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Modify the new rsa_verify routine. We now also check the integrity of

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the private data (verifying that p > q and that iqmp really is the
inverse of q mod p). In addition, we _no longer_ check that e*d == 1
mod (p-1)(q-1): instead we do separate checks mod (p-1) and mod (q-1),
since the order of the multiplicative group mod n is actually equal to
lcm(p-1,q-1) rather than phi(n)=(p-1)(q-1). (In other words, the
Fermat-Euler theorem doesn't point both ways.)

[originally from svn r1024]
This commit is contained in:
Simon Tatham 2001-03-23 13:02:39 +00:00
parent 6a4294fbac
commit 0962190a1b
1 changed files with 28 additions and 10 deletions
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38
sshrsa.c
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@ -153,10 +153,11 @@ void rsa_fingerprint(char *str, int len, struct RSAKey *key) {
/*
* Verify that the public data in an RSA key matches the private
* data.
* data. We also check the private data itself: we ensure that p >
* q and that iqmp really is the inverse of q mod p.
*/
int rsa_verify(struct RSAKey *key) {
Bignum n, ed, pm1, qm1, pm1qm1;
Bignum n, ed, pm1, qm1;
int cmp;
/* n must equal pq. */
@ -166,21 +167,38 @@ int rsa_verify(struct RSAKey *key) {
if (cmp != 0)
return 0;
/* e * d must be congruent to 1, modulo (p-1)(q-1). */
/* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
pm1 = copybn(key->p);
decbn(pm1);
qm1 = copybn(key->q);
decbn(qm1);
pm1qm1 = bigmul(pm1, qm1);
freebn(pm1);
freebn(qm1);
ed = modmul(key->exponent, key->private_exponent, pm1qm1);
sfree(pm1qm1);
ed = modmul(key->exponent, key->private_exponent, pm1);
cmp = bignum_cmp(ed, One);
sfree(ed);
if (cmp != 0)
return 0;
qm1 = copybn(key->q);
decbn(qm1);
ed = modmul(key->exponent, key->private_exponent, qm1);
cmp = bignum_cmp(ed, One);
sfree(ed);
if (cmp != 0)
return 0;
/*
* Ensure p > q.
*/
if (bignum_cmp(key->p, key->q) <= 0)
return 0;
/*
* Ensure iqmp * q is congruent to 1, modulo p.
*/
n = modmul(key->iqmp, key->q, key->p);
cmp = bignum_cmp(n, One);
sfree(n);
if (cmp != 0)
return 0;
return 1;
}