Incompatibility between gnupg 0.9.7 and >0.9.10 in conv. 3des encryption

Werner Koch
Sat, 8 Jan 2000 11:13:09 +0100

On Sat, 8 Jan 2000, Enzo Michelangeli wrote:

> I'm not sure whether it's a known problem, but if one encrypts with:
> ./gpg097 -a -c --cipher-algo 3des q
> and then tries to decrypt with gpg version 0.9.10 or later:
There are more problems with that. The reason is that I changed the internal API form the hash algorithms somewhere between these versions with the result that all ciphers needing a key lasrger than the hash size didn't work anymore or better the string-to-key algorithm was not compatible. This is a problem with 3DES and Twofish. The only solution to reencypt these messages - I am yery soory about this. GnuPG 1.0.1 now works like required by the standard and produces valid 3DES, Twofish symmetric only encryptions which interoperate with PGP. 1.0.1 has an option to emulate the bug: --emulate-3des-s2k-bug . Please note that this option will be removed in gpg 1.1, so either re-encrypt all these messages or keep a copy of gpg 1.0.0 which has this bug.
> However, I would expect that backward compatibility with older s2k values be
> preserved in decryption.
It is not possible because the bug reduces the keylength to 160 bit which is effective then less than 112 bits for 3DES. -- Werner Koch at keyid 621CC013 Boycott Amazon! -