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In BN_mod_exp_mont_word, avoid one application of BN_MOD_MUL_WORD,

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and for small 'a' also a couple of calls to
BN_mod_mul_montgomery(r, r, r, ...).
This commit is contained in:
Bodo Möller 2000-06-23 05:51:37 +00:00
parent 431b0cce7d
commit e958c5afe7
1 changed files with 51 additions and 14 deletions
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65
crypto/bn/bn_exp.c
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@ -643,7 +643,7 @@ int BN_mod_exp_mont(BIGNUM *rr, BIGNUM *a, const BIGNUM *p,
start=0; start=0;
if (wstart < 0) break; if (wstart < 0) break;
} }
BN_from_montgomery(rr,r,mont,ctx); if (!BN_from_montgomery(rr,r,mont,ctx)) goto err;
ret=1; ret=1;
err: err:
if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont); if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
@ -658,14 +658,20 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
{ {
BN_MONT_CTX *mont = NULL; BN_MONT_CTX *mont = NULL;
int b, bits, ret=0; int b, bits, ret=0;
int r_is_one;
BN_ULONG w, next_w; BN_ULONG w, next_w;
BIGNUM *d, *r, *t; BIGNUM *d, *r, *t;
BIGNUM *swap_tmp; BIGNUM *swap_tmp;
#define BN_MOD_MUL_WORD(r, w, m) \ #define BN_MOD_MUL_WORD(r, w, m) \
(BN_mul_word(r, (w)) && \ (BN_mul_word(r, (w)) && \
(BN_ucmp(r, (m)) >= 0 ? \ (BN_ucmp(r, (m)) < 0 ? 1 : \
(BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1)) : \ (BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
1)) /* BN_MOD_MUL_WORD is only used with 'w' large,
* so the BN_ucmp test is probably more overhead
* than always using BN_mod (which uses BN_copy if
* a similar test returns true). */
#define BN_TO_MONTGOMERY_WORD(r, w, mont) \
(BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
bn_check_top(p); bn_check_top(p);
bn_check_top(m); bn_check_top(m);
@ -708,7 +714,7 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
if (!BN_MONT_CTX_set(mont, m, ctx)) goto err; if (!BN_MONT_CTX_set(mont, m, ctx)) goto err;
} }
if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) goto err; r_is_one = 1; /* except for Montgomery factor */
/* bits-1 >= 0 */ /* bits-1 >= 0 */
@ -720,13 +726,22 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
next_w = w*w; next_w = w*w;
if ((next_w/w) != w) /* overflow */ if ((next_w/w) != w) /* overflow */
{ {
if (!BN_MOD_MUL_WORD(r, w, m)) if (r_is_one)
goto err; {
if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
r_is_one = 0;
}
else
{
if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
}
next_w = 1; next_w = 1;
} }
w = next_w; w = next_w;
if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) if (!r_is_one)
goto err; {
if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) goto err;
}
/* Second, multiply r*w by 'a' if exponent bit is set. */ /* Second, multiply r*w by 'a' if exponent bit is set. */
if (BN_is_bit_set(p, b)) if (BN_is_bit_set(p, b))
@ -734,21 +749,43 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
next_w = w*a; next_w = w*a;
if ((next_w/a) != w) /* overflow */ if ((next_w/a) != w) /* overflow */
{ {
if (!BN_MOD_MUL_WORD(r, w, m)) if (r_is_one)
goto err; {
if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
r_is_one = 0;
}
else
{
if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
}
next_w = a; next_w = a;
} }
w = next_w; w = next_w;
} }
} }
/* Finally, set r:=r*w. */ /* Finally, set r:=r*w. */
if (w != 1) if (w != 1)
{ {
if (!BN_MOD_MUL_WORD(r, w, m)) if (r_is_one)
goto err; {
if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
r_is_one = 0;
}
else
{
if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
}
} }
BN_from_montgomery(rr, r, mont, ctx); if (r_is_one) /* can happen only if a == 1*/
{
if (!BN_one(rr)) goto err;
}
else
{
if (!BN_from_montgomery(rr, r, mont, ctx)) goto err;
}
ret = 1; ret = 1;
err: err:
if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont); if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);