/* Shared parts of step 1 exchange calculation */
void
jpake_step1(struct modp_group *grp,
u_char **id, u_int *id_len,
BIGNUM **priv1, BIGNUM **priv2, BIGNUM **g_priv1, BIGNUM **g_priv2,
u_char **priv1_proof, u_int *priv1_proof_len,
u_char **priv2_proof, u_int *priv2_proof_len)
{
BN_CTX *bn_ctx;
if ((bn_ctx = BN_CTX_new()) == NULL)
fatal("%s: BN_CTX_new", __func__);
/* Random nonce to prevent replay */
*id = xmalloc(KZP_ID_LEN);
*id_len = KZP_ID_LEN;
arc4random_buf(*id, *id_len);
/*
* x1/x3 is a random element of Zq
* x2/x4 is a random element of Z*q
* We also exclude [1] from x1/x3 candidates and [0, 1] from
* x2/x4 candiates to avoid possible degeneracy (i.e. g^0, g^1).
*/
if ((*priv1 = bn_rand_range_gt_one(grp->q)) == NULL ||
(*priv2 = bn_rand_range_gt_one(grp->q)) == NULL)
fatal("%s: bn_rand_range_gt_one", __func__);
/*
* client: g_x1 = g^x1 mod p / server: g_x3 = g^x3 mod p
* client: g_x2 = g^x2 mod p / server: g_x4 = g^x4 mod p
*/
if ((*g_priv1 = BN_new()) == NULL ||
(*g_priv2 = BN_new()) == NULL)
fatal("%s: BN_new", __func__);
if (BN_mod_exp(*g_priv1, grp->g, *priv1, grp->p, bn_ctx) == -1)
fatal("%s: BN_mod_exp", __func__);
if (BN_mod_exp(*g_priv2, grp->g, *priv2, grp->p, bn_ctx) == -1)
fatal("%s: BN_mod_exp", __func__);
/* Generate proofs for holding x1/x3 and x2/x4 */
if (schnorr_sign_buf(grp->p, grp->q, grp->g,
*priv1, *g_priv1, *id, *id_len,
priv1_proof, priv1_proof_len) != 0)
fatal("%s: schnorr_sign", __func__);
if (schnorr_sign_buf(grp->p, grp->q, grp->g,
*priv2, *g_priv2, *id, *id_len,
priv2_proof, priv2_proof_len) != 0)
fatal("%s: schnorr_sign", __func__);
BN_CTX_free(bn_ctx);
}
static void
schnorr_selftest_one(const BIGNUM *grp_p, const BIGNUM *grp_q,
const BIGNUM *grp_g, const BIGNUM *x)
{
BIGNUM *g_x;
u_char *sig;
u_int siglen;
BN_CTX *bn_ctx;
if ((bn_ctx = BN_CTX_new()) == NULL)
fatal("%s: BN_CTX_new", __func__);
if ((g_x = BN_new()) == NULL)
fatal("%s: BN_new", __func__);
if (BN_mod_exp(g_x, grp_g, x, grp_p, bn_ctx) == -1)
fatal("%s: g_x", __func__);
if (schnorr_sign_buf(grp_p, grp_q, grp_g, x, g_x, "junk", 4,
&sig, &siglen))
fatal("%s: schnorr_sign", __func__);
if (schnorr_verify_buf(grp_p, grp_q, grp_g, g_x, "junk", 4,
sig, siglen) != 1)
fatal("%s: verify fail", __func__);
if (schnorr_verify_buf(grp_p, grp_q, grp_g, g_x, "JUNK", 4,
sig, siglen) != 0)
fatal("%s: verify should have failed (bad ID)", __func__);
sig[4] ^= 1;
if (schnorr_verify_buf(grp_p, grp_q, grp_g, g_x, "junk", 4,
sig, siglen) != 0)
fatal("%s: verify should have failed (bit error)", __func__);
free(sig);
BN_free(g_x);
BN_CTX_free(bn_ctx);
}
/* Shared parts of step 2 exchange calculation */
void
jpake_step2(struct modp_group *grp, BIGNUM *s,
BIGNUM *mypub1, BIGNUM *theirpub1, BIGNUM *theirpub2, BIGNUM *mypriv2,
const u_char *theirid, u_int theirid_len,
const u_char *myid, u_int myid_len,
const u_char *theirpub1_proof, u_int theirpub1_proof_len,
const u_char *theirpub2_proof, u_int theirpub2_proof_len,
BIGNUM **newpub,
u_char **newpub_exponent_proof, u_int *newpub_exponent_proof_len)
{
BN_CTX *bn_ctx;
BIGNUM *tmp, *exponent;
/* Validate peer's step 1 values */
if (BN_cmp(theirpub1, BN_value_one()) <= 0)
fatal("%s: theirpub1 <= 1", __func__);
if (BN_cmp(theirpub1, grp->p) >= 0)
fatal("%s: theirpub1 >= p", __func__);
if (BN_cmp(theirpub2, BN_value_one()) <= 0)
fatal("%s: theirpub2 <= 1", __func__);
if (BN_cmp(theirpub2, grp->p) >= 0)
fatal("%s: theirpub2 >= p", __func__);
if (schnorr_verify_buf(grp->p, grp->q, grp->g, theirpub1,
theirid, theirid_len, theirpub1_proof, theirpub1_proof_len) != 1)
fatal("%s: schnorr_verify theirpub1 failed", __func__);
if (schnorr_verify_buf(grp->p, grp->q, grp->g, theirpub2,
theirid, theirid_len, theirpub2_proof, theirpub2_proof_len) != 1)
fatal("%s: schnorr_verify theirpub2 failed", __func__);
if ((bn_ctx = BN_CTX_new()) == NULL)
fatal("%s: BN_CTX_new", __func__);
if ((*newpub = BN_new()) == NULL ||
(tmp = BN_new()) == NULL ||
(exponent = BN_new()) == NULL)
fatal("%s: BN_new", __func__);
/*
* client: exponent = x2 * s mod p
* server: exponent = x4 * s mod p
*/
if (BN_mod_mul(exponent, mypriv2, s, grp->q, bn_ctx) != 1)
fatal("%s: BN_mod_mul (exponent = mypriv2 * s mod p)",
__func__);
/*
* client: tmp = g^(x1 + x3 + x4) mod p
* server: tmp = g^(x1 + x2 + x3) mod p
*/
if (BN_mod_mul(tmp, mypub1, theirpub1, grp->p, bn_ctx) != 1)
fatal("%s: BN_mod_mul (tmp = mypub1 * theirpub1 mod p)",
__func__);
if (BN_mod_mul(tmp, tmp, theirpub2, grp->p, bn_ctx) != 1)
fatal("%s: BN_mod_mul (tmp = tmp * theirpub2 mod p)", __func__);
/*
* client: a = tmp^exponent = g^((x1+x3+x4) * x2 * s) mod p
* server: b = tmp^exponent = g^((x1+x2+x3) * x4 * s) mod p
*/
if (BN_mod_exp(*newpub, tmp, exponent, grp->p, bn_ctx) != 1)
fatal("%s: BN_mod_mul (newpub = tmp^exponent mod p)", __func__);
JPAKE_DEBUG_BN((tmp, "%s: tmp = ", __func__));
JPAKE_DEBUG_BN((exponent, "%s: exponent = ", __func__));
/* Note the generator here is 'tmp', not g */
if (schnorr_sign_buf(grp->p, grp->q, tmp, exponent, *newpub,
myid, myid_len,
newpub_exponent_proof, newpub_exponent_proof_len) != 0)
fatal("%s: schnorr_sign newpub", __func__);
BN_clear_free(tmp); /* XXX stash for later use? */
BN_clear_free(exponent); /* XXX stash for later use? (yes, in conf) */
BN_CTX_free(bn_ctx);
}
