The hashed ECDSA operations not support multipart operations

[Jakuje]

The #683 introduced the hashed ECDSA mechanisms, but did not implement multipart operations. The specs clearly say that the multipart operation should work and this is breaking, for example I had to workaround this in pkcs11-provider:

• Workardound new bug in softhsm 2.7.0 latchset/pkcs11-provider#669

and today I need to write same workaround for the libssh.

[bukka]

Yeah that looks wrong.

[Jakuje]

I actually started working on that so some of the code could be reused, but I did not get into the crypto backends as they will need some more love to support digest + hashing per partes:

https://github.com/Jakuje/SoftHSMv2/tree/ecdsa-hashing

There are tests adjusted for this. Feel free to reuse if anyone will want to work on this. I am not sure if I will get to finalize that any time soon