Add ML-KEM implementation for gcrypt

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/crypto.h

@@ -160,7 +160,12 @@ struct ssh_crypto_struct {
     ssh_curve25519_pubkey curve25519_server_pubkey;
 #endif
 #ifdef HAVE_MLKEM
+#ifdef HAVE_LIBGCRYPT
+    unsigned char *mlkem_privkey;
+    size_t mlkem_privkey_len;
+#else
     EVP_PKEY *mlkem_privkey;
+#endif
     ssh_string mlkem_client_pubkey;
     ssh_string mlkem_ciphertext;
 #endif

include/libssh/mlkem.h

@@ -36,7 +36,12 @@ extern "C" {
 struct mlkem_type_info {
     size_t pubkey_size;
     size_t ciphertext_size;
+#ifdef HAVE_LIBGCRYPT
+    size_t privkey_size;
+    enum gcry_kem_algos alg;
+#else
     const char *name;
+#endif
 };
 
 extern const struct mlkem_type_info MLKEM768_INFO;