115 lines
2.7 KiB
Diff
115 lines
2.7 KiB
Diff
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--- crypto/bn/bn_mont.c
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+++ crypto/bn/bn_mont.c 2007-08-02 11:49:15.251420366 +0200
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@@ -176,7 +176,6 @@ int BN_from_montgomery(BIGNUM *ret, cons
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max=(nl+al+1); /* allow for overflow (no?) XXX */
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if (bn_wexpand(r,max) == NULL) goto err;
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- if (bn_wexpand(ret,max) == NULL) goto err;
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r->neg=a->neg^n->neg;
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np=n->d;
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@@ -228,19 +227,70 @@ int BN_from_montgomery(BIGNUM *ret, cons
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}
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bn_correct_top(r);
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- /* mont->ri will be a multiple of the word size */
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-#if 0
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- BN_rshift(ret,r,mont->ri);
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-#else
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- ret->neg = r->neg;
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- x=ri;
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+ /* mont->ri will be a multiple of the word size and below code
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+ * is kind of BN_rshift(ret,r,mont->ri) equivalent */
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+ if (r->top <= ri)
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+ {
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+ ret->top=0;
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+ retn=1;
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+ goto err;
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+ }
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+ al=r->top-ri;
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+
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+# define BRANCH_FREE 1
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+# if BRANCH_FREE
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+ if (bn_wexpand(ret,ri) == NULL) goto err;
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+ x=0-(((al-ri)>>(sizeof(al)*8-1))&1);
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+ ret->top=x=(ri&~x)|(al&x); /* min(ri,al) */
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+ ret->neg=r->neg;
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+
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rp=ret->d;
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- ap= &(r->d[x]);
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- if (r->top < x)
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- al=0;
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- else
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- al=r->top-x;
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+ ap=&(r->d[ri]);
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+
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+ {
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+ size_t m1,m2;
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+
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+ v=bn_sub_words(rp,ap,np,ri);
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+ /* this ----------------^^ works even in al<ri case
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+ * thanks to zealous zeroing of top of the vector in the
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+ * beginning. */
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+
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+ /* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */
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+ /* in other words if subtraction result is real, then
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+ * trick unconditional memcpy below to perform in-place
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+ * "refresh" instead of actual copy. */
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+ m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1); /* al<ri */
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+ m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1); /* al>ri */
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+ m1|=m2; /* (al!=ri) */
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+ m1|=(0-(size_t)v); /* (al!=ri || v) */
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+ m1&=~m2; /* (al!=ri || v) && !al>ri */
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+ nrp=(BN_ULONG *)(((size_t)rp&~m1)|((size_t)ap&m1));
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+ }
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+
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+ /* 'i<ri' is chosen to eliminate dependency on input data, even
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+ * though it results in redundant copy in al<ri case. */
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+ for (i=0,ri-=4; i<ri; i+=4)
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+ {
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+ BN_ULONG t1,t2,t3,t4;
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+
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+ t1=nrp[i+0];
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+ t2=nrp[i+1];
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+ t3=nrp[i+2]; ap[i+0]=0;
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+ t4=nrp[i+3]; ap[i+1]=0;
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+ rp[i+0]=t1; ap[i+2]=0;
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+ rp[i+1]=t2; ap[i+3]=0;
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+ rp[i+2]=t3;
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+ rp[i+3]=t4;
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+ }
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+ for (ri+=4; i<ri; i++)
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+ rp[i]=nrp[i], ap[i]=0;
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+# else
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+ if (bn_wexpand(ret,al) == NULL) goto err;
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ret->top=al;
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+ ret->neg=r->neg;
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+
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+ rp=ret->d;
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+ ap=&(r->d[ri]);
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al-=4;
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for (i=0; i<al; i+=4)
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{
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@@ -258,7 +308,7 @@ int BN_from_montgomery(BIGNUM *ret, cons
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al+=4;
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for (; i<al; i++)
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rp[i]=ap[i];
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-#endif
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+# endif
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#else /* !MONT_WORD */
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BIGNUM *t1,*t2;
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@@ -278,10 +328,12 @@ int BN_from_montgomery(BIGNUM *ret, cons
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if (!BN_rshift(ret,t2,mont->ri)) goto err;
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#endif /* MONT_WORD */
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+#if !defined(BRANCH_FREE) || BRANCH_FREE==0
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if (BN_ucmp(ret, &(mont->N)) >= 0)
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{
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if (!BN_usub(ret,ret,&(mont->N))) goto err;
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}
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+#endif
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retn=1;
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bn_check_top(ret);
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err:
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