SHA-224 problem

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SHA-224 problem

by David Shaw :: Rate this Message:

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A typo was recently discovered in the new OpenPGP RFC.  While an
errata document will be issued to take care of the RFC, there is some
impact to GPG as well.  The typo was in the encoded ASN.1 OID for
SHA-224: a number that forms part of the signature when the hash is
used with an RSA key.

I've committed a fix for this for 1.4.8, so that new RSA + SHA-224
signatures use the right constants.  I've also added some
bug-compatibility code so that 1.4.8 (and later) will be able to
verify the old, incorrect signatures.

What this means:

* If you make a RSA + SHA-224 signature with 1.4.8 or later, earlier
  versions will not be able to verify it.

* Existing RSA + SHA-224 signatures that were made with 1.4.7 or
  earlier will still be verifiable with 1.4.8 or later.

Remember that this only applies to an RSA signature made with the
SHA-224 hash.  There is no problem with any DSA signatures (whether
they use SHA-224 or not), or RSA signatures with any other hash.

Also note that this does not make the signature insecure or unsafe in
any way.  This is strictly a compatibility issue.

David

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Re: SHA-224 problem

by David Shaw :: Rate this Message:

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On Thu, Nov 29, 2007 at 08:05:15PM -0500, David Shaw wrote:

> I've committed a fix for this for 1.4.8, so that new RSA + SHA-224
> signatures use the right constants.  I've also added some
> bug-compatibility code so that 1.4.8 (and later) will be able to
> verify the old, incorrect signatures.

I should also add that GPG2 does not have this problem as it uses
libgcrypt for its crypto, and libgcrypt does not currently support
SHA-224.  The version of libgcrypt currently in development does have
this problem, but it will be fixed before it is released.

David

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