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Use ecp_gen_privkey() in ECDSA sign

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Two different changes:

- the first one will allow us to store k in the restart context while
  restarting the following ecp_mul() operation

- the second one is an simplification, unrelated to restartability, made
  possible by the fact that ecp_gen_privkey() is now public
This commit is contained in:
Manuel Pégourié-Gonnard 2017-04-25 12:57:22 +02:00
parent 675439620d
commit 50b63ba2f5
1 changed files with 6 additions and 15 deletions
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21
library/ecdsa.c
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@ -225,7 +225,7 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
mbedtls_ecdsa_restart_ctx *rs_ctx )
{
int ret, key_tries, sign_tries, blind_tries;
int ret, key_tries, sign_tries;
mbedtls_ecp_point R;
mbedtls_mpi k, e, t;
@ -271,7 +271,10 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
goto cleanup;
}
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, &k, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, &R, &k, &grp->G,
f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
}
while( mbedtls_mpi_cmp_int( r, 0 ) == 0 );
@ -285,19 +288,7 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
* Generate a random value to blind inv_mod in next step,
* avoiding a potential timing leak.
*/
blind_tries = 0;
do
{
size_t n_size = ( grp->nbits + 7 ) / 8;
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &t, n_size, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &t, 8 * n_size - grp->nbits ) );
/* See mbedtls_ecp_gen_keypair() */
if( ++blind_tries > 30 )
return( MBEDTLS_ERR_ECP_RANDOM_FAILED );
}
while( mbedtls_mpi_cmp_int( &t, 1 ) < 0 ||
mbedtls_mpi_cmp_mpi( &t, &grp->N ) >= 0 );
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, &t, f_rng, p_rng ) );
/*
* Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n