Internet DRAFT - draft-howard-gss-browserid
draft-howard-gss-browserid
Network Working Group L. Howard
Internet-Draft PADL
Intended status: Experimental N. Williams
Expires: June 12, 2014 Cryptonector
December 9, 2013
A SASL and GSS-API Mechanism for the BrowserID Authentication Protocol
draft-howard-gss-browserid-07.txt
Abstract
This document defines protocols, procedures and conventions for a
Generic Security Service Application Program Interface (GSS-API)
security mechanism based on the BrowserID authentication mechanism.
Through the GS2 family of mechanisms defined in RFC 5801, these
protocols also define how Simple Authentication and Security Layer
(SASL, RFC 4422) applications may use BrowserID.
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
Task Force (IETF). Note that other groups may also distribute
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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 June 12, 2014.
Copyright Notice
Copyright (c) 2013 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
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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 . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Discovery and Negotiation . . . . . . . . . . . . . . . . 5
1.2. Authentication . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Message protection services . . . . . . . . . . . . . . . 6
2. Requirements notation . . . . . . . . . . . . . . . . . . 7
3. Naming . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. GSS name types . . . . . . . . . . . . . . . . . . . . . . 8
3.1.1. GSS_C_NT_BROWSERID_PRINCIPAL . . . . . . . . . . . . . . . 8
3.1.2. GSS_C_NT_USER_NAME . . . . . . . . . . . . . . . . . . . . 8
3.1.3. GSS_C_NT_HOSTBASED_SERVICE . . . . . . . . . . . . . . . . 8
3.1.4. GSS_C_NT_DOMAINBASED_SERVICE . . . . . . . . . . . . . . . 9
3.1.5. GSS_C_NT_ANONYMOUS . . . . . . . . . . . . . . . . . . . . 9
3.2. Name canonicalization . . . . . . . . . . . . . . . . . . 9
3.3. Exported name token format . . . . . . . . . . . . . . . . 9
3.4. Naming extensions . . . . . . . . . . . . . . . . . . . . 9
4. Context tokens . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Base protocol . . . . . . . . . . . . . . . . . . . . . . 10
4.1.1. Initial context token . . . . . . . . . . . . . . . . . . 10
4.1.2. Acceptor context token . . . . . . . . . . . . . . . . . . 11
4.1.3. Initiator context completion . . . . . . . . . . . . . . . 12
4.2. Mutual authentication . . . . . . . . . . . . . . . . . . 12
4.2.1. Initiator mutual authentication context token . . . . . . 13
4.2.2. Acceptor mutual authentication context token . . . . . . . 13
4.2.3. Initiator mutual authentication context completion . . . . 13
4.2.4. Acceptor certificate advertisement . . . . . . . . . . . . 14
4.3. Fast re-authentication . . . . . . . . . . . . . . . . . . 15
4.3.1. Ticket generation . . . . . . . . . . . . . . . . . . . . 15
4.3.2. Initiator re-authentication context token . . . . . . . . 15
4.3.3. Acceptor re-authentication context token . . . . . . . . . 16
4.3.4. Interaction with mutual authentication . . . . . . . . . . 17
4.3.5. Ticket renewal . . . . . . . . . . . . . . . . . . . . . . 17
4.4. Extra round-trip (XRT) option . . . . . . . . . . . . . . 17
4.4.1. Initiator XRT advertisement . . . . . . . . . . . . . . . 17
4.4.2. Acceptor XRT advertisement . . . . . . . . . . . . . . . . 18
4.4.3. Initiator XRT context token . . . . . . . . . . . . . . . 18
4.4.4. Acceptor XRT context token validation . . . . . . . . . . 18
4.4.5. Interaction with message protection services . . . . . . . 18
5. Validation . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1. Expiry times . . . . . . . . . . . . . . . . . . . . . . . 19
5.2. Audience . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3. Channel bindings . . . . . . . . . . . . . . . . . . . . . 19
5.4. Key agreement . . . . . . . . . . . . . . . . . . . . . . 19
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5.5. Signatures . . . . . . . . . . . . . . . . . . . . . . . . 20
5.6. Replay detection . . . . . . . . . . . . . . . . . . . . . 20
5.7. Return flags . . . . . . . . . . . . . . . . . . . . . . . 20
6. Assertion claims . . . . . . . . . . . . . . . . . . . . . 21
6.1. Request (initiator/UA) assertion . . . . . . . . . . . . . 21
6.1.1. "aud" (Audience) . . . . . . . . . . . . . . . . . . . . . 21
6.1.2. "exp" (Expiry time) . . . . . . . . . . . . . . . . . . . 22
6.1.3. "iat" (Issued at time) . . . . . . . . . . . . . . . . . . 22
6.1.4. "nbf" (Not before time) . . . . . . . . . . . . . . . . . 22
6.1.5. "epk" (Ephemeral Public Key) . . . . . . . . . . . . . . . 22
6.1.6. "cb" (Channel binding) . . . . . . . . . . . . . . . . . . 22
6.1.7. "nonce" (Mutual authentication nonce) . . . . . . . . . . 22
6.1.8. "tkt" (Ticket) . . . . . . . . . . . . . . . . . . . . . . 23
6.1.9. "opts" (Options) . . . . . . . . . . . . . . . . . . . . . 23
6.2. Response (acceptor/RP) assertion . . . . . . . . . . . . . 23
6.2.1. "iat" (Issued at time) . . . . . . . . . . . . . . . . . . 24
6.2.2. "epk" (Ephemeral Public Key) . . . . . . . . . . . . . . . 24
6.2.3. "exp" (Expiry time) . . . . . . . . . . . . . . . . . . . 24
6.2.4. "nonce" (Mutual authentication nonce) . . . . . . . . . . 25
6.2.5. "tkt" (Ticket) . . . . . . . . . . . . . . . . . . . . . . 25
6.2.6. "jti" (JWT ID) . . . . . . . . . . . . . . . . . . . . . . 25
6.3. Error (acceptor/RP) assertion . . . . . . . . . . . . . . 25
6.3.1. "gss-maj" (GSS major status code) . . . . . . . . . . . . 25
6.3.2. "gss-min" (GSS minor status code) . . . . . . . . . . . . 25
6.4. XRT assertion . . . . . . . . . . . . . . . . . . . . . . 28
7. Key derivation . . . . . . . . . . . . . . . . . . . . . . 29
7.1. Diffie-Hellman Key (DHK) . . . . . . . . . . . . . . . . . 29
7.2. Context Master Key (CMK) . . . . . . . . . . . . . . . . . 29
7.3. RP Response Key (RRK) . . . . . . . . . . . . . . . . . . 29
7.4. Context Root Key (CRK) . . . . . . . . . . . . . . . . . . 29
7.5. Authenticator Root Key (ARK) . . . . . . . . . . . . . . . 30
7.6. Authenticator Session Key (ASK) . . . . . . . . . . . . . 30
7.6.1. Extra Round Trip Key (XRTK) . . . . . . . . . . . . . . . 30
7.7. GSS Pseudo-Random Function (PRF) . . . . . . . . . . . . . 30
8. Example . . . . . . . . . . . . . . . . . . . . . . . . . 31
9. Security Considerations . . . . . . . . . . . . . . . . . 39
9.1. Host certificates for mutual authentication . . . . . . . 39
9.2. Error statuses . . . . . . . . . . . . . . . . . . . . . . 39
10. IANA Considerations . . . . . . . . . . . . . . . . . . . 40
10.1. OID Registry . . . . . . . . . . . . . . . . . . . . . . . 40
10.2. SASL Registry . . . . . . . . . . . . . . . . . . . . . . 41
11. References . . . . . . . . . . . . . . . . . . . . . . . . 42
11.1. Normative References . . . . . . . . . . . . . . . . . . . 42
11.2. Informative References . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 45
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1. Introduction
[BrowserID] is a web-based three-party security protocol by which
user agents can present to a Relying Party (RP) a signed assertion of
e-mail address ownership. BrowserID was intended to be used for web
authentication. We find BrowserID to be useful in general, therefore
we define herein how to use it in many more applications.
The Simple Authentication and Security Layer (SASL) [RFC4422] is a
framework for providing authentication and message protection
services via pluggable mechanisms. Protocols that support it include
IMAP, SMTP, and XMPP.
The Generic Security Service Application Program Interface (GSS-API)
[RFC2743] provides a framework for authentication and message
protection services through a common programming interface. This
document conforms to the SASL and GSS-API bridge specified in
[RFC5801], so it defines both a SASL and GSS-API mechanism.
The BrowserID mechanism described in this document reuses the
existing web-based BrowserID protocol, but profiles it for use in
applications that support SASL or GSS-API, adding features such as
key agreement, mutual authentication, and fast re-authentication.
The following diagram illustrates the interactions between the three
parties in the GSS BrowserID protocol. Note that the terms client,
initiator and user agent (UA) are used interchangeably in this
document, as are server, acceptor and relying party (RP).
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+------------+
| BrowserID |
| identity |
| provider |
+------------+
// \\
// \\
// \\
// \\
make signed // \\ fetch IdP public
certificate // \\ key over HTTPS
for user's // \\ (RP may cache)
public key // \\
// \\
// \\
// \\
|/ \|
+-------------+ +-------------+
| SASL or GSS | GSS BrowserID | SASL or GSS |
| client/UA |<------------------->| server/RP |
| (initiator) | | (acceptor) |
+-------------+ +-------------+
Figure 1: Interworking Architecture
1.1. Discovery and Negotiation
The means of discovering GSS-API peers and their supported mechanisms
is out of this specification's scope. They may use SASL [RFC4422] or
the Simple and Protected Negotiation mechanism (SPNEGO) [RFC4178].
Discovery of a BrowserID identity provider (IdP) for a user is
described in the BrowserID specification. A domain publishes a
document containing their public key and URIs for authenticating and
provisioning users, or pointer to an authority containing such a
document.
1.2. Authentication
The GSS-API protocol involves a client, known as the initiator,
sending an initial security context token of a chosen GSS-API
security mechanism to a peer, known as the acceptor. The two peers
subsequently exchange, synchronously, as many security context tokens
as necessary to complete the authentication or fail. The specific
number of context tokens exchanged varies by security mechanism: in
the case of the BrowserID mechanism, it is typically two (i.e. a
single round trip), however it can be more in some cases. Once
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authentication is complete, the initiator and acceptor share a
security context which identifies the peers and can optionally be
used for integrity or confidentiality protecting subsequent
application messages.
The original BrowserID protocol, as defined outside this document,
specifies a bearer token authentication protocol for web
applications. The user agent generates a short-term key pair, the
public key of which is signed by the user's IdP. (The user must have
already authenticated to the IdP; how this is done is not specified
by BrowserID, but forms-based authentication is common.) The IdP
returns a certificate for the user which may be cached by the user's
browser. When authenticating to a Relying Party (RP), the browser
generates an identity assertion containing the RP domain and an
expiration time. The user agent signs this and presents both the
assertion and certificate to the RP. (The combination of an
assertion and zero or more certificates is termed a "backed
assertion".) The RP fetches the public key for the IdP, validates
the user's certificate (and those of any intermediate certifying
parties) and then verifies the assertion.
The GSS BrowserID protocol extends this by having the RP always send
back a response to the user agent, which at a minimum provides key
confirmation (this is needed for some key agreement methods) and
indicates the lifetime of the established security context. The key
confirmation token is also required for mutual authentication, when
the initiator application requests that feature.
1.3. Message protection services
GSS-API provides a number of a message protection services:
GSS_Wrap() integrity and optional confidentiality for a message
GSS_GetMIC() integrity for a message sent separately
GSS_Pseudo_random() shared key derivation (e.g., for keying external
confidentiality+integrity layers)
These services may be used with security contexts that have a shared
session key, to protect application-layer messages.
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2. Requirements notation
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 [RFC2119].
The reader is assumed to be familiar with the terms used in the
BrowserID specification.
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3. Naming
The GSS-API provides a rich security principal naming model. At its
most basic the query forms of names consist of a user-entered/
displayable string and a "name-type". Name-types are constants with
names prefixed with "GSS_C_NT_" in the GSS-API. Names may also have
attributes [RFC6680].
3.1. GSS name types
3.1.1. GSS_C_NT_BROWSERID_PRINCIPAL
This name may contain an e-mail address, or a service principal name
identifying an acceptor. The encoding of service principal names is
intended to be somewhat compatible with the Kerberos [RFC4120]
security protocol (without the realm name).
The following ABNF defines the 'name' rule that names of this type
must match.
[[anchor1: Should we reference RFC2822 here? The Mozilla BrowserID
docs sure don't.]]
char-normal = %x00-2E/%x30-3F/%x41-5B/%x5D-FF
char-escaped = "\" %x2F / "\" %x40 / "\" %x5C
name-char = char-normal / char-escaped
name-string = 1*name-char
user = name-string
domain = name-string
email = user "@" domain
service-name = name-string
service-host = name-string
service-specific = name-string
service-specifics = service-specific 0*("/" service-specifics)
spn = service-name ["/" service-host [ "/" service-specifics]]
name = email / spn
3.1.2. GSS_C_NT_USER_NAME
This name is implicitly converted to a GSS_C_NT_BROWSERID_PRINCIPAL.
A default domain may be appended when importing names of this type.
3.1.3. GSS_C_NT_HOSTBASED_SERVICE
This name is transformed by replacing the "@" symbol with a "/", and
then implicitly converted to a GSS_C_NT_BROWSERID_PRINCIPAL.
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3.1.4. GSS_C_NT_DOMAINBASED_SERVICE
[RFC5178] domain-based service names are transformed into a
GSS_C_NT_BROWSERID_PRINCIPAL as follows:
o the <service> name becomes the first component of the BrowserID
principal name (service-name in ABNF)
o the <hostname> becomes the second component (service-host)
o the <domain> name becomes the third component (service-specific)
3.1.5. GSS_C_NT_ANONYMOUS
If the initiator principal's leaf certificate does not contain a
"principal" claim, then the initiator name has this name type.
3.2. Name canonicalization
The BrowserID GSS-API mechanism performs no name canonicalization.
The mechanism's GSS_Canonicalize_name() returns an MN whose display
form is the same as the query form. Of course, the principal named
obtained from a CREDENTIAL HANDLE may be canonical in that the IdP
might only issue credentials for canonical names, but credential
acquisition is out of scope here.
3.3. Exported name token format
The exported name token format for the BrowserID GSS-API mechanism is
the same as the query form, plus the standard exported name token
format header mandated by the GSS-API [RFC2743].
[[anchor2: Do we wish to say anything about the exported composite
name token format? It should be an encoding of the initiator's leaf
certificate.]]
3.4. Naming extensions
The acceptor MAY surface attributes from the assertion and any
certificates using GSS_Get_name_attribute() (see [RFC6680]). The URN
prefix is "urn:<TBD>:params:gss:jwt". If a SAML assertion is present
in the "saml" parameter of the leaf certificate, it may be surfaced
using the URN prefix "urn:<TBD>:params:gss:federated-saml-attribute".
Attributes from the assertion MUST be marked as unauthenticated
unless otherwise validated by the acceptor (e.g. the audience).
Attributes from certificates SHOULD be marked as authenticated.
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4. Context tokens
All context tokens include a two-byte token identifier followed by a
backed BrowserID assertion. This document defines the following
token IDs:
+---------+----------+-------+--------------------------+
| Section | Token ID | ASCII | Description |
+---------+----------+-------+--------------------------+
| 4.1.1 | 0x632C | c, | Initiator context token |
| | | | |
| 4.1.2 | 0x432C | C, | Acceptor context token |
| | | | |
| | 0x442C | D, | Context deletion token |
| | | | |
| 4.2.4 | 0x6D2C | m, | Initiator metadata token |
| | | | |
| 4.2.4 | 0x4D2C | M, | Acceptor metadata token |
+---------+----------+-------+--------------------------+
The token ID has a human-readable ASCII encoding for the benefit of
pure SASL implementations of this mechanism.
4.1. Base protocol
4.1.1. Initial context token
The initial context token is framed per Section 1 of [RFC2743]:
GSS-API DEFINITIONS ::=
BEGIN
MechType ::= OBJECT IDENTIFIER
-- representing BrowserID mechanism
GSSAPI-Token ::=
[APPLICATION 0] IMPLICIT SEQUENCE {
thisMech MechType,
innerToken ANY DEFINED BY thisMech
-- token ID and backed assertion
}
END
Unlike many other GSS-API mechanisms such as Kerberos, this token
framing is not used by subsequent context or by [I-D.zhu-negoex]
metadata tokens. As such, pure SASL implementations of this
mechanism do not need to deal with DER encoding the mechanism object
identifier.
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GSS BrowserID is a family of mechanisms, where the last element in
the OID arc indicates the [RFC4121] encryption type supported for
message protection services. The OID prefix is
1.3.6.1.4.1.5322.24.1. The NULL encryption type is valid, in which
case services that require a key are not available.
The innerToken consists of the initiator context token ID
concatenated with a backed assertion for the audience corresponding
to the target name passed into GSS_Init_sec_context(). In addition,
the assertion MAY contain the additional claims, which are described
later in this document:
o ECDH key agreement parameters (see Section 6.1.5)
o Channel binding information (see Section 6.1.6)
o A nonce for binding the request to a response signed with a
private key for mutual authentication (see Section 6.1.7)
o A ticket identifier for fast re-authentication using an
established session key rather than a BrowserID certificate (see
Section 6.1.8)
The call to GSS_Init_sec_context() returns GSS_C_CONTINUE_NEEDED to
indicate that a subsequent context token from the acceptor is
expected.
4.1.2. Acceptor context token
Upon receiving a context token from the initiator, the acceptor
validates that the token is well formed and contains a valid
BrowserID mechanism OID and the initiator context token ID.
The acceptor then verifies the backed identity assertion per the
BrowserID specification. This includes validating the expiry times,
audience, certificate chain, and assertion signature. The acceptor
then verifies the channel binding token, if present, and any other
GSS-specific claims in the assertion. In case of failure, a response
assertion containing GSS major and minor status codes SHOULD be
returned.
If the [RFC3961] encryption type for the selected mechanism is not
ENCTYPE_NULL, the acceptor generates a ECDH public key using the
parameters received from the client (see Section 6.2.2), and from it
derives the RP Response Key (RRK) (see Section 7.3). The acceptor
then generates a response assertion containing its ECDH public key
and context expiration time (note that the context expiration time is
a purely informational quantity). The response assertion will be:
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o signed in the acceptor's private key, if mutual authentication was
requested, and the acceptor has a key (see Section 4.2);
o signed in the RRK, if the encryption type for the selected
mechanism is not ENCTYPE_NULL;
o not signed in all other cases.
The response assertion is encoded as a backed assertion, prefixed
with the acceptor context token ID. It SHALL have a certificate
count of zero.
Finally, the Context Root Key (CRK) (see Section 7.4) is derived from
the ECDH shared secret (if present) and GSS_S_COMPLETE is returned,
along with the initiator name from the verified assertion. If the
CRK is available, the replay_det_state (GSS_C_REPLAY_FLAG),
sequence_state (GSS_C_SEQUENCE_FLAG), conf_avail (GSS_C_CONF_FLAG)
and integ_avail (GSS_C_INTEG_FLAG) security context flags are set to
TRUE.
Other assertion/certificate claims MAY be made available via
GSS_Get_name_attribute().
4.1.3. Initiator context completion
Upon receiving the acceptor context token, the initiator unpacks the
response assertion and, if applicable, computes the ECDH shared
secret and RRK. The RRK is used to verify the response assertion
unless mutual authentication is available, in which case the
acceptor's public key will be used.
The initiator sets the context expiry time with that received in the
response assertion, if present; otherwise, the context expires when
the initiator principal's certificate expires.
The CRK is derived from the ECDH shared secret and GSS_S_COMPLETE is
returned to indicate the initiator is authenticated and the context
is ready for use. No output token is emitted. Security context
flags are set as for the acceptor context.
4.2. Mutual authentication
Mutual authentication allows the acceptor to be authenticated to the
initiator. The mechanism SHALL set the mutual_state security context
flag (GSS_C_MUTUAL_FLAG) to TRUE if mutual authentication succeeded.
Support for mutual authentication is OPTIONAL.
The base protocol is extended as follows to support this:
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4.2.1. Initiator mutual authentication context token
If the initiator requested the mutual_state flag, it sends in its
request assertion an "opts" claim (see Section 6.1.9) containing the
"ma" value. It also includes a nonce (see Section 6.1.7) in order to
bind the initiator and acceptor assertions.
4.2.2. Acceptor mutual authentication context token
If the acceptor has a private key and certificate available and the
initiator indicated it desired mutual authentication by including the
"ma" protocol option, the acceptor signs the response using a private
key rather than the RP Response Key (RRK). The response includes the
nonce from the initiator's assertion. The acceptor MUST reject
requests for mutual authentication lacking a nonce.
While the response is a backed assertion, in order to take advantage
of existing keying infrastructures BrowserID certificates MUST NOT be
included in the backed assertion. Rather, an X.509 certificate SHALL
be included as a value for the "x5c" header parameter in the
assertion (see [I-D.ietf-jose-json-web-signature] 4.1.6). The
certificate MUST be valid for signing.
[[anchor3: We don't want to burden the initiator with having to
implement both methods of authenticating acceptors, and given that
initiators and acceptors both will generally need a PKIX
implementation, and given that acceptors will need a PKIX credential
for TLS, and that there is as yet no standard protocol for automatic
provisioning of BrowserID credentials for servers, using PKIX to
authenticate the server seems to be the easiest way to go.]]
4.2.3. Initiator mutual authentication context completion
The initiator verifies the assertion signature and that the nonce
matches, and validates the certificate chain according to [RFC5280].
Initiators MUST authenticate the service name using the matching
rules below:
o A service-name EKU from the registry defined by [I-D.zhu-pku2u];
id-kpServerAuth maps to the "http" service
o A spn expressed as a KRB5PrincipalName in the id-pkinit-san
otherName SAN (see [RFC4556] Section 3.2.2; the realm is ignored)
o A service-name expressed as a SRVName SAN (see [RFC4985])
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o Optionally, an out-of-band binding to the certificate
If there are no EKUs, or a single EKU containing id-kp-
anyExtendedKeyUsage, and no SAN containing the service name is
present, then all service names match. If a SAN containing the
service name is present, then any EKUs are ignored.
If the the host component of the service name (service-host) is not
expressed in a SAN as specified above, it MUST be present as a value
for the dNSName SAN or as the least significant Common Name RDN.
Note only the id-pkinit-san or SRVName SANs provide the ability to
authenticate the a service name containing a service-specific
component.
4.2.4. Acceptor certificate advertisement
[I-D.zhu-negoex] may be used to advertise acceptor certificates.
If the acceptor supports mutual authentication, it MAY include its
certificate and any additional certificates inside a backed assertion
with an empty payload as output for GSS_Query_meta_data(). The
"assertion" is prefixed with the two byte token identifier "M,".
Upon receiving this, the initiator MAY validate the certificate or
fingerprint, or present either to the initiator before committing to
authenticate.
The NegoEx signing key is the output of GSS_Pseudo_random() (see
Section 7.7) with an input of GSS_C_PRF_KEY_FULL and "gss-browserid-
negoex-initiator" or "gss-browserid-negoex-acceptor" (without
quotes), depending on the party generating the signature.
The NegoEx authentication scheme is the binary encoding of the
following hexadecimal string:
535538008647F5BC624BD8076949F0
where the third byte (zero above) is set to the [RFC3961] encryption
type for the selected mechanism. The authentication scheme for
encryption types greater than 255 is not specified here.
There is currently no initiator-sent metadata defined and acceptors
should ignore any sent. The metadata is advisory and the initiator
is free to ignore it.
[[anchor4: Delete this section as NegoEx will likely not be
progressed.]]
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4.3. Fast re-authentication
Fast re-authentication allows a security context to be established
using a secret key derived from the initial certificate-signed ECDH
key agreement.
The re-authentication assertion is signed with a HMAC using the
Authenticator Root Key (ARK) (see Section 7.5), rather than a
initiator principal's BrowserID certificate.
Support for fast re-authentication is OPTIONAL and is indicated by
the acceptor returning a ticket in the response assertion.
4.3.1. Ticket generation
If the acceptor supports re-authentication, the following steps are
added to Section 4.1.2:
1. A unique, opaque ticket identifier is generated.
2. The acceptor creates a JSON object containing the ticket
identifier and expiry time and returns it in the response to the
initiator (see Section 6.2.5).
The acceptor must be able to use the ticket identifier to securely
retrieve the subject, issuer, audience, expiry time, ARK and any
other relevant properties of the original security context. One
implementation choice may be to use the ticket identifier as a key
into a dictionary containing this information. Another would be to
encrypt this information in a long-term secret only known to the
acceptor and encode the resulting cipher-text in the opaque ticket
identifier.
The ticket expiry time by default SHOULD match the initiator's
certificate expiry, however it MAY be configurable so the ticket
expires before or after the certificate.
The initiator MAY cache tickets, along with the ARK, received from
the acceptor in order to re-authenticate to it at a future time.
4.3.2. Initiator re-authentication context token
The initiator looks in its ticket cache for an unexpired ticket for
the desired acceptor. If none is found, the normal certificate-based
authentication flow is performed, otherwise:
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1. The initiator generates a re-authentication assertion containing:
the name of the acceptor (see Section 6.1.1), an expiry time (see
Section 6.1.2) and/or the current time (see Section 6.1.3),
optional channel binding information (see Section 6.1.6), a
random nonce (see Section 6.1.7), and the ticket identifier (see
Section 6.1.8).
2. The initiator signs the re-authentication assertion with the ARK,
using the hash algorithm associated with the original context key
(see Section 10.1; HS256 is specified for the encryption types
referenced in this document).
3. The re-authentication assertion is packed into a backed
assertion. The certificate count is zero as the assertion is
signed with an established symmetric key.
4. The initiator generates an Authenticator Session Key (ASK) (see
Section 7.6) which is used to verify the response and derive the
CRK.
[[anchor5: Question: do we want an option to do an ECDH session key
exchange in the fast re-auth case? If we had a GSS req_flag for
requesting perfect forward security (PFS) then we would want to have
this option.]]
4.3.3. Acceptor re-authentication context token
1. The acceptor unpacks the re-authentication assertion and
retrieves the ARK, ticket expiry time, mutual authentication
state and any other properties (such as the initiator name)
associated with the ticket identifier.
2. The acceptor validates that the ticket and re-authentication
assertion have not expired.
3. The acceptor verifies the assertion using the ARK.
4. The acceptor generates the ASK (see Section 7.6) and derives the
RRK and CRK from this (see Section 7.3 and Section 7.4,
respectively).
5. The acceptor generates a response and signs and returns it. Note
that, unlike the certificate-based mutual authentication case,
the nonce need not be echoed back as the ASK (and thus the RRK)
is cryptographically bound to the nonce.
If the ticket cannot be found, or the authentication fails, the
acceptor SHOULD return a REAUTH_FAILED error, permitting the
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initiator to recover and fallback to generating a BrowserID
assertion. It MAY also include its local timestamp (see
Section 6.2.1) so that the initiator can perform clock skew
compensation.
4.3.4. Interaction with mutual authentication
The mutual authentication state of a re-authenticated context is
transitive. The initiator and acceptor MUST NOT set the mutual_state
flag for a re-authenticated context unless the original context was
mutually authenticated.
As such, the mutual authentication state of the original context must
be associated with the ticket.
4.3.5. Ticket renewal
Normally, re-authentication tickets are only issued when the
initiator authenticated with a certificate-signed assertion.
Acceptors MAY issue a new ticket with an expiry beyond the ticket
lifetime when the initiator used a re-authentication assertion. The
issuing of new tickets MUST be subject to a policy that prevents them
from being renewed indefinitely.
4.4. Extra round-trip (XRT) option
The extra round-trip (XRT) option adds an additional round trip to
the context token exchange. It allows the initiator to prove
knowledge of the Context Master Key (CMK) (see Section 7.2) by
sending an additional token signed in a key derived from the CMK and
an acceptor-issued challenge. Support for the XRT option is OPTIONAL
in the acceptor and REQUIRED in the initiator. The initiator is
allowed to not request it, but MUST perform XRT if the acceptor
requires it.
(Note that the term "extra round trip" is something of a misnomer; it
only adds an additional token to the context token exchange. It is
anticipated however that this mechanism will most commonly be used
with pseudo-mechanisms or application protocols that require an even
number of tokens.)
4.4.1. Initiator XRT advertisement
The initiator may advertise to the acceptor that it desires the XRT
option by sending in its request assertion an "opts" claim (see
Section 6.1.9) containing the "xrt" value. This option MUST be set
if the caller requested GSS_C_DCE_STYLE (see [RFC4757]). Otherwise,
the setting of this option is implementation dependent.
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4.4.2. Acceptor XRT advertisement
If the initiator requested the XRT option and the acceptor supports
it, or the acceptor requires it, the acceptor sends a "jti" claim
(see Section 6.2.6) in the response assertion containing a random
base 64 URL encoded value. This value MUST be at least 64 bits in
length. The acceptor then returns GSS_C_CONTINUE_NEEDED to indicate
that an additional context token is expected from the initiator.
4.4.3. Initiator XRT context token
If the acceptor indicated support for the XRT option by including a
"jti" claim in its response, then the initiator sends an additional
context token to the acceptor. This token contains the initiator
context token ID concatenated with a backed assertion with zero
certificates and an empty payload, signed using the XRTK (see
Section 7.6.1).
4.4.4. Acceptor XRT context token validation
The acceptor MUST validate the XRT context token by first validating
the context token ID, and then verifying the assertion signature with
the XRTK. The acceptor SHOULD reject XRT context tokens with a
certificate count greater than zero. Unknown claims in the assertion
payload MUST be ignored. The acceptor then returns GSS_C_COMPLETE to
the caller.
The acceptor MAY avoid using a replay cache when this option is in
effect.
4.4.5. Interaction with message protection services
When the XRT option is in effect, the XRTK is used instead of the CMK
to derive the Context Root Key (CRK) (see Section 7.4). Per-message
tokens MUST have the AcceptorSubkey flag set (see [RFC4121] Section
4.2.2).
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5. Validation
5.1. Expiry times
The expiry and, if present, issued-at and not-before times of all
elements in a backed assertion, MUST be validated. This applies
equally to re-authentication assertions, public key assertions, and
the entire certificate chain. If the expiry time is absent, the
issued-at time MUST be present, and the JWT implicitly expires a
short, implementation-defined interval after the issued-at time. (A
suggested interval is five minutes.)
The GSS context lifetime SHOULD NOT exceed the lifetime of the
initiator principal's certificate.
The lifetime of a re-authentication ticket SHOULD NOT exceed the
lifetime of the initiator principal's certificate. The acceptor MUST
validate the ticket expiry time when performing re-authentication.
Message protections services such as GSS_Wrap() SHOULD be available
beyond the GSS context lifetime for maximum application
compatibility.
5.2. Audience
If the credential passed to GSS_Accept_sec_context() is not for
GSS_C_NO_NAME, then its string representation as a BrowserID
principal (see Section 3.1.1) MUST match the audience claim in the
assertion.
5.3. Channel bindings
GSS-API channel binding is a protected facility for naming an
enclosing channel between the initiator and acceptor. If the
acceptor passed in channel bindings to GSS_Accept_sec_context(), the
assertion MUST contain a matching channel binding claim. (Only the
application_data component is validated.)
The acceptor SHOULD accept any channel binding provided by the
initiator if NULL channel bindings are passed to
GSS_Accept_sec_context().
5.4. Key agreement
The initiator MUST choose an ECDH curve with an equivalent strength
to the negotiated [RFC4121] encryption type. Appropriate curves are
given in Section 10.1.
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The curve strength MUST be verified by the acceptor. A stronger than
required curve MAY be selected by the initiator.
5.5. Signatures
Signature validation on assertions is the same as for the web usage
of BrowserID, with the addition that response assertions may and re-
authentication assertions must be signed with a symmetric key. In
this case the HMAC algorithm associated with the mechanism OID is
used, and there are no certificates in the backed assertion.
5.6. Replay detection
If the XRT option is not in effect, the acceptor MUST maintain a
cache of received assertions in order to guard against replay
attacks.
5.7. Return flags
The initiator and acceptor should set the returned flags as follows:
deleg_state never set
mutual_state set if the initiator requested mutual authentication
and mutual authentication succeeded
replay_det_state set if message protection services are available
sequence_state set if message protection services are available
anon_state set if the initiator principal's leaf certificate lacks a
"principal" claim
trans_state set if the implementation supports importing and
exporting of security contexts
prot_ready_state may be set when or after the RP Response Token is
produced or consumed
conf_avail set if message protection services are available
integ_avail set if message protection services are available
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6. Assertion claims
6.1. Request (initiator/UA) assertion
These claims are included in the assertion sent to the acceptor and
are authenticated by the initiator's private key and certificate
chain (directly, or in the case of re-authentication assertions,
transitively). Claims not specified here MUST be ignored by the
acceptor.
Here is an example assertion containing Elliptic Curve Diffie-Hellman
parameters, along with options and nonce claims indicating that
mutual authentication is desired:
{
"opts": [
"ma"
],
"exp": 1360158396188,
"epk": {
"kty": "EC",
"crv": "P-256",
"x": "JR5UPDgMLFPZwOGaKKSF24658tB1DccM1_oHPbCHeZg",
"y": "S45Esx_6DfE5-xdB3X7sIIJ16MwO0Y_RiDc-i5ZTLQ8"
},
"nonce": "bbqT10Gyx3s",
"aud": "imap/mail.example.com"
}
The following claims are permitted in the request assertion:
6.1.1. "aud" (Audience)
The audience is a StringOrURI (see [I-D.ietf-oauth-json-web-token]
Section 2) containing the target service's principal name, formatted
according to Section 3.1.1. This claim is REQUIRED. If the
initiator specified a target name of GSS_C_NO_NAME, then the audience
is the empty string.
[[anchor6: If the initiator wanted mutual authentication then we
could find out the acceptor's name and provide it via
GSS_Inquire_context(). This is only really useful and secure with
mechanisms like this one where the initiator credential is based on a
public/private key pair and either we use key agreement and per-
message tokens or channel binding to a secure channel. This really
should [have] be[en] explained in RFC2743.]]
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6.1.2. "exp" (Expiry time)
This contains the time when the assertion expires, in milliseconds
since January 1, 1970. At least one of "exp" or "iat" MUST be
present.
6.1.3. "iat" (Issued at time)
This contains the time the assertion was issued (in milliseconds
since January 1, 1970). If present, the acceptor MUST validate that
the assertion was recently issued. At least one of "exp" or "iat"
MUST be present.
6.1.4. "nbf" (Not before time)
This contains the time, in milliseconds since January 1, 1970, from
which the assertion begins to be valid. This claim is OPTIONAL.
6.1.5. "epk" (Ephemeral Public Key)
These contain key parameters for deriving a shared session key with
the relying party, represented as a JSON Web Key
[I-D.ietf-jose-json-web-key] public key value. The key type MUST be
EC and the parameters for Elliptic Curve Public Keys specified in
[I-D.ietf-jose-json-web-algorithms] Section 6.2.1 MUST be present.
The "epk" claim is REQUIRED unless the associated encryption type is
ENCTYPE_NULL, or there is already a prior session key (as is the case
for re-authentication assertions).
6.1.6. "cb" (Channel binding)
This contains channel binding information for binding the GSS context
to an outer channel (e.g. see [RFC5929]). Its value is the base64
URL encoding of the application-specific data component of the
channel bindings passed to GSS_Init_sec_context() or
GSS_Accept_sec_context(). This claim is OPTIONAL.
6.1.7. "nonce" (Mutual authentication nonce)
This is a random quantity of at least 64 bits, base 64 URL encoded,
which is used to bind the request and response assertions in the case
a freshly agreed key is not used to sign the response assertion.
This claim is REQUIRED if mutual authentication is desired and the
assertion is signed using a certificate, or if re-authentication is
being performed.
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6.1.8. "tkt" (Ticket)
When the assertion is being used for fast re-authentication, this
contains a JSON object with a single parameter, "tid". The "tid"
parameter matches the "tid" parameter from the initial response
assertion ticket (see Section 6.2.5). This claim is REQUIRED for re-
authentication assertions, otherwise it the assertion MUST be
rejected. Other parameters SHOULD NOT be present in the "tkt"
object.
6.1.9. "opts" (Options)
This contains a JSON array of string values indicating various
protocol options that are supported by the initiator. Unknown
options MUST be ignored by the acceptor. This document defines the
following extensions:
+------+------------------------------------------------------------+
| Name | Description |
+------+------------------------------------------------------------+
| ma | The initiator requested GSS_C_MUTUAL_FLAG |
| | |
| xrt | The initiator supports the extra round trip option (see |
| | Section 4.4) |
| | |
| dce | The initiator requested GSS_C_DCE_STYLE (see RFC4757 |
| | Section 7.1) |
| | |
| ify | The initiator requested GSS_C_IDENTIFY_FLAG (see RFC4757 |
| | Section 7.1) |
+------+------------------------------------------------------------+
6.2. Response (acceptor/RP) assertion
The response assertion is sent from the acceptor to the initiator to
provide key agreement, and either key confirmation or mutual
authentication. It is formatted as a backed assertion, however in
the current specification it consists of a single assertion with zero
certificates; that is, it is "unbacked". (It is encoded as a backed
assertion in order to provide future support for mutual
authentication using native BrowserID certificates. Such support is
not specified here.)
In the case of a key successfully being negotiated, the response
assertion is signed with the RP Response Key (RRK) (see Section 7.3).
Alternatively, it may be signed with the acceptor's private RSA or
DSA key. In this case, the acceptor's X.509 certificate is included
in the "x5c" claim of the JWT header.
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The HMAC-SHA256 (HS256) algorithm MUST be supported by implementors
of this specification.
If the [RFC3961] encryption type for the mechanism is ENCTYPE_NULL,
then the signature is absent and the value of the "alg" header
parameter is "none". No signature verification is required in this
case.
Claims not specified here MUST be ignored by the initiator.
Here is an example response assertion:
{
"exp": 1362960258000,
"nonce": "bbqT10Gyx3s",
"epk": {
"x": "bvNF6V1rpMeQyGOKCj0kBaOaSh3tlhUcbffaji4uCEI",
"y": "Iuqs650FXzXFUD9kHknETfbqiB8XBbCHlJXoysx3rvw"
},
"tkt": {
"tid": "Jgg7vKX2sEKlCWBfmLTg_n4qz3NVZxOU-a2B4qYMkXI",
"exp": 1362992660000
}
}
The following claims are permitted in the response assertion:
6.2.1. "iat" (Issued at time)
The current acceptor time, in milliseconds since January 1, 1970.
This allows the initiator to compensate for clock differences when
generating assertions. This claim is OPTIONAL.
6.2.2. "epk" (Ephemeral Public Key)
This contains a JSON object containing the x and y coordinates of the
acceptor's ECDH public key (see [I-D.ietf-jose-json-web-algorithms]
Section 6.2.1). This claim is REQUIRED unless the associated
encryption type is ENCTYPE_NULL, or there is already an established
session key, as is the case for re-authentication assertions.
The "crv" and "kty" properties SHOULD NOT be present; they are
determined by the initiator.
6.2.3. "exp" (Expiry time)
This contains the time when the context expires, in milliseconds
since January 1, 1970. This claim is OPTIONAL; the initiator should
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use the certificate or ticket expiry time if absent.
6.2.4. "nonce" (Mutual authentication nonce)
The nonce as received from the initiator. This MUST NOT be present
unless a nonce was received from the initiator, and the acceptor is
signing the assertion with a private key.
6.2.5. "tkt" (Ticket)
This contains a JSON object that may be used for re-authenticating to
the acceptor without acquiring an assertion. It has two parameters:
"tid", an opaque identifier to be presented in a re-authentication
assertion (this need not be a string); and "exp", the expiry time of
the ticket. This claim is OPTIONAL.
6.2.6. "jti" (JWT ID)
This contains a base64 URL encoded random value of at least 64 bits
that is used to uniquely identify the acceptor response, in the case
that the extra round trip option is used. It SHOULD not be present
unless the initiator requested the extra round trip option.
6.3. Error (acceptor/RP) assertion
Error assertions are backed assertions containing any or all of the
following claims. In addition, they MUST have the "iat" claim, for
initiator clock skew correction. All other response assertion claims
are OPTIONAL or not applicable in error assertions. Conversely, the
claims listed below MUST NOT be present in a non-error response
assertion.
The error assertion MAY be signed if a key is available, otherwise
the signature is absent and the value of the "alg" header parameter
is "none".
6.3.1. "gss-maj" (GSS major status code)
This contains a GSS major status code represented as a number.
6.3.2. "gss-min" (GSS minor status code)
This contains a GSS minor status code represented as a number.
If REAUTH_FAILED is received, the initiator SHOULD attempt to send
another initial context token containing a fresh assertion.
The following protocol minor status codes are defined. Note that the
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API representation of these status codes is implementation dependent.
Status codes with the high bit set are GSS BrowserID protocol errors;
the remainder are BrowserID protocol errors.
+---------------------------+------------+--------------------------+
| Error | Protocol | Description |
+---------------------------+------------+--------------------------+
| INVALID_JSON | 8 | Invalid JSON encoding |
| | | |
| INVALID_BASE64 | 9 | Invalid Base64 encoding |
| | | |
| INVALID_ASSERTION | 10 | Invalid assertion |
| | | |
| TOO_MANY_CERTS | 13 | Too many certificates |
| | | |
| UNTRUSTED_ISSUER | 14 | Untrusted issuer |
| | | |
| INVALID_ISSUER | 15 | Invalid issuer |
| | | |
| MISSING_ISSUER | 16 | Missing issuer |
| | | |
| MISSING_AUDIENCE | 17 | Missing audience |
| | | |
| BAD_AUDIENCE | 18 | Bad audience |
| | | |
| EXPIRED_ASSERTION | 19 | Assertion expired |
| | | |
| ASSERTION_NOT_YET_VALID | 20 | Assertion not yet valid |
| | | |
| EXPIRED_CERT | 21 | Certificate expired |
| | | |
| CERT_NOT_YET_VALID | 22 | Certificate not yet |
| | | valid |
| | | |
| INVALID_SIGNATURE | 23 | Invalid signature |
| | | |
| MISSING_ALGORITHM | 24 | Missing JWS algorithm |
| | | |
| UNKNOWN_ALGORITHM | 25 | Unknown JWS algorithm |
| | | |
| MISSING_PRINCIPAL | 34 | Missing principal |
| | | attribute |
| | | |
| UNKNOWN_PRINCIPAL_TYPE | 35 | Unknown principal type |
| | | |
| MISSING_CERT | 36 | Missing certificate |
| | | |
| MISSING_CHANNEL_BINDINGS | 38 | Missing channel bindings |
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| CHANNEL_BINDINGS_MISMATCH | 39 | Channel bindings do not |
| | | match |
| | | |
| NOT_REAUTH_ASSERTION | 70 | Not a re-authentication |
| | | assertion |
| | | |
| BAD_SUBJECT | 71 | Bad subject name |
| | | |
| MISMATCHED_RP_RESPONSE | 72 | Mismatched RP response |
| | | token |
| | | |
| REFLECTED_RP_RESPOSNE | 73 | Reflected RP response |
| | | token |
| | | |
| UNKNOWN_EC_CURVE | 77 | Unknown ECC curve |
| | | |
| INVALID_EC_CURVE | 78 | Invalid ECC curve |
| | | |
| MISSING_NONCE | 79 | Missing nonce |
| | | |
| WRONG_SIZE | 0x80000001 | Buffer is incorrect size |
| | | |
| WRONG_MECH | 0x80000002 | Mechanism OID is |
| | | incorrect |
| | | |
| BAD_TOK_HEADER | 0x80000003 | Token header is |
| | | malformed or corrupt |
| | | |
| TOK_TRUNC | 0x80000004 | Token is missing data |
| | | |
| BAD_DIRECTION | 0x80000005 | Packet was replayed in |
| | | wrong direction |
| | | |
| WRONG_TOK_ID | 0x80000006 | Received token ID does |
| | | not match expected |
| | | |
| KEY_UNAVAILABLE | 0x80000007 | Key unavailable |
| | | |
| KEY_TOO_SHORT | 0x80000008 | Key too weak |
| | | |
| CONTEXT_ESTABLISHED | 0x80000009 | Context already |
| | | established |
| | | |
| CONTEXT_INCOMPLETE | 0x8000000A | Context incomplete |
| | | |
| BAD_CONTEXT_TOKEN | 0x8000000B | Context token malformed |
| | | or corrupt |
| | | |
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| BAD_ERROR_TOKEN | 0x8000000C | Error token malformed or |
| | | corrupt |
| | | |
| BAD_CONTEXT_OPTION | 0x8000000D | Bad context option |
| | | |
| REAUTH_FAILED | 0x8000000E | Re-authentication |
| | | failure |
+---------------------------+------------+--------------------------+
6.4. XRT assertion
No claims are presently defined for the extra round trip assertion.
Unknown claims MUST be ignored by the acceptor.
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7. Key derivation
The following function is used as the base algorithm for deriving
keys:
browserid-derive-key(K, usage) = HMAC(K, "BrowserID" || K || usage ||
0x01)
The HMAC hash algorithm for all currently specified key lengths is
SHA-256. Note that the inclusion of K in the HMAC input is for
interoperability with some crypto implementations.
7.1. Diffie-Hellman Key (DHK)
This key is the shared secret resulting from the ECDH exchange. Its
length corresponds to the selected EC curve. It is never used
without derivation and thus may be used with implementations that do
not expose the ECDH value directly.
7.2. Context Master Key (CMK)
This is the Diffie-Hellman Key (DHK) for all initially authenticated
contexts and the Authenticator Session Key (ASK) for re-authenticated
contexts.
7.3. RP Response Key (RRK)
If mutual authentication without a fast re-authentication ticket is
performed then the response assertion will be signed with a public
key signature using the private key for the acceptor's certificate.
Otherwise a symmetric RP Response Key (RRK) is derived as follows:
RRK = browserid-derive-key(CMK, "RRK")
7.4. Context Root Key (CRK)
The Context Root Key (CRK) is used for [RFC4121] message protection
services, e.g. GSS_Wrap() and GSS_Get_MIC(). If the extra round-
trip option is in effect, it is derived as follows:
CRK = random-to-key(browserid-derive-key(XRTK, "CRK"))
Otherwise, the CMK is used:
CRK = random-to-key(browserid-derive-key(CMK, "CRK"))
The random-to-key function is defined in [RFC3961].
Howard & Williams Expires June 12, 2014 [Page 29]
Internet-Draft BrowserID SASL & GSS-API December 2013
7.5. Authenticator Root Key (ARK)
The Authenticator Root Key (ARK) is used to sign assertions used for
fast re-authentication. (The term "authenticator" is equivalent to
"re-authentication assertion" and exists for historical reasons.) It
is derived as follows:
ARK = browserid-derive-key(CMK, "ARK")
7.6. Authenticator Session Key (ASK)
The Authenticator Session Key (ASK) is used instead of the DHK for
re-authenticated contexts. It is derived as follows:
ASK = browserid-derive-key(ARK, nonce-binary)
The usage (nonce-binary) is the base64 URL decoding of the initiator
"nonce" claim.
7.6.1. Extra Round Trip Key (XRTK)
The Extra Round Trip Key (XRTK) is used to sign the extra round trip
token, and also as the master key for the CRK when the extra round
trip option is used.
XRTK = browserid-derive-key(CMK, acceptor-jti-binary)
The usage (acceptor-jti-binary) is the base64 URL decoding of the
acceptor "jti" claim.
7.7. GSS Pseudo-Random Function (PRF)
The BrowserID mechanism shares the same Pseudo-Random Function (PRF)
as the Kerberos GSS mechanism, defined in [RFC4402].
GSS_C_PRF_KEY_FULL and GSS_C_PRF_KEY_PARTIAL are equivalent. The
protocol key to be used for GSS_Pseudo_random() SHALL by the Context
Root Key (CRK).
[[anchor7: Can we replace this with a function that imports less of
RFC3962? We arguably should, because otherwise the only things we
import from RFC3962 (and 3961) are random-to-key (the identity
function in RFC3962) and the crypto bits needed for RFC4121 per-
message tokens.]]
Howard & Williams Expires June 12, 2014 [Page 30]
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8. Example
Suppose a mail user agent for the principal lukeh@lukktone.com wishes
to authenticate to an IMAP server rand.mit.de.padl.com. They do not
have a re-authentication ticket. The mail user agent would display a
dialog box in which the principal would sign in to their IdP and
request a fresh assertion be generated.
C: <connects to IMAP port>
S: * OK
C: C1 CAPABILITY
S: * CAPABILITY IMAP4rev1 SASL-IR SORT [...] AUTH=BROWSERID-AES128
S: C1 OK Capability Completed
C: C2 AUTHENTICATE BROWSERID-AES128
biwsYyxleUpoYkdjaU9pSlNVekkxTmlKOS5leUp3ZFdKc2FXTXRhMlY
1SWpwN0ltRnNaMjl5YVhSb2JTSTZJa1JUSWl3aWVTSTZJak01TVRObE
9EZ3laRGhqTXpWa01qSm1ObVEwTURZNVkyVTJNREJrWW1OallqTTVOR
0ZqWVdGaFl6WTBPV1prTjJZNVptTmtObU0wTVRJME5tWTFOakk1TUdW
bU1HTmpNemMwTnpaaE1EUmhOREU0WXpGbE9ETXhPV0kxTkdJeFpXTml
ObVkyWTJWaE56VTBOR1kyWlRFMU5qTmxaR05sWkdNNU1EWmtOamcwTT
JRd01XSmpaVFJtTjJFMVpqY3dOMk5tWVRZd1lXTTVNVE0yWm1GbU5qS
m1aR0ZtTkRoa09HRTVPRGxoWVdGbE5EUXdOMlZrTmpjeU56ZGhNVGM0
TW1WallXRXhOVFppWkdOaFpXRXhOamRtTWpZek56STFaR1UyTTJWa09
HWXlPR0UyTUROaU5tWm1OVEV3WmpRNE1ESmtOelJrTjJWaFpUZGhZbU
15WldJaUxDSndJam9pWm1ZMk1EQTBPRE5rWWpaaFltWmpOV0kwTldWa
FlqYzROVGswWWpNMU16TmtOVFV3WkRsbU1XSm1NbUU1T1RKaE4yRTRa
R0ZoTm1Sak16Um1PREEwTldGa05HVTJaVEJqTkRJNVpETXpOR1ZsWld
GaFpXWmtOMlV5TTJRME9ERXdZbVV3TUdVMFkyTXhORGt5WTJKaE16ST
FZbUU0TVdabU1tUTFZVFZpTXpBMVlUaGtNVGRsWWpOaVpqUmhNRFpoT
XpRNVpETTVNbVV3TUdRek1qazNORFJoTlRFM09UTTRNRE0wTkdVNE1t
RXhPR00wTnprek16UXpPR1k0T1RGbE1qSmhaV1ZtT0RFeVpEWTVZemh
tTnpWbE16STJZMkkzTUdWaE1EQXdZek5tTnpjMlpHWmtZbVEyTURRMk
16aGpNbVZtTnpFM1ptTXlObVF3TW1VeE55SXNJbkVpT2lKbE1qRmxNR
FJtT1RFeFpERmxaRGM1T1RFd01EaGxZMkZoWWpOaVpqYzNOVGs0TkRN
d09XTXpJaXdpWnlJNkltTTFNbUUwWVRCbVpqTmlOMlUyTVdaa1pqRTR
OamRqWlRnME1UTTRNelk1WVRZeE5UUm1OR0ZtWVRreU9UWTJaVE5qT0
RJM1pUSTFZMlpoTm1ObU5UQTRZamt3WlRWa1pUUXhPV1V4TXpNM1pUQ
TNZVEpsT1dVeVlUTmpaRFZrWldFM01EUmtNVGMxWmpobFltWTJZV1l6
T1Rka05qbGxNVEV3WWprMllXWmlNVGRqTjJFd016STFPVE15T1dVME9
ESTVZakJrTUROaVltTTNPRGsyWWpFMVlqUmhaR1UxTTJVeE16QTROVG
hqWXpNMFpEazJNalk1WVdFNE9UQTBNV1kwTURreE16WmpOekkwTW1Fe
k9EZzVOV001WkRWaVkyTmhaRFJtTXpnNVlXWXhaRGRoTkdKa01UTTVP
R0prTURjeVpHWm1ZVGc1TmpJek16TTVOMkVpZlN3aWNISnBibU5wY0d
Gc0lqcDdJbVZ0WVdsc0lqb2liSFZyWldoQWJIVnJhM1J2Ym1VdVkyOX
RJbjBzSW1saGRDSTZNVE0yTWprMk1UQTVOakV5TWl3aVpYaHdJam94T
XpZeU9UWTBOamsyTVRJeUxDSnBjM01pT2lKc2IyZHBiaTV3WlhKemIy
NWhMbTl5WnlKOS5mT3V5ZlZkNWFZZ285ckJncmdHVDJHYjkzUUoxVnp
LSE9rNjdFUXBEeU9pUENPdXFweUw5a2tVVDdxcGNZaWZsb0NTWjlPej
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UtVWRrcldlcTZXUkRLcUdOeXg0OFdyVGduVkoyRlM3MU1Mbl9DeWhGM
Go1Y1ZsQ0E5WWh3YVlWTHhsbW9YU01uWTdyRzFWa0VSdjRtaWtCM3FD
cFB2NXJtSEswbkNiRlpiN1dXR3JkVEdkcmNHTkRkZHlDQkQ5a1dpUUd
VbkktenN3WXdiZXJUTmQ3Nmc1Z2N1c1MtbWxjVk5jbzNMTG4zMlNhbG
x0eDBCUHAtVTAyMXpvR00wWEhibm1Sa2VRdGVtblVXZGloYzRVbVpNR
EJJZ05nSFFCSmdXMGhBcTlHWVFmYzVObFNzZW5RX0p5MGR4anE1bHdE
Wll3SExsUXlmYnVYbGFtRTNDZ3ZkZUF+ZXlKaGJHY2lPaUpFVXpFeU9
DSjkuZXlKdWIyNWpaU0k2SW1nMVVEUkxja2M0ZVc1bklpd2laV05rYU
NJNmV5SjRJam9pWm1wYVRuQnpRbXBIYmw5WVFVTnRaMkpPZDBGemRuS
TRPR2MwUmxkNmRHOWljWEExVkUxaVgxbEdNQ0lzSW1OeWRpSTZJbEF0
TWpVMklpd2llU0k2SWxKTFJYWktlalU1WTNOaGRqaExZM2RsVlhZMVd
IRkdaM1E0UVZkRFFXdHlTa0o2TTFCUWNVeEtkSE1pZlN3aVkySjBJam
9pWW1sM2N5SXNJbVY0Y0NJNk1UTTJNamsyTVRJeE5qRTBPU3dpWVhWa
0lqb2lkWEp1T25ndFozTnpPbWx0WVhBdmNtRnVaQzV0YVhRdVpHVXVj
R0ZrYkM1amIyMGlmUS51ZHRvSTNVNUMtM3BwNHhJSloxbWstQ3o0Ymh
sQkxlSzAyNlVhbWRhMjhwTFk4c013Tk50Y0E=
S: + Qyx
+ZXlKaGJHY2lPaUpTVXpJMU5pSXNJbmcxWXlJNld5Sk5TVWxFZW1wRF
EwRnlZV2RCZDBsQ1FXZEpRa0o2UVU1Q1oydHhhR3RwUnpsM01FSkJVV
lZHUVVSQ1pFMVJjM2REVVZsRVZsRlJSMFYzU2tKV1ZFVmxUVUozUjBF
eFZVVkRaM2RXVlVWR1JWUkRRbFJpTWxvd1pESkdlVnBUUWxGa1NHdG5
WRWhTYTAxVE5IZE1RVmxFVmxGUlJFUkRWbEZSVlZKTlNVWk9kbHB1VW
pOWldFcHNTVVZPYkdOdVVuQmFiV3hxV1ZoU2NHSXlOR2RSV0ZZd1lVY
zVlV0ZZVWpWTlFqUllSRlJGZWsxRVJYaE5WRUV4VFhwUmVVMUdiMWhF
VkVVeVRVUkZlRTFVUVRGTmVsRjVUVVp2ZDFSRVJVeE5RV3RIUVRGVlJ
VSm9UVU5SVmxWNFNHcEJZMEpuVGxaQ1FXOU5SbFpDUWxKRmQyZFZNam
x0WkVoa2FHTnRWV2RWU0ZJMVNVVjRNRnBFUldSTlFuTkhRVEZWUlVGM
2QxVmpiVVoxV2tNMWRHRllVWFZhUjFWMVkwZEdhMkpETldwaU1qQjNa
MmRGYVUxQk1FZERVM0ZIVTBsaU0wUlJSVUpCVVZWQlFUUkpRa1IzUVh
kblowVkxRVzlKUWtGUlJFSm9la1p3Wmt3MmRraDRjM2d5UkhaR1dsQX
JSMUl3Vlc5dFJIQXZRMFZsSzA5SVRqQmFNR00yT1RGWlp6bG5WMWh0V
lROdVVIRldWR0pCU1hGWVNEaEJWWFIyWmpkTmVtSlpNamh2Vm14d1ds
UXdOWHB0TW1NdmRFVXpaMnRvVkhodFdFOVNaMUZ5WTNWMVozVnFUMWh
OUm1oSk5ITjJSVm9yUTJKSVVHeGFhVm92VkhwcldFeElVREk1UlhvM2
QwNWFiakZJTlRkQlRIRnRVMEZ2TlZRMGNYaE5SbWRDV1hWa2R5OWFlR
kJTZWtSMFZXOUpWakJ6TWpOWlp6UjRWRGxoZDBwdWNqRkhaMDFWVW1s
aVZVSnFSamQ1WW1OdE1FczRjMHBVSzFWSFpVSTNjbTFNYkZCM0syWkJ
hMDltTjFwcVdqbDBjRlJyUlUxcE9IVk1SVTF4WTNoaFIxTkJTeThyYT
FjM05YRlBlR1JCUmtrNGVsbGFXRFV6WjNCbk5HMXBLMUZYWmtkWk1Wc
E9VVXBOZFVoSFVWaG5MM1ZtZUUxNllYaE9UalJvTVdGUGJHMWFXbGxy
UWtod05USkJPWGxKVFZWaVFXZE5Ra0ZCUjJwbllXdDNaMkZaZDBOUld
VUldVakJVUWtGSmQwRkVRWE5DWjJ4bmFHdG5RbWgyYUVOQlVUQkZTSG
haWkZRelFteGliRTVVVkVOQ1NGcFhOV3hqYlVZd1dsZFJaMUV5Vm5sa
1IyeHRZVmRPYUdSSFZYZElVVmxFVmxJd1QwSkNXVVZHUzFOemRXSkZS
SFZpVWtsSFNFTkNkSFJCYkZSMk1rWlhSMllyVFVJNFIwRXhWV1JKZDF
GWlRVSmhRVVpNYVhwYWJFMVhia3RMTVZCWllXZGtTbXByVm5WU2FFVl
JTbXBOUVd0SFFURlZaRVZSVVVOTlFVRjNRM2RaUkZaU01GQkNRVkZFU
VdkWVowMUNUVWRCTVZWa1NsRlJUVTFCYjBkRFEzTkhRVkZWUmtKM1RV
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Uk5RVEJIUTFOeFIxTkpZak5FVVVWQ1FsRlZRVUUwU1VKQlVVSkVNVUo
2VVZBcmNrNHhWVlY2TjBFMmVpdExSRkJoY1Roek1tbENSekJHZWxwNG
MxZ3lVVlZQZFhCQ1JVbGlkVnB3TUV0S1lYVnFWazFuTURGbVpHcHpkV
WRITUhWWVlrMW1aVkpIZVU1c1ZYTk5UaXRhUkhrNEwwMUpUMmd4WVZW
SGRqQlRWWGRMZEVOMFRIUlhja3AyTmpWMWQwaEhSM1ExZFVaTGVFMUZ
OakZXVkRRcmNYQkpNa0ZIY1hoNE5XUnljM2hGVEVKUFpIbFFibVYxUV
dsTVVIaEdkV0pTUm0xNmRXaFdVMGszUVZCTmJEYzVUMnN6TUc5WGRXU
kJORGxzVlZnNWQzb3paemx4T1haa2JEbDVhR2RsWlZWVFZYQk5hR3hh
TWpSVll6bFFkVXg2Y2pFMWFqWjJOak5ZZW5KVFpGZDBUbnAyTUVZeE1
HVkViRFI1VkZWT1YxTkthRGR4UW1obmNURkpiMWc1UVZCUFQzVk1Zaz
FPY25BMlltVkZaVzkzYURNMGNGWlhabFJoVTNoSk4yNUxOVGRyU3pKN
GFGSlZORE5sZDFscU1ta3ZVM0o2T0VkelRWTTVNWFZ5TWpWSmRDSmRm
US5leUowYTNRaU9uc2lhblJwSWpvaVlXVmhlVEJIU21sNlJIZzNPVUZ
uTFMxWFRDMTJkelpaT1VKWWVGSjFRekZZYzFwNGNuazFNVk5WU1NJc0
ltVjRjQ0k2TVRNMk1qazVOekE1T0RBd01IMHNJbVZqWkdnaU9uc2llQ
0k2SWtveFNWZGlTREpCTlVNelkyaFBWVWx4YldaWWNGQmZVbEZGUlU5
dFpESkZlRmh2UzNKeFVWRllURTBpTENKNUlqb2lYekpGZEhoaWVsOTJ
TbVZsVlZWaWVUSnlabVJsYTFSVVVGVlNjR0pIU2tnM2EzbEpWM0Z0YT
BsRlp5SjlMQ0p1YjI1alpTSTZJbWcxVURSTGNrYzRlVzVuSWl3aVpYa
HdJam94TXpZeU9UWTBOamsyTURBd2ZRLnFaaFVxdXBWUHgzRTdNSTBH
dnNIZjZER3pzc3ByMkJsdUVUMFNwMERxdkpFS1F4S3BiOG9faVZsWHZ
Qa2p2SXp0Qm5JajNNb084UlZMUWJwdE9QZDFrN3FoTUVwRkhOVGI1WF
pKYWVJTlBpQUNSSzA5dUZpVE5ud1cxanMxQ3pPY2FMakxsSTN4bFdkL
Ul1em8zODhyTUxsSXVkbmkxak5uRS0yOXZfc1NUTnRxLUMwQmNoNUMw
T3drbDcxQk54eHgzaFVxeEcxT0w0UHQyZ0JKWUFQX3NOVk12aDFwWDl
hRzd0Vms0S2sxS2NjaXRqUFdGN0dXc3JGeld4ekRSMHU2REZ0RmFjaE
NPYmVmcmZnZkUxOXFlWnJLcnpJMFVkQ3JEUHpZazlYb1dKR2twRlNPd
1dhY192Q0N1dXY1VjNHZF9MTlNJM3JCaS1GYWVoWUhBRjFJUQ==
Unpacking the mail user agent's AUTHENTICATE message reveals the
following:
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n,,c,eyJhbGciOiJSUzI1NiJ9.eyJwdWJsaWMta2V5Ijp7ImFsZ29yaXRob
SI6IkRTIiwieSI6IjM5MTNlODgyZDhjMzVkMjJmNmQ0MDY5Y2U2MDBkYmNj
YjM5NGFjYWFhYzY0OWZkN2Y5ZmNkNmM0MTI0NmY1NjI5MGVmMGNjMzc0NzZ
hMDRhNDE4YzFlODMxOWI1NGIxZWNiNmY2Y2VhNzU0NGY2ZTE1NjNlZGNlZG
M5MDZkNjg0M2QwMWJjZTRmN2E1ZjcwN2NmYTYwYWM5MTM2ZmFmNjJmZGFmN
DhkOGE5ODlhYWFlNDQwN2VkNjcyNzdhMTc4MmVjYWExNTZiZGNhZWExNjdm
MjYzNzI1ZGU2M2VkOGYyOGE2MDNiNmZmNTEwZjQ4MDJkNzRkN2VhZTdhYmM
yZWIiLCJwIjoiZmY2MDA0ODNkYjZhYmZjNWI0NWVhYjc4NTk0YjM1MzNkNT
UwZDlmMWJmMmE5OTJhN2E4ZGFhNmRjMzRmODA0NWFkNGU2ZTBjNDI5ZDMzN
GVlZWFhZWZkN2UyM2Q0ODEwYmUwMGU0Y2MxNDkyY2JhMzI1YmE4MWZmMmQ1
YTViMzA1YThkMTdlYjNiZjRhMDZhMzQ5ZDM5MmUwMGQzMjk3NDRhNTE3OTM
4MDM0NGU4MmExOGM0NzkzMzQzOGY4OTFlMjJhZWVmODEyZDY5YzhmNzVlMz
I2Y2I3MGVhMDAwYzNmNzc2ZGZkYmQ2MDQ2MzhjMmVmNzE3ZmMyNmQwMmUxN
yIsInEiOiJlMjFlMDRmOTExZDFlZDc5OTEwMDhlY2FhYjNiZjc3NTk4NDMw
OWMzIiwiZyI6ImM1MmE0YTBmZjNiN2U2MWZkZjE4NjdjZTg0MTM4MzY5YTY
xNTRmNGFmYTkyOTY2ZTNjODI3ZTI1Y2ZhNmNmNTA4YjkwZTVkZTQxOWUxMz
M3ZTA3YTJlOWUyYTNjZDVkZWE3MDRkMTc1ZjhlYmY2YWYzOTdkNjllMTEwY
jk2YWZiMTdjN2EwMzI1OTMyOWU0ODI5YjBkMDNiYmM3ODk2YjE1YjRhZGU1
M2UxMzA4NThjYzM0ZDk2MjY5YWE4OTA0MWY0MDkxMzZjNzI0MmEzODg5NWM
5ZDViY2NhZDRmMzg5YWYxZDdhNGJkMTM5OGJkMDcyZGZmYTg5NjIzMzM5N2
EifSwicHJpbmNpcGFsIjp7ImVtYWlsIjoibHVrZWhAbHVra3RvbmUuY29tI
n0sImlhdCI6MTM2Mjk2MTA5NjEyMiwiZXhwIjoxMzYyOTY0Njk2MTIyLCJp
c3MiOiJsb2dpbi5wZXJzb25hLm9yZyJ9.fOuyfVd5aYgo9rBgrgGT2Gb93Q
J1VzKHOk67EQpDyOiPCOuqpyL9kkUT7qpcYifloCSZ9Oz5-UdkrWeq6WRDK
qGNyx48WrTgnVJ2FS71MLn_CyhF0j5cVlCA9YhwaYVLxlmoXSMnY7rG1VkE
Rv4mikB3qCpPv5rmHK0nCbFZb7WWGrdTGdrcGNDddyCBD9kWiQGUnI-zswY
wberTNd76g5gcusS-mlcVNco3LLn32Salltx0BPp-U021zoGM0XHbnmRkeQ
temnUWdihc4UmZMDBIgNgHQBJgW0hAq9GYQfc5NlSsenQ_Jy0dxjq5lwDZY
wHLlQyfbuXlamE3CgvdeA~eyJhbGciOiJEUzEyOCJ9.eyJub25jZSI6Img1
UDRLckc4eW5nIiwiZWNkaCI6eyJ4IjoiZmpaTnBzQmpHbl9YQUNtZ2JOd0F
zdnI4OGc0Rld6dG9icXA1VE1iX1lGMCIsImNydiI6IlAtMjU2IiwieSI6Il
JLRXZKejU5Y3NhdjhLY3dlVXY1WHFGZ3Q4QVdDQWtySkJ6M1BQcUxKdHMif
SwiY2J0IjoiYml3cyIsImV4cCI6MTM2Mjk2MTIxNjE0OSwiYXVkIjoidXJu
OngtZ3NzOmltYXAvcmFuZC5taXQuZGUucGFkbC5jb20ifQ.udtoI3U5C-3p
p4xIJZ1mk-Cz4bhlBLeK026Uamda28pLY8sMwNNtcA
The initial "n,," is the GS2 header (indicating that there are no
channel bindings). The "c," denotes the token as being a BrowserID
initial context token. The remaining base64 URL encoded data is a
BrowserID backed assertion, containing the following certificate (for
clarity, the payload has been reformatted and JWT header and
signature omitted):
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{
"public-key": {
"algorithm": "DS",
"y": "3913e882d8c35d22f6d4069ce600dbccb394acaaac649
fd7f9fcd6c41246f56290ef0cc37476a04a418c1e8319
b54b1ecb6f6cea7544f6e1563edcedc906d6843d01bce
4f7a5f707cfa60ac9136faf62fdaf48d8a989aaae4407
ed67277a1782ecaa156bdcaea167f263725de63ed8f28
a603b6ff510f4802d74d7eae7abc2eb",
"p": "ff600483db6abfc5b45eab78594b3533d550d9f1bf2a9
92a7a8daa6dc34f8045ad4e6e0c429d334eeeaaefd7e2
3d4810be00e4cc1492cba325ba81ff2d5a5b305a8d17e
b3bf4a06a349d392e00d329744a5179380344e82a18c4
7933438f891e22aeef812d69c8f75e326cb70ea000c3f
776dfdbd604638c2ef717fc26d02e17",
"q": "e21e04f911d1ed7991008ecaab3bf775984309c3",
"g": "c52a4a0ff3b7e61fdf1867ce84138369a6154f4afa929
66e3c827e25cfa6cf508b90e5de419e1337e07a2e9e2a
3cd5dea704d175f8ebf6af397d69e110b96afb17c7a03
259329e4829b0d03bbc7896b15b4ade53e130858cc34d
96269aa89041f409136c7242a38895c9d5bccad4f389a
f1d7a4bd1398bd072dffa896233397a"
},
"principal": {
"email": "lukeh@lukktone.com"
},
"iat": 1362961096122,
"exp": 1362964696122,
"iss": "login.persona.org"
}
and assertion:
{
"nonce": "h5P4KrG8yng",
"epk": {
"x": "fjZNpsBjGn_XACmgbNwAsvr88g4FWztobqp5TMb_YF0",
"crv": "P-256",
"kty": "EC",
"y": "RKEvJz59csav8KcweUv5XqFgt8AWCAkrJBz3PPqLJts"
},
"cb": "biws",
"exp": 1362961216149,
"aud": "imap/rand.mit.de.padl.com"
}
Note the channel binding token that protects the GS2 header.
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Internet-Draft BrowserID SASL & GSS-API December 2013
[[anchor8: The encoded example needs to be regenerated to reflect
that "cb" is now used for channel bindings.]]
Turning to the response backed assertion sent from the IMAP server to
the mail user agent, we have the following after base64 decoding:
eyJhbGciOiJSUzI1NiIsIng1YyI6WyJNSUlEempDQ0FyYWdBd0lCQWdJQkJ
6QU5CZ2txaGtpRzl3MEJBUVVGQURCZE1Rc3dDUVlEVlFRR0V3SkJWVEVlTU
J3R0ExVUVDZ3dWVUVGRVRDQlRiMlowZDJGeVpTQlFkSGtnVEhSa01TNHdMQ
VlEVlFRRERDVlFRVVJNSUZOdlpuUjNZWEpsSUVObGNuUnBabWxqWVhScGIy
NGdRWFYwYUc5eWFYUjVNQjRYRFRFek1ERXhNVEExTXpReU1Gb1hEVEUyTUR
FeE1UQTFNelF5TUZvd1RERUxNQWtHQTFVRUJoTUNRVlV4SGpBY0JnTlZCQW
9NRlZCQlJFd2dVMjltZEhkaGNtVWdVSFI1SUV4MFpERWRNQnNHQTFVRUF3d
1VjbUZ1WkM1dGFYUXVaR1V1Y0dGa2JDNWpiMjB3Z2dFaU1BMEdDU3FHU0li
M0RRRUJBUVVBQTRJQkR3QXdnZ0VLQW9JQkFRREJoekZwZkw2dkh4c3gyRHZ
GWlArR1IwVW9tRHAvQ0VlK09ITjBaMGM2OTFZZzlnV1htVTNuUHFWVGJBSX
FYSDhBVXR2ZjdNemJZMjhvVmxwWlQwNXptMmMvdEUzZ2toVHhtWE9SZ1FyY
3V1Z3VqT1hNRmhJNHN2RVorQ2JIUGxaaVovVHprWExIUDI5RXo3d05abjFI
NTdBTHFtU0FvNVQ0cXhNRmdCWXVkdy9aeFBSekR0VW9JVjBzMjNZZzR4VDl
hd0pucjFHZ01VUmliVUJqRjd5YmNtMEs4c0pUK1VHZUI3cm1MbFB3K2ZBa0
9mN1pqWjl0cFRrRU1pOHVMRU1xY3hhR1NBSy8ra1c3NXFPeGRBRkk4ellaW
DUzZ3BnNG1pK1FXZkdZMVpOUUpNdUhHUVhnL3VmeE16YXhOTjRoMWFPbG1a
WllrQkhwNTJBOXlJTVViQWdNQkFBR2pnYWt3Z2FZd0NRWURWUjBUQkFJd0F
EQXNCZ2xnaGtnQmh2aENBUTBFSHhZZFQzQmxibE5UVENCSFpXNWxjbUYwWl
dRZ1EyVnlkR2xtYVdOaGRHVXdIUVlEVlIwT0JCWUVGS1NzdWJFRHViUklHS
ENCdHRBbFR2MkZXR2YrTUI4R0ExVWRJd1FZTUJhQUZMaXpabE1XbktLMVBZ
YWdkSmprVnVSaEVRSmpNQWtHQTFVZEVRUUNNQUF3Q3dZRFZSMFBCQVFEQWd
YZ01CTUdBMVVkSlFRTU1Bb0dDQ3NHQVFVRkJ3TURNQTBHQ1NxR1NJYjNEUU
VCQlFVQUE0SUJBUUJEMUJ6UVArck4xVVV6N0E2eitLRFBhcThzMmlCRzBGe
lp4c1gyUVVPdXBCRUlidVpwMEtKYXVqVk1nMDFmZGpzdUdHMHVYYk1mZVJH
eU5sVXNNTitaRHk4L01JT2gxYVVHdjBTVXdLdEN0THRXckp2NjV1d0hHR3Q
1dUZLeE1FNjFWVDQrcXBJMkFHcXh4NWRyc3hFTEJPZHlQbmV1QWlMUHhGdW
JSRm16dWhWU0k3QVBNbDc5T2szMG9XdWRBNDlsVVg5d3ozZzlxOXZkbDl5a
GdlZVVTVXBNaGxaMjRVYzlQdUx6cjE1ajZ2NjNYenJTZFd0Tnp2MEYxMGVE
bDR5VFVOV1NKaDdxQmhncTFJb1g5QVBPT3VMYk1OcnA2YmVFZW93aDM0cFZ
XZlRhU3hJN25LNTdrSzJ4aFJVNDNld1lqMmkvU3J6OEdzTVM5MXVyMjVJdC
JdfQ.eyJ0a3QiOnsianRpIjoiYWVheTBHSml6RHg3OUFnLS1XTC12dzZZOU
JYeFJ1QzFYc1p4cnk1MVNVSSIsImV4cCI6MTM2Mjk5NzA5ODAwMH0sImVjZ
GgiOnsieCI6IkoxSVdiSDJBNUMzY2hPVUlxbWZYcFBfUlFFRU9tZDJFeFhv
S3JxUVFYTE0iLCJ5IjoiXzJFdHhiel92SmVlVVVieTJyZmRla1RUUFVScGJ
HSkg3a3lJV3Fta0lFZyJ9LCJub25jZSI6Img1UDRLckc4eW5nIiwiZXhwIj
oxMzYyOTY0Njk2MDAwfQ.qZhUqupVPx3E7MI0GvsHf6DGzsspr2BluET0Sp
0DqvJEKQxKpb8o_iVlXvPkjvIztBnIj3MoO8RVLQbptOPd1k7qhMEpFHNTb
5XZJaeINPiACRK09uFiTNnwW1js1CzOcaLjLlI3xlWd-Iuzo388rMLlIudn
i1jNnE-29v_sSTNtq-C0Bch5C0Owkl71BNxxx3hUqxG1OL4Pt2gBJYAP_sN
VMvh1pX9aG7tVk4Kk1KccitjPWF7GWsrFzWxzDR0u6DFtFachCObefrfgfE
19qeZrKrzI0UdCrDPzYk9XoWJGkpFSOwWac_vCCuuv5V3Gd_LNSI3rBi-Fa
ehYHAF1IQ
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Here we show the JWT header for the response assertion, as it
includes an ASN.1 encoded X.509 certificate, which is used to
mutually authenticate the IMAP server to the UA:
{
"alg": "RS256",
"x5c": [
"MIIDzjCCAragAwIBAgIBBzANBgkqhkiG9w0BAQUFADBdMQswCQ
YDVQQGEwJBVTEeMBwGA1UECgwVUEFETCBTb2Z0d2FyZSBQdHkg
THRkMS4wLAYDVQQDDCVQQURMIFNvZnR3YXJlIENlcnRpZmljYX
Rpb24gQXV0aG9yaXR5MB4XDTEzMDExMTA1MzQyMFoXDTE2MDEx
MTA1MzQyMFowTDELMAkGA1UEBhMCQVUxHjAcBgNVBAoMFVBBRE
wgU29mdHdhcmUgUHR5IEx0ZDEdMBsGA1UEAwwUcmFuZC5taXQu
ZGUucGFkbC5jb20wggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwgg
EKAoIBAQDBhzFpfL6vHxsx2DvFZP+GR0UomDp/CEe+OHN0Z0c6
91Yg9gWXmU3nPqVTbAIqXH8AUtvf7MzbY28oVlpZT05zm2c/tE
3gkhTxmXORgQrcuugujOXMFhI4svEZ+CbHPlZiZ/TzkXLHP29E
z7wNZn1H57ALqmSAo5T4qxMFgBYudw/ZxPRzDtUoIV0s23Yg4x
T9awJnr1GgMURibUBjF7ybcm0K8sJT+UGeB7rmLlPw+fAkOf7Z
jZ9tpTkEMi8uLEMqcxaGSAK/+kW75qOxdAFI8zYZX53gpg4mi+
QWfGY1ZNQJMuHGQXg/ufxMzaxNN4h1aOlmZZYkBHp52A9yIMUb
AgMBAAGjgakwgaYwCQYDVR0TBAIwADAsBglghkgBhvhCAQ0EHx
YdT3BlblNTTCBHZW5lcmF0ZWQgQ2VydGlmaWNhdGUwHQYDVR0O
BBYEFKSsubEDubRIGHCBttAlTv2FWGf+MB8GA1UdIwQYMBaAFL
izZlMWnKK1PYagdJjkVuRhEQJjMAkGA1UdEQQCMAAwCwYDVR0P
BAQDAgXgMBMGA1UdJQQMMAoGCCsGAQUFBwMDMA0GCSqGSIb3DQ
EBBQUAA4IBAQBD1BzQP+rN1UUz7A6z+KDPaq8s2iBG0FzZxsX2
QUOupBEIbuZp0KJaujVMg01fdjsuGG0uXbMfeRGyNlUsMN+ZDy
8/MIOh1aUGv0SUwKtCtLtWrJv65uwHGGt5uFKxME61VT4+qpI2
AGqxx5drsxELBOdyPneuAiLPxFubRFmzuhVSI7APMl79Ok30oW
udA49lUX9wz3g9q9vdl9yhgeeUSUpMhlZ24Uc9PuLzr15j6v63
XzrSdWtNzv0F10eDl4yTUNWSJh7qBhgq1IoX9APOOuLbMNrp6b
eEeowh34pVWfTaSxI7nK57kK2xhRU43ewYj2i/Srz8GsMS91ur
25It"]
}
The assertion payload is below (again, for clarity the actual JWT
signature has been omitted):
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Internet-Draft BrowserID SASL & GSS-API December 2013
{
"tkt": {
"tid": "aeay0GJizDx79Ag--WL-vw6Y9BXxRuC1XsZxry51SUI",
"exp": 1362997098000
},
"epk": {
"x": "J1IWbH2A5C3chOUIqmfXpP_RQEEOmd2ExXoKrqQQXLM",
"y": "_2Etxbz_vJeeUUby2rfdekTTPURpbGJH7kyIWqmkIEg"
},
"nonce": "h5P4KrG8yng",
"exp": 1362964696000
}
Note the fast re-authentication ticket and the nonce echoed back from
the initiator.
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Internet-Draft BrowserID SASL & GSS-API December 2013
9. Security Considerations
This document defines a GSS-API security mechanism, and therefore
deals in security and has security considerations text embedded
throughout. This section only addresses security considerations
associated with the BrowserID GSS mechanism described in this
document. It does not address security considerations associated
with the BrowserID protocol or the GSS-API themselves.
This mechanism provides for authentication of initiator principals
using private keys to public key crypto-systems, using the BrowserID
specification for user certificates (which are NOT PKIX [RFC5280]
certificates). Authentication of the acceptor principal is optional.
Fast re-authentication is supported via acceptor-issued fast re-
authentication tickets.
All cryptography for per-message tokens is imported from the Kerberos
GSS-API mechanism [RFC4121].
This mechanism actually has several mechanism OIDs, composed of a
prefix identifying this family of mechanisms followed by an arc
identifying the [RFC3961] encryption type for use with per-message
tokens and the GSS_Pseudo_random() function. The NULL encryption
type is supported, and when it is used then the GSS-API per-message
tokens and GSS_Pseudo_random() function are not available, but
channel binding and mutual authentication may be available. Also,
when using the NULL encryption type the fast re-authentication
feature is not available because key exchange is only performed the
initiator application uses the variant of this mechanism that
supports per-message tokens and the GSS_Pseudo_random() function.
Acceptor credentials are PKIX [RFC5280] certificates and their
private keys.
9.1. Host certificates for mutual authentication
Allowing a match on only the DNS subjectAltName in an acceptor's
X.509 certificate permits different services on the same host to
impersonate each other. This should be subject to local policy.
9.2. Error statuses
Returning rich error information in the clear (see Section 6.3.2) may
leak information. Implementations may squash status codes and/or
avoid returning minor statuses entirely. Indeed, applications may
even not send back error tokens at all, instead closing the
connection or whatever might be appropriate for the application.
(This is a generic GSS-API security consideration.)
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Internet-Draft BrowserID SASL & GSS-API December 2013
10. IANA Considerations
This specification creates a number of IANA registries.
10.1. OID Registry
Prefix: iso.org.dod.internet.private.enterprise.padl.gssBrowserID
(1.3.6.1.4.1.5322.24)
+---------+------------+-------------------------------------------+
| Decimal | Name | Description |
+---------+------------+-------------------------------------------+
| 0 | Reserved | Reserved |
| | | |
| 1 | mechanisms | A sub-arc containing BrowserID mechanisms |
| | | |
| 2 | nametypes | A sub-arc containing BrowserID name types |
+---------+------------+-------------------------------------------+
Prefix:
iso.org.dod.internet.private.enterprise.padl.gssBrowserID.mechanisms
(1.3.6.1.4.1.5322.24.1)
+-------+------------------+---------------------+-------+----------+
| Decim | Name | Description | ECDH | Symmetri |
| al | | | curve | c hash |
+-------+------------------+---------------------+-------+----------+
| 0 | gss-browserid-nu | The NULL security | N/A | N/A |
| | ll | mechanism | | |
| | | | | |
| 17 | gss-browserid-ae | The | P-256 | HS256 |
| | s128 | aes128-cts-hmac-sha | | |
| | | 1-96 mechanism | | |
| | | | | |
| 18 | gss-browserid-ae | The | P-521 | HS256 |
| | s256 | aes256-cts-hmac-sha | | |
| | | 1-96 mechanism | | |
+-------+------------------+---------------------+-------+----------+
Prefix:
iso.org.dod.internet.private.enterprise.padl.gssBrowserID.nametypes
(1.3.6.1.4.1.5322.24.2)
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Internet-Draft BrowserID SASL & GSS-API December 2013
+---------+------------------------------+-------------+
| Decimal | Name | Description |
+---------+------------------------------+-------------+
| 0 | Reserved | Reserved |
| | | |
| 1 | GSS_C_NT_BROWSERID_PRINCIPAL | 3.1.1 |
+---------+------------------------------+-------------+
10.2. SASL Registry
Subject: Registration of SASL mechanisms BROWSERID-AES128 and
BROWSERID-AES128-PLUS
SASL mechanism names: BROWSERID-AES128 and BROWSERID-AES128-PLUS
Security considerations: See RFC 5801 and draft-howard-gss-browserid
Published specification (recommended): draft-howard-gss-browserid
Person & email address to contact for further information:
Luke Howard lukeh@padl.com
Intended usage: common
Owner/Change controller: iesg@ietf.org
Note: This mechanism describes the GSS BrowserID mechanism used with
the aes128-cts-hmac-sha1-96 encryption type. The GSS-API OID for
this mechanism is 1.3.6.1.4.1.5322.24.1.17. As described in RFC 5801
a PLUS variant of this mechanism is also required.
[[anchor9: We could use the NULL encryption type variant for SASL, as
the GS2 bridge does not use message protection services. However,
because that mechanisms is unkeyed, re-authentication would not be
available. Defining a single AES128 mechanism is consistent with GSS
EAP.]]
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Internet-Draft BrowserID SASL & GSS-API December 2013
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005.
[RFC4402] Williams, N., "A Pseudo-Random Function (PRF) for the
Kerberos V Generic Security Service Application Program
Interface (GSS-API) Mechanism", RFC 4402, February 2006.
[RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121,
July 2005.
[RFC4178] Zhu, L., Leach, P., Jaganathan, K., and W. Ingersoll, "The
Simple and Protected Generic Security Service Application
Program Interface (GSS-API) Negotiation Mechanism",
RFC 4178, October 2005.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
[RFC4757] Jaganathan, K., Zhu, L., and J. Brezak, "The RC4-HMAC
Kerberos Encryption Types Used by Microsoft Windows",
RFC 4757, December 2006.
[RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure
Subject Alternative Name for Expression of Service Name",
RFC 4985, August 2007.
[RFC5178] Williams, N. and A. Melnikov, "Generic Security Service
Application Program Interface (GSS-API)
Internationalization and Domain-Based Service Names and
Name Type", RFC 5178, May 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
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Internet-Draft BrowserID SASL & GSS-API December 2013
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The
GS2 Mechanism Family", RFC 5801, July 2010.
[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
for TLS", RFC 5929, July 2010.
[RFC6680] Williams, N., Johansson, L., Hartman, S., and S.
Josefsson, "Generic Security Service Application
Programming Interface (GSS-API) Naming Extensions",
RFC 6680, August 2012.
[I-D.ietf-jose-json-web-algorithms]
Jones, M., "JSON Web Algorithms (JWA)",
draft-ietf-jose-json-web-algorithms-18 (work in progress),
November 2013.
[I-D.ietf-jose-json-web-key]
Jones, M., "JSON Web Key (JWK)",
draft-ietf-jose-json-web-key-18 (work in progress),
November 2013.
[I-D.ietf-jose-json-web-signature]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", draft-ietf-jose-json-web-signature-18
(work in progress), November 2013.
[I-D.ietf-oauth-json-web-token]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", draft-ietf-oauth-json-web-token-13 (work in
progress), November 2013.
[I-D.zhu-negoex]
Short, M., Zhu, L., Damour, K., and D. McPherson, "SPNEGO
Extended Negotiation (NEGOEX) Security Mechanism",
draft-zhu-negoex-04 (work in progress), January 2011.
[I-D.zhu-pku2u]
Zhu, L., Altman, J., and N. Williams, "Public Key
Cryptography Based User-to-User Authentication - (PKU2U)",
draft-zhu-pku2u-09 (work in progress), November 2008.
[BrowserID]
Adida, B., "BrowserID Specification", February 2013.
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11.2. Informative References
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
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Internet-Draft BrowserID SASL & GSS-API December 2013
Authors' Addresses
Luke Howard
PADL Software
PO Box 59
Central Park, VIC 3145
Australia
Email: lukeh@padl.com
Nicolas Williams
Cryptonector, LLC
Email: nico@cryptonector.com
Howard & Williams Expires June 12, 2014 [Page 45]
