gpg: Initial support for generating Kyber subkeys.

* common/openpgpdefs.h (PUBKEY_ALGO_KY768_25519): Remove.
(PUBKEY_ALGO_KY1024_448): Remove.
(PUBKEY_ALGO_KYBER): New.  Use them everywhere instead of the removed.

* g10/build-packet.c (gpg_mpi_write_nohdr): Rename to
(gpg_mpi_write_opaque_nohdr): this.  Change callers.
(gpg_mpi_write_opaque_32): New.
(do_key): Support Kyber keys using the revised format.
* g10/gpg.h (MAX_EXTERN_KEYPARM_BITS): New.
* g10/parse-packet.c (read_octet_string): Add arg nbytes so support
reading with a length prefix.  Adjust callers.
(parse_key): Parse Kyber public keys.
* g10/misc.c (pubkey_get_npkey): Support Kyber.
(pubkey_get_nskey): Ditto.

* g10/keyid.c (pubkey_string): Support dual algorithms.
(do_hash_public_key): Support Kyber.
(nbits_from_pk): Ditto.
(keygrip_from_pk): Return the Kyber part for the ECC+Kyber dual algo.

* g10/keygen.c (struct common_gen_cb_parm_s): Add genkey_result2.
Note that this callback is not yet used.
(ecckey_from_sexp): Add optional arg sexp2 and use it for Kyber.
Change callers.
(ecckey_from_sexp): Do not leak LIST in case of an error.
(common_gen): Add arg keyparms2, change callers, and support Kyber.
(gen_kyber): New.
(get_keysize_range): Support Kyber.
(fixup_keysize): Simplify and support Kyber.
(do_create): Handle Kyber.
(parse_key_parameter_part): Remove algo strings "ky768" and "ky1024"
and add a generic "kyber" with default parameters.
--

This uses a revised format which is more aligned with the usual
OpenPGP structure.  A lot of things are still missing.  For example
support for handling two keygrips and checking both of them in a -K
listing.  There is also only ky768_bp384 as fixed algorithm for now.
No passphrase for the Kyber part of the dual algorithm is on purpose.

A test was done using

  gpg --quick-gen-key pqc1 nistp256

and then running

  gpg -v --quick-add-key <fingerprint> kyber

which creates a v5 subkey on a v4 primary key.  A second test using

  gpg --quick-gen-key pqc2 Ed448

followed by a --quick-add-key created a v5 key with a v5 subkey.

GnuPG-bug-id: 6815

g10/ecdh.c

@@ -156,11 +156,11 @@ build_kdf_params (unsigned char kdf_params[256], size_t *r_size,
     return gpg_error_from_syserror ();
 
   /* variable-length field 1, curve name OID */
-  err = gpg_mpi_write_nohdr (obuf, pkey[0]);
+  err = gpg_mpi_write_opaque_nohdr (obuf, pkey[0]);
   /* fixed-length field 2 */
   iobuf_put (obuf, PUBKEY_ALGO_ECDH);
   /* variable-length field 3, KDF params */
-  err = (err ? err : gpg_mpi_write_nohdr (obuf, pkey[2]));
+  err = (err ? err : gpg_mpi_write_opaque_nohdr (obuf, pkey[2]));
   /* fixed-length field 4 */
   iobuf_write (obuf, "Anonymous Sender    ", 20);
   /* fixed-length field 5, recipient fp (or first 20 octets of fp) */