/*
* Verify that the public data in an RSA key matches the private
* data. We also check the private data itself: we ensure that p >
* q and that iqmp really is the inverse of q mod p.
*/
bool rsa_verify(RSAKey *key)
{
mp_int *n, *ed, *pm1, *qm1;
unsigned ok = 1;
/* Preliminary checks: p,q must actually be nonzero. */
if (mp_eq_integer(key->p, 0) | mp_eq_integer(key->q, 0))
return false;
/* n must equal pq. */
n = mp_mul(key->p, key->q);
ok &= mp_cmp_eq(n, key->modulus);
mp_free(n);
/* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
pm1 = mp_copy(key->p);
mp_sub_integer_into(pm1, pm1, 1);
ed = mp_modmul(key->exponent, key->private_exponent, pm1);
mp_free(pm1);
ok &= mp_eq_integer(ed, 1);
mp_free(ed);
qm1 = mp_copy(key->q);
mp_sub_integer_into(qm1, qm1, 1);
ed = mp_modmul(key->exponent, key->private_exponent, qm1);
mp_free(qm1);
ok &= mp_eq_integer(ed, 1);
mp_free(ed);
/*
* 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.
*/
mp_int *p_new = mp_max(key->p, key->q);
mp_int *q_new = mp_min(key->p, key->q);
mp_free(key->p);
mp_free(key->q);
mp_free(key->iqmp);
key->p = p_new;
key->q = q_new;
key->iqmp = mp_invert(key->q, key->p);
return ok;
}
static bool ecdsa_verify(ssh_key *key, ptrlen sig, ptrlen data)
{
struct ecdsa_key *ek = container_of(key, struct ecdsa_key, sshk);
const struct ecsign_extra *extra =
(const struct ecsign_extra *)ek->sshk.vt->extra;
BinarySource src[1];
BinarySource_BARE_INIT_PL(src, sig);
/* Check the signature starts with the algorithm name */
if (!ptrlen_eq_string(get_string(src), ek->sshk.vt->ssh_id))
return false;
/* Everything else is nested inside a sub-string. Descend into that. */
ptrlen sigstr = get_string(src);
if (get_err(src))
return false;
BinarySource_BARE_INIT_PL(src, sigstr);
/* Extract the signature integers r,s */
mp_int *r = get_mp_ssh2(src);
mp_int *s = get_mp_ssh2(src);
if (get_err(src)) {
mp_free(r);
mp_free(s);
return false;
}
/* Basic sanity checks: 0 < r,s < order(G) */
unsigned invalid = 0;
invalid |= mp_eq_integer(r, 0);
invalid |= mp_eq_integer(s, 0);
invalid |= mp_cmp_hs(r, ek->curve->w.G_order);
invalid |= mp_cmp_hs(s, ek->curve->w.G_order);
/* Get the hash of the signed data, converted to an integer */
mp_int *z = ecdsa_signing_exponent_from_data(ek->curve, extra, data);
/* Verify the signature integers against the hash */
mp_int *w = mp_invert(s, ek->curve->w.G_order);
mp_int *u1 = mp_modmul(z, w, ek->curve->w.G_order);
mp_free(z);
mp_int *u2 = mp_modmul(r, w, ek->curve->w.G_order);
mp_free(w);
WeierstrassPoint *u1G = ecc_weierstrass_multiply(ek->curve->w.G, u1);
mp_free(u1);
WeierstrassPoint *u2P = ecc_weierstrass_multiply(ek->publicKey, u2);
mp_free(u2);
WeierstrassPoint *sum = ecc_weierstrass_add_general(u1G, u2P);
ecc_weierstrass_point_free(u1G);
ecc_weierstrass_point_free(u2P);
mp_int *x;
ecc_weierstrass_get_affine(sum, &x, NULL);
ecc_weierstrass_point_free(sum);
mp_divmod_into(x, ek->curve->w.G_order, NULL, x);
invalid |= (1 ^ mp_cmp_eq(r, x));
mp_free(x);
mp_free(r);
mp_free(s);
return !invalid;
}
