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Merge pull request #547 from toddouska/mathca

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Remove timing resistant cache key bit monitor leaks
This commit is contained in:
John Safranek
2016-09-13 14:34:23 -07:00
committed by GitHub
parent 05d78dc2ce 46a0ee8e69
commit b77c350153
3 changed files with 87 additions and 3 deletions
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57
wolfcrypt/src/ecc.c
View File

@ -1876,6 +1876,27 @@ int wc_ecc_mulmod(mp_int* k, ecc_point *G, ecc_point *R, mp_int* a,
#else /* ECC_TIMING_RESISTANT */
#if defined(TFM_TIMINING_RESISTANT) && defined(USE_FAST_MATH)
/* let's use the one we already have */
extern const wolfssl_word wc_off_on_addr[2];
#else
static const wolfssl_word wc_off_on_addr[2] =
{
#if defined(WC_64BIT_CPU)
W64LIT(0x0000000000000000),
W64LIT(0xffffffffffffffff)
#elif defined(WC_16BIT_CPU)
0x0000U,
0xffffU
#else
/* 32 bit */
0x00000000U,
0xffffffffU
#endif
};
#endif
/**
Perform a point multiplication (timing resistant)
k The scalar to multiply by
@ -2013,8 +2034,42 @@ int wc_ecc_mulmod_ex(mp_int* k, ecc_point *G, ecc_point *R,
if (err == MP_OKAY)
err = ecc_projective_add_point(M[0], M[1], M[i^1], a, modulus,
mp);
/* instead of using M[i] for double, which leaks key bit to cache
* monitor, use M[2] as temp, make sure address calc is constant,
* keep &M[0] and &M[1] in cache */
if (err == MP_OKAY)
err = ecc_projective_dbl_point(M[i], M[i], a, modulus, mp);
err = mp_copy((mp_int*)
( ((wolfssl_word)&M[0]->x & wc_off_on_addr[i^1]) +
((wolfssl_word)&M[1]->x & wc_off_on_addr[i])),
M[2]->x);
if (err == MP_OKAY)
err = mp_copy((mp_int*)
( ((wolfssl_word)&M[0]->y & wc_off_on_addr[i^1]) +
((wolfssl_word)&M[1]->y & wc_off_on_addr[i])),
M[2]->y);
if (err == MP_OKAY)
err = mp_copy((mp_int*)
( ((wolfssl_word)&M[0]->z & wc_off_on_addr[i^1]) +
((wolfssl_word)&M[1]->z & wc_off_on_addr[i])),
M[2]->z);
if (err == MP_OKAY)
err = ecc_projective_dbl_point(M[2], M[2], a, modulus, mp);
/* copy M[2] back to M[i] */
if (err == MP_OKAY)
err = mp_copy(M[2]->x,
(mp_int*)
( ((wolfssl_word)&M[0]->x & wc_off_on_addr[i^1]) +
((wolfssl_word)&M[1]->x & wc_off_on_addr[i])) );
if (err == MP_OKAY)
err = mp_copy(M[2]->y,
(mp_int*)
( ((wolfssl_word)&M[0]->y & wc_off_on_addr[i^1]) +
((wolfssl_word)&M[1]->y & wc_off_on_addr[i])) );
if (err == MP_OKAY)
err = mp_copy(M[2]->z,
(mp_int*)
( ((wolfssl_word)&M[0]->z & wc_off_on_addr[i^1]) +
((wolfssl_word)&M[1]->z & wc_off_on_addr[i])) );
if (err != MP_OKAY)
break;
} /* end for */

32
wolfcrypt/src/tfm.c
View File

@ -1035,13 +1035,30 @@ int fp_addmod(fp_int *a, fp_int *b, fp_int *c, fp_int *d)
#ifdef TFM_TIMING_RESISTANT
/* all off / all on pointer addresses for constant calculations */
/* ecc.c uses same table */
const wolfssl_word wc_off_on_addr[2] =
{
#if defined(WC_64BIT_CPU)
W64LIT(0x0000000000000000),
W64LIT(0xffffffffffffffff)
#elif defined(WC_16BIT_CPU)
0x0000U,
0xffffU
#else
/* 32 bit */
0x00000000U,
0xffffffffU
#endif
};
/* timing resistant montgomery ladder based exptmod
Based on work by Marc Joye, Sung-Ming Yen, "The Montgomery Powering Ladder",
Cryptographic Hardware and Embedded Systems, CHES 2002
*/
static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
{
fp_int R[2];
fp_int R[3];
fp_digit buf, mp;
int err, bitcnt, digidx, y;
@ -1052,6 +1069,7 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
fp_init(&R[0]);
fp_init(&R[1]);
fp_init(&R[2]);
/* now we need R mod m */
fp_montgomery_calc_normalization (&R[0], P);
@ -1092,7 +1110,17 @@ static int _fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* do ops */
fp_mul(&R[0], &R[1], &R[y^1]); fp_montgomery_reduce(&R[y^1], P, mp);
fp_sqr(&R[y], &R[y]); fp_montgomery_reduce(&R[y], P, mp);
/* instead of using R[y] for sqr, which leaks key bit to cache monitor,
* use R[2] as temp, make sure address calc is constant, keep
* &R[0] and &R[1] in cache */
fp_copy((fp_int*) ( ((wolfssl_word)&R[0] & wc_off_on_addr[y^1]) +
((wolfssl_word)&R[1] & wc_off_on_addr[y]) ),
&R[2]);
fp_sqr(&R[2], &R[2]); fp_montgomery_reduce(&R[2], P, mp);
fp_copy(&R[2],
(fp_int*) ( ((wolfssl_word)&R[0] & wc_off_on_addr[y^1]) +
((wolfssl_word)&R[1] & wc_off_on_addr[y]) ) );
}
fp_montgomery_reduce(&R[0], P, mp);

1
wolfssl/wolfcrypt/types.h
View File

@ -91,6 +91,7 @@
defined(__mips64) || defined(__x86_64__) || defined(_M_X64)) || \
defined(__aarch64__)
typedef word64 wolfssl_word;
#define WC_64BIT_CPU
#else
typedef word32 wolfssl_word;
#ifdef WORD64_AVAILABLE