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RSA: remove redundant GCD call in prepare_blinding()

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inv_mod() already returns a specific error code if the value is not
invertible, so no need to check in advance that it is. Also, this is a
preparation for blinding the call to inv_mod(), which is made easier by
avoiding the redundancy (otherwise the call to gcd() would need to be blinded
too).

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This commit is contained in:
Manuel Pégourié-Gonnard 2020-06-26 11:03:19 +02:00
parent a35e98a060
commit 6ab924de1d
1 changed files with 6 additions and 3 deletions
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9
library/rsa.c
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@ -764,11 +764,14 @@ static int rsa_prepare_blinding( mbedtls_rsa_context *ctx,
return( MBEDTLS_ERR_RSA_RNG_FAILED );
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->Vf, ctx->len - 1, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_gcd( &ctx->Vi, &ctx->Vf, &ctx->N ) );
} while( mbedtls_mpi_cmp_int( &ctx->Vi, 1 ) != 0 );
ret = mbedtls_mpi_inv_mod( &ctx->Vi, &ctx->Vf, &ctx->N );
if( ret != 0 && ret != MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
goto cleanup;
} while( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
/* Blinding value: Vi = Vf^(-e) mod N */
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &ctx->Vi, &ctx->Vf, &ctx->N ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->Vi, &ctx->Vi, &ctx->E, &ctx->N, &ctx->RN ) );