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Implement the Chinese Remainder Theorem optimisation for speeding up

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RSA private key operations by making use of the fact that we know the
factors of the modulus.

[originally from svn r9095]
This commit is contained in:
Simon Tatham
2011-02-18 08:25:39 +00:00
parent 61875b87e3
commit fa85085640
3 changed files with 146 additions and 5 deletions
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63
sshbn.c
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@ -1190,6 +1190,69 @@ Bignum bigmul(Bignum a, Bignum b)
return bigmuladd(a, b, NULL);
}
/*
* Simple addition.
*/
Bignum bigadd(Bignum a, Bignum b)
{
int alen = a[0], blen = b[0];
int rlen = (alen > blen ? alen : blen) + 1;
int i, maxspot;
Bignum ret;
BignumDblInt carry;
ret = newbn(rlen);
carry = 0;
maxspot = 0;
for (i = 1; i <= rlen; i++) {
carry += (i <= (int)a[0] ? a[i] : 0);
carry += (i <= (int)b[0] ? b[i] : 0);
ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
carry >>= BIGNUM_INT_BITS;
if (ret[i] != 0 && i > maxspot)
maxspot = i;
}
ret[0] = maxspot;
return ret;
}
/*
* Subtraction. Returns a-b, or NULL if the result would come out
* negative (recall that this entire bignum module only handles
* positive numbers).
*/
Bignum bigsub(Bignum a, Bignum b)
{
int alen = a[0], blen = b[0];
int rlen = (alen > blen ? alen : blen);
int i, maxspot;
Bignum ret;
BignumDblInt carry;
ret = newbn(rlen);
carry = 1;
maxspot = 0;
for (i = 1; i <= rlen; i++) {
carry += (i <= (int)a[0] ? a[i] : 0);
carry += (i <= (int)b[0] ? b[i] ^ BIGNUM_INT_MASK : BIGNUM_INT_MASK);
ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
carry >>= BIGNUM_INT_BITS;
if (ret[i] != 0 && i > maxspot)
maxspot = i;
}
ret[0] = maxspot;
if (!carry) {
freebn(ret);
return NULL;
}
return ret;
}
/*
* Create a bignum which is the bitmask covering another one. That
* is, the smallest integer which is >= N and is also one less than