diff options
Diffstat (limited to 'rsa.c')
| -rw-r--r-- | rsa.c | 22 |
1 files changed, 15 insertions, 7 deletions
@@ -76,7 +76,7 @@ */ #ifndef HAL_RSA_USE_MODEXP -#define HAL_RSA_USE_MODEXP 0 +#define HAL_RSA_USE_MODEXP 1 #endif /* @@ -169,7 +169,7 @@ static hal_error_t unpack_fp(const fp_int * const bn, uint8_t *buffer, const siz * wrap result back up as a bignum. */ -static hal_error_t modexp(const fp_int * const msg, +static hal_error_t modexp(const fp_int * msg, const fp_int * const exp, const fp_int * const mod, fp_int *res) @@ -178,13 +178,21 @@ static hal_error_t modexp(const fp_int * const msg, assert(msg != NULL && exp != NULL && mod != NULL && res != NULL); - const size_t msg_len = fp_unsigned_bin_size(msg); - const size_t exp_len = fp_unsigned_bin_size(exp); - const size_t mod_len = fp_unsigned_bin_size(mod); + fp_int reduced_msg; + + if (fp_cmp_mag(unconst_fp_int(msg), unconst_fp_int(mod)) != FP_LT) { + fp_init(&reduced_msg); + fp_mod(unconst_fp_int(msg), unconst_fp_int(mod), &reduced_msg); + msg = &reduced_msg; + } - const size_t len = (MAX(MAX(msg_len, exp_len), mod_len) + 3) & ~3; + const size_t exp_len = (fp_unsigned_bin_size(unconst_fp_int(exp)) + 3) & ~3; + const size_t mod_len = (fp_unsigned_bin_size(unconst_fp_int(mod)) + 3) & ~3; - uint8_t msgbuf[len], expbuf[len], modbuf[len], resbuf[len]; + uint8_t msgbuf[mod_len]; + uint8_t expbuf[exp_len]; + uint8_t modbuf[mod_len]; + uint8_t resbuf[mod_len]; if ((err = unpack_fp(msg, msgbuf, sizeof(msgbuf))) != HAL_OK || (err = unpack_fp(exp, expbuf, sizeof(expbuf))) != HAL_OK || |