lenbuf[0] = bignum_byte(b, len);
SHA512_Bytes(s, lenbuf, 1);
}
- memset(lenbuf, 0, sizeof(lenbuf));
+ smemclr(lenbuf, sizeof(lenbuf));
}
/*
- * This function is a wrapper on modpow(). It has the same effect
- * as modpow(), but employs RSA blinding to protect against timing
- * attacks.
+ * Compute (base ^ exp) % mod, provided mod == p * q, with p,q
+ * distinct primes, and iqmp is the multiplicative inverse of q mod p.
+ * Uses Chinese Remainder Theorem to speed computation up over the
+ * obvious implementation of a single big modpow.
+ */
+Bignum crt_modpow(Bignum base, Bignum exp, Bignum mod,
+ Bignum p, Bignum q, Bignum iqmp)
+{
+ Bignum pm1, qm1, pexp, qexp, presult, qresult, diff, multiplier, ret0, ret;
+
+ /*
+ * Reduce the exponent mod phi(p) and phi(q), to save time when
+ * exponentiating mod p and mod q respectively. Of course, since p
+ * and q are prime, phi(p) == p-1 and similarly for q.
+ */
+ pm1 = copybn(p);
+ decbn(pm1);
+ qm1 = copybn(q);
+ decbn(qm1);
+ pexp = bigmod(exp, pm1);
+ qexp = bigmod(exp, qm1);
+
+ /*
+ * Do the two modpows.
+ */
+ presult = modpow(base, pexp, p);
+ qresult = modpow(base, qexp, q);
+
+ /*
+ * Recombine the results. We want a value which is congruent to
+ * qresult mod q, and to presult mod p.
+ *
+ * We know that iqmp * q is congruent to 1 * mod p (by definition
+ * of iqmp) and to 0 mod q (obviously). So we start with qresult
+ * (which is congruent to qresult mod both primes), and add on
+ * (presult-qresult) * (iqmp * q) which adjusts it to be congruent
+ * to presult mod p without affecting its value mod q.
+ */
+ if (bignum_cmp(presult, qresult) < 0) {
+ /*
+ * Can't subtract presult from qresult without first adding on
+ * p.
+ */
+ Bignum tmp = presult;
+ presult = bigadd(presult, p);
+ freebn(tmp);
+ }
+ diff = bigsub(presult, qresult);
+ multiplier = bigmul(iqmp, q);
+ ret0 = bigmuladd(multiplier, diff, qresult);
+
+ /*
+ * Finally, reduce the result mod n.
+ */
+ ret = bigmod(ret0, mod);
+
+ /*
+ * Free all the intermediate results before returning.
+ */
+ freebn(pm1);
+ freebn(qm1);
+ freebn(pexp);
+ freebn(qexp);
+ freebn(presult);
+ freebn(qresult);
+ freebn(diff);
+ freebn(multiplier);
+ freebn(ret0);
+
+ return ret;
+}
+
+/*
+ * This function is a wrapper on modpow(). It has the same effect as
+ * modpow(), but employs RSA blinding to protect against timing
+ * attacks and also uses the Chinese Remainder Theorem (implemented
+ * above, in crt_modpow()) to speed up the main operation.
*/
static Bignum rsa_privkey_op(Bignum input, struct RSAKey *key)
{
* _y^d_, and use the _public_ exponent to compute (y^d)^e = y
* from it, which is much faster to do.
*/
- random_encrypted = modpow(random, key->exponent, key->modulus);
+ random_encrypted = crt_modpow(random, key->exponent,
+ key->modulus, key->p, key->q, key->iqmp);
random_inverse = modinv(random, key->modulus);
input_blinded = modmul(input, random_encrypted, key->modulus);
- ret_blinded = modpow(input_blinded, key->private_exponent, key->modulus);
+ ret_blinded = crt_modpow(input_blinded, key->private_exponent,
+ key->modulus, key->p, key->q, key->iqmp);
ret = modmul(ret_blinded, random_inverse, key->modulus);
freebn(ret_blinded);
pm1 = copybn(key->p);
decbn(pm1);
ed = modmul(key->exponent, key->private_exponent, pm1);
+ freebn(pm1);
cmp = bignum_cmp(ed, One);
sfree(ed);
if (cmp != 0)
qm1 = copybn(key->q);
decbn(qm1);
ed = modmul(key->exponent, key->private_exponent, qm1);
+ freebn(qm1);
cmp = bignum_cmp(ed, One);
sfree(ed);
if (cmp != 0)
/*
* Ensure p > q.
+ *
+ * I have seen key blobs in the wild which were generated with
+ * p < q, so instead of rejecting the key in this case we
+ * should instead flip them round into the canonical order of
+ * p > q. This also involves regenerating iqmp.
*/
- if (bignum_cmp(key->p, key->q) <= 0)
- return 0;
+ if (bignum_cmp(key->p, key->q) <= 0) {
+ Bignum tmp = key->p;
+ key->p = key->q;
+ key->q = tmp;
+
+ freebn(key->iqmp);
+ key->iqmp = modinv(key->q, key->p);
+ }
/*
* Ensure iqmp * q is congruent to 1, modulo p.
freebn(key->exponent);
if (key->private_exponent)
freebn(key->private_exponent);
+ if (key->p)
+ freebn(key->p);
+ if (key->q)
+ freebn(key->q);
+ if (key->iqmp)
+ freebn(key->iqmp);
if (key->comment)
sfree(key->comment);
}
*p = NULL;
if (*datalen < 4)
return;
- *length = GET_32BIT(*data);
+ *length = toint(GET_32BIT(*data));
+ if (*length < 0)
+ return;
*datalen -= 4;
*data += 4;
if (*datalen < *length)
rsa->exponent = getmp(&data, &len);
rsa->modulus = getmp(&data, &len);
rsa->private_exponent = NULL;
+ rsa->p = rsa->q = rsa->iqmp = NULL;
rsa->comment = NULL;
return rsa;
*/
b1 = bignum_from_bytes(out, outlen);
b2 = modpow(b1, rsa->exponent, rsa->modulus);
- p = out;
+ p = (char *)out;
for (i = outlen; i--;) {
*p++ = bignum_byte(b2, i);
}
projects / u / mdw / putty / blobdiff