |
| | | |
| T_SIGTIME | SignatureTime | A millsecond timestamp |
| | (Section 3.6.4.1.4.5) | indicating the time when |
| | | the signature was created. |
+-------------+-----------------------+-----------------------------+
Table 11: CCNx Validation Dependent Data Types
3.6.4.1.4.1. KeyId
The KeyId is the publisher key identifier. It is similar to a
Subject Key Identifier from X509 [RFC 5280, Section 4.2.1.2]. It
should be derived from the key used to sign, such as from the SHA-256
hash of the key. It applies to both public/private key systems and
to symmetric key systems.
The KeyId is represented using the Section 3.3.3. If a protocol uses
a non-hash identifier, it should use one of the reserved values.
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+---------------+---------------+---------------+---------------+
| T_KEYID | LENGTH+4 |
+---------------+---------------+---------------+---------------+
| <hash type> | LENGTH |
+---------------+---------------+---------------+---------------+
/ LENGTH octets of hash /
+---------------+---------------+---------------+---------------+
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3.6.4.1.4.2. Public Key
A Public Key is a DER encoded Subject Public Key Info block, as in an
X509 certificate.
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+---------------+---------------+
| T_PUBLICKEY | Length |
+---------------+---------------+---------------+---------------+
/ Public Key (DER encoded SPKI) /
+---------------+---------------+---------------+---------------+
3.6.4.1.4.3. Certificate
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_CERT | Length |
+---------------+---------------+---------------+---------------+
/ Certificate (DER encoded X509) /
+---------------+---------------+---------------+---------------+
3.6.4.1.4.4. KeyLink
A KeyLink type KeyLocator is a Link.
The KeyLink ContentObjectHashRestr, if included, is the digest of the
Content Object identified by KeyLink, not the digest of the public
key. Likewise, the KeyIdRestr of the KeyLink is the KeyId of the
ContentObject, not necessarily of the wrapped key.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| T_KEYKINK | Length |
+---------------+---------------+-------------------------------+
/ Link /
+---------------------------------------------------------------+
3.6.4.1.4.5. SignatureTime
The SignatureTime is a millisecond timestamp indicating the time at
which a signature was created. The signer sets this field to the
current time when creating a signature. A verifier may use this time
to determine whether or not the signature was created during the
validity period of a key, or if it occurred in a reasonable sequence
with other associated signatures. The SignatureTime is unrelated to
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any time associated with the actual CCNx Message, which could have
been created long before the signature. The default behavior is to
always include a SignatureTime when creating an authenticated message
(e.g. HMAC or RSA).
SignatureTime is a network byte ordered unsigned integer of the
number of milliseconds since the epoch in UTC of when the signature
was created. It is a fixed 64-bit field.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| T_SIGTIME | 8 |
+---------------+---------------+-------------------------------+
/ SignatureTime /
+---------------------------------------------------------------+
3.6.4.1.5. Validation Examples
As an example of a MIC type validation, the encoding for CRC32C
validation would be:
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+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | 4 |
+---------------+---------------+---------------+---------------+
| T_CRC32C | 0 |
+---------------+---------------+---------------+---------------+
As an example of a MAC type validation, the encoding for an HMAC
using a SHA256 hash would be:
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+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | 40 |
+---------------+---------------+---------------+---------------+
| T_HMAC-SHA256 | 36 |
+---------------+---------------+---------------+---------------+
| T_KEYID | 32 |
+---------------+---------------+---------------+---------------+
/ KeyId /
/---------------+---------------+-------------------------------+
As an example of a Signature type validation, the encoding for an RSA
public key signing using a SHA256 digest and Public Key would be:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | 44 + Variable Length |
+---------------+---------------+---------------+---------------+
| T_RSA-SHA256 | 40 + Variable Length |
+---------------+---------------+---------------+---------------+
| T_KEYID | 32 |
+---------------+---------------+---------------+---------------+
/ KeyId /
/---------------+---------------+-------------------------------+
| T_PUBLICKEY | Variable Length (~ 160) |
+---------------+---------------+---------------+---------------+
/ Public Key (DER encoded SPKI) /
+---------------+---------------+---------------+---------------+
3.6.4.2. Validation Payload
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+---------------+---------------+---------------+---------------+
| T_VALIDATION_PAYLOAD | ValidationPayloadLength |
+---------------+---------------+---------------+---------------+
/ Type-dependent data /
+---------------+---------------+---------------+---------------+
The ValidationPayload contains the validation output, such as the
CRC32C code or the RSA signature.
4. IANA Considerations
This section details each kind of protocol value that can be
registered. Each type registry can be updated by incrementally
expanding the type space, i.e., by allocating and reserving new
types. As per [RFC5226] this section details the creation of the
"CCNx Registry" and several sub-registries.
+----------+---------------+
| Property | Value |
+----------+---------------+
| Name | CCNx Registry |
| | |
| Abbrev | CCNx |
+----------+---------------+
Registry Creation
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4.1. Packet Type Registry
The following packet types should be allocated. A PacketType MUST be
1 byte. New packet types are allocated via "RFC Required" action.
+----------------+----------------------+
| Property | Value |
+----------------+----------------------+
| Name | Packet Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | RFC Required |
| | |
| Syntax | 1 octet |
+----------------+----------------------+
Registry Creation
+------+-------------+----------------------------------+
| Type | Name | Reference |
+------+-------------+----------------------------------+
| %x00 | PT_INTEREST | Fixed Header Types (Section 3.2) |
| | | |
| %x01 | PT_CONTENT | Fixed Header Types (Section 3.2) |
| | | |
| %x02 | PT_RETURN | Fixed Header Types (Section 3.2) |
+------+-------------+----------------------------------+
Packet Type Namespace
4.2. Interest Return Code Registry
The following InterestReturn code types should be allocated.
+----------------+------------------------+
| Property | Value |
+----------------+------------------------+
| Name | Interest Return Code |
| | |
| Parent | CCNx Registry |
| | |
| Review process | Specification Required |
| | |
| Syntax | 1 octet |
+----------------+------------------------+
Registry Creation
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+------+---------------------------------------+--------------------+
| Type | Name | Reference |
+------+---------------------------------------+--------------------+
| %x00 | Reserved | |
| | | |
| %x01 | T_RETURN_NO_ROUTE | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x02 | T_RETURN_LIMIT_EXCEEDED | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x03 | T_RETURN_NO_RESOURCES | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x04 | T_RETURN_PATH_ERROR | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x05 | T_RETURN_PROHIBITED | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x06 | T_RETURN_CONGESTED | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x07 | T_RETURN_MTU_TOO_LARGE | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x08 | T_RETURN_UNSUPPORTED_HASH_RESTRICTION | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x09 | T_RETURN_MALFORMED_INTEREST | Fixed Header Types |
| | | (Section 3.2.3.3) |
+------+---------------------------------------+--------------------+
Interest Return Type Namespace
4.3. Hop-by-Hop Type Registry
The following hop-by-hop types should be allocated.
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+----------------+--------------------------+
| Property | Value |
+----------------+--------------------------+
| Name | Hop-by-Hop Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | RFC Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+--------------------------+
Registry Creation
+---------------+-------------+-------------------------------------+
| Type | Name | Reference |
+---------------+-------------+-------------------------------------+
| %x0000 | Reserved | |
| | | |
| %x0001 | T_INTLIFE | Hop-by-hop TLV headers (Section |
| | | 3.4) |
| | | |
| %x0002 | T_CACHETIME | Hop-by-hop TLV headers (Section |
| | | 3.4) |
| | | |
| %x0003 | T_MSGHASH | Hop-by-hop TLV headers (Section |
| | | 3.4) |
| | | |
| %x0004 - | Reserved | |
| %x0007 | | |
| | | |
| %x0FFE | T_PAD | Pad (Section 3.3.1) |
| | | |
| %x0FFF | T_ORG | Organization-Specific TLVs (Section |
| | | 3.3.2) |
| | | |
| %x1000-%x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+-------------+-------------------------------------+
Hop-by-Hop Type Namespace
4.4. Top-Level Type Registry
The following top-level types should be allocated.
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+----------------+-------------------------+
| Property | Value |
+----------------+-------------------------+
| Name | Top-Level Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | RFC Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+-------------------------+
Registry Creation
+--------+----------------------+-------------------------------+
| Type | Name | Reference |
+--------+----------------------+-------------------------------+
| %x0000 | Reserved | |
| | | |
| %x0001 | T_INTEREST | Top-Level Types (Section 3.5) |
| | | |
| %x0002 | T_OBJECT | Top-Level Types (Section 3.5) |
| | | |
| %x0003 | T_VALIDATION_ALG | Top-Level Types (Section 3.5) |
| | | |
| %x0004 | T_VALIDATION_PAYLOAD | Top-Level Types (Section 3.5) |
+--------+----------------------+-------------------------------+
Top-Level Type Namespace
4.5. Name Segment Type Registry
The following name segment types should be allocated.
+----------------+----------------------------+
| Property | Value |
+----------------+----------------------------+
| Name | Name Segment Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | Specification Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+----------------------------+
Registry Creation
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+--------------+------------------+---------------------------------+
| Type | Name | Reference |
+--------------+------------------+---------------------------------+
| %x0000 | Reserved | |
| | | |
| %x0001 | T_NAMESEGMENT | Name (Section 3.6.1) |
| | | |
| %x0002 | T_IPID | Name (Section 3.6.1) |
| | | |
| %x0010 - | Reserved | Used in other drafts |
| %x0013 | | |
| | | |
| %x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000 - | T_APP:00 - | Application Components (Section |
| %x1FFF | T_APP:4096 | 3.6.1) |
+--------------+------------------+---------------------------------+
Name Segment Type Namespace
4.6. Message Type Registry
The following CCNx message segment types should be allocated.
+----------------+-----------------------+
| Property | Value |
+----------------+-----------------------+
| Name | Message Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | RFC Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+-----------------------+
Registry Creation
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+---------------+----------------+----------------------------------+
| Type | Name | Reference |
+---------------+----------------+----------------------------------+
| %x0000 | T_NAME | Message Types (Section 3.6) |
| | | |
| %x0001 | T_PAYLOAD | Message Types (Section 3.6) |
| | | |
| %x0002 | T_KEYIDRESTR | Message Types (Section 3.6) |
| | | |
| %x0003 | T_OBJHASHRESTR | Message Types (Section 3.6) |
| | | |
| %x0005 | T_PAYLDTYPE | Content Object Message Types |
| | | (Section 3.6.2.2) |
| | | |
| %x0006 | T_EXPIRY | Content Object Message Types |
| | | (Section 3.6.2.2) |
| | | |
| %x0007 - | Reserved | Used in other RFC drafts |
| %x000C | | |
| | | |
| %x0FFE | T_PAD | Pad (Section 3.3.1) |
| | | |
| %x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000-%x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+----------------+----------------------------------+
CCNx Message Type Namespace
4.7. Payload Type Registry
The following payload types should be allocated.
+----------------+----------------------------------+
| Property | Value |
+----------------+----------------------------------+
| Name | PayloadType Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | Specification Required |
| | |
| Syntax | Variable length unsigned integer |
+----------------+----------------------------------+
Registry Creation
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+------+--------------------+-----------------------------------+
| Type | Name | Reference |
+------+--------------------+-----------------------------------+
| %x00 | T_PAYLOADTYPE_DATA | Payload Types (Section 3.6.2.2.1) |
| | | |
| %x01 | T_PAYLOADTYPE_KEY | Payload Types (Section 3.6.2.2.1) |
| | | |
| %x02 | T_PAYLOADTYPE_LINK | Payload Types (Section 3.6.2.2.1) |
+------+--------------------+-----------------------------------+
Payload Type Namespace
4.8. Validation Algorithm Type Registry
The following validation algorithm types should be allocated. Note:
registration requires public specification of the algorithm.
+----------------+------------------------------------+
| Property | Value |
+----------------+------------------------------------+
| Name | Validation Algorithm Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | Specification Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+------------------------------------+
Registry Creation
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+---------------+---------------+-----------------------------------+
| Type | Name | Reference |
+---------------+---------------+-----------------------------------+
| %x0000 | Reserved | |
| | | |
| %x0001 | Unassigned | |
| | | |
| %x0002 | T_CRC32C | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0003 | Unassigned | |
| | | |
| %x0004 | T_HMAC-SHA256 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0005 | T_RSA-SHA256 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0006 | EC-SECP-256K1 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0007 | EC-SECP-384R1 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0FFE | T_PAD | Pad (Section 3.3.1) |
| | | |
| %x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000-%x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+---------------+-----------------------------------+
Validation Algorithm Type Namespace
4.9. Validation Dependent Data Type Registry
The following validation dependent data types should be allocated.
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+----------------+-----------------------------------------+
| Property | Value |
+----------------+-----------------------------------------+
| Name | Validation Dependent Data Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | RFC Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+-----------------------------------------+
Registry Creation
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+---------------+----------------+----------------------------------+
| Type | Name | Reference |
+---------------+----------------+----------------------------------+
| %x0000 | Reserved | |
| | | |
| %x0001 - | Unassigned | |
| %x0008 | | |
| | | |
| %x0009 | T_KEYID | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000A | T_PUBLICKEYLOC | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000B | T_PUBLICKEY | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000C | T_CERT | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000D | T_LINK | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000E | T_KEYLINK | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000F | T_SIGTIME | Validation Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000-%x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+----------------+----------------------------------+
Validation Dependent Data Type Namespace
4.10. Hash Function Type Registry
The following CCNx hash function types should be allocated. Note:
registration requires public specification of the algorithm.
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+----------------+-----------------------------+
| Property | Value |
+----------------+-----------------------------+
| Name | Hash Function Type Registry |
| | |
| Parent | CCNx Registry |
| | |
| Review process | Specification Required |
| | |
| Syntax | 2 octet TLV type |
+----------------+-----------------------------+
Registry Creation
+---------------+-----------+---------------------------------------+
| Type | Name | Reference |
+---------------+-----------+---------------------------------------+
| %x0000 | Reserved | |
| | | |
| %x0001 | T_SHA-256 | Hash Format (Section 3.3.3) |
| | | |
| %x0002 | T_SHA-512 | Hash Format (Section 3.3.3) |
| | | |
| %x0FFF | T_ORG | Organization-Specific TLVs (Section |
| | | 3.3.2) |
| | | |
| %x1000-%x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+-----------+---------------------------------------+
CCNx Hash Function Type Namespace
5. Security Considerations
The CCNx protocol is a layer 3 network protocol, which may also
operate as an overlay using other transports, such as UDP or other
tunnels. It includes intrinsic support for message authentication
via a signature (e.g. RSA or elliptic curve) or message
authentication code (e.g. HMAC). In lieu of an authenticator, it
may instead use a message integrity check (e.g. SHA or CRC). CCNx
does not specify an encryption envelope, that function is left to a
high-layer protocol (e.g. [esic]).
The CCNx message format includes the ability to attach MICs (e.g.
SHA-256 or CRC), MACs (e.g. HMAC), and Signatures (e.g. RSA or
ECDSA) to all packet types. This does not mean that it is a good
idea to use an arbitrary ValidationAlgorithm, nor to include
computationally expensive algorithms in Interest packets, as that
could lead to computational DoS attacks. Applications should use an
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explicit protocol to guide their use of packet signatures. As a
general guideline, an application might use a MIC on an Interest to
detect unintentionally corrupted packets. If one wishes to secure an
Interest, one should consider using an encrypted wrapper and a
protocol that prevents replay attacks, especially if the Interest is
being used as an actuator. Simply using an authentication code or
signature does not make an Interests secure. There are several
examples in the literature on how to secure ICN-style messaging
[mobile] [ace].
As a layer 3 protocol, this document does not describe how one
arrives at keys or how one trusts keys. The CCNx content object may
include a public key embedded in the object or may use the
PublicKeyLocator field to point to a public key (or public key
certificate) that authenticates the message. One key exchange
specification is CCNxKE [ccnxke] [mobile], which is similar to the
TLS 1.3 key exchange except it is over the CCNx layer 3 messages.
Trust is beyond the scope of a layer-3 protocol protocol and left to
applications or application frameworks.
The combination of an ephemeral key exchange (e.g. CCNxKE [ccnxke])
and an encapsulating encryption (e.g. [esic]) provides the equivalent
of a TLS tunnel. Intermediate nodes may forward the Interests and
Content Objects, but have no visibility inside. It also completely
hides the internal names in those used by the encryption layer. This
type of tunneling encryption is useful for content that has little or
no cache-ability as it can only be used by someone with the ephemeral
key. Short term caching may help with lossy links or mobility, but
long term caching is usually not of interest.
Broadcast encryption or proxy re-encryption may be useful for content
with multiple uses over time or many consumers. There is currently
no recommendation for this form of encryption.
The specific encoding of messages will have security implications.
This document uses a type-length-value (TLV) encoding. We chose to
compromise between extensibility and unambiguous encodings of types
and lengths. Some TLVs use variable length T and variable length L
fields to accomodate a wide gamut of values while trying to be byte-
efficient. Our TLV encoding uses a fixed length 2-byte T and 2-byte
L. Using a fixed-length T and L field solves two problems. The
first is aliases. If one is able to encode the same value, such as
0x2 and 0x02, in different byte lengths then one must decide if they
mean the same thing, if they are different, or if one is illegal. If
they are different, then one must always compare on the buffers not
the integer equivalents. If one is illegal, then one must validate
the TLV encoding -- every field of every packet at every hop. If
they are the same, then one has the second problem: how to specify
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packet filters. For example, if a name has 6 name components, then
there are 7 T's and 7 L's, each of which might have up to 4
representations of the same value. That would be 14 fields with 4
encodings each, or 1001 combinations. It also means that one cannot
compare, for example, a name via a memory function as one needs to
consider that any embedded T or L might have a different format.
The Interest Return message has no authenticator from the previous
hop. Therefore, the payload of the Interest Return should only be
used locally to match an Interest. A node should never forward that
Interest payload as an Interest. It should also verify that it sent
the Interest in the Interest Return to that node and not allow anyone
to negate Interest messages.
Caching nodes must take caution when processing content objects. It
is essential that the Content Store obey the rules outlined in
[CCNSemantics] to avoid certain types of attacks. Unlike NDN, CCNx
1.0 has no mechanism to work around an undesired result from the
network (there are no "excludes"), so if a cache becomes poisoned
with bad content it might cause problems retrieving content. There
are three types of access to content from a content store:
unrestricted, signature restricted, and hash restricted. If an
Interest has no restrictions, then the requester is not particular
about what they get back, so any matching cached object is OK. In
the hash restricted case, the requester is very specific about what
they want and the content store (and every forward hop) can easily
verify that the content matches the request. In the signature
verified case (often used for initial manifest discovery), the
requester only knows the KeyId that signed the content. It is this
case that requires the closest attention in the content store to
avoid amplifying bad data. The content store must only respond with
a content object if it can verify the signature -- this means either
the content object carries the public key inside it or the Interest
carries the public key in addition to the KeyId. If that is not the
case, then the content store should treat the Interest as a cache
miss and let an endpoint respond.
A user-level cache could perform full signature verification by
fetching a public key according to the PublicKeyLocator. That is
not, however, a burden we wish to impose on the forwarder. A user-
level cache could also rely on out-of-band attestation, such as the
cache operator only inserting content that it knows has the correct
signature.
The CCNx grammar allows for hash algorithm agility via the HashType.
It specifies a short list of acceptable hash algorithms that should
be implemented at each forwarder. Some hash values only apply to end
systems, so updating the hash algorithm does not affect forwarders --
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they would simply match the buffer that includes the type-length-hash
buffer. Some fields, such as the ConObjHash, must be verified at
each hop, so a forwarder (or related system) must know the hash
algorithm and it could cause backward compatibility problems if the
hash type is updated.
A CCNx name uses binary matching whereas a URI uses a case
insensitive hostname. Some systems may also use case insensitive
matching of the URI path to a resource. An implication of this is
that human-entered CCNx names will likely have case or non-ASCII
symbol mismatches unless one uses a consistent URI normalization to
the CCNx name. It also means that an entity that registers a CCNx
routable prefix, say ccnx:/example.com, would need separate
registrations for simple variations like ccnx:/Example.com. Unless
this is addressed in URI normalization and routing protocol
conventions, there could be phishing attacks.
For a more general introduction to ICN-related security concerns and
approaches, see [RFC7927] and [RFC7945]
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
6.2. Informative References
[ace] Shang, W., Yu, Y., Liang, T., Zhang, B., and L. Zhang,
"NDN-ACE: Access control for constrained environments over
named data networking", NDN Technical Report NDN-0036,
2015, <http://new.named-data.net/wp-
content/uploads/2015/12/ndn-0036-1-ndn-ace.pdf>.
[CCNSemantics]
Mosko, M., Solis, I., and C. Wood, "CCNx Semantics
(Internet draft)", 2018, <https://www.ietf.org/id/draft-
irtf-icnrg-ccnxsemantics-09.txt>.
[ccnxke] Mosko, M., Uzun, E., and C. Wood, "CCNx Key Exchange
Protocol Version 1.0", 2017,
<https://www.ietf.org/archive/id/draft-wood-icnrg-
ccnxkeyexchange-02.txt>.
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[CCNxURI] Mosko, M. and C. Wood, "The CCNx URI Scheme (Internet
draft)", 2017,
<http://tools.ietf.org/html/draft-mosko-icnrg-ccnxuri-02>.
[CCNxz] Mosko, M., "CCNxz TLV Header Compression Experimental
Code", 2016-2018, <https://github.com/PARC/CCNxz>.
[compress]
Mosko, M., "Header Compression for TLV-based Packets",
2016, <https://datatracker.ietf.org/meeting/interim-2016-
icnrg-02/materials/slides-interim-2016-icnrg-2-7>.
[ECC] Certicom Research, "SEC 2: Recommended Elliptic Curve
Domain Parameters", 2010,
<http://www.secg.org/sec2-v2.pdf>.
[EpriseNumbers]
IANA, "IANA Private Enterprise Numbers", 2015,
<http://www.iana.org/assignments/enterprise-numbers/
enterprise-numbers>.
[esic] Mosko, M. and C. Wood, "Encrypted Sessions In CCNx
(ESIC)", 2017, <https://www.ietf.org/id/draft-wood-icnrg-
esic-01.txt>.
[mobile] Mosko, M., Uzun, E., and C. Wood, "Mobile Sessions in
Content-Centric Networks", IFIP Networking, 2017,
<http://dl.ifip.org/db/conf/networking/
networking2017/1570334964.pdf>.
[nnc] Jacobson, V., Smetters, D., Thornton, J., Plass, M.,
Briggs, N., and R. Braynard, "Networking Named Content",
2009, <http://dx.doi.org/10.1145/1658939.1658941>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008, <https://www.rfc-
editor.org/info/rfc5226>.
[RFC7927] Kutscher, D., Eum, S., Pentikousis, K., Psaras, I.,
Corujo, D., Saucez, D., Schmidt, T., and M. Waehlisch,
"Information-Centric Networking (ICN) Research
Challenges", 2016, <https://trac.tools.ietf.org/html/
rfc7927>.
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[RFC7945] Pentikousis, K., Ohlman, B., Davies, E., Spirou, S., and
G. Boggia, "Information-Centric Networking: Evaluation and
Security Considerations", 2016,
<https://trac.tools.ietf.org/html/rfc7945>.
Authors' Addresses
Marc Mosko
PARC, Inc.
Palo Alto, California 94304
USA
Phone: +01 650-812-4405
Email: marc.mosko@parc.com
Ignacio Solis
LinkedIn
Mountain View, California 94043
USA
Email: nsolis@linkedin.com
Christopher A. Wood
University of California Irvine
Irvine, California 92697
USA
Phone: +01 315-806-5939
Email: woodc1@uci.edu
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