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Add exponent blinding to RSA with CRT

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The sliding window exponentiation algorithm is vulnerable to
side-channel attacks. As a countermeasure we add exponent blinding in
order to prevent combining the results of different measurements.

This commit handles the case when the Chinese Remainder Theorem is used
to accelerate the computation.
This commit is contained in:
Janos Follath 2017-03-22 15:13:15 +00:00 committed by Simon Butcher
parent e81102e476
commit f9203b4139
1 changed files with 50 additions and 9 deletions
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59
library/rsa.c
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@ -394,10 +394,14 @@ int mbedtls_rsa_private( mbedtls_rsa_context *ctx,
int ret;
size_t olen;
mbedtls_mpi T, T1, T2;
mbedtls_mpi P1, Q1, R;
#if defined(MBEDTLS_RSA_NO_CRT)
mbedtls_mpi P1, Q1;
mbedtls_mpi D_blind, R;
mbedtls_mpi D_blind;
mbedtls_mpi *D = &ctx->D;
#else
mbedtls_mpi DP_blind, DQ_blind;
mbedtls_mpi *DP = &ctx->DP;
mbedtls_mpi *DQ = &ctx->DQ;
#endif
/* Make sure we have private key info, prevent possible misuse */
@ -405,10 +409,18 @@ int mbedtls_rsa_private( mbedtls_rsa_context *ctx,
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
mbedtls_mpi_init( &T ); mbedtls_mpi_init( &T1 ); mbedtls_mpi_init( &T2 );
mbedtls_mpi_init( &P1 ); mbedtls_mpi_init( &Q1 ); mbedtls_mpi_init( &R );
if( f_rng != NULL )
{
#if defined(MBEDTLS_RSA_NO_CRT)
mbedtls_mpi_init( &P1 ); mbedtls_mpi_init( &Q1 );
mbedtls_mpi_init( &R ); mbedtls_mpi_init( &D_blind );
mbedtls_mpi_init( &D_blind );
#else
mbedtls_mpi_init( &DP_blind );
mbedtls_mpi_init( &DQ_blind );
#endif
}
#if defined(MBEDTLS_THREADING_C)
@ -433,13 +445,13 @@ int mbedtls_rsa_private( mbedtls_rsa_context *ctx,
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T, &T, &ctx->Vi ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &T, &T, &ctx->N ) );
#if defined(MBEDTLS_RSA_NO_CRT)
/*
* Exponent blinding
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &P1, &ctx->P, 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &Q1, &ctx->Q, 1 ) );
#if defined(MBEDTLS_RSA_NO_CRT)
/*
* D_blind = ( P - 1 ) * ( Q - 1 ) * R + D
*/
@ -450,6 +462,28 @@ int mbedtls_rsa_private( mbedtls_rsa_context *ctx,
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &D_blind, &D_blind, &ctx->D ) );
D = &D_blind;
#else
/*
* DP_blind = ( P - 1 ) * R + DP
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &R, RSA_EXPONENT_BLINDING,
f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &DP_blind, &P1, &R ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &DP_blind, &DP_blind,
&ctx->DP ) );
DP = &DP_blind;
/*
* DQ_blind = ( Q - 1 ) * R + DQ
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &R, RSA_EXPONENT_BLINDING,
f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &DQ_blind, &Q1, &R ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &DQ_blind, &DQ_blind,
&ctx->DQ ) );
DQ = &DQ_blind;
#endif /* MBEDTLS_RSA_NO_CRT */
}
@ -462,8 +496,8 @@ int mbedtls_rsa_private( mbedtls_rsa_context *ctx,
* T1 = input ^ dP mod P
* T2 = input ^ dQ mod Q
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &T1, &T, &ctx->DP, &ctx->P, &ctx->RP ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &T2, &T, &ctx->DQ, &ctx->Q, &ctx->RQ ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &T1, &T, DP, &ctx->P, &ctx->RP ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &T2, &T, DQ, &ctx->Q, &ctx->RQ ) );
/*
* T = (T1 - T2) * (Q^-1 mod P) mod P
@ -499,10 +533,17 @@ cleanup:
#endif
mbedtls_mpi_free( &T ); mbedtls_mpi_free( &T1 ); mbedtls_mpi_free( &T2 );
mbedtls_mpi_free( &P1 ); mbedtls_mpi_free( &Q1 ); mbedtls_mpi_free( &R );
if( f_rng != NULL )
{
#if defined(MBEDTLS_RSA_NO_CRT)
mbedtls_mpi_free( &P1 ); mbedtls_mpi_free( &Q1 );
mbedtls_mpi_free( &R ); mbedtls_mpi_free( &D_blind );
mbedtls_mpi_free( &D_blind );
#else
mbedtls_mpi_free( &DP_blind );
mbedtls_mpi_free( &DQ_blind );
#endif
}
if( ret != 0 )
return( MBEDTLS_ERR_RSA_PRIVATE_FAILED + ret );