draft-ietf-sasl-gs2-00.txt   draft-ietf-sasl-gs2-01.txt 
Network Working Group S. Josefsson Network Working Group S. Josefsson
Expires: August 17, 2006 Expires: December 28, 2006
Using GSS-API Mechanisms in SASL: The GS2 Mechanism Family Using GSS-API Mechanisms in SASL: The GS2 Mechanism Family
draft-ietf-sasl-gs2-00 draft-ietf-sasl-gs2-01
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document describes how to use a Generic Security Service This document describes how to use a Generic Security Service
Application Program Interface (GSS-API) mechanism in the the Simple Application Program Interface (GSS-API) mechanism in the the Simple
Authentication and Security Layer (SASL) framework. Authentication and Security Layer (SASL) framework.
See <http://josefsson.org/sasl-gs2-*/> for more information. See <http://josefsson.org/sasl-gs2-*/> for more information.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in this Document . . . . . . . . . . . . . . 3 2. Conventions Used in this Document . . . . . . . . . . . . . . 3
3. Mechanism Name . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Mechanism Name . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Generating SASL mechanism names from GSS-API OIDs . . . . 3 3.1. Generating SASL Mechanism Names From GSS-API OIDs . . . . 3
3.2. Computing mechanism names manually . . . . . . . . . . . . 4 3.2. Computing Mechanism Names Manually . . . . . . . . . . . . 4
3.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Packet format . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. SASL tokens . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. SASL Tokens . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Context token . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Wrap token . . . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Context Token . . . . . . . . . . . . . . . . . . . . . . 6
4.3.1. Wrap token input for client requests . . . . . . . . . 7 4.4. Wrap Token . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3.2. Wrap token input for server responses . . . . . . . . 8 4.4.1. Wrap Token Input For Client Requests . . . . . . . . . 7
4.3.3. Wrap token input for server requests . . . . . . . . . 8 4.4.2. WraP Token Input For Server Responses . . . . . . . . 8
4.3.4. Wrap token input for client responses . . . . . . . . 9 4.4.3. Wrap Token Input For Server Requests . . . . . . . . . 9
5. Protocol overview . . . . . . . . . . . . . . . . . . . . . . 9 4.4.4. Wrap Token Input For Client Responses . . . . . . . . 9
6. Authentication Conditions . . . . . . . . . . . . . . . . . . 12 5. Channel Bindings . . . . . . . . . . . . . . . . . . . . . . . 10
7. GSS-API parameters . . . . . . . . . . . . . . . . . . . . . . 12 5.1. Name Of Tls Channel For Use As Channel Binding . . . . . . 11
8. Security layer bits . . . . . . . . . . . . . . . . . . . . . 13 6. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11
9. Interoperability with the GSSAPI mechanism . . . . . . . . . . 13 7. Authentication Conditions . . . . . . . . . . . . . . . . . . 14
9.1. Interoperability problem . . . . . . . . . . . . . . . . . 13 8. GSS-API Parameters . . . . . . . . . . . . . . . . . . . . . . 14
9.2. Resolving the problem . . . . . . . . . . . . . . . . . . 13 9. Security Layer Bits . . . . . . . . . . . . . . . . . . . . . 15
9.3. Additional recommendations . . . . . . . . . . . . . . . . 13 10. Interoperability With The Gssapi Mechanism . . . . . . . . . . 15
10. Mechanisms that negotiate other mechanisms . . . . . . . . . . 14 10.1. The Interoperability problem . . . . . . . . . . . . . . . 15
10.1. Interoperability problem . . . . . . . . . . . . . . . . . 14 10.2. Resolving the problem . . . . . . . . . . . . . . . . . . 15
10.2. Security problem . . . . . . . . . . . . . . . . . . . . . 14 10.3. Additional recommendations . . . . . . . . . . . . . . . . 15
10.3. Resolving the problems . . . . . . . . . . . . . . . . . . 14 11. Mechanisms That Negotiate Other Mechanisms . . . . . . . . . . 16
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 11.1. The Interoperability Problem . . . . . . . . . . . . . . . 16
12. Security Considerations . . . . . . . . . . . . . . . . . . . 15 11.2. Security Problem . . . . . . . . . . . . . . . . . . . . . 16
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 11.3. Resolving the Problems . . . . . . . . . . . . . . . . . . 16
14. Copying conditions . . . . . . . . . . . . . . . . . . . . . . 16 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 13. Security Considerations . . . . . . . . . . . . . . . . . . . 17
15.1. Normative References . . . . . . . . . . . . . . . . . . . 16 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
15.2. Informative References . . . . . . . . . . . . . . . . . . 17 15. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 19 16.1. Normative References . . . . . . . . . . . . . . . . . . . 18
16.2. Informative References . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . . . . . 21
1. Introduction 1. Introduction
Generic Security Service Application Program Interface (GSS-API) [3] Generic Security Service Application Program Interface (GSS-API) [3]
is a framework that provide security services to applications. is a framework that provide security services to applications.
Simple Authentication and Security Layer (SASL) [2] is a framework to Simple Authentication and Security Layer (SASL) [2] is a framework to
provide authentication and security layers for connection based provide authentication and security layers for connection based
protocols. This document describe how to use a GSS-API mechanism in protocols. This document describe how to use a GSS-API mechanism in
a connection-based protocol using the SASL framework. a connection-based protocol using the SASL framework.
skipping to change at page 3, line 48 skipping to change at page 3, line 48
mechanism. mechanism.
2. Conventions Used in this Document 2. Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1]. document are to be interpreted as described in [1].
3. Mechanism Name 3. Mechanism Name
3.1. Generating SASL mechanism names from GSS-API OIDs 3.1. Generating SASL Mechanism Names From GSS-API OIDs
The SASL mechanism name for a GSS-API mechanism is the concatenation The SASL mechanism name for a GSS-API mechanism is the concatenation
of the string "GS2-" and the Base32 encoding [5] (with an upper case of the string "GS2-" and the Base32 encoding [5] (with an upper case
alphabet) of the first ten bytes of the binary SHA-1 hash [4] string alphabet) of the first ten bytes of the binary SHA-1 hash [4] string
computed over the ASN.1 DER encoding [7] of the GSS-API mechanism's computed over the ASN.1 DER encoding [7] of the GSS-API mechanism's
Object Identifier. The Base32 rules on padding characters and Object Identifier. The Base32 rules on padding characters and
characters outside of the base32 alphabet are not relevant to this characters outside of the base32 alphabet are not relevant to this
use of Base32. If any padding or non-alphabet characters are use of Base32. If any padding or non-alphabet characters are
encountered, the name is not a GS2 family mechanism name. encountered, the name is not a GS2 family mechanism name.
3.2. Computing mechanism names manually 3.2. Computing Mechanism Names Manually
The SASL mechanism name may be computed manually. This is useful The SASL mechanism name may be computed manually. This is useful
when the set of supported GSS-API mechanisms is known in advance. It when the set of supported GSS-API mechanisms is known in advance. It
also obliterate the need to implement Base32, SHA-1 and DER in the also obliterate the need to implement Base32, SHA-1 and DER in the
SASL mechanism. The computed mechanism name can be used directly in SASL mechanism. The computed mechanism name can be used directly in
the implementation, and the implementation need not concern itself the implementation, and the implementation need not concern itself
with that the mechanism is part of a mechanism family. with that the mechanism is part of a mechanism family.
3.3. Example 3.3. Example
For example, the OID for the SPKM-1 mechanism [12] is For example, the OID for the SPKM-1 mechanism [12] is
1.3.6.1.5.5.1.1. The ASN.1 DER encoding of the OID is 06 07 2b 06 01 1.3.6.1.5.5.1.1. The ASN.1 DER encoding of the OID is 06 07 2b 06 01
05 05 01 01. The SHA-1 hash of the ASN.1 DER encoding is 05 05 01 01. The SHA-1 hash of the ASN.1 DER encoding is
1cf8f42b5a9f80fae9f831226d5d9d56278661ad. The Base32 encoding of the 1cf8f42b5a9f80fae9f831226d5d9d56278661ad. The Base32 encoding of the
first ten bytes of this is "dt4pik22t6epv2py". Thus the SASL first ten bytes of this is "dt4pik22t6epv2py". Thus the SASL
mechanism name for the SPKM-1 GSSAPI mechanism is "GS2- mechanism name for the SPKM-1 GSSAPI mechanism is "GS2-
DT4PIK22T6EPV2PY". DT4PIK22T6EPV2PY".
4. Packet format 4. Packet Format
4.1. SASL tokens 4.1. SASL Tokens
All top-level SASL packets for the GS2 mechanism family follow the All top-level SASL packets for the GS2 mechanism family follow the
following format: following format:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context length | | Context length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| / | /
/ Context token / / Context token /
/ --------------------/ / --------------------/
/ ---------------------/ / / ---------------------/ /
/--------------------/ / /--------------------/ /
/ [Wrap token] / / [Wrap token] /
/ / / /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Context length" field is a 4 octet (32 bit) integer encoded in The "Context length" field is a 4 octet (32 bit) integer encoded in
network byte order, it indicate the length of the "Context token" network byte order, it indicate the length of the "Context token"
field. field.
The "Flags" field is a 4 octet (32 bit) bitmask that holds flags that
influence the authentication process.
The "Context token" field contain a GSS-API context establishment The "Context token" field contain a GSS-API context establishment
token generated by GSS_Init_sec_context or GSS_Accept_sec_context. token generated by GSS_Init_sec_context or GSS_Accept_sec_context.
The "Wrap token" field is optional, and if present will contain the The "Wrap token" field is optional, and if present will contain the
output generated by GSS_Wrap. output generated by GSS_Wrap.
The length field does not include the length of the length field The length field does not include the length of the length field
itself. Whether the "Wrap token" field is included or not can be itself. Whether the "Wrap token" field is included or not can be
infered from the length field; if the length field is shorter than infered from the length field; if the length field is shorter than
the entire packet size minus 4 octets, the "Wrap token" field is the entire packet size minus 4 octets, the "Wrap token" field is
present and begins after length+4 octets into the packet. The tokens present and begins after length+4 octets into the packet. The tokens
need not be aligned to 32-bit a boundary. There is no padding need not be aligned to 32-bit a boundary. There is no padding
between the tokens. between the tokens.
Packets shorter than 4 octets are invalid. If the length field is Packets shorter than 4 octets are invalid. If the length field is
longer than the entire packet size, minus 4 octets, the packet is longer than the entire packet size, minus 4 octets, the packet is
invalid. invalid.
4.2. Context token 4.2. Flags
Bit 0 signal whether GSS-API Channel bindings are used. It is only
useful in the first token sent from the client, and MUST be set to 0
in all other tokens. The bit is called the "Native Channel Bindings"
bit. The client chooses whether to set this bit or not depending on
local policy or user requests.
The other bits are not specified and MUST be zero. If a bit is set
that is not understood by the implementation, it MUST be ignored.
4.3. Context Token
The format of the "Context token" field inside the SASL token are The format of the "Context token" field inside the SASL token are
defined by the GSS-API specifications, see GSS_Init_sec_context and defined by the GSS-API specifications, and the data is computed by
GSS_Accept_sec_context. the GSS_Init_sec_context and GSS_Accept_sec_context functions.
The client calls GSS_Init_sec_context, passing in The client calls GSS_Init_sec_context, passing in
input_context_handle of 0 (initially), mech_type of the GSSAPI input_context_handle of 0 (initially), mech_type of the GSSAPI
mechanism for which this SASL mechanism is registered, any mechanism for which this SASL mechanism is registered, the
chan_binding if requested by the application (XXX?), and targ_name chan_binding is set to NULL or the channel binding data depending on
equal to output_name from GSS_Import_Name called with input_name_type the Native Channel Binding flag, and targ_name equal to output_name
of GSS_C_NT_HOSTBASED_SERVICE and input_name_string of from GSS_Import_Name called with input_name_type of
GSS_C_NT_HOSTBASED_SERVICE and input_name_string of
"service@hostname" where "service" is the service name specified in "service@hostname" where "service" is the service name specified in
the protocol's profile, and "hostname" is the fully qualified host the protocol's profile, and "hostname" is the fully qualified host
name of the server. If the client will be requesting a security name of the server. If the client will be requesting a security
layer, it MUST also supply to the GSS_Init_sec_context a layer, it MUST also supply to the GSS_Init_sec_context a
mutual_req_flag of TRUE, a sequence_req_flag of TRUE, and an mutual_req_flag of TRUE, a sequence_req_flag of TRUE, and an
integ_req_flag of TRUE. If the client will be requesting a security integ_req_flag of TRUE. If the client will be requesting a security
layer providing confidentiality protection, it MUST also supply to layer providing confidentiality protection, it MUST also supply to
the GSS_Init_sec_context a conf_req_flag of TRUE. If the GSS_Init_sec_context a conf_req_flag of TRUE. If
GSS_Init_sec_context returns GSS_S_CONTINUE_NEEDED, then the client GSS_Init_sec_context returns GSS_S_CONTINUE_NEEDED, then the client
should expect the server to issue a token in a subsequent challenge should expect the server to issue a token in a subsequent challenge
skipping to change at page 6, line 13 skipping to change at page 6, line 44
GSS_S_COMPLETE is returned or authentication is aborted. If the GSS_S_COMPLETE is returned or authentication is aborted. If the
server supply data beyond the context token, the context token should server supply data beyond the context token, the context token should
be processed first, and then the overflow data should be passed to be processed first, and then the overflow data should be passed to
GSS_Unwrap and the unwrapped data should be interpreted. During the GSS_Unwrap and the unwrapped data should be interpreted. During the
authentication exchange, the client will generate one Wrap token authentication exchange, the client will generate one Wrap token
using GSS_Wrap. using GSS_Wrap.
The server passes the first client response to GSS_Accept_sec_context The server passes the first client response to GSS_Accept_sec_context
as input_token, setting input_context_handle to 0 (initially), as input_token, setting input_context_handle to 0 (initially),
mech_type of the GSSAPI mechanism for which this SASL mechanism is mech_type of the GSSAPI mechanism for which this SASL mechanism is
registered, any chan_binding if requested by the application (XXX?), registered, the chan_binding set to NULL or the channel binding data
and acceptor_cred_handle equal to output_cred_handle from depending on the Native Channel Binding bit, and acceptor_cred_handle
GSS_Acquire_cred called with desired_name equal to output_name from equal to output_cred_handle from GSS_Acquire_cred called with
GSS_Import_name with input_name_type of GSS_C_NT_HOSTBASED_SERVICE desired_name equal to output_name from GSS_Import_name with
and input_name_string of "service@hostname" where "service" is the input_name_type of GSS_C_NT_HOSTBASED_SERVICE and input_name_string
service name specified in the protocol's profile, and "hostname" is of "service@hostname" where "service" is the service name specified
the fully qualified host name of the server. The server must pass in the protocol's profile, and "hostname" is the fully qualified host
any resulting challenge from the client to another call to name of the server. The server must pass any resulting challenge
GSS_Accept_sec_context, repeating the actions in this paragraph, from the client to another call to GSS_Accept_sec_context, repeating
until GSS_S_COMPLETE is returned or authentication is aborted. If the actions in this paragraph, until GSS_S_COMPLETE is returned or
the client supply data beyond the context token, the context token authentication is aborted. If the client supply data beyond the
should be processed first, and then the overflow data should be context token, the context token should be processed first, and then
passed to GSS_Unwrap and the unwrapped data should be interpreted. the overflow data should be passed to GSS_Unwrap and the unwrapped
During the authentication exchange, the server will generate one Wrap data should be interpreted. During the authentication exchange, the
token using GSS_Wrap. server will generate one Wrap token using GSS_Wrap.
4.3. Wrap token 4.4. Wrap Token
The Wrap token MUST NOT be sent before the PROT_READY flag has been The Wrap token MUST NOT be sent before the PROT_READY flag has been
set locally (by GSS_Init_sec_context or Gss_Accept_sec_context), or set locally (by GSS_Init_sec_context or Gss_Accept_sec_context), or
if the PROT_READY flag is never set, before the context has been if the PROT_READY flag is never set, before the context has been
fully established. The GSS_Wrap token does not have to be sent fully established. The GSS_Wrap token does not have to be sent
directly when the PROT_READY flag is set. During any exchange, directly when the PROT_READY flag is set. During any exchange,
exactly one GSS_Wrap token is sent in each direction. The input to exactly one GSS_Wrap token is sent in each direction. The input to
the GSS_Wrap function MUST follow the format described below. If not the GSS_Wrap function MUST follow the format described below. If not
exactly one GSS_Wrap token is received by the client and by the exactly one GSS_Wrap token is received by the client and by the
server, the authentication MUST fail. server, the authentication MUST fail.
skipping to change at page 7, line 18 skipping to change at page 7, line 47
when the server sends the GSS_Wrap token first and the client when the server sends the GSS_Wrap token first and the client
responds. responds.
The input formats below are passed to GSS_Wrap with conf_flag set to The input formats below are passed to GSS_Wrap with conf_flag set to
FALSE, and the Wrap token output will be the generated FALSE, and the Wrap token output will be the generated
output_message. output_message.
Some fields in the input formats are optional, indicated by brackets Some fields in the input formats are optional, indicated by brackets
("[" and "]") and explained by the text below. ("[" and "]") and explained by the text below.
4.3.1. Wrap token input for client requests 4.4.1. Wrap Token Input For Client Requests
The input to GSS_Wrap when the client sends the GSS_Wrap token first The input to GSS_Wrap when the client sends the GSS_Wrap token first
is as follows. is as follows.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| client_qops | client_maxbuf | | client_qops | client_maxbuf |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| channel_binding_length | | channel_binding_length |
skipping to change at page 8, line 10 skipping to change at page 8, line 41
The optional field "channel_binding_data" is present only if The optional field "channel_binding_data" is present only if
"channel_binding_length" is non-zero, and contain the actual channel "channel_binding_length" is non-zero, and contain the actual channel
binding data. binding data.
The optional field "authzid" contain the authorization identity. The The optional field "authzid" contain the authorization identity. The
authorization identity is encoded using UTF-8 [6]. The authorization authorization identity is encoded using UTF-8 [6]. The authorization
identity is not terminated with the NUL (U+0000) character. Servers identity is not terminated with the NUL (U+0000) character. Servers
MUST validate that the authorization identity is valid UTF-8. MUST validate that the authorization identity is valid UTF-8.
4.3.2. Wrap token input for server responses 4.4.2. WraP Token Input For Server Responses
The data format for input to GSS_Wrap when the server responds to the The data format for input to GSS_Wrap when the server responds to the
previous GSS_Wrap token data is as follows. previous GSS_Wrap token data is as follows.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server_qop | server_maxbuf | | server_qop | server_maxbuf |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "server_qop" field integer indicate the selected quality of The "server_qop" field integer indicate the selected quality of
protection. protection.
The "server_maxbuf" field indicate the maximum data buffer size the The "server_maxbuf" field indicate the maximum data buffer size the
server can receive. It MUST be 0 if the server doesn't advertise server can receive. It MUST be 0 if the server doesn't advertise
support for any security layer, the client MUST verify this. support for any security layer, the client MUST verify this.
4.3.3. Wrap token input for server requests 4.4.3. Wrap Token Input For Server Requests
The data format for input to GSS_Wrap when the server sends the The data format for input to GSS_Wrap when the server sends the
GSS_Wrap token first is as follows. GSS_Wrap token first is as follows.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server_qops | server_maxbuf | | server_qops | server_maxbuf |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| channel_binding_length | | channel_binding_length |
skipping to change at page 9, line 12 skipping to change at page 9, line 43
The optional field "server_cbqops" is present only if The optional field "server_cbqops" is present only if
"channel_binding_length" is non-zero, and indicate the server's "channel_binding_length" is non-zero, and indicate the server's
preferred quality of protection if channel binding negotiation preferred quality of protection if channel binding negotiation
succeeds. succeeds.
The optional field "channel_binding_data" is present only if The optional field "channel_binding_data" is present only if
"channel_binding_length" is non-zero, and contain the actual channel "channel_binding_length" is non-zero, and contain the actual channel
binding data. binding data.
4.3.4. Wrap token input for client responses 4.4.4. Wrap Token Input For Client Responses
The data format for input to GSS_Wrap when the client responds to the The data format for input to GSS_Wrap when the client responds to the
previous token is as follows. previous token is as follows.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| client_qop | client_maxbuf | | client_qop | client_maxbuf |
/ [authzid] | / [authzid] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "client_qop" field is the selected quality of protection. The "client_qop" field is the selected quality of protection.
The "client_maxbuf" and "authzid" fields are as above. The "client_maxbuf" and "authzid" fields are as above.
5. Protocol overview 5. Channel Bindings
[[This section is tentative further discussion on the topic. This
was written to provide an example of how the details of how one
approach to this concept could look like. There are other approaches
that may be preferable.]]
The GS2 mechanism provide its own token field for channel bindings,
in addition to the "chan_binding" parameter in the GSS-API context
functions. The reason for this is that the GS2 mechanism wish to
provide an option to proceed even if the channel bindings does not
match. The GSS-API framework specifies that authentication cannot
proceed if channel bindings does not match. The GSS-API framework
also does not specify the kind of privacy layer the channel binding
should be transferred under, thus making it possible for attackers to
modify it to always make channel binding negotiation succeed.
The client can select, using the "Native Channel Bindings" bit,
whether it wishes to use the "chan_bindings" parameter in the GSS-API
layer or not. If it wishes to use this, it is not possible to
continue after a failed channel binding negotiation.
A client that wish to continue with the authentication even if the
channel bindings does not match, set the "Native Channel Binding" bit
to 0. It MUST use the channel binding field in the GS2 token. It
MUST set the "chan_binding" parameter in the calls to
GSS_Init_sec_context to GSS_Accept_sec_context to NULL. The
application MUST set the "client_qops" field to include privacy
protection (to protect the SASL application data), and MAY set the
"client_cbqops" to no security layer (to avoid performance
degradation due to two security layers).
If a client do not wish to continue the authentication if channel
binding negotiation fails, or wishes to use the channel binding in
the GSS-API layer, it will set the "Native Channel Binding" bit to 1
in its first token. It MUST use both the channel binding field in
the GS2 token and the "chan_binding" parameter in the calls to
GSS_Init_sec_context and GSS_Accept_sec_context. The authentication
will fail in the GSS-API layer if the channel bindings does not
match, and thus the "client_qops" and "client_cbqops" MUST be set to
the same value. It MAY be set to no security layer (to avoid
performance degradation due to two security layers).
For TLS, the channel binding data is specified in the next section.
For other security layers, channel binding data will have to
specified elsewhere, and this specification will have to be updated
with explicit considerations.
[[All channel bindings should go into a separate document.]]
5.1. Name Of Tls Channel For Use As Channel Binding
The TLS Pseudo-Random Function (PRF) generate, using the constant
string "TLS channel binding", and based on the master secret and the
random values established during a TLS handshake, a 64 octet string
that make up the SASL channel binding data.
Using the terminology of TLS [13], the channel binding data is
computed as follows:
SASL_channel_binding =
PRF(SecurityParameters.master_secret,
"TLS channel binding",
SecurityParameters.server_random +
SecurityParameters.client_random) [0..64];
The derived data is intended to be used as a name of the TLS channel
that is cryptographically bound to the channel, for use in
authentication mechanisms tunneled over TLS.
6. Protocol Overview
This section describe several high-level protocol exchanges. The This section describe several high-level protocol exchanges. The
descriptions do not assume any properties of the actual GSS-API descriptions do not assume any properties of the actual GSS-API
mechanism. Protocol profiles, GSS-API mechanism specific behaviour, mechanism. Protocol profiles, GSS-API mechanism specific behaviour,
and to some extent implementation and policy choices, will dictate and to some extent implementation and policy choices, will dictate
which packets are sent in what order. The protocol exchanges are which packets are sent in what order. The protocol exchanges are
examples and other exchanges are permitted and will occur. examples and other exchanges are permitted and will occur.
An authentication exchange using GS2 may look like: An authentication exchange using GS2 may look like:
skipping to change at page 12, line 24 skipping to change at page 14, line 24
GSS_Wrap (client_qops, client_maxbuf, GSS_Wrap (client_qops, client_maxbuf,
channel_binding_length=0, authzid)] token channel_binding_length=0, authzid)] token
S: Indicate successful authentication and S: Indicate successful authentication and
send [length, GSS_Accept_sec_context, send [length, GSS_Accept_sec_context,
GSS_Wrap(server_qop, server_maxbuf)] token GSS_Wrap(server_qop, server_maxbuf)] token
as additional information. as additional information.
The last example illustrate the optimal (round-trip wise) The last example illustrate the optimal (round-trip wise)
authentication possible using this protocol. authentication possible using this protocol.
6. Authentication Conditions 7. Authentication Conditions
Authentication MUST NOT succeed if any one of the following Authentication MUST NOT succeed if any one of the following
conditions are true: conditions are true:
o An invalid SASL token is received (i.e., length shorter than 4 o An invalid SASL token is received (i.e., length shorter than 4
octets). octets).
o GSS_Init/Accept_sec_context() return anything other than o GSS_Init/Accept_sec_context() return anything other than
GSS_S_CONTINUE_NEEDED or GSS_S_COMPLETE. GSS_S_CONTINUE_NEEDED or GSS_S_COMPLETE.
o GSS_Wrap() returns anything other than GSS_S_COMPLETE. o GSS_Wrap() returns anything other than GSS_S_COMPLETE.
o GSS_Unwrap() returns anything other than GSS_S_COMPLETE. (There o GSS_Unwrap() returns anything other than GSS_S_COMPLETE. (There
can't be supplementary status codes in GS2 at this point, so any can't be supplementary status codes in GS2 at this point, so any
indications of out of order processing or replays should be indications of out of order processing or replays should be
fatal.) fatal.)
o The token returned from GSS_Unwrap fail to parse correctly (e.g., o The token returned from GSS_Unwrap fail to parse correctly (e.g.,
too short, invalid maximum buffer size) as the expected Wrap too short, invalid maximum buffer size) as the expected Wrap
token. token.
o Local policy reject the attempt. For example, client and server o Local policy reject the attempt. For example, client and server
can't agree on qop proposal. can't agree on qop proposal.
o (server-side) Authorization of client principal (i.e., src_name in o (server-side) Authorization of client principal (i.e., src_name in
GSS_Acecpt_sec_context) to requested authzid failed. GSS_Acecpt_sec_context) to requested authzid failed.
7. GSS-API parameters 8. GSS-API Parameters
The implementation MAY set any GSSAPI flags or arguments not The implementation MAY set any GSSAPI flags or arguments not
mentioned in this specification as is necessary for the mentioned in this specification as is necessary for the
implementation to enforce its security policy. implementation to enforce its security policy.
8. Security layer bits 9. Security Layer Bits
The security layers and their corresponding bit-masks are as follows: The security layers and their corresponding bit-masks are as follows:
1 No security layer 1 No security layer
2 Integrity protection. 2 Integrity protection.
Sender calls GSS_Wrap with conf_flag set to FALSE Sender calls GSS_Wrap with conf_flag set to FALSE
4 Confidentiality protection. 4 Confidentiality protection.
Sender calls GSS_Wrap with conf_flag set to TRUE Sender calls GSS_Wrap with conf_flag set to TRUE
Other bit-masks may be defined in the future; bits which are not Other bit-masks may be defined in the future; bits which are not
understood must be negotiated off. understood must be negotiated off.
Note that SASL negotiates the maximum size of the output_message to Note that SASL negotiates the maximum size of the output_message to
send. Implementations can use the GSS_Wrap_size_limit call to send. Implementations can use the GSS_Wrap_size_limit call to
determine the corresponding maximum size input_message. determine the corresponding maximum size input_message.
9. Interoperability with the GSSAPI mechanism 10. Interoperability With The Gssapi Mechanism
The GSSAPI mechanism [11] describe how the Kerberos V5 GSS-API The GSSAPI mechanism [11] describe how the Kerberos V5 GSS-API
mechanism [9] is used in SASL under the mechanism name "GSSAPI". The mechanism [9] is used in SASL under the mechanism name "GSSAPI". The
same mechanism may also be used with the GS2 family. This causes an same mechanism may also be used with the GS2 family. This causes an
interopability problem, which is discussed and resolved below. interopability problem, which is discussed and resolved below.
9.1. Interoperability problem 10.1. The Interoperability problem
If a client (or server) only support Kerberos V5 under the "GSSAPI" If a client (or server) only support Kerberos V5 under the "GSSAPI"
name and the server (or client) only support Kerberos V5 under the name and the server (or client) only support Kerberos V5 under the
GS2 family, the authentication negotiation will fail. GS2 family, the authentication negotiation will fail.
9.2. Resolving the problem 10.2. Resolving the problem
If the Kerberos V5 mechanism is supported under GS2 in a server, the If the Kerberos V5 mechanism is supported under GS2 in a server, the
server SHOULD also support Kerberos V5 through the "GSSAPI" server SHOULD also support Kerberos V5 through the "GSSAPI"
mechanism, to avoid interoperability problems with older clients. mechanism, to avoid interoperability problems with older clients.
Reasons for violating this recommendation may include security Reasons for violating this recommendation may include security
considerations regarding the absent features in the GS2 mechanism. considerations regarding the absent features in the GS2 mechanism.
The Kerberos V5 "GSSAPI" SASL mechanism lack channel bindings, which The Kerberos V5 "GSSAPI" SASL mechanism lack channel bindings, which
could enable certain tunnel attacks [16]. could enable certain tunnel attacks [16].
9.3. Additional recommendations 10.3. Additional recommendations
It is RECOMMENDED to negotiate Kerberos V5 through the GS2 mechanism It is RECOMMENDED to negotiate Kerberos V5 through the GS2 mechanism
rather than through the "GSSAPI" mechanism, if both are available, rather than through the "GSSAPI" mechanism, if both are available,
because of the additional features in the GS2 mechanism. because of the additional features in the GS2 mechanism.
10. Mechanisms that negotiate other mechanisms 11. Mechanisms That Negotiate Other Mechanisms
A GSS-API mechanism that negotiate other mechanisms interact badly A GSS-API mechanism that negotiate other mechanisms interact badly
with the SASL mechanism negotiation. There are two problems. The with the SASL mechanism negotiation. There are two problems. The
first is an interoperability problem and the second is a security first is an interoperability problem and the second is a security
concern. The problems are described and resolved below. concern. The problems are described and resolved below.
10.1. Interoperability problem 11.1. The Interoperability Problem
If a client implement GSS-API mechanism X, potentially negotiated If a client implement GSS-API mechanism X, potentially negotiated
through a GSS-API mechanism Y, and the server also implement GSS-API through a GSS-API mechanism Y, and the server also implement GSS-API
mechanism X negotiated through a GSS-API mechanism Z, the mechanism X negotiated through a GSS-API mechanism Z, the
authentication negotiation will fail. authentication negotiation will fail.
10.2. Security problem 11.2. Security Problem
If a client's policy is to first prefer GSSAPI mechanism X, then non- If a client's policy is to first prefer GSSAPI mechanism X, then non-
GSSAPI mechanism Y, then GSSAPI mechanism Z, and if a server supports GSSAPI mechanism Y, then GSSAPI mechanism Z, and if a server supports
mechanisms Y and Z but not X, then if the client attempts to mechanisms Y and Z but not X, then if the client attempts to
negotiate mechanism X by using a GSS-API mechanism that negotiate negotiate mechanism X by using a GSS-API mechanism that negotiate
other mechanisms (such as SPNEGO), it may end up using mechanism Z other mechanisms (such as SPNEGO), it may end up using mechanism Z
when it should have used mechanism Y. For this reason, the use of when it should have used mechanism Y. For this reason, the use of
GSS-API mechanisms that negotiate other mechanisms are disallowed GSS-API mechanisms that negotiate other mechanisms are disallowed
under GS2. under GS2.
10.3. Resolving the problems 11.3. Resolving the Problems
GSS-API mechanisms that negotiate other mechanisms MUST NOT be used GSS-API mechanisms that negotiate other mechanisms MUST NOT be used
with the GS2 SASL mechanism. This specifically exclude negotiating with the GS2 SASL mechanism. This specifically exclude negotiating
SPNEGO [10] under GS2. SPNEGO [10] under GS2.
The GSS_C_MA_MECH_NEGO attribute of GSS_Inquire_attrs_for_mech() [15] The GSS_C_MA_MECH_NEGO attribute of GSS_Inquire_attrs_for_mech() [15]
can be used to identify such mechanisms. can be used to identify such mechanisms.
11. IANA Considerations 12. IANA Considerations
The IANA is advised that SASL mechanism names starting with "GS2-" The IANA is advised that SASL mechanism names starting with "GS2-"
are reserved for SASL mechanisms which conform to this document. The are reserved for SASL mechanisms which conform to this document. The
IANA is directed to place a statement to that effect in the sasl- IANA is directed to place a statement to that effect in the sasl-
mechanisms registry. mechanisms registry.
Subject: Registration of SASL mechanism GS2-* Subject: Registration of SASL mechanism GS2-*
Family of SASL mechanisms: YES Family of SASL mechanisms: YES
SASL mechanism prefix: GS2- SASL mechanism prefix: GS2-
Security considerations: RFC [THIS-DOC] Security considerations: RFC [THIS-DOC]
Published specification: RFC [THIS-DOC] Published specification: RFC [THIS-DOC]
Person & email address to contact for further information: Person & email address to contact for further information:
Simon Josefsson <simon@josefsson.org> Simon Josefsson <simon@josefsson.org>
Intended usage: COMMON Intended usage: COMMON
Owner/Change controller: iesg@ietf.org Owner/Change controller: iesg@ietf.org
Note: Compare with the GSSAPI and GSS-SPNEGO mechanisms. Note: Compare with the GSSAPI and GSS-SPNEGO mechanisms.
12. Security Considerations 13. Security Considerations
Security issues are discussed throughout this memo. Security issues are discussed throughout this memo.
When a server or client supports multiple authentication mechanisms, When a server or client supports multiple authentication mechanisms,
each of which has a different security strength, it is possible for each of which has a different security strength, it is possible for
an active attacker to cause a party to use the least secure mechanism an active attacker to cause a party to use the least secure mechanism
supported. There are several ways to mitigate this problem: supported. There are several ways to mitigate this problem:
1. Integrity protected transports can be used, e.g., TLS [13]. To 1. Integrity protected transports can be used, e.g., TLS [13]. To
protect against certain tunnel attacks [16] with that solution, a protect against certain tunnel attacks [16] with that solution, a
skipping to change at page 16, line 12 skipping to change at page 18, line 12
canonicalize the server's fully qualified domain name using an canonicalize the server's fully qualified domain name using an
insecure or untrusted directory service, e.g., the Domain Name System insecure or untrusted directory service, e.g., the Domain Name System
[8] without DNSSEC [14]. [8] without DNSSEC [14].
Additional security considerations are in the SASL and GSSAPI Additional security considerations are in the SASL and GSSAPI
specifications. Additional security considerations for the Kerberos specifications. Additional security considerations for the Kerberos
V5 GSSAPI mechanism can be found in [9]. We stress that service V5 GSSAPI mechanism can be found in [9]. We stress that service
names should not be canonicalized using an unsecured directory names should not be canonicalized using an unsecured directory
service such as the DNS without DNSSEC. service such as the DNS without DNSSEC.
13. Acknowledgements 14. Acknowledgements
This document is a revision of RFC 2222. This version was derived This document is a revision of RFC 2222. This version was derived
from draft-ietf-sasl-gssapi-02 which was prepared by Alexey Melnikov from draft-ietf-sasl-gssapi-02 which was prepared by Alexey Melnikov
with significant contributions from John G. Myers, although this with significant contributions from John G. Myers, although this
document has been rewritten by the current author. document has been rewritten by the current author.
Contributions of many members of the SASL mailing list are gratefully Contributions of many members of the SASL mailing list are gratefully
acknowledged. In particular, ideas from Sam Hartman, Jeffrey acknowledged. In particular, ideas from Sam Hartman, Jeffrey
Hutzelman, and Nicolas Williams influenced the design of this Hutzelman, and Nicolas Williams influenced the design of this
protocol. protocol.
14. Copying conditions 15. Copying Conditions
Regarding the portion of this document that was written by Simon Regarding the portion of this document that was written by Simon
Josefsson ("the author", for the remainder of this section), the Josefsson ("the author", for the remainder of this section), the
author makes no guarantees and is not responsible for any damage author makes no guarantees and is not responsible for any damage
resulting from its use. The author grants irrevocable permission to resulting from its use. The author grants irrevocable permission to
anyone to use, modify, and distribute it in any way that does not anyone to use, modify, and distribute it in any way that does not
diminish the rights of anyone else to use, modify, and distribute it, diminish the rights of anyone else to use, modify, and distribute it,
provided that redistributed derivative works do not contain provided that redistributed derivative works do not contain
misleading author or version information. Derivative works need not misleading author or version information. Derivative works need not
be licensed under similar terms. Contact the author to confirm which be licensed under similar terms. Contact the author to confirm which
sections are available under this license. sections are available under this license.
15. References 16. References
15.1. Normative References 16.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Myers, J., "Simple Authentication and Security Layer (SASL)", [2] Myers, J., "Simple Authentication and Security Layer (SASL)",
RFC 2222, October 1997. RFC 2222, October 1997.
[3] Linn, J., "Generic Security Service Application Program [3] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000. Interface Version 2, Update 1", RFC 2743, January 2000.
[4] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", [4] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)",
RFC 3174, September 2001. RFC 3174, September 2001.
[5] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", [5] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
draft-josefsson-rfc3548bis-00 (work in progress), November 2005. draft-josefsson-rfc3548bis-04 (work in progress), May 2006.
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", [6] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003. STD 63, RFC 3629, November 2003.
[7] "Information Processing Systems - Open Systems Interconnection - [7] "Information Processing Systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1)", ISO Specification of Abstract Syntax Notation One (ASN.1)", ISO
Standard 8824. Standard 8824.
15.2. Informative References 16.2. Informative References
[8] Mockapetris, P., "Domain names - concepts and facilities", [8] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[9] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964, [9] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964,
June 1996. June 1996.
[10] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API [10] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API
Negotiation Mechanism", RFC 2478, December 1998. Negotiation Mechanism", RFC 2478, December 1998.
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