ssh: Simplify the curve name lookup.
* agent/command-ssh.c (struct ssh_key_type_spec): Add field alt_curve_name. (ssh_key_types): Add some alternate curve names. (ssh_identifier_from_curve_name): Lookup also bey alternative names and return the canonical name. (ssh_key_to_blob): Simplify the ECDSA case by using gcry_pk_get_curve instead of the explicit mapping. (ssh_receive_key): Likewise. Use ssh_identifier_from_curve_name to validate the curve name. Remove the reverse mapping because since GnuPG-2.2 Libgcrypt 1.7 is required. (ssh_handler_request_identities): Log an error message.
This change will make it easier to support other curves, in particular
those from tokens. Libgcrypt has a large list of alias names which we
now use to to make the mapping more flexible.
- Signed-off-by: Werner Koch <email@example.com>