1 files changed, 604 insertions, 0 deletions

diff --git a/jpake.c b/jpake.c
new file mode 100644
index 000000000..565f2e255
--- /dev/null
+++ b/jpake.c
@@ -0,0 +1,604 @@
+/* $OpenBSD: jpake.c,v 1.1 2008/11/04 08:22:12 djm Exp $ */
+/*
+ * Copyright (c) 2008 Damien Miller.  All rights reserved.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * Shared components of zero-knowledge password auth using J-PAKE protocol
+ * as described in:
+ *
+ * F. Hao, P. Ryan, "Password Authenticated Key Exchange by Juggling",
+ * 16th Workshop on Security Protocols, Cambridge, April 2008
+ *
+ * http://grouper.ieee.org/groups/1363/Research/contributions/hao-ryan-2008.pdf
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+
+#include <openssl/bn.h>
+#include <openssl/evp.h>
+
+#include "xmalloc.h"
+#include "ssh2.h"
+#include "key.h"
+#include "hostfile.h"
+#include "auth.h"
+#include "buffer.h"
+#include "packet.h"
+#include "dispatch.h"
+#include "log.h"
+
+#include "jpake.h"
+
+#ifdef JPAKE
+
+/* RFC3526 group 5, 1536 bits */
+#define JPAKE_GROUP_G "2"
+#define JPAKE_GROUP_P \
+        "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74" \
+        "020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F1437" \
+        "4FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
+        "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF05" \
+        "98DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB" \
+        "9ED529077096966D670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF"
+
+struct jpake_group *
+jpake_default_group(void)
+{
+        struct jpake_group *ret;
+
+        ret = xmalloc(sizeof(*ret));
+        ret->p = ret->q = ret->g = NULL;
+        if (BN_hex2bn(&ret->p, JPAKE_GROUP_P) == 0 ||
+            BN_hex2bn(&ret->g, JPAKE_GROUP_G) == 0)
+                fatal("%s: BN_hex2bn", __func__);
+        /* Subgroup order is p/2 (p is a safe prime) */
+        if ((ret->q = BN_new()) == NULL)
+                fatal("%s: BN_new", __func__);
+        if (BN_rshift1(ret->q, ret->p) != 1)
+                fatal("%s: BN_rshift1", __func__);
+
+        return ret;
+}
+
+/*
+ * Generate uniformly distributed random number in range (1, high).
+ * Return number on success, NULL on failure.
+ */
+BIGNUM *
+bn_rand_range_gt_one(const BIGNUM *high)
+{
+        BIGNUM *r, *tmp;
+        int success = -1;
+
+        if ((tmp = BN_new()) == NULL) {
+                error("%s: BN_new", __func__);
+                return NULL;
+        }
+        if ((r = BN_new()) == NULL) {
+                error("%s: BN_new failed", __func__);
+                goto out;
+        }
+        if (BN_set_word(tmp, 2) != 1) {
+                error("%s: BN_set_word(tmp, 2)", __func__);
+                goto out;
+        }
+        if (BN_sub(tmp, high, tmp) == -1) {
+                error("%s: BN_sub failed (tmp = high - 2)", __func__);
+                goto out;
+        }
+        if (BN_rand_range(r, tmp) == -1) {
+                error("%s: BN_rand_range failed", __func__);
+                goto out;
+        }
+        if (BN_set_word(tmp, 2) != 1) {
+                error("%s: BN_set_word(tmp, 2)", __func__);
+                goto out;
+        }
+        if (BN_add(r, r, tmp) == -1) {
+                error("%s: BN_add failed (r = r + 2)", __func__);
+                goto out;
+        }
+        success = 0;
+ out:
+        BN_clear_free(tmp);
+        if (success == 0)
+                return r;
+        BN_clear_free(r);
+        return NULL;
+}
+
+/*
+ * Hash contents of buffer 'b' with hash 'md'. Returns 0 on success,
+ * with digest via 'digestp' (caller to free) and length via 'lenp'.
+ * Returns -1 on failure.
+ */
+int
+hash_buffer(const u_char *buf, u_int len, const EVP_MD *md,
+    u_char **digestp, u_int *lenp)
+{
+        u_char digest[EVP_MAX_MD_SIZE];
+        u_int digest_len;
+        EVP_MD_CTX evp_md_ctx;
+        int success = -1;
+
+        EVP_MD_CTX_init(&evp_md_ctx);
+
+        if (EVP_DigestInit_ex(&evp_md_ctx, md, NULL) != 1) {
+                error("%s: EVP_DigestInit_ex", __func__);
+                goto out;
+        }
+        if (EVP_DigestUpdate(&evp_md_ctx, buf, len) != 1) {
+                error("%s: EVP_DigestUpdate", __func__);
+                goto out;
+        }
+        if (EVP_DigestFinal_ex(&evp_md_ctx, digest, &digest_len) != 1) {
+                error("%s: EVP_DigestFinal_ex", __func__);
+                goto out;
+        }
+        *digestp = xmalloc(digest_len);
+        *lenp = digest_len;
+        memcpy(*digestp, digest, *lenp);
+        success = 0;
+ out:
+        EVP_MD_CTX_cleanup(&evp_md_ctx);
+        bzero(digest, sizeof(digest));
+        digest_len = 0;
+        return success;
+}
+
+/* print formatted string followed by bignum */
+void
+jpake_debug3_bn(const BIGNUM *n, const char *fmt, ...)
+{
+        char *out, *h;
+        va_list args;
+
+        out = NULL;
+        va_start(args, fmt);
+        vasprintf(&out, fmt, args);
+        va_end(args);
+        if (out == NULL)
+                fatal("%s: vasprintf failed", __func__);
+
+        if (n == NULL)
+                debug3("%s(null)", out);
+        else {
+                h = BN_bn2hex(n);
+                debug3("%s0x%s", out, h);
+                free(h);
+        }
+        free(out);
+}
+
+/* print formatted string followed by buffer contents in hex */
+void
+jpake_debug3_buf(const u_char *buf, u_int len, const char *fmt, ...)
+{
+        char *out, h[65];
+        u_int i, j;
+        va_list args;
+
+        out = NULL;
+        va_start(args, fmt);
+        vasprintf(&out, fmt, args);
+        va_end(args);
+        if (out == NULL)
+                fatal("%s: vasprintf failed", __func__);
+
+        debug3("%s length %u%s", out, len, buf == NULL ? " (null)" : "");
+        free(out);
+        if (buf == NULL)
+                return;
+
+        *h = '\0';
+        for (i = j = 0; i < len; i++) {
+                snprintf(h + j, sizeof(h) - j, "%02x", buf[i]);
+                j += 2;
+                if (j >= sizeof(h) - 1 || i == len - 1) {
+                        debug3("    %s", h);
+                        *h = '\0';
+                        j = 0;
+                }
+        }
+}
+
+struct jpake_ctx *
+jpake_new(void)
+{
+        struct jpake_ctx *ret;
+
+        ret = xcalloc(1, sizeof(*ret));
+
+        ret->grp = jpake_default_group();
+
+        ret->s = ret->k = NULL;
+        ret->x1 = ret->x2 = ret->x3 = ret->x4 = NULL;
+        ret->g_x1 = ret->g_x2 = ret->g_x3 = ret->g_x4 = NULL;
+        ret->a = ret->b = NULL;
+
+        ret->client_id = ret->server_id = NULL;
+        ret->h_k_cid_sessid = ret->h_k_sid_sessid = NULL;
+
+        debug3("%s: alloc %p", __func__, ret);
+
+        return ret;
+}
+
+
+void
+jpake_free(struct jpake_ctx *pctx)
+{
+        debug3("%s: free %p", __func__, pctx);
+
+#define JPAKE_BN_CLEAR_FREE(v)                  \
+        do {                                    \
+                if ((v) != NULL) {              \
+                        BN_clear_free(v);       \
+                        (v) = NULL;             \
+                }                               \
+        } while (0)
+#define JPAKE_BUF_CLEAR_FREE(v, l)              \
+        do {                                    \
+                if ((v) != NULL) {              \
+                        bzero((v), (l));        \
+                        xfree(v);               \
+                        (v) = NULL;             \
+                        (l) = 0;                \
+                }                               \
+        } while (0)
+
+        JPAKE_BN_CLEAR_FREE(pctx->s);
+        JPAKE_BN_CLEAR_FREE(pctx->k);
+        JPAKE_BN_CLEAR_FREE(pctx->x1);
+        JPAKE_BN_CLEAR_FREE(pctx->x2);
+        JPAKE_BN_CLEAR_FREE(pctx->x3);
+        JPAKE_BN_CLEAR_FREE(pctx->x4);
+        JPAKE_BN_CLEAR_FREE(pctx->g_x1);
+        JPAKE_BN_CLEAR_FREE(pctx->g_x2);
+        JPAKE_BN_CLEAR_FREE(pctx->g_x3);
+        JPAKE_BN_CLEAR_FREE(pctx->g_x4);
+        JPAKE_BN_CLEAR_FREE(pctx->a);
+        JPAKE_BN_CLEAR_FREE(pctx->b);
+
+        JPAKE_BUF_CLEAR_FREE(pctx->client_id, pctx->client_id_len);
+        JPAKE_BUF_CLEAR_FREE(pctx->server_id, pctx->server_id_len);
+        JPAKE_BUF_CLEAR_FREE(pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len);
+        JPAKE_BUF_CLEAR_FREE(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
+
+#undef JPAKE_BN_CLEAR_FREE
+#undef JPAKE_BUF_CLEAR_FREE
+
+        bzero(pctx, sizeof(pctx));
+        xfree(pctx);
+}
+
+/* dump entire jpake_ctx. NB. includes private values! */
+void
+jpake_dump(struct jpake_ctx *pctx, const char *fmt, ...)
+{
+        char *out;
+        va_list args;
+
+        out = NULL;
+        va_start(args, fmt);
+        vasprintf(&out, fmt, args);
+        va_end(args);
+        if (out == NULL)
+                fatal("%s: vasprintf failed", __func__);
+
+        debug3("%s: %s (ctx at %p)", __func__, out, pctx);
+        if (pctx == NULL) {
+                free(out);
+                return;
+        }
+
+#define JPAKE_DUMP_BN(a)        do { \
+                if ((a) != NULL) \
+                        JPAKE_DEBUG_BN(((a), "%s = ", #a)); \
+        } while (0)
+#define JPAKE_DUMP_BUF(a, b)    do { \
+                if ((a) != NULL) \
+                        JPAKE_DEBUG_BUF((a, b, "%s", #a)); \
+        } while (0)
+
+        JPAKE_DUMP_BN(pctx->s);
+        JPAKE_DUMP_BN(pctx->k);
+        JPAKE_DUMP_BN(pctx->x1);
+        JPAKE_DUMP_BN(pctx->x2);
+        JPAKE_DUMP_BN(pctx->x3);
+        JPAKE_DUMP_BN(pctx->x4);
+        JPAKE_DUMP_BN(pctx->g_x1);
+        JPAKE_DUMP_BN(pctx->g_x2);
+        JPAKE_DUMP_BN(pctx->g_x3);
+        JPAKE_DUMP_BN(pctx->g_x4);
+        JPAKE_DUMP_BN(pctx->a);
+        JPAKE_DUMP_BN(pctx->b);
+
+        JPAKE_DUMP_BUF(pctx->client_id, pctx->client_id_len);
+        JPAKE_DUMP_BUF(pctx->server_id, pctx->server_id_len);
+        JPAKE_DUMP_BUF(pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len);
+        JPAKE_DUMP_BUF(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
+
+        debug3("%s: %s done", __func__, out);
+        free(out);
+}
+
+/* Shared parts of step 1 exchange calculation */
+void
+jpake_step1(struct jpake_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(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(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);
+}
+
+/* Shared parts of step 2 exchange calculation */
+void
+jpake_step2(struct jpake_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(theirpub2, BN_value_one()) <= 0)
+                fatal("%s: theirpub2 <= 1", __func__);
+
+        if (schnorr_verify(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(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(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);
+}
+
+/* Confirmation hash calculation */
+void
+jpake_confirm_hash(const BIGNUM *k,
+    const u_char *endpoint_id, u_int endpoint_id_len,
+    const u_char *sess_id, u_int sess_id_len,
+    u_char **confirm_hash, u_int *confirm_hash_len)
+{
+        Buffer b;
+
+        /*
+         * Calculate confirmation proof:
+         *     client: H(k || client_id || session_id)
+         *     server: H(k || server_id || session_id)
+         */
+        buffer_init(&b);
+        buffer_put_bignum2(&b, k);
+        buffer_put_string(&b, endpoint_id, endpoint_id_len);
+        buffer_put_string(&b, sess_id, sess_id_len);
+        if (hash_buffer(buffer_ptr(&b), buffer_len(&b), EVP_sha256(),
+            confirm_hash, confirm_hash_len) != 0)
+                fatal("%s: hash_buffer", __func__);
+        buffer_free(&b);
+}
+
+/* Shared parts of key derivation and confirmation calculation */
+void
+jpake_key_confirm(struct jpake_group *grp, BIGNUM *s, BIGNUM *step2_val,
+    BIGNUM *mypriv2, BIGNUM *mypub1, BIGNUM *mypub2,
+    BIGNUM *theirpub1, BIGNUM *theirpub2,
+    const u_char *my_id, u_int my_id_len,
+    const u_char *their_id, u_int their_id_len,
+    const u_char *sess_id, u_int sess_id_len,
+    const u_char *theirpriv2_s_proof, u_int theirpriv2_s_proof_len,
+    BIGNUM **k,
+    u_char **confirm_hash, u_int *confirm_hash_len)
+{
+        BN_CTX *bn_ctx;
+        BIGNUM *tmp;
+
+        if ((bn_ctx = BN_CTX_new()) == NULL)
+                fatal("%s: BN_CTX_new", __func__);
+        if ((tmp = BN_new()) == NULL ||
+            (*k = BN_new()) == NULL)
+                fatal("%s: BN_new", __func__);
+
+        /* Validate step 2 values */
+        if (BN_cmp(step2_val, BN_value_one()) <= 0)
+                fatal("%s: step2_val <= 1", __func__);
+
+        /*
+         * theirpriv2_s_proof is calculated with a different generator:
+         * tmp = g^(mypriv1+mypriv2+theirpub1) = g^mypub1*g^mypub2*g^theirpub1
+         * Calculate it here so we can check the signature.
+         */
+        if (BN_mod_mul(tmp, mypub1, mypub2, grp->p, bn_ctx) != 1)
+                fatal("%s: BN_mod_mul (tmp = mypub1 * mypub2 mod p)", __func__);
+        if (BN_mod_mul(tmp, tmp, theirpub1, grp->p, bn_ctx) != 1)
+                fatal("%s: BN_mod_mul (tmp = tmp * theirpub1 mod p)", __func__);
+
+        JPAKE_DEBUG_BN((tmp, "%s: tmp = ", __func__));
+
+        if (schnorr_verify(grp->p, grp->q, tmp, step2_val, 
+            their_id, their_id_len,
+            theirpriv2_s_proof, theirpriv2_s_proof_len) != 1)
+                fatal("%s: schnorr_verify theirpriv2_s_proof failed", __func__);
+
+        /*
+         * Derive shared key:
+         *     client: k = (b / g^(x2*x4*s))^x2 = g^((x1+x3)*x2*x4*s)
+         *     server: k = (a / g^(x2*x4*s))^x4 = g^((x1+x3)*x2*x4*s)
+         *
+         * Computed as:
+         *     client: k = (g_x4^(q - (x2 * s)) * b)^x2 mod p
+         *     server: k = (g_x2^(q - (x4 * s)) * b)^x4 mod p
+         */
+        if (BN_mul(tmp, mypriv2, s, bn_ctx) != 1)
+                fatal("%s: BN_mul (tmp = mypriv2 * s)", __func__);
+        if (BN_mod_sub(tmp, grp->q, tmp, grp->q, bn_ctx) != 1)
+                fatal("%s: BN_mod_sub (tmp = q - tmp mod q)", __func__);
+        if (BN_mod_exp(tmp, theirpub2, tmp, grp->p, bn_ctx) != 1)
+                fatal("%s: BN_mod_exp (tmp = theirpub2^tmp) mod p", __func__);
+        if (BN_mod_mul(tmp, tmp, step2_val, grp->p, bn_ctx) != 1)
+                fatal("%s: BN_mod_mul (tmp = tmp * step2_val) mod p", __func__);
+        if (BN_mod_exp(*k, tmp, mypriv2, grp->p, bn_ctx) != 1)
+                fatal("%s: BN_mod_exp (k = tmp^mypriv2) mod p", __func__);
+        
+        BN_CTX_free(bn_ctx);
+        BN_clear_free(tmp);
+
+        jpake_confirm_hash(*k, my_id, my_id_len, sess_id, sess_id_len,
+            confirm_hash, confirm_hash_len);
+}
+
+/*
+ * Calculate and check confirmation hash from peer. Returns 1 on success
+ * 0 on failure/mismatch.
+ */
+int
+jpake_check_confirm(const BIGNUM *k,
+    const u_char *peer_id, u_int peer_id_len,
+    const u_char *sess_id, u_int sess_id_len,
+    const u_char *peer_confirm_hash, u_int peer_confirm_hash_len)
+{
+        u_char *expected_confirm_hash;
+        u_int expected_confirm_hash_len;
+        int success = 0;
+
+        /* Calculate and verify expected confirmation hash */
+        jpake_confirm_hash(k, peer_id, peer_id_len, sess_id, sess_id_len,
+            &expected_confirm_hash, &expected_confirm_hash_len);
+
+        JPAKE_DEBUG_BUF((expected_confirm_hash, expected_confirm_hash_len,
+            "%s: expected confirm hash", __func__));
+        JPAKE_DEBUG_BUF((peer_confirm_hash, peer_confirm_hash_len,
+            "%s: received confirm hash", __func__));
+
+        if (peer_confirm_hash_len != expected_confirm_hash_len)
+                error("%s: confirmation length mismatch (my %u them %u)",
+                    __func__, expected_confirm_hash_len, peer_confirm_hash_len);
+        else if (memcmp(peer_confirm_hash, expected_confirm_hash,
+            expected_confirm_hash_len) == 0)
+                success = 1;
+        bzero(expected_confirm_hash, expected_confirm_hash_len);
+        xfree(expected_confirm_hash);
+        debug3("%s: success = %d", __func__, success);
+        return success;
+}
+
+/* XXX main() function with tests */
+
+#endif /* JPAKE */
+