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Improve sign/key_tries handling

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(Unrelated to restartable work, just noticed while staring at the code.)

Checking at the end is inefficient as we might give up when we just generated
a valid signature or key.
This commit is contained in:
Manuel Pégourié-Gonnard 2017-04-21 13:19:43 +02:00
parent b90883dc1d
commit 675439620d
2 changed files with 20 additions and 21 deletions
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18
library/ecdsa.c
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@ -252,6 +252,12 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
sign_tries = 0;
do
{
if( sign_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
/*
* Steps 1-3: generate a suitable ephemeral keypair
* and set r = xR mod n
@ -259,14 +265,14 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
key_tries = 0;
do
{
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
if( key_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
}
while( mbedtls_mpi_cmp_int( r, 0 ) == 0 );
@ -303,12 +309,6 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( s, &k, &grp->N ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, s, &e ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( s, s, &grp->N ) );
if( sign_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( s, 0 ) == 0 );