diff options
Diffstat (limited to 'library/rsa.c')
-rw-r--r-- | library/rsa.c | 36 |
1 files changed, 31 insertions, 5 deletions
diff --git a/library/rsa.c b/library/rsa.c index 376afa4..c5dbdac 100644 --- a/library/rsa.c +++ b/library/rsa.c @@ -744,6 +744,9 @@ static int rsa_prepare_blinding( mbedtls_rsa_context *ctx, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret, count = 0; + mbedtls_mpi R; + + mbedtls_mpi_init( &R ); if( ctx->Vf.p != NULL ) { @@ -759,18 +762,41 @@ static int rsa_prepare_blinding( mbedtls_rsa_context *ctx, /* Unblinding value: Vf = random number, invertible mod N */ do { if( count++ > 10 ) - return( MBEDTLS_ERR_RSA_RNG_FAILED ); + { + ret = MBEDTLS_ERR_RSA_RNG_FAILED; + goto cleanup; + } 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 ); - /* Blinding value: Vi = Vf^(-e) mod N */ - MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &ctx->Vi, &ctx->Vf, &ctx->N ) ); + /* Compute Vf^-1 as R * (R Vf)^-1 to avoid leaks from inv_mod. */ + MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &R, ctx->len - 1, f_rng, p_rng ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vi, &ctx->Vf, &R ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->N ) ); + + /* At this point, Vi is invertible mod N if and only if both Vf and R + * are invertible mod N. If one of them isn't, we don't need to know + * which one, we just loop and choose new values for both of them. + * (Each iteration succeeds with overwhelming probability.) */ + ret = mbedtls_mpi_inv_mod( &ctx->Vi, &ctx->Vi, &ctx->N ); + if( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE ) + continue; + if( ret != 0 ) + goto cleanup; + + /* Finish the computation of Vf^-1 = R * (R Vf)^-1 */ + MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &R ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->N ) ); + } while( 0 ); + + /* Blinding value: Vi = Vf^(-e) mod N + * (Vi already contains Vf^-1 at this point) */ MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->Vi, &ctx->Vi, &ctx->E, &ctx->N, &ctx->RN ) ); cleanup: + mbedtls_mpi_free( &R ); + return( ret ); } |