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A fix in modmul: don't segfault or fill the result with rubbish if

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the unreduced product is shorter than the modulus.

[originally from svn r965]
This commit is contained in:
Simon Tatham 2001-03-02 10:29:23 +00:00
parent 5f0d3bd19d
commit 47fc223782
1 changed files with 5 additions and 4 deletions
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9
sshbn.c
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@ -289,7 +289,7 @@ Bignum modmul(Bignum p, Bignum q, Bignum mod)
{ {
unsigned short *a, *n, *m, *o; unsigned short *a, *n, *m, *o;
int mshift; int mshift;
int pqlen, mlen, i, j; int pqlen, mlen, rlen, i, j;
Bignum result; Bignum result;
/* Allocate m of size mlen, copy mod to m */ /* Allocate m of size mlen, copy mod to m */
@ -339,9 +339,10 @@ Bignum modmul(Bignum p, Bignum q, Bignum mod)
} }
/* Copy result to buffer */ /* Copy result to buffer */
result = newbn(mod[0]); rlen = (mlen < pqlen*2 ? mlen : pqlen*2);
for (i = 0; i < mlen; i++) result = newbn(rlen);
result[result[0] - i] = a[i+2*pqlen-mlen]; for (i = 0; i < rlen; i++)
result[result[0] - i] = a[i+2*pqlen-rlen];
while (result[0] > 1 && result[result[0]] == 0) result[0]--; while (result[0] > 1 && result[result[0]] == 0) result[0]--;
/* Free temporary arrays */ /* Free temporary arrays */