ecc-sos: Compatible mode for SOS.

* g10/build-packet.c (sos_write): Add an argument COMPAT.  When
COMPAT=1, NBITS specifies number of bits when interpreted as MPI,
except the case when the first octet is zero.

Signed-off-by: NIIBE Yutaka <[email protected]>

1 files changed, 27 insertions, 6 deletions

diff --git a/g10/build-packet.c b/g10/build-packet.c
index 7636407b3..2eabbb51d 100644
--- a/g10/build-packet.c
+++ b/g10/build-packet.c
@@ -355,7 +355,7 @@ gpg_mpi_write (iobuf_t out, gcry_mpi_t a, unsigned int *r_nwritten)
  * written, NULL may be passed for OUT.
  */
 static gpg_error_t
-sos_write (iobuf_t out, gcry_mpi_t a, unsigned int *r_nwritten)
+sos_write (iobuf_t out, gcry_mpi_t a, unsigned int *r_nwritten, int compat)
 {
   gpg_error_t err;
   unsigned int nwritten = 0;
@@ -370,6 +370,22 @@ sos_write (iobuf_t out, gcry_mpi_t a, unsigned int *r_nwritten)
       p = gcry_mpi_get_opaque (a, &nbits);
       /* gcry_log_debug ("   [%u bit]\n", nbits); */
       /* gcry_log_debughex (" ", p, (nbits+7)/8); */
+
+      if (p && *p && compat)
+        {
+          nbits = ((nbits + 7) / 8) * 8;
+
+          if (nbits >= 8 && !(*p & 0x80))
+            if (--nbits >= 7 && !(*p & 0x40))
+              if (--nbits >= 6 && !(*p & 0x20))
+                if (--nbits >= 5 && !(*p & 0x10))
+                  if (--nbits >= 4 && !(*p & 0x08))
+                    if (--nbits >= 3 && !(*p & 0x04))
+                      if (--nbits >= 2 && !(*p & 0x02))
+                        if (--nbits >= 1 && !(*p & 0x01))
+                          --nbits;
+        }
+
       lenhdr[0] = nbits >> 8;
       lenhdr[1] = nbits;
       err = out? iobuf_write (out, lenhdr, 2) : 0;
@@ -604,12 +620,13 @@ do_key (iobuf_t out, int ctb, PKT_public_key *pk)
 
   for (i=0; i < npkey; i++ )
     {
+      /* FIXME: For newer curve, sos_write should be called with COMPAT=0. */
       if (   (pk->pubkey_algo == PUBKEY_ALGO_ECDSA && (i == 0))
           || (pk->pubkey_algo == PUBKEY_ALGO_EDDSA && (i == 0))
           || (pk->pubkey_algo == PUBKEY_ALGO_ECDH  && (i == 0 || i == 2)))
         err = gpg_mpi_write_nohdr (a, pk->pkey[i]);
       else if (pk->pubkey_algo == PUBKEY_ALGO_ECDH)
-        err = sos_write (a, pk->pkey[i], NULL);
+        err = sos_write (a, pk->pkey[i], NULL, 1);
       else
         err = gpg_mpi_write (a, pk->pkey[i], NULL);
       if (err)
@@ -724,12 +741,13 @@ do_key (iobuf_t out, int ctb, PKT_public_key *pk)
               unsigned int n;
               int j;
 
+              /* FIXME: For newer curve, sos_write should be called with COMPAT=0. */
               for (j=i; j < nskey; j++ )
                 {
                   if (pk->pubkey_algo == PUBKEY_ALGO_EDDSA
                       || pk->pubkey_algo == PUBKEY_ALGO_ECDH)
                     {
-                      if ((err = sos_write (NULL, pk->pkey[j], &n)))
+                      if ((err = sos_write (NULL, pk->pkey[j], &n, 1)))
                         goto leave;
                     }
                   else
@@ -747,7 +765,8 @@ do_key (iobuf_t out, int ctb, PKT_public_key *pk)
             if (pk->pubkey_algo == PUBKEY_ALGO_EDDSA
                 || pk->pubkey_algo == PUBKEY_ALGO_ECDH)
               {
-                if ( (err = sos_write (a, pk->pkey[i], NULL)))
+                /* FIXME: For newer curve, sos_write should be called with COMPAT=0. */
+                if ( (err = sos_write (a, pk->pkey[i], NULL, 1)))
                   goto leave;
               }
             else
@@ -869,7 +888,8 @@ do_pubkey_enc( IOBUF out, int ctb, PKT_pubkey_enc *enc )
       if (enc->pubkey_algo == PUBKEY_ALGO_ECDH && i == 1)
         rc = gpg_mpi_write_nohdr (a, enc->data[i]);
       else if (enc->pubkey_algo == PUBKEY_ALGO_ECDH)
-        rc = sos_write (a, enc->data[i], NULL);
+        /* FIXME: For newer curve, sos_write should be called with COMPAT=0. */
+        rc = sos_write (a, enc->data[i], NULL, 1);
       else
         rc = gpg_mpi_write (a, enc->data[i], NULL);
     }
@@ -1749,9 +1769,10 @@ do_signature( IOBUF out, int ctb, PKT_signature *sig )
   n = pubkey_get_nsig( sig->pubkey_algo );
   if ( !n )
     write_fake_data( a, sig->data[0] );
+  /* FIXME: For newer curve, sos_write should be called with COMPAT=0. */
   if (sig->pubkey_algo == PUBKEY_ALGO_EDDSA)
     for (i=0; i < n && !rc ; i++ )
-      rc = sos_write (a, sig->data[i], NULL);
+      rc = sos_write (a, sig->data[i], NULL, 1);
   else
     for (i=0; i < n && !rc ; i++ )
       rc = gpg_mpi_write (a, sig->data[i], NULL);