gpg: Add X448 support.

* common/openpgp-oid.c (oidtable): Add X448.
(oid_x448,openpgp_oidbuf_is_x448,openpgp_oid_is_x448): New.
* common/util.h (openpgp_oid_is_x448): New.
* g10/ecdh.c (gen_k): Add handling of opaque MPI and support
endianness.
(pk_ecdh_generate_ephemeral_key): X448 requires opaque MPI.
* g10/keygen.c (gen_ecc): Add support for X448.
(ask_algo, parse_key_parameter_part): Likewise.

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

common/openpgp-oid.c

@@ -48,6 +48,7 @@ static struct {
 
   { "Curve25519", "1.3.6.1.4.1.3029.1.5.1", 255, "cv25519", PUBKEY_ALGO_ECDH },
   { "Ed25519",    "1.3.6.1.4.1.11591.15.1", 255, "ed25519", PUBKEY_ALGO_EDDSA },
+  { "X448",       "1.3.101.111",            448, "x448",    PUBKEY_ALGO_ECDH },
 
   { "NIST P-256",      "1.2.840.10045.3.1.7",    256, "nistp256" },
   { "NIST P-384",      "1.3.132.0.34",           384, "nistp384" },
@@ -71,6 +72,9 @@ static const char oid_ed25519[] =
 static const char oid_cv25519[] =
   { 0x0a, 0x2b, 0x06, 0x01, 0x04, 0x01, 0x97, 0x55, 0x01, 0x05, 0x01 };
 
+/* The OID for X448 in OpenPGP format.  */
+static const char oid_x448[] = { 0x03, 0x2b, 0x65, 0x6f };
+
 /* A table to store keyalgo strings like "rsa2048 or "ed25519" so that
  * we do not need to allocate them.  This is currently a simple array
  * but may eventually be changed to a fast data structure.  Noet that
@@ -334,6 +338,15 @@ openpgp_oidbuf_is_cv25519 (const void *buf, size_t len)
 }
 
 
+/* Return true if (BUF,LEN) represents the OID for X448.  */
+static int
+openpgp_oidbuf_is_x448 (const void *buf, size_t len)
+{
+  return (buf && len == DIM (oid_x448)
+          && !memcmp (buf, oid_x448, DIM (oid_x448)));
+}
+
+
 /* Return true if the MPI A represents the OID for Curve25519.  */
 int
 openpgp_oid_is_cv25519 (gcry_mpi_t a)
@@ -349,6 +362,21 @@ openpgp_oid_is_cv25519 (gcry_mpi_t a)
 }
 
 
+/* Return true if the MPI A represents the OID for X448.  */
+int
+openpgp_oid_is_x448 (gcry_mpi_t a)
+{
+  const unsigned char *buf;
+  unsigned int nbits;
+
+  if (!a || !gcry_mpi_get_flag (a, GCRYMPI_FLAG_OPAQUE))
+    return 0;
+
+  buf = gcry_mpi_get_opaque (a, &nbits);
+  return openpgp_oidbuf_is_x448 (buf, (nbits+7)/8);
+}
+
+
 /* Map the Libgcrypt ECC curve NAME to an OID.  If R_NBITS is not NULL
    store the bit size of the curve there.  Returns NULL for unknown
    curve names.  If R_ALGO is not NULL and a specific ECC algorithm is

common/util.h

@@ -238,6 +238,7 @@ int openpgp_oidbuf_is_ed25519 (const void *buf, size_t len);
 int openpgp_oid_is_ed25519 (gcry_mpi_t a);
 int openpgp_oidbuf_is_cv25519 (const void *buf, size_t len);
 int openpgp_oid_is_cv25519 (gcry_mpi_t a);
+int openpgp_oid_is_x448 (gcry_mpi_t a);
 const char *openpgp_curve_to_oid (const char *name,
                                   unsigned int *r_nbits, int *r_algo);
 const char *openpgp_oid_to_curve (const char *oid, int canon);

g10/ecdh.c

@@ -422,10 +422,27 @@ pk_ecdh_encrypt_with_shared_point (gcry_mpi_t shared_mpi,
 
 
 static gcry_mpi_t
-gen_k (unsigned nbits)
+gen_k (unsigned nbits, int little_endian, int is_opaque)
 {
   gcry_mpi_t k;
 
+  if (is_opaque)
+    {
+      unsigned char *p;
+      size_t nbytes = (nbits+7)/8;
+
+      p = gcry_random_bytes_secure (nbytes, GCRY_STRONG_RANDOM);
+      if ((nbits % 8))
+        {
+          if (little_endian)
+            p[nbytes-1] &= ((1 << (nbits % 8)) - 1);
+          else
+            p[0] &= ((1 << (nbits % 8)) - 1);
+        }
+      k = gcry_mpi_set_opaque (NULL, p, nbits);
+      return k;
+    }
+
   k = gcry_mpi_snew (nbits);
   if (DBG_CRYPTO)
     log_debug ("choosing a random k of %u bits\n", nbits);
@@ -453,13 +470,21 @@ pk_ecdh_generate_ephemeral_key (gcry_mpi_t *pkey, gcry_mpi_t *r_k)
 {
   unsigned int nbits;
   gcry_mpi_t k;
+  int is_little_endian = 0;
+  int require_opaque = 0;
+
+  if (openpgp_oid_is_x448 (pkey[0]))
+    {
+      is_little_endian = 1;
+      require_opaque = 1;
+    }
 
   *r_k = NULL;
 
   nbits = pubkey_nbits (PUBKEY_ALGO_ECDH, pkey);
   if (!nbits)
     return gpg_error (GPG_ERR_TOO_SHORT);
-  k = gen_k (nbits);
+  k = gen_k (nbits, is_little_endian, require_opaque);
   if (!k)
     BUG ();
 

g10/keygen.c

@@ -1748,6 +1748,8 @@ gen_ecc (int algo, const char *curve, kbnode_t pub_root,
     curve = "Curve25519";
   else if (!ascii_strcasecmp (curve, "ed25519"))
     curve = "Ed25519";
+  else if (!ascii_strcasecmp (curve, "x448"))
+    curve = "X448";
 
   /* Note that we use the "comp" flag with EdDSA to request the use of
      a 0x40 compression prefix octet.  */
@@ -1765,6 +1767,13 @@ gen_ecc (int algo, const char *curve, kbnode_t pub_root,
        (((keygen_flags & KEYGEN_FLAG_TRANSIENT_KEY)
          && (keygen_flags & KEYGEN_FLAG_NO_PROTECTION))?
         " transient-key" : ""));
+  else if (algo == PUBKEY_ALGO_ECDH && !strcmp (curve, "X448"))
+    keyparms = xtryasprintf
+      ("(genkey(ecc(curve %zu:%s)(flags comp%s)))",
+       strlen (curve), curve,
+       (((keygen_flags & KEYGEN_FLAG_TRANSIENT_KEY)
+         && (keygen_flags & KEYGEN_FLAG_NO_PROTECTION))?
+        " transient-key" : ""));
   else
     keyparms = xtryasprintf
       ("(genkey(ecc(curve %zu:%s)(flags nocomp%s)))",
@@ -2319,6 +2328,8 @@ ask_algo (ctrl_t ctrl, int addmode, int *r_subkey_algo, unsigned int *r_usage,
                         kpi->algo = PUBKEY_ALGO_EDDSA;
                       else if (!strcmp (algostr, "cv25519"))
                         kpi->algo = PUBKEY_ALGO_ECDH;
+                      else if (!strcmp (algostr, "x448"))
+                        kpi->algo = PUBKEY_ALGO_ECDH;
                       else if ((kpi->usage & GCRY_PK_USAGE_ENCR))
                         kpi->algo = PUBKEY_ALGO_ECDH;
                       else
@@ -3472,6 +3483,8 @@ parse_key_parameter_part (ctrl_t ctrl,
                 algo = PUBKEY_ALGO_EDDSA;
               else if (!strcmp (algostr, "cv25519"))
                 algo = PUBKEY_ALGO_ECDH;
+              else if (!strcmp (algostr, "x448"))
+                algo = PUBKEY_ALGO_ECDH;
               else if ((kpi->usage & GCRY_PK_USAGE_ENCR))
                 algo = PUBKEY_ALGO_ECDH;
               else
@@ -3599,6 +3612,7 @@ parse_key_parameter_part (ctrl_t ctrl,
  *   elg2048 := Elgamal with 2048 bit.
  *   ed25519 := EDDSA using curve Ed25519.
  *   cv25519 := ECDH using curve Curve25519.
+ *   x448    := ECDH using curve X448.
  *   nistp256:= ECDSA or ECDH using curve NIST P-256
  *
  * All strings with an unknown prefix are considered an elliptic