Optimize RSA blinding by caching-updating values
diff --git a/library/rsa.c b/library/rsa.c
index 0a943c2..c82ffaa 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -255,13 +255,27 @@
#if !defined(POLARSSL_RSA_NO_CRT)
/*
- * Generate blinding values
+ * Generate or update blinding values, see section 10 of:
+ * KOCHER, Paul C. Timing attacks on implementations of Diffie-Hellman, RSA,
+ * DSS, and other systems. In : Advances in Cryptology—CRYPTO’96. Springer
+ * Berlin Heidelberg, 1996. p. 104-113.
*/
static int rsa_prepare_blinding( rsa_context *ctx,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret;
+ if( ctx->Vf.p != NULL )
+ {
+ /* We already have blinding values, just update them by squaring */
+ MPI_CHK( mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
+ MPI_CHK( mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->P ) );
+ MPI_CHK( mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
+ MPI_CHK( mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
+
+ return( 0 );
+ }
+
/* Unblinding value: Vf = random number */
MPI_CHK( mpi_fill_random( &ctx->Vf, ctx->len - 1, f_rng, p_rng ) );
