Howto use libgrcypt for signature?

[Stef Bon]

Hi,

I'm writing a fuse fs for sftp, and using libgcrypt for encryption,
hmac, digest and dh.

Now I m working on the checking of the signature of H send by the
sender. The client creates also H,
and has to check the signature of H using the public key.

I've got the signature of H from the server, H and the public hostkey
of the server as string (length, buffer).

How to go futher? I know I have to use the function  gcry_pk_verify, but how?

Do I have to convert the strings to some s-expressions using a format first?

Thanks in advance,

Stef