Commit message: None
CVE: CVE-2018-0495
CWE: CWE-200
Vulnerability description: Libgcrypt before 1.7.10 and 1.8.x before 1.8.3 allows a memory-cache side-channel attack on ECDSA signatures that can be mitigated through the use of blinding during the signing process in the _gcry_ecc_ecdsa_sign function in cipher/ecc-ecdsa.c, aka the Return Of the Hidden Number Problem or ROHNP. To discover an ECDSA key, the attacker needs access to either the local machine or a different virtual machine on the same physical host.

Project: gnupg

_gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
                      gcry_mpi_t r, gcry_mpi_t s,
                      int flags, int hashalgo)
{
  gpg_err_code_t rc = 0;
  int extraloops = 0;
  gcry_mpi_t k, dr, sum, k_1, x;
  mpi_point_struct I;
  gcry_mpi_t hash;
   const void *abuf;
   unsigned int abits, qbits;
   mpi_ec_t ctx;
  gcry_mpi_t b;                /* Random number needed for blinding.  */
  gcry_mpi_t bi;               /* multiplicative inverse of B.        */
 
   if (DBG_CIPHER)
     log_mpidump ("ecdsa sign hash  ", input );

  /* Convert the INPUT into an MPI if needed.  */
  rc = _gcry_dsa_normalize_hash (input, &hash, qbits);
  if (rc)
    return rc;
   if (rc)
     return rc;
 
  b  = mpi_snew (qbits);
  bi = mpi_snew (qbits);
  do
    {
      _gcry_mpi_randomize (b, qbits, GCRY_WEAK_RANDOM);
      mpi_mod (b, b, skey->E.n);
    }
  while (!mpi_invm (bi, b, skey->E.n));

   k = NULL;
   dr = mpi_alloc (0);
   sum = mpi_alloc (0);
    {
      do
        {
          mpi_free (k);
          k = NULL;
          if ((flags & PUBKEY_FLAG_RFC6979) && hashalgo)
            {
              /* Use Pornin's method for deterministic DSA.  If this
                 flag is set, it is expected that HASH is an opaque
                 MPI with the to be signed hash.  That hash is also
                 used as h1 from 3.2.a.  */
              if (!mpi_is_opaque (input))
                {
                  rc = GPG_ERR_CONFLICT;
                  goto leave;
                }

              abuf = mpi_get_opaque (input, &abits);
              rc = _gcry_dsa_gen_rfc6979_k (&k, skey->E.n, skey->d,
                                            abuf, (abits+7)/8,
                                            hashalgo, extraloops);
              if (rc)
                goto leave;
              extraloops++;
            }
          else
            k = _gcry_dsa_gen_k (skey->E.n, GCRY_STRONG_RANDOM);

          _gcry_mpi_ec_mul_point (&I, k, &skey->E.G, ctx);
          if (_gcry_mpi_ec_get_affine (x, NULL, &I, ctx))
            {
              if (DBG_CIPHER)
                log_debug ("ecc sign: Failed to get affine coordinates\n");
              rc = GPG_ERR_BAD_SIGNATURE;
              goto leave;
            }
          mpi_mod (r, x, skey->E.n);  /* r = x mod n */
        }
      while (!mpi_cmp_ui (r, 0));

      mpi_mulm (dr, skey->d, r, skey->E.n); /* dr = d*r mod n  */
      mpi_addm (sum, hash, dr, skey->E.n);  /* sum = hash + (d*r) mod n  */
      mpi_invm (k_1, k, skey->E.n);         /* k_1 = k^(-1) mod n  */
      mpi_mulm (s, k_1, sum, skey->E.n);    /* s = k^(-1)*(hash+(d*r)) mod n */
    }
  while (!mpi_cmp_ui (s, 0));

  if (DBG_CIPHER)
         }