cannot talk much about the application as such, but I have a byte- oriented structure which is limited in size, and need to ensure that the structure is authentic to the originator. Thus I thought EC signature was about the only thing appropriate, however even that seems to be too long, as I only have 20 bytes space left for the signature.
The counterpart verifying it, must not have posession any secret key, thus I thought HMAC would be out of question. Chris On 16 Mrz., 13:52, Geoff Beier <[email protected]> wrote: > Can you talk about what you're trying to accomplish? It sounds like > maybe you're trying to use a signature where a truncated HMAC would be > more appropriate. > > Geoff > > > > > > > > On Wed, Mar 16, 2011 at 07:24, Chris Garbers <[email protected]> wrote: > > My bad. I think signatures cannot be shorter than the key, thus in the > > example the signature will always be 28 bytes regardless of the hash > > digest. > > > Instead, one would have to use a different curve definition with a > > shorter key. > > > Chris > > > On 14 Mrz., 15:44, skubo <[email protected]> wrote: > >> Hello Everyone, > > >> I'm fairly new to crypto++, so bare my potentially silly question: > > >> I need to calculate a signature with an eliptic curve dsa scheme, > >> using SHA-1 hash. The issue is that space for the signature is > >> limited, so I need to truncate the SHA-1 digest in order to reduce > >> resulting signature length (yes, I know that the overall resulting > >> security of the hash is lower, but that is accepted). I have found > >> some methods in the SHA implementation for that, however I'm stuck on > >> how I could use this together with ECDSA templates like in the example > >> below. > > >> ECDSA<ECP, SHA1>::PrivateKey key; > >> key.Load(...); > >> ECDSA<ECP,SHA1>::Signer signer(key); > > >> StringSource( message, true, > >> new SignerFilter( prng, > >> signer, > >> new StringSink( signature ) > >> ) // SignerFilter > >> ); // StringSource > > >> // signature is always resulting in 28 bytes length for e.g. secp112r1 > > >> Can anyone pinpoint me to the right direction? Any examples in how to > >> calculate this signature with a truncated hash digest, so that the > >> above signature would result in - say 20 bytes? > > >> Regards > >> Chris > > > -- > > You received this message because you are subscribed to the "Crypto++ > > Users" Google Group. > > To unsubscribe, send an email to > > [email protected]. > > More information about Crypto++ and this group is available > > athttp://www.cryptopp.com. -- You received this message because you are subscribed to the "Crypto++ Users" Google Group. To unsubscribe, send an email to [email protected]. More information about Crypto++ and this group is available at http://www.cryptopp.com.
