| Delay-Tolerant Networking | E. Birrane |
| Internet-Draft | JHU/APL |
| Intended status: Experimental | J. Mayer |
| Expires: July 2, 2016 | INSYEN AG |
| D. Iannicca | |
| NASA GRC | |
| December 30, 2015 |
Bundle Protocol Security Specification
draft-ietf-dtn-bpsec-00
This document defines a security protocol providing data authentication, integrity, and confidentiality services for the Bundle Protocol. Capabilities are provided to protect blocks in a bundle along a single path through a network.
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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 2, 2016.
Copyright (c) 2015 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 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document defines security features for the Bundle Protocol [RFC5050] intended for use in delay-tolerant networks, in order to provide Delay-Tolerant Networking (DTN) security services.
The Bundle Protocol is used in DTNs that overlay multiple networks, some of which may be challenged by limitations such as intermittent and possibly unpredictable loss of connectivity, long or variable delay, asymmetric data rates, and high error rates. The purpose of the Bundle Protocol is to support interoperability across such stressed networks.
The stressed environment of the underlying networks over which the Bundle Protocol operates makes it important for the DTN to be protected from unauthorized use, and this stressed environment poses unique challenges for the mechanisms needed to secure the Bundle Protocol. Furthermore, DTNs may be deployed in environments where a portion of the network might become compromised, posing the usual security challenges related to confidentiality, integrity, and availability.
This document describes the Bundle Protocol Security Specification (BPSec), which provides security services for blocks within a bundle from the bundle source to the bundle destination. Specifically, BPSec provides authentication, integrity, and confidentiality for bundles along a path through a DTN.
BPSec applies, by definition, only to those nodes that implement it, known as "security-aware" nodes. There MAY be other nodes in the DTN that do not implement BPSec. All nodes can interoperate with the exception that BPSec security operations can only happen at BPSec security-aware nodes.
This document is best read and understood within the context of the following other DTN documents:
"Delay-Tolerant Networking Architecture" [RFC4838] defines the architecture for delay-tolerant networks, but does not discuss security at any length.
The DTN Bundle Protocol [RFC5050] defines the format and processing of the blocks used to implement the Bundle Protocol, excluding the security-specific blocks defined here.
The Bundle Security Protocol [RFC6257] and Streamlind Bundle Security Protocol [SBSP] introduce the concepts of security blocks for authentication, confidentiality, and integrity. BPSec is based off of this document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
We introduce the following terminology for purposes of clarity.
Figure 1 below is adapted from [RFC5050] and shows four bundle nodes (denoted BN1, BN2, BN3, and BN4) that reside above some transport layer(s). Three distinct transport and network protocols (denoted T1/N1, T2/N2, and T3/N3) are also shown.
+---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+ | BN1 v | | ^ BN2 v | | ^ BN3 v | | ^ BN4 | +---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+ | T1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ T3 | +---------v-+ +-^---------v-+ +-^---------v + +-^---------+ | N1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ N3 | +---------v-+ +-^---------v + +-^---------v-+ +-^---------+ | >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ | +-----------+ +------------+ +-------------+ +-----------+ | | | | |<-- An Internet --->| |<--- An Internet --->| | | | |
Figure 1: Bundle Nodes Sit at the Application Layer of the Internet Model
BN1 originates a bundle that it forwards to BN2. BN2 forwards the bundle to BN3, and BN3 forwards the bundle to BN4. BN1 is the source of the bundle and BN4 is the destination of the bundle. BN1 is the first forwarder, and BN2 is the first intermediate receiver; BN2 then becomes the forwarder, and BN3 the intermediate receiver; BN3 then becomes the last forwarder, and BN4 the last intermediate receiver, as well as the destination.
If node BN2 originates a bundle (for example, a bundle status report or a custodial signal), which is then forwarded on to BN3, and then to BN4, then BN2 is the source of the bundle (as well as being the first forwarder of the bundle) and BN4 is the destination of the bundle (as well as being the final intermediate receiver).
We introduce the following security-specific DTN terminology.
The application of security services in a DTN is a complex endeavor that must consider physical properties of the network, policies at each node, and various application security requirements. Rather than enumerate all potential security implementations in all potential DTN topologies, this specification defines a set of key properties of a security system. The security primitives outlined in this document MUST enable the realization of these properties in a DTN deploying the Bundle Protocol.
Blocks within a bundle represent different types of information. The primary block contains identification and routing information. The payload block carries application data. Extension blocks carry a variety of data that may augment or annotate the payload, or otherwise provide information necessary for the proper processing of a bundle along a path. Therefore, applying a single level and type of security across an entire bundle fails to recognize that blocks in a bundle may represent different types of information with different security needs.
Security services within this specification MUST provide block level granularity where applicable such that different blocks within a bundle may have different security services applied to them.
For example, within a bundle, a payload might be encrypted to protect its contents, whereas an extension block containing summary information related to the payload might be integrity signed but otherwise unencrypted to provide certain nodes access to payload-related data without providing access to the payload.
The Bundle Protocol allows extension blocks to be added to a bundle at any time during its existence in the DTN. When a waypoint node adds a new extension block to a bundle, that extension block may have security services applied to it by that waypoint. Similarly, a waypoint node may add a security service to an existing extension block, consistent with its security policy. For example, a node representing a boundary between a trusted part of the network and an untrusted part of the network may wish to apply payload encryption for bundles leaving the trusted portion of the network.
In each case, a node other than the bundle originator may be adding a security service to the bundle and, as such, the source for the security service will be different than the source of the bundle itself. Security services MUST track their orginating node so as to properly apply policy and key selection associated with processing the security service at the bundle destination.
Referring to Figure 1, if the bundle that originates at BN1 is given security blocks by BN1, then BN1 is the security-source for those blocks as well as being the source of the bundle. If the bundle that originates at BN1 is then given a security block by BN2, then BN2 is the security-source for that block even though BN1 remains the bundle source.
A bundle MAY have multiple security blocks and these blocks MAY have different security-sources. Each security block in a bundle will be associated with a specific security-operation. All security blocks comprising a security-operation MUST have the same security-source and security-destination.
As required in [RFC5050], forwarding nodes MUST transmit blocks in a bundle in the same order in which they were received. This requirement applies to all DTN nodes, not just ones that implement security processing. Blocks in a bundle MAY be added or deleted according to the applicable specification, but those blocks that are both received and transmitted MUST be transmitted in the same order that they were received.
The destination of all security blocks in a bundle MUST be the bundle destination, with the exception of authentication security blocks, whose destination is the next hop along the bundle path. In a DTN, there is typically no guarantee that a bundle will visit a particular intermediate receiver during its journey, or that a particular series of intermediate receivers will be visited in a particular order. Security-destinations different from bundle destinations would place a tight (and possibly intractable) coupling between security and routing services in an overlay network.
Different nodes in a DTN may have different security-related capabilities. Some nodes may not be security-aware and will not understand any security-related extension blocks. Other nodes may have security policies that require evaluation of security services at places other than the bundle destination (such as verifying integrity signatures at certain waypoint nodes). Other nodes may ignore any security processing if they are not the destination of the bundle. The security services described in this specification must allow each of these scenarios.
Extension blocks representing security services MUST have their block processing flags set such that the block (and bundle, where applicable) will be treated appropriately by non-security-aware nodes.
Extension blocks providing integrity and authentication services within a bundle MUST support options to allow waypoint nodes to evaluate these signatures if such nodes have the proper configuraton to do so.
The security services defined in this specification rely on a a variety of ciphersuites providing integrity signatures, ciphertext, and other information necessary to populate security blocks. Users may wish to select differing ciphersuites to implement different security services. For example, some users may wish to use a SHA-1 based hash for integrity whereas other users may require a SHA-2 hash instead. The security services defined in this specification MUST provide a mechanism for identifying what ciphersuite has been used to populate a security block.
In all cases, the processing order of security services within a bundle must avoid ambiguity when evaluating security at the bundle destination. This specification MUST provide determinism in the application and evaluation of security services, even when doing so results in a loss of flexibility.
There are four types of security blocks that MAY be included in a bundle. These are the Bundle Authentication Block (BAB), the Block Integrity Block (BIB), the Block Confidentiality Block (BCB), and the Cryptographic Messaging Syntax Block (CMSB).
Certain cipher suites may allow or require multiple instances of a block to appear in the bundle. For example, an authentication cipher suite may require two security blocks, one before the payload block and one after. Despite the presence of two security blocks, they both comprise the same security-operation - OP(authentication,bundle) in this example.
A security-operation MUST NOT be applied more than once in a bundle. For example, the two security-operations: OP(integrity, payload) and OP(integrity, payload) are considered redundant and MUST NOT appear together in a bundle. However, the two security operations OP(integrity, payload) and OP(integrity, extension_block_1) MAY both be present in the bundle. Also, the two security operations OP(integrity, extension_block_1) and OP(integrity, extension_block_2) are unique and may both appear in the same bundle.
Many of the fields in these block definitions use the Self-Delimiting Numeric Value (SDNV) type whose format and encoding is as defined in [RFC5050].
This specification requires that every target block of a security operation be uniquely identifiable. In cases where there can only be a single instance of a block in the bundle (as is the case with the primary block and the payload block) then the unique identifier is simply the block type. These blocks are described as "singleton blocks". It is possible that a bundle may contain multiple instances of a block type. In such a case, each instance of the block type must be uniquely identifiable and the block type itself is not sufficient for this identification. These blocks are described as "non-singleton blocks".
The definition of the extension block header from [RFC5050] does not provide additional identifying information for a block beyond the block type. The addition of an occurrence number to the block is necessary to identify the block instance in the bundle. This section describes the use of an Artificial EID (AEID) reference in a block header to add unique identification for non-singleton blocks.
Figure 7 of [RFC5050] illustrates that an EID reference in a block header is the 2-tuple of the reference scheme and the reference scheme specific part (SSP), each of which are encoded as SDNVs. The AEID MUST encode the occurrence number in the reference scheme SDNV and MUST set the reference SSP to 0. A reference SSP value of 0 is an invalid offset for an SSP in the bundle dictionary and, therefore, the use of 0 in this field identifies the reference as an AEID.
The occurrence number MAY be any positive value that is not already present as an occurrence number for the same block type in the bundle. These numbers are independent of relative block position within the bundle, and whether blocks of the same type have been added or removed from the bundle. Once an AEID has been added to a block instance, it MUST NOT be changed until all security operations that target the block instance have been removed from the bundle.
If a node wishes to apply a security operation to a target block it MUST determine whether the target block is a singleton block or a non-singleton block. If the target block is non-singleton, then the node MUST find the AEID for the target. If an AEID is not present in the target block header then the node MAY choose to either cancel the security operation or add an AEID to the block, in accordance with security policy.
If a node chooses to add an AEID to a target block header it MUST perform the following activities.
If there is no AEID present in a block, and if a node is unable to add an AEID by following the above process, then the block MUST NOT have an BPSec security operation applied to it.
It is RECOMMENDED that every block in a bundle other than the primary and payload blocks be treated as a non-singleton block. However, the identification of singleton blocks SHOULD be in accordance with the security policy of a node.
Each security block uses the Canonical Bundle Block Format as defined in [RFC5050]. That is, each security block is comprised of the following elements:
Since the four security block types have most fields in common, we can shorten the description of the block type specific data fields if we first define an abstract security block (ASB) and then specify each of the real blocks in terms of the fields that are present/absent in an ASB. Note that no bundle ever contains an actual ASB, which is simply a specification artifact.
The structure of an Abstract Security Block is given in Figure 2. Although the diagram hints at a fixed-format layout, this is purely for the purpose of exposition. Except for the "type" field, all fields are variable in length.
+-----------------------------+----------------------------------+ | Block Type Code (BYTE) | Processing Control Flags (SDNV) | +-----------------------------+----------------------------------+ | EID Reference Count and List (Compound List) | +-----------------------------+----------------------------------+ | Block Length (SDNV) | Security Target (Compound) | +-----------------------------+----------------------------------+ | Cipher suite ID (SDNV) | Cipher suite Flags (SDNV) | +-----------------------------+----------------------------------+ | Params Length (SDNV) | Params Data (Compound) | +-----------------------------+----------------------------------+ | Result Length (SDNV) | Result Data (Compound) | +-----------------------------+----------------------------------+
Figure 2: Abstract Security Block Structure
An ASB consists of the following fields, some of which are optional.
The structure of the cipher suite flags field is shown in Figure 3. In each case, the presence of an optional field is indicated by setting the value of the corresponding flag to one. A value of zero indicates the corresponding optional field is missing. Presently, there are three flags defined for the field; for convenience, these are shown as they would be extracted from a single-byte SDNV. Future additions may cause the field to grow to the left so, as with the flags fields defined in [RFC5050], the description below numbers the bit positions from the right rather than the standard RFC definition, which numbers bits from the left.
Bit Bit Bit Bit Bit Bit Bit 6 5 4 3 2 1 0 +-----+-----+-----+-----+-----+-----+-----+ | reserved | src |parm | res | +-----+-----+-----+-----+-----+-----+-----+
Figure 3: Cipher Suite Flags
A security-operation may be implemented in a bundle using either one or two security blocks. For example, the operation OP(authentication, bundle) MAY be accomplished by a single BAB block in the bundle, or it MAY be accomplished by two BAB blocks in the bundle. To avoid confusion, we use the following terminology to identify the block or blocks comprising a security-operation.
The terms "First" and "Last" are used ONLY when describing multiple security blocks comprising a single security-operation. A "First" block refers to the security block that is closest to the primary block in the canonical form of the bundle. A "Last" block refers to the security block that is furthest from the primary block in the canonical form of the bundle.
If a single security block implements the security-operation, then it is referred to as a "Lone" block. For example, when a bundle authentication cipher suite requires a single BAB block we refer to it as a Lone BAB. When a bundle authentication cipher suite requires two BAB blocks we refer to them as the First BAB and the Last BAB.
This specification and individual cipher suites impose restrictions on what optional fields must and must not appear in First blocks, Last blocks, and Lone blocks.
This section describes typical field values for the BAB, which is solely used to implement OP(authentication, bundle).
Notes:
A BIB is an ASB with the following additional restrictions:
Notes:
A BCB is an ASB with the following additional restrictions:
The BCB is the only security block that modifies the contents of its security-target. When a BCB is applied, the security-target body data are encrypted "in-place". Following encryption, the security-target body data contains cipher-text, not plain-text. Other security-target block fields (such as type, processing control flags, and length) remain unmodified.
Fragmentation, reassembly, and custody transfer are adversely affected by a change in size of the payload due to ambiguity about what byte range of the block is actually in any particular fragment. Therefore, when the security-target of a BCB is the bundle payload, the BCB MUST NOT alter the size of the payload block body data. Cipher suites SHOULD place any block expansion, such as authentication tags (integrity check values) and any padding generated by a block-mode cipher, into an integrity check value item in the security-result field (see Section 3.9) of the BCB. This "in-place" encryption allows fragmentation, reassembly, and custody transfer to operate without knowledge of whether or not encryption has occurred.
Notes:
A CMSB is an ASB with the following additional restrictions:
A CMSB block is created with its corresponding security-target field pointing to a unique bundle block. The CMS security operations are performed upon the security-target's data field and the resulting encoded CMS content is stored within the CMS security-result field of the CMSB's payload. The security-target block's data MAY be left intact, replaced with alternate data, or completely erased based on the specification of the utilized CMS ciphersuite definition and applicable policy.
Multiple CMS operations may be nested within a single CMSB block to allow more than one security operation to be performed upon a security-target.
CMS Operations can be considered to have BPSec parallels: CMSB Enveloped-Data content type SHALL be considered as equivalent to a BPSec BCB block, and a CMSB Signed-Data type SHALL be considered as equivalent to a BPSec BIB block.
The four security-block types defined in this specification are designed to be as independent as possible. However, there are some cases where security blocks may share a security-target creating processing dependencies.
If confidentiality is being applied to a target that already has integrity applied to it, then an undesirable condition occurs where a security-aware intermediate node would be unable to check the integrity result of a block because the block contents have been encrypted after the integrity signature was generated. To address this concern, the following processing rules MUST be followed.
Additionally, since the CMSB block may contain either integrity or confidentiality information in its encapsulated CMS, there is no way to evaluate conflicts when a BIB/BCB and a CMSB have the same security target. To address this concern, the following processing rules MUST be followed.
These restrictions on block interactions impose a necessary ordering when applying security operations within a bundle. Specifically, for a given security-target, BIBs MUST be added before BCBs, and BABs MUST be added after all other security blocks. This ordering MUST be preserved in cases where the current BPA is adding all of the security blocks for the bundle or whether the BPA is a waypoint adding new security blocks to a bundle that already contains security blocks.
Various cipher suites include several items in the cipher suite parameters and/or security-result fields. Which items MAY appear is defined by the particular cipher suite description. A cipher suite MAY support several instances of the same type within a single block.
Each item is represented as a type-length-value. Type is a single byte indicating the item. Length is the count of data bytes to follow, and is an SDNV-encoded integer. Value is the data content of the item.
Item types, name, and descriptions are defined as follows.
Cipher suite parameters and result fields.
| Type | Name | Description |
|---|---|---|
| 0 | Reserved | |
| 1 | Initialization Vector (IV) | A random value, typically eight to sixteen bytes. |
| 2 | Reserved | |
| 3 | Key Information | Material encoded or protected by the key management system and used to transport an ephemeral key protected by a long-term key. |
| 4 | Content Range | Pair of SDNV values (offset,length) specifying the range of payload bytes to which an operation applies. The offset MUST be the offset within the original bundle, even if the current bundle is a fragment. |
| 5 | Integrity Signatures | Result of BAB or BIB digest or other signing operation. |
| 6 | Unassigned | |
| 7 | Salt | An IV-like value used by certain confidentiality suites. |
| 8 | BCB Integrity Check Value (ICV) / Authentication Tag | Output from certain confidentiality cipher suite operations to be used at the destination to verify that the protected data has not been modified. This value MAY contain padding if required by the cipher suite. |
| 9-255 | Reserved |
An example of BPSec blocks applied to a bundle is illustrated in Figure 4. In this figure the first column represents blocks within a bundle and the second column represents a unique identifier for each block, suitable for use as the security-target of a BPSec security-block. Since the mechanism and format of a security-target is not specified in this document, the terminology B1...Bn is used to identify blocks in the bundle for the purposes of illustration.
Block in Bundle ID
+=================================+====+
| Primary Block | B1 |
+---------------------------------+----+
| First BAB | B2 |
| OP(authentication, Bundle) | |
+---------------------------------+----+
| Lone BIB | B3 |
| OP(integrity, target=B1) | |
+---------------------------------+----+
| Lone BCB | B4 |
| OP(confidentiality, target=B5) | |
+---------------------------------+----+
| Extension Block | B5 |
+---------------------------------+----+
| Lone BIB | B6 |
| OP(integrity, target=B7) | |
+---------------------------------+----+
| Extension Block | B7 |
+---------------------------------+----+
| Lone BCB | B8 |
| OP(confidentiality, target=B9) | |
+---------------------------------+----+
| Lone BIB (encrypted by B8) | B9 |
| OP(integrity, target=B11) | |
+---------------------------------+----+
| Lone BCB |B10 |
| OP(confidentiality, target=B11) | |
+---------------------------------+----+
| Payload Block |B11 |
+---------------------------------+----+
| Last BAB |B12 |
| OP(authentication, Bundle) | |
+---------------------------------+----+
Figure 4: Sample Use of BSP Blocks
In this example a bundle has four non-security-related blocks: the primary block (B1), two extension blocks (B5,B7), and a payload block (B11). The following security applications are applied to this bundle.
Block in Bundle ID
+=========================================+====+
| Primary Block | B1 |
+-----------------------------------------+----+
| First BAB | B2 |
| OP(authentication, Bundle) | |
+-----------------------------------------+----+
| Lone CMSB | B3 |
| security-target=0x01 | |
| security-result= | |
| | |
| Signed-Data { | |
| Digest Algorithm(s), | |
| Enveloped-Data { | |
| Encrypted Data, | |
| Encrypted Encryption Key(s) | |
| }, | |
| Signature(s) and Certificate Chain(s) | |
| } | |
| | |
+-----------------------------------------+----+
| Payload Block | B4 |
| (Empty Data Field) | |
+-----------------------------------------+----+
| Last BAB | B5 |
| OP(authentication, Bundle) | |
+-----------------------------------------+----+
Figure 5: Sample Bundle With CMS Block
In this example a bundle has two non-security-related blocks: the primary block (B1) and a payload block (B4). This method would allow for the bundle to carry multiple CMS payloads by utilizing a multiple CMSB ASBs. The following security applications are applied to this bundle.
This section describes the security aspects of bundle processing.
In order to verify a signature of a bundle, the exact same bits, in the exact same order, MUST be input to the calculation upon verification as were input upon initial computation of the original signature value. Consequently, a node MUST NOT change the encoding of any URI [RFC3986] in the dictionary field, e.g., changing the DNS part of some HTTP URL from lower case to upper case. Because bundles MAY be modified while in transit (either correctly or due to implementation errors), canonical forms of security-targets MUST be defined.
Many fields in various blocks are stored as variable-length SDNVs. These are canonicalized into an "unpacked form" as eight-byte fixed-width fields in network byte order. The size of eight bytes is chosen because implementations MAY handle larger SDNV values as invalid, as noted in [RFC5050].
Bundle canonicalization permits no changes at all to the bundle between the security-source and the destination, with the exception of one of the Block Processing Control Flags, as described below. It is intended for use in BAB cipher suites. This algorithm conceptually catenates all blocks in the order presented, but omits all security-result data fields in security blocks having the bundle as their security-target. For example, when a BAB cipher suite specifies this algorithm, we omit the BAB security-result from the catenation. The inclusion of security-result length fields is as determined by the specified cipher suite. A security-result length field MAY be present even when the corresponding security-result data fields are omitted.
Notes:
This algorithm protects those parts of a block that SHOULD NOT be changed in transit.
There are three types of blocks that may undergo block canonicalization: the primary block, the payload block, or an extension block.
The canonical form of the primary block is shown in Figure 6. Essentially, it de-references the dictionary block, adjusts lengths where necessary, and ignores flags that may change in transit.
+----------------+----------------+----------------+----------------+ | Version | Processing flags (incl. COS and SRR) | +----------------+----------------+---------------------------------+ | Canonical primary block length | +----------------+----------------+---------------------------------+ | Destination endpoint ID length | +----------------+----------------+---------------------------------+ | Destination endpoint ID | +----------------+----------------+---------------------------------+ | Source endpoint ID length | +----------------+----------------+----------------+----------------+ | Source endpoint ID | +----------------+----------------+---------------------------------+ | Report-to endpoint ID length | +----------------+----------------+----------------+----------------+ | Report-to endpoint ID | +----------------+----------------+----------------+----------------+ + Creation Timestamp (2 x SDNV) + +---------------------------------+---------------------------------+ | Lifetime | +----------------+----------------+----------------+----------------+
Figure 6: The Canonical Form of the Primary Bundle Block
The fields shown in Figure 6 are as follows:
When canonicalizing the payload block, the block processing control flags value used for canonicalization is the unpacked SDNV value with reserved and mutable bits masked to zero. The unpacked value is ANDed with mask 0x0000 0000 0000 0077 to zero reserved bits and the "last block" bit. The "last block" bit is ignored because BABs and other security blocks MAY be added for some parts of the journey but not others, so the setting of this bit might change from hop to hop.
Payload blocks are canonicalized as-is, with the exception that, in some instances, only a portion of the payload data is to be protected. In such a case, only those bytes are included in the canonical form, and additional cipher suite parameters are required to specify which part of the payload is protected, as discussed further below.
When canonicalizing an extension block, the block processing control flags value used for canonicalization is the unpacked SDNV value with reserved and mutable bits masked to zero. The unpacked value is ANDed with mask 0x0000 0000 0000 0057 to zero reserved bits, the "last block" flag and the "Block was forwarded without being processed" bit. The "last block" flag is ignored because BABs and other security blocks MAY be added for some parts of the journey but not others, so the setting of this bit might change from hop to hop.
The "Block was forwarded without being processed" flag is ignored because the bundle may pass through nodes that do not understand that extension block and this flag would be set.
Endpoint ID references in blocks are canonicalized using the de-referenced text form in place of the reference pair. The reference count is not included, nor is the length of the endpoint ID text. The EID reference is, therefore, canonicalized as <scheme>:<SSP>, which includes the ":" character.
Since neither the length of the canonicalized EID text nor a null-terminator is used in EID canonicalization, a separator token MUST be used to determine when one EID ends and another begins. When multiple EIDs are canonicalized together, the character "," SHALL be placed between adjacent instances of EID text.
The block-length is canonicalized as its unpacked SDNV value. If the data to be canonicalized is less than the complete, original block data, this field contains the size of the data being canonicalized (the "effective block") rather than the actual size of the block.
Every bundle has a primary block that contains the source and destination endpoint IDs, and possibly other EIDs (in the dictionary field) that cannot be encrypted. If endpoint ID confidentiality is required, then bundle-in-bundle encapsulation can solve this problem in some instances.
Similarly, confidentiality requirements MAY also apply to other parts of the primary block (e.g., the current-custodian), and that is supported in the same manner.
Security blocks MUST be processed in a specific order when received by a security-aware node. The processing order is as follows.
Nodes implementing this specification SHALL consult their security policy to determine whether or not a received bundle is required by policy to include a BAB.
If the bundle is not required to have a BAB then BAB processing on the received bundle is complete, and the bundle is ready to be further processed for BIB/BCB handling or delivery or forwarding. Security policy may provide a means to override this default behavior and require processing of a BAB if it exists.
If the bundle is required to have a BAB but does not, then the bundle MUST be discarded and processed no further. If the bundle is required to have a BAB but the key information for the security-source cannot be determined or the security-result value check fails, then the bundle has failed to authenticate, and the bundle MUST be discarded and processed no further.
If the bundle is required to have a BAB, and a BAB exists, and the BAB information is verified, then the BAB processing on the received bundle is complete, and the bundle is ready to be further processed for BIB/BCB handling or delivery or forwarding.
A BAB received in a bundle MUST be stripped before the bundle is forwarded. A new BAB MAY be added as required by policy. This MAY require correcting the "last block" field of the to-be-forwarded bundle.
If the bundle has a BCB and the receiving node is the destination for the bundle, the node MUST decrypt the relevant parts of the security-target in accordance with the cipher suite specification.
If the relevant parts of an encrypted payload cannot be decrypted (i.e., the decryption key cannot be deduced or decryption fails), then the bundle MUST be discarded and processed no further; in this case, a bundle deletion status report (see [RFC5050]) indicating the decryption failure MAY be generated. If any other encrypted security-target cannot be decrypted then the associated security-target and all security blocks associated with that target MUST be discarded and processed no further.
When a BCB is decrypted, the recovered plain-text MUST replace the cipher-text in the security-target body data
A BIB MUST NOT be processed if the security-target of the BIB is also the security-target of a BCB in the bundle. Given the order of operations mandated by this specification, when both a BIB and a BCB share a security-target, it means that the security-target MUST have been encrypted after it was integrity signed and, therefore, the BIB cannot be verified until the security-target has been decrypted by processing the BCB.
If the security policy of a security-aware node specifies that a bundle SHOULD apply integrity to a specific security-target and no such BIB is present in the bundle, then the node MUST process this security-target in accordance with the security policy. This MAY involve removing the security-target from the bundle. If the removed security-target is the payload or primary block, the bundle MAY be discarded. This action may occur at any node that has the ability to verify an integrity signature, not just the bundle destination.
If the bundle has a BIB and the receiving node is the destination for the bundle, the node MUST verify the security-target in accordance with the cipher suite specification. If a BIB check fails, the security-target has failed to authenticate and the security-target SHALL be processed according to the security policy. A bundle status report indicating the failure MAY be generated. Otherwise, if the BIB verifies, the security-target is ready to be processed for delivery.
If the bundle has a BIB and the receiving node is not the bundle destination, the receiving node MAY attempt to verify the value in the security-result field. If the check fails, the node SHALL process the security-target in accordance to local security policy. It is RECOMMENDED that if a payload integrity check fails at a waypoint that it is processed in the same way as if the check fails at the destination.
A CMSB MUST NOT be processed if its security target is also the security target of any BAB, BIB, or BCB in the bundle.
The security services provided by a CMSB will be considered successful if all services in the CMSB are validated. If any one service encapsulated in the CMSB fails to validate, then the CMSB MUST be considered as having failed to validate and MUST be dispositioned in accordance with security policy.
If it is necessary for a node to fragment a bundle and security services have been applied to that bundle, the fragmentation rules described in [RFC5050] MUST be followed. As defined there and repeated here for completeness, only the payload may be fragmented; security blocks, like all extension blocks, can never be fragmented. In addition, the following security-specific processing is REQUIRED:
When a partial bundle has been received, the receiving node SHALL consult its security policy to determine if it MAY fragment the bundle, converting the received portion into a bundle fragment for further forwarding. Whether or not reactive fragmentation is permitted SHALL depend on the security policy and the cipher suite used to calculate the BAB authentication information, if required.
Specifically, if the security policy does not require authentication, then reactive fragmentation MAY be permitted. If the security policy does require authentication, then reactive fragmentation MUST NOT be permitted if the partial bundle is not sufficient to allow authentication.
If reactive fragmentation is allowed, then all BAB blocks must be removed from created fragments.
Key management in delay-tolerant networks is recognized as a difficult topic and is one that this specification does not attempt to solve.
When implementing BPSec, several policy decisions must be considered. This section describes key policies that affect the generation, forwarding, and receipt of bundles that are secured using this specification.
Certain applications of DTN need to both sign and encrypt a message, and there are security issues to consider with this.
All implementations are strongly RECOMMENDED to provide at least a BAB cipher suite. A relay node, for example, might not deal with end-to-end confidentiality and data integrity, but it SHOULD exclude unauthorized traffic and perform hop-by-hop bundle verification.
This protocol has fields that have been registered by IANA.
This specification allocates three block types from the existing "Bundle Block Types" registry defined in [RFC6255].
Additional Entries for the Bundle Block-Type Codes Registry:
| Value | Description | Reference |
|---|---|---|
| 2 | Bundle Authentication Block | This document |
| 3 | Block Integrity Block | This document |
| 4 | Block Confidentiality Block | This document |
This protocol has a cipher suite flags field and certain flags are defined. An IANA registry has been set up as follows.
The registration policy for this registry is: Specification Required
The Value range is: Variable Length
Cipher Suite Flag Registry:
| Bit Position (right to left) | Description | Reference |
|---|---|---|
| 0 | Block contains result | This document |
| 1 | Block Contains parameters | This document |
| 2 | Source EID ref present | This document |
| >3 | Reserved | This document |
This protocol has fields for cipher suite parameters and results. The field is a type-length-value triple and a registry is required for the "type" sub-field. The values for "type" apply to both the cipher suite parameters and the cipher suite results fields. Certain values are defined. An IANA registry has been set up as follows.
The registration policy for this registry is: Specification Required
The Value range is: 8-bit unsigned integer.
Cipher Suite Parameters and Results Type Registry:
| Value | Description | Reference |
|---|---|---|
| 0 | reserved | This document |
| 1 | initialization vector (IV) | This document |
| 2 | reserved | This document |
| 3 | key-information | This document |
| 4 | content-range (pair of SDNVs) | This document |
| 5 | integrity signature | This document |
| 6 | unassigned | This document |
| 7 | salt | This document |
| 8 | BCB integrity check value (ICV) | This document |
| 9-191 | reserved | This document |
| 192-250 | private use | This document |
| 251-255 | reserved | This document |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5050] | Scott, K. and S. Burleigh, "Bundle Protocol Specification", RFC 5050, November 2007. |
| [RFC5652] | Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009. |
| [RFC6255] | Blanchet, M., "Delay-Tolerant Networking Bundle Protocol IANA Registries", RFC 6255, May 2011. |
| [RFC3986] | Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. |
| [RFC4838] | Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R., Scott, K., Fall, K. and H. Weiss, "Delay-Tolerant Networking Architecture", RFC 4838, April 2007. |
| [RFC5751] | Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010. |
| [RFC6257] | Symington, S., Farrell, S., Weiss, H. and P. Lovell, "Bundle Security Protocol Specification", RFC 6257, May 2011. |
| [SBSP] | Birrane, E., "Streamlined Bundle Security Protocol", Internet-Draft draft-birrane-dtn-sbsp-01, October 2015. |
The following participants contributed technical material, use cases, and useful thoughts on the overall approach to this security specification: Scott Burleigh of the Jet Propulsion Laboratory, Amy Alford and Angela Hennessy of the Laboratory for Telecommunications Sciences, and Angela Dalton and Cherita Corbett of the Johns Hopkins University Applied Physics Laboratory.