RSA blinding on CRT operations to counter timing attacks
diff --git a/library/rsa.c b/library/rsa.c
index e53d9a2..1ef97f8 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -252,10 +252,47 @@
return( 0 );
}
+#if !defined(POLARSSL_RSA_NO_CRT)
+/*
+ * 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->N ) );
+ MPI_CHK( mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
+ MPI_CHK( mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->N ) );
+
+ return( 0 );
+ }
+
+ /* Unblinding value: Vf = random number */
+ MPI_CHK( mpi_fill_random( &ctx->Vf, ctx->len - 1, f_rng, p_rng ) );
+
+ /* Blinding value: Vi = Vf^(-e) mod N */
+ MPI_CHK( mpi_inv_mod( &ctx->Vi, &ctx->Vf, &ctx->N ) );
+ MPI_CHK( mpi_exp_mod( &ctx->Vi, &ctx->Vi, &ctx->E, &ctx->N, &ctx->RN ) );
+
+cleanup:
+ return( ret );
+}
+#endif
+
/*
* Do an RSA private key operation
*/
int rsa_private( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
const unsigned char *input,
unsigned char *output )
{
@@ -276,6 +313,17 @@
#if defined(POLARSSL_RSA_NO_CRT)
MPI_CHK( mpi_exp_mod( &T, &T, &ctx->D, &ctx->N, &ctx->RN ) );
#else
+ if( f_rng != NULL )
+ {
+ /*
+ * Blinding
+ * T = T * Vi mod N
+ */
+ MPI_CHK( rsa_prepare_blinding( ctx, f_rng, p_rng ) );
+ MPI_CHK( mpi_mul_mpi( &T, &T, &ctx->Vi ) );
+ MPI_CHK( mpi_mod_mpi( &T, &T, &ctx->N ) );
+ }
+
/*
* faster decryption using the CRT
*
@@ -297,6 +345,16 @@
*/
MPI_CHK( mpi_mul_mpi( &T1, &T, &ctx->Q ) );
MPI_CHK( mpi_add_mpi( &T, &T2, &T1 ) );
+
+ if( f_rng != NULL )
+ {
+ /*
+ * Unblind
+ * T = T * Vf mod N
+ */
+ MPI_CHK( mpi_mul_mpi( &T, &T, &ctx->Vf ) );
+ MPI_CHK( mpi_mod_mpi( &T, &T, &ctx->N ) );
+ }
#endif
olen = ctx->len;
@@ -430,7 +488,7 @@
return( ( mode == RSA_PUBLIC )
? rsa_public( ctx, output, output )
- : rsa_private( ctx, output, output ) );
+ : rsa_private( ctx, f_rng, p_rng, output, output ) );
}
#endif /* POLARSSL_PKCS1_V21 */
@@ -492,7 +550,7 @@
return( ( mode == RSA_PUBLIC )
? rsa_public( ctx, output, output )
- : rsa_private( ctx, output, output ) );
+ : rsa_private( ctx, f_rng, p_rng, output, output ) );
}
/*
@@ -527,7 +585,9 @@
* Implementation of the PKCS#1 v2.1 RSAES-OAEP-DECRYPT function
*/
int rsa_rsaes_oaep_decrypt( rsa_context *ctx,
- int mode,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
+ int mode,
const unsigned char *label, size_t label_len,
size_t *olen,
const unsigned char *input,
@@ -553,7 +613,7 @@
ret = ( mode == RSA_PUBLIC )
? rsa_public( ctx, input, buf )
- : rsa_private( ctx, input, buf );
+ : rsa_private( ctx, f_rng, p_rng, input, buf );
if( ret != 0 )
return( ret );
@@ -618,6 +678,8 @@
* Implementation of the PKCS#1 v2.1 RSAES-PKCS1-V1_5-DECRYPT function
*/
int rsa_rsaes_pkcs1_v15_decrypt( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
int mode, size_t *olen,
const unsigned char *input,
unsigned char *output,
@@ -639,7 +701,7 @@
ret = ( mode == RSA_PUBLIC )
? rsa_public( ctx, input, buf )
- : rsa_private( ctx, input, buf );
+ : rsa_private( ctx, f_rng, p_rng, input, buf );
if( ret != 0 )
return( ret );
@@ -711,6 +773,8 @@
* Do an RSA operation, then remove the message padding
*/
int rsa_pkcs1_decrypt( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
int mode, size_t *olen,
const unsigned char *input,
unsigned char *output,
@@ -719,13 +783,13 @@
switch( ctx->padding )
{
case RSA_PKCS_V15:
- return rsa_rsaes_pkcs1_v15_decrypt( ctx, mode, olen, input, output,
- output_max_len );
+ return rsa_rsaes_pkcs1_v15_decrypt( ctx, f_rng, p_rng, mode, olen,
+ input, output, output_max_len );
#if defined(POLARSSL_PKCS1_V21)
case RSA_PKCS_V21:
- return rsa_rsaes_oaep_decrypt( ctx, mode, NULL, 0, olen, input,
- output, output_max_len );
+ return rsa_rsaes_oaep_decrypt( ctx, f_rng, p_rng, mode, NULL, 0,
+ olen, input, output, output_max_len );
#endif
default:
@@ -848,7 +912,7 @@
return( ( mode == RSA_PUBLIC )
? rsa_public( ctx, sig, sig )
- : rsa_private( ctx, sig, sig ) );
+ : rsa_private( ctx, f_rng, p_rng, sig, sig ) );
}
#endif /* POLARSSL_PKCS1_V21 */
@@ -859,6 +923,8 @@
* Do an RSA operation to sign the message digest
*/
int rsa_rsassa_pkcs1_v15_sign( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
int mode,
int hash_id,
unsigned int hashlen,
@@ -971,7 +1037,7 @@
return( ( mode == RSA_PUBLIC )
? rsa_public( ctx, sig, sig )
- : rsa_private( ctx, sig, sig ) );
+ : rsa_private( ctx, f_rng, p_rng, sig, sig ) );
}
/*
@@ -989,7 +1055,7 @@
switch( ctx->padding )
{
case RSA_PKCS_V15:
- return rsa_rsassa_pkcs1_v15_sign( ctx, mode, hash_id,
+ return rsa_rsassa_pkcs1_v15_sign( ctx, f_rng, p_rng, mode, hash_id,
hashlen, hash, sig );
#if defined(POLARSSL_PKCS1_V21)
@@ -1008,6 +1074,8 @@
* Implementation of the PKCS#1 v2.1 RSASSA-PSS-VERIFY function
*/
int rsa_rsassa_pss_verify( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
int mode,
int hash_id,
unsigned int hashlen,
@@ -1035,7 +1103,7 @@
ret = ( mode == RSA_PUBLIC )
? rsa_public( ctx, sig, buf )
- : rsa_private( ctx, sig, buf );
+ : rsa_private( ctx, f_rng, p_rng, sig, buf );
if( ret != 0 )
return( ret );
@@ -1139,6 +1207,8 @@
* Implementation of the PKCS#1 v2.1 RSASSA-PKCS1-v1_5-VERIFY function
*/
int rsa_rsassa_pkcs1_v15_verify( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
int mode,
int hash_id,
unsigned int hashlen,
@@ -1160,7 +1230,7 @@
ret = ( mode == RSA_PUBLIC )
? rsa_public( ctx, sig, buf )
- : rsa_private( ctx, sig, buf );
+ : rsa_private( ctx, f_rng, p_rng, sig, buf );
if( ret != 0 )
return( ret );
@@ -1247,6 +1317,8 @@
* Do an RSA operation and check the message digest
*/
int rsa_pkcs1_verify( rsa_context *ctx,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng,
int mode,
int hash_id,
unsigned int hashlen,
@@ -1256,12 +1328,12 @@
switch( ctx->padding )
{
case RSA_PKCS_V15:
- return rsa_rsassa_pkcs1_v15_verify( ctx, mode, hash_id,
- hashlen, hash, sig );
+ return rsa_rsassa_pkcs1_v15_verify( ctx, f_rng, p_rng, mode,
+ hash_id, hashlen, hash, sig );
#if defined(POLARSSL_PKCS1_V21)
case RSA_PKCS_V21:
- return rsa_rsassa_pss_verify( ctx, mode, hash_id,
+ return rsa_rsassa_pss_verify( ctx, f_rng, p_rng, mode, hash_id,
hashlen, hash, sig );
#endif
@@ -1348,7 +1420,7 @@
for( i = 0; i < len; ++i )
output[i] = rand();
-
+
return( 0 );
}
@@ -1407,7 +1479,7 @@
if( verbose != 0 )
printf( "passed\n PKCS#1 decryption : " );
- if( rsa_pkcs1_decrypt( &rsa, RSA_PRIVATE, &len,
+ if( rsa_pkcs1_decrypt( &rsa, &myrand, NULL, RSA_PRIVATE, &len,
rsa_ciphertext, rsa_decrypted,
sizeof(rsa_decrypted) ) != 0 )
{
@@ -1431,7 +1503,7 @@
sha1( rsa_plaintext, PT_LEN, sha1sum );
- if( rsa_pkcs1_sign( &rsa, NULL, NULL, RSA_PRIVATE, SIG_RSA_SHA1, 20,
+ if( rsa_pkcs1_sign( &rsa, &myrand, NULL, RSA_PRIVATE, SIG_RSA_SHA1, 20,
sha1sum, rsa_ciphertext ) != 0 )
{
if( verbose != 0 )
@@ -1443,7 +1515,7 @@
if( verbose != 0 )
printf( "passed\n PKCS#1 sig. verify: " );
- if( rsa_pkcs1_verify( &rsa, RSA_PUBLIC, SIG_RSA_SHA1, 20,
+ if( rsa_pkcs1_verify( &rsa, &myrand, NULL, RSA_PUBLIC, SIG_RSA_SHA1, 20,
sha1sum, rsa_ciphertext ) != 0 )
{
if( verbose != 0 )