Torsten,
Brain Campbell points out that previous discussions suggest that the
authorization code is meant to be a cryptographically protected one-use
token (vs. a random string) but that these
key (essential!) details are not available draft 10.
http://www.ietf.org/mail-archive/web/oauth/current/msg03885.html
I would say then that the analogy with the SAML Web SSO browser profile
isn't exact but nevertheless some threats are common to both scenarios.
I will try to summarize
these once a concrete proposal for authorization code is made available
by the authors.
- prateek
Thank you for your advice. The Oauth security considerations are not finished yet. They will handle the issues you raised, too.
Regards,
Torsten.
Am 30.09.2010 um 01:33 schrieb PRATEEK MISHRA <prateek.mis...@oracle.com>:
I read through v10 from the perspective of an implementor, and it seemed to me
that properties of generated authorization code and its treatment by various
entities need to be called out explicitly as a counter-measure against various
simple attacks.
I would also comment that the exchanges between the end-user, client and
authorization endpoints, beginning with the issuance of an authorization code
(in SAML 2.0 called a browser artifact) and terminating with the client
obtaining an access token (in SAML 2.0 the RP obtaining a SAML assertion)
essentially follow the SAML web browser artifact profile and are therefore open
to all of the attacks that the SSTC considered for this protocol.
1) For example, given the current description it seems that perfectly
reasonable for an end-user authorization endpoint to generate a sequence of
increasing integers as an authorization code or always return a constant value
for a request with a given (client_id, redirection_uri) pair of inputs. So this
leads to the possibility of an adversary using some simple techniques to guess
valid authorization codes and obtain an access token.
2) There is a need to articulate some of the minimum properties that an
authorization code should possess. I understand that there is an attempt here
to give maximum choice to implementors.
For example, the SAML 2.0 artifact format description includes the following
language -
[quote]
The MessageHandle value is constructed from a cryptographically strong random or
pseudorandom number sequence [RFC1750] generated by the issuer. The sequence
consists of
values of at least 16 bytes in size.
[\quote]
3) I am also puzzled by the discrepancy between the language used to describe
the generation and use of an authorization code -
[quote - generation - p.18]
The authorization code
SHOULD expire shortly after it is issued. The authorization
server MUST invalidate the authorization code after a single
usage. The authorization code is bound to the client
identifier and redirection URI.
[\quote]
VS
[quote - use - p.23]
The authorization server MUST:
o Validate the client credentials (if present) and ensure they match
the authorization code.
o Verify that the authorization code and redirection URI are all
valid and match its stored association.
[\quote]
I dont understand how the authorization code is related to the client credentials, or
what is meant by "valid" or the reference
to "stored association". Is there an assumption that authorization server has a
stateful table of (authorization code, client id, redirection uri) values?
Shouldnt this test be limited to checking whether the authorization code is
being used with the correct client identifier and redirection URI?
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