/*
* Use the blinding method and optimisation suggested in 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 dhm_update_blinding( mbedtls_dhm_context *ctx,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret, count;
/*
* Don't use any blinding the first time a particular X is used,
* but remember it to use blinding next time.
*/
if( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->pX ) != 0 )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &ctx->pX, &ctx->X ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &ctx->Vi, 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &ctx->Vf, 1 ) );
return( 0 );
}
/*
* Ok, we need blinding. Can we re-use existing values?
* If yes, just update them by squaring them.
*/
if( mbedtls_mpi_cmp_int( &ctx->Vi, 1 ) != 0 )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->P ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
return( 0 );
}
/*
* We need to generate blinding values from scratch
*/
/* Vi = random( 2, P-1 ) */
count = 0;
do
{
mbedtls_mpi_fill_random( &ctx->Vi, mbedtls_mpi_size( &ctx->P ), f_rng, p_rng );
while( mbedtls_mpi_cmp_mpi( &ctx->Vi, &ctx->P ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->Vi, 1 ) );
if( count++ > 10 )
return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE );
}
while( mbedtls_mpi_cmp_int( &ctx->Vi, 1 ) <= 0 );
/* Vf = Vi^-X mod P */
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &ctx->Vf, &ctx->Vi, &ctx->P ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->Vf, &ctx->Vf, &ctx->X, &ctx->P, &ctx->RP ) );
cleanup:
return( ret );
}
static int div_2(void *a, void *b)
{
if (mbedtls_mpi_copy(b, a))
return CRYPT_MEM;
if (mbedtls_mpi_shift_r(b, 1))
return CRYPT_MEM;
return CRYPT_OK;
}
void TEE_BigIntShiftRight(TEE_BigInt *dest, const TEE_BigInt *op, size_t bits)
{
mbedtls_mpi mpi_dest;
mbedtls_mpi mpi_op;
get_mpi(&mpi_dest, dest);
if (dest == op) {
MPI_CHECK(mbedtls_mpi_shift_r(&mpi_dest, bits));
goto out;
}
get_mpi(&mpi_op, op);
if (mbedtls_mpi_size(&mpi_dest) >= mbedtls_mpi_size(&mpi_op)) {
MPI_CHECK(mbedtls_mpi_copy(&mpi_dest, &mpi_op));
MPI_CHECK(mbedtls_mpi_shift_r(&mpi_dest, bits));
} else {
mbedtls_mpi mpi_t;
get_mpi(&mpi_t, NULL);
/*
* We're using a temporary buffer to avoid the corner case
* where destination is unexpectedly overflowed by up to
* @bits number of bits.
*/
MPI_CHECK(mbedtls_mpi_copy(&mpi_t, &mpi_op));
MPI_CHECK(mbedtls_mpi_shift_r(&mpi_t, bits));
MPI_CHECK(mbedtls_mpi_copy(&mpi_dest, &mpi_t));
mbedtls_mpi_free(&mpi_t);
}
mbedtls_mpi_free(&mpi_op);
out:
MPI_CHECK(copy_mpi_to_bigint(&mpi_dest, dest));
mbedtls_mpi_free(&mpi_dest);
}
/*
* Derive a suitable integer for group grp from a buffer of length len
* SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
*/
static int derive_mpi( const mbedtls_ecp_group *grp, mbedtls_mpi *x,
const unsigned char *buf, size_t blen )
{
int ret;
size_t n_size = ( grp->nbits + 7 ) / 8;
size_t use_size = blen > n_size ? n_size : blen;
MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( x, buf, use_size ) );
if( use_size * 8 > grp->nbits )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( x, use_size * 8 - grp->nbits ) );
/* While at it, reduce modulo N */
if( mbedtls_mpi_cmp_mpi( x, &grp->N ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( x, x, &grp->N ) );
cleanup:
return( ret );
}
/*
* Create own private value X and export G^X
*/
int mbedtls_dhm_make_public( mbedtls_dhm_context *ctx, int x_size,
unsigned char *output, size_t olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret, count = 0;
if( ctx == NULL || olen < 1 || olen > ctx->len )
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
if( mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 )
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
/*
* generate X and calculate GX = G^X mod P
*/
do
{
mbedtls_mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
while( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->X, 1 ) );
if( count++ > 10 )
return( MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED );
}
while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
&ctx->P , &ctx->RP ) );
if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
return( ret );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &ctx->GX, output, olen ) );
cleanup:
if( ret != 0 )
return( MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED + ret );
return( 0 );
}
/*
* Setup and write the ServerKeyExchange parameters
*/
int mbedtls_dhm_make_params( mbedtls_dhm_context *ctx, int x_size,
unsigned char *output, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret, count = 0;
size_t n1, n2, n3;
unsigned char *p;
if( mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 )
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
/*
* Generate X as large as possible ( < P )
*/
do
{
mbedtls_mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
while( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->X, 1 ) );
if( count++ > 10 )
return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED );
}
while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
/*
* Calculate GX = G^X mod P
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
&ctx->P , &ctx->RP ) );
if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
return( ret );
/*
* export P, G, GX
*/
#define DHM_MPI_EXPORT(X,n) \
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( X, p + 2, n ) ); \
*p++ = (unsigned char)( n >> 8 ); \
*p++ = (unsigned char)( n ); p += n;
n1 = mbedtls_mpi_size( &ctx->P );
n2 = mbedtls_mpi_size( &ctx->G );
n3 = mbedtls_mpi_size( &ctx->GX );
p = output;
DHM_MPI_EXPORT( &ctx->P , n1 );
DHM_MPI_EXPORT( &ctx->G , n2 );
DHM_MPI_EXPORT( &ctx->GX, n3 );
*olen = p - output;
ctx->len = n1;
cleanup:
if( ret != 0 )
return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED + ret );
return( 0 );
}
/*
* Compute ECDSA signature of a hashed message (SEC1 4.1.3)
* Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
*/
int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret, key_tries, sign_tries, blind_tries;
mbedtls_ecp_point R;
mbedtls_mpi k, e, t;
/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
if( grp->N.p == NULL )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
mbedtls_ecp_point_init( &R );
mbedtls_mpi_init( &k ); mbedtls_mpi_init( &e ); mbedtls_mpi_init( &t );
sign_tries = 0;
do
{
/*
* Steps 1-3: generate a suitable ephemeral keypair
* and set r = xR mod n
*/
key_tries = 0;
do
{
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
if( key_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( r, 0 ) == 0 );
/*
* Step 5: derive MPI from hashed message
*/
MBEDTLS_MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
/*
* Generate a random value to blind inv_mod in next step,
* avoiding a potential timing leak.
*/
blind_tries = 0;
do
{
size_t n_size = ( grp->nbits + 7 ) / 8;
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &t, n_size, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &t, 8 * n_size - grp->nbits ) );
/* See mbedtls_ecp_gen_keypair() */
if( ++blind_tries > 30 )
return( MBEDTLS_ERR_ECP_RANDOM_FAILED );
}
while( mbedtls_mpi_cmp_int( &t, 1 ) < 0 ||
mbedtls_mpi_cmp_mpi( &t, &grp->N ) >= 0 );
/*
* Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, r, d ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &e, &e, s ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &e, &e, &t ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &k, &k, &t ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( s, &k, &grp->N ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, s, &e ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( s, s, &grp->N ) );
if( sign_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( s, 0 ) == 0 );
cleanup:
mbedtls_ecp_point_free( &R );
mbedtls_mpi_free( &k ); mbedtls_mpi_free( &e ); mbedtls_mpi_free( &t );
return( ret );
}
/*
* Based on libmpa implementation __mpa_egcd(), modified to work with MPI
* instead.
*/
static void mpi_egcd(mbedtls_mpi *gcd, mbedtls_mpi *a, mbedtls_mpi *b,
mbedtls_mpi *x_in, mbedtls_mpi *y_in)
{
mbedtls_mpi_uint k;
mbedtls_mpi A;
mbedtls_mpi B;
mbedtls_mpi C;
mbedtls_mpi D;
mbedtls_mpi x;
mbedtls_mpi y;
mbedtls_mpi u;
get_mpi(&A, NULL);
get_mpi(&B, NULL);
get_mpi(&C, NULL);
get_mpi(&D, NULL);
get_mpi(&x, NULL);
get_mpi(&y, NULL);
get_mpi(&u, NULL);
/* have y < x from assumption */
if (!mbedtls_mpi_cmp_int(y_in, 0)) {
MPI_CHECK(mbedtls_mpi_lset(a, 1));
MPI_CHECK(mbedtls_mpi_lset(b, 0));
MPI_CHECK(mbedtls_mpi_copy(gcd, x_in));
goto out;
}
MPI_CHECK(mbedtls_mpi_copy(&x, x_in));
MPI_CHECK(mbedtls_mpi_copy(&y, y_in));
k = 0;
while (mpi_is_even(&x) && mpi_is_even(&y)) {
k++;
MPI_CHECK(mbedtls_mpi_shift_r(&x, 1));
MPI_CHECK(mbedtls_mpi_shift_r(&y, 1));
}
MPI_CHECK(mbedtls_mpi_copy(&u, &x));
MPI_CHECK(mbedtls_mpi_copy(gcd, &y));
MPI_CHECK(mbedtls_mpi_lset(&A, 1));
MPI_CHECK(mbedtls_mpi_lset(&B, 0));
MPI_CHECK(mbedtls_mpi_lset(&C, 0));
MPI_CHECK(mbedtls_mpi_lset(&D, 1));
while (mbedtls_mpi_cmp_int(&u, 0)) {
while (mpi_is_even(&u)) {
MPI_CHECK(mbedtls_mpi_shift_r(&u, 1));
if (mpi_is_odd(&A) || mpi_is_odd(&B)) {
MPI_CHECK(mbedtls_mpi_add_mpi(&A, &A, &y));
MPI_CHECK(mbedtls_mpi_sub_mpi(&B, &B, &x));
}
MPI_CHECK(mbedtls_mpi_shift_r(&A, 1));
MPI_CHECK(mbedtls_mpi_shift_r(&B, 1));
}
while (mpi_is_even(gcd)) {
MPI_CHECK(mbedtls_mpi_shift_r(gcd, 1));
if (mpi_is_odd(&C) || mpi_is_odd(&D)) {
MPI_CHECK(mbedtls_mpi_add_mpi(&C, &C, &y));
MPI_CHECK(mbedtls_mpi_sub_mpi(&D, &D, &x));
}
MPI_CHECK(mbedtls_mpi_shift_r(&C, 1));
MPI_CHECK(mbedtls_mpi_shift_r(&D, 1));
}
if (mbedtls_mpi_cmp_mpi(&u, gcd) >= 0) {
MPI_CHECK(mbedtls_mpi_sub_mpi(&u, &u, gcd));
MPI_CHECK(mbedtls_mpi_sub_mpi(&A, &A, &C));
MPI_CHECK(mbedtls_mpi_sub_mpi(&B, &B, &D));
} else {
MPI_CHECK(mbedtls_mpi_sub_mpi(gcd, gcd, &u));
MPI_CHECK(mbedtls_mpi_sub_mpi(&C, &C, &A));
MPI_CHECK(mbedtls_mpi_sub_mpi(&D, &D, &B));
}
}
MPI_CHECK(mbedtls_mpi_copy(a, &C));
MPI_CHECK(mbedtls_mpi_copy(b, &D));
MPI_CHECK(mbedtls_mpi_shift_l(gcd, k));
out:
mbedtls_mpi_free(&A);
mbedtls_mpi_free(&B);
mbedtls_mpi_free(&C);
mbedtls_mpi_free(&D);
mbedtls_mpi_free(&x);
mbedtls_mpi_free(&y);
mbedtls_mpi_free(&u);
}
