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Re: [keyassure] Interpreting certificates (and summary)

Martin Rex <mrex@sap.com> Wed, 23 February 2011 18:56 UTC

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From: Martin Rex <mrex@sap.com>
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Date: Wed, 23 Feb 2011 19:57:28 +0100
In-Reply-To: <20110221144527.GB25182@odin.mars.sol> from "Scott Schmit" at Feb 21, 11 09:45:27 am
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Cc: keyassure@ietf.org
Subject: Re: [keyassure] Interpreting certificates (and summary)
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Scott Schmit wrote:
> 
> An item for security considerations:
> * Now that CAs aren't necessarily issuing these certs, the client needs
>   to be much more careful in its parsing (the null terminated vs length-
>   delimited string bug comes to mind)

This sounds somewhat strange to me.

When doing TLS authentication of a peer, the peer's certificate
is always untrusted at the time when it is parsed.  Parsing the
received X.509 cert is a prerequisite to being able to validate
the cert and determining whether it is trusted/trustworthy or not.

An ASN.1 parser that is not careful is an unconditionally bad idea
and asking for trouble; lots of trouble.  Tolerance to common
bugs of encodings produced by peers should never be accepted
"by accident", only by conscious trade-off decisions that are
clearly documented for the caller/consumer of the technology.


-Martin

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