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RSA: blind call to mpi_inv_mod() on secret value
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
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@ -808,6 +808,9 @@ static int rsa_prepare_blinding( mbedtls_rsa_context *ctx,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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int ret, count = 0;
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mbedtls_mpi R;
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mbedtls_mpi_init( &R );
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if( ctx->Vf.p != NULL )
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{
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@ -827,17 +830,32 @@ static int rsa_prepare_blinding( mbedtls_rsa_context *ctx,
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MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->Vf, ctx->len - 1, f_rng, p_rng ) );
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ret = mbedtls_mpi_inv_mod( &ctx->Vi, &ctx->Vf, &ctx->N );
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if( ret != 0 && ret != MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
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/* Compute the Vf^1 as R * (R Vf)^-1 to avoid leaks from inv_mod.
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* There's a negligible but non-zero probability that R is not
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* invertible mod N, in that case we'd just loop one more time,
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* just as if Vf itself wasn't invertible - no need to distinguish. */
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MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &R, ctx->len - 1, f_rng, p_rng ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vi, &ctx->Vf, &R ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->N ) );
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ret = mbedtls_mpi_inv_mod( &ctx->Vi, &ctx->Vi, &ctx->N );
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if( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
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continue;
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if( ret != 0 )
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goto cleanup;
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} while( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &R ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->N ) );
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} while( 0 );
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/* Blinding value: Vi = Vf^(-e) mod N */
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/* Blinding value: Vi = Vf^(-e) mod N
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* (Vi already contains Vf^-1 at this point) */
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MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->Vi, &ctx->Vi, &ctx->E, &ctx->N, &ctx->RN ) );
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cleanup:
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mbedtls_mpi_free( &R );
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return( ret );
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}
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