468 lines
11 KiB
C
468 lines
11 KiB
C
#include "jpake.h"
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#include <openssl/crypto.h>
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#include <openssl/sha.h>
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#include <openssl/err.h>
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#include <memory.h>
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#include <assert.h>
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/*
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* In the definition, (xa, xb, xc, xd) are Alice's (x1, x2, x3, x4) or
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* Bob's (x3, x4, x1, x2). If you see what I mean.
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*/
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typedef struct
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{
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char *name; // Must be unique
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char *peer_name;
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BIGNUM *p;
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BIGNUM *g;
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BIGNUM *q;
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BIGNUM *gxc; // Alice's g^{x3} or Bob's g^{x1}
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BIGNUM *gxd; // Alice's g^{x4} or Bob's g^{x2}
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} JPAKE_CTX_PUBLIC;
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struct JPAKE_CTX
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{
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JPAKE_CTX_PUBLIC p;
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BIGNUM *secret; // The shared secret
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BN_CTX *ctx;
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BIGNUM *xa; // Alice's x1 or Bob's x3
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BIGNUM *xb; // Alice's x2 or Bob's x4
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BIGNUM *key; // The calculated (shared) key
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};
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static void JPAKE_ZKP_init(JPAKE_ZKP *zkp)
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{
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zkp->gr = BN_new();
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zkp->b = BN_new();
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}
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static void JPAKE_ZKP_release(JPAKE_ZKP *zkp)
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{
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BN_free(zkp->b);
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BN_free(zkp->gr);
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}
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// Two birds with one stone - make the global name as expected
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#define JPAKE_STEP_PART_init JPAKE_STEP2_init
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#define JPAKE_STEP_PART_release JPAKE_STEP2_release
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void JPAKE_STEP_PART_init(JPAKE_STEP_PART *p)
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{
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p->gx = BN_new();
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JPAKE_ZKP_init(&p->zkpx);
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}
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void JPAKE_STEP_PART_release(JPAKE_STEP_PART *p)
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{
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JPAKE_ZKP_release(&p->zkpx);
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BN_free(p->gx);
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}
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void JPAKE_STEP1_init(JPAKE_STEP1 *s1)
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{
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JPAKE_STEP_PART_init(&s1->p1);
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JPAKE_STEP_PART_init(&s1->p2);
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}
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void JPAKE_STEP1_release(JPAKE_STEP1 *s1)
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{
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JPAKE_STEP_PART_release(&s1->p2);
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JPAKE_STEP_PART_release(&s1->p1);
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}
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static void JPAKE_CTX_init(JPAKE_CTX *ctx, const char *name,
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const char *peer_name, const BIGNUM *p,
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const BIGNUM *g, const BIGNUM *q,
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const BIGNUM *secret)
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{
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ctx->p.name = OPENSSL_strdup(name);
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ctx->p.peer_name = OPENSSL_strdup(peer_name);
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ctx->p.p = BN_dup(p);
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ctx->p.g = BN_dup(g);
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ctx->p.q = BN_dup(q);
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ctx->secret = BN_dup(secret);
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ctx->p.gxc = BN_new();
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ctx->p.gxd = BN_new();
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ctx->xa = BN_new();
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ctx->xb = BN_new();
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ctx->key = BN_new();
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ctx->ctx = BN_CTX_new();
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}
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static void JPAKE_CTX_release(JPAKE_CTX *ctx)
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{
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BN_CTX_free(ctx->ctx);
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BN_clear_free(ctx->key);
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BN_clear_free(ctx->xb);
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BN_clear_free(ctx->xa);
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BN_free(ctx->p.gxd);
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BN_free(ctx->p.gxc);
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BN_clear_free(ctx->secret);
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BN_free(ctx->p.q);
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BN_free(ctx->p.g);
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BN_free(ctx->p.p);
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OPENSSL_free(ctx->p.peer_name);
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OPENSSL_free(ctx->p.name);
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memset(ctx, '\0', sizeof *ctx);
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}
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JPAKE_CTX *JPAKE_CTX_new(const char *name, const char *peer_name,
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const BIGNUM *p, const BIGNUM *g, const BIGNUM *q,
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const BIGNUM *secret)
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{
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JPAKE_CTX *ctx = OPENSSL_malloc(sizeof *ctx);
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JPAKE_CTX_init(ctx, name, peer_name, p, g, q, secret);
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return ctx;
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}
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void JPAKE_CTX_free(JPAKE_CTX *ctx)
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{
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JPAKE_CTX_release(ctx);
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OPENSSL_free(ctx);
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}
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static void hashlength(SHA_CTX *sha, size_t l)
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{
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unsigned char b[2];
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assert(l <= 0xffff);
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b[0] = l >> 8;
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b[1] = l&0xff;
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SHA1_Update(sha, b, 2);
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}
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static void hashstring(SHA_CTX *sha, const char *string)
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{
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size_t l = strlen(string);
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hashlength(sha, l);
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SHA1_Update(sha, string, l);
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}
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static void hashbn(SHA_CTX *sha, const BIGNUM *bn)
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{
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size_t l = BN_num_bytes(bn);
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unsigned char *bin = alloca(l);
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hashlength(sha, l);
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BN_bn2bin(bn, bin);
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SHA1_Update(sha, bin, l);
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}
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// h=hash(g, g^r, g^x, name)
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static void zkp_hash(BIGNUM *h, const BIGNUM *zkpg, const JPAKE_STEP_PART *p,
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const char *proof_name)
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{
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unsigned char md[SHA_DIGEST_LENGTH];
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SHA_CTX sha;
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// XXX: hash should not allow moving of the boundaries - Java code
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// is flawed in this respect. Length encoding seems simplest.
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SHA1_Init(&sha);
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hashbn(&sha, zkpg);
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assert(!BN_is_zero(p->zkpx.gr));
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hashbn(&sha, p->zkpx.gr);
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hashbn(&sha, p->gx);
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hashstring(&sha, proof_name);
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SHA1_Final(md, &sha);
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BN_bin2bn(md, SHA_DIGEST_LENGTH, h);
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}
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// Prove knowledge of x
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// Note that p->gx has already been calculated
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static void generate_zkp(JPAKE_STEP_PART *p, const BIGNUM *x,
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const BIGNUM *zkpg, JPAKE_CTX *ctx)
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{
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BIGNUM *r = BN_new();
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BIGNUM *h = BN_new();
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BIGNUM *t = BN_new();
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// r in [0,q)
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// XXX: Java chooses r in [0, 2^160) - i.e. distribution not uniform
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BN_rand_range(r, ctx->p.q);
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// g^r
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BN_mod_exp(p->zkpx.gr, zkpg, r, ctx->p.p, ctx->ctx);
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// h=hash...
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zkp_hash(h, zkpg, p, ctx->p.name);
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// b = r - x*h
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BN_mod_mul(t, x, h, ctx->p.q, ctx->ctx);
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BN_mod_sub(p->zkpx.b, r, t, ctx->p.q, ctx->ctx);
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// cleanup
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BN_free(t);
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BN_free(h);
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BN_free(r);
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}
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static int verify_zkp(const JPAKE_STEP_PART *p, const BIGNUM *zkpg,
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JPAKE_CTX *ctx)
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{
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BIGNUM *h = BN_new();
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BIGNUM *t1 = BN_new();
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BIGNUM *t2 = BN_new();
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BIGNUM *t3 = BN_new();
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int ret = 0;
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zkp_hash(h, zkpg, p, ctx->p.peer_name);
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// t1 = g^b
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BN_mod_exp(t1, zkpg, p->zkpx.b, ctx->p.p, ctx->ctx);
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// t2 = (g^x)^h = g^{hx}
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BN_mod_exp(t2, p->gx, h, ctx->p.p, ctx->ctx);
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// t3 = t1 * t2 = g^{hx} * g^b = g^{hx+b} = g^r (allegedly)
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BN_mod_mul(t3, t1, t2, ctx->p.p, ctx->ctx);
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// verify t3 == g^r
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if(BN_cmp(t3, p->zkpx.gr) == 0)
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ret = 1;
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else
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JPAKEerr(JPAKE_F_VERIFY_ZKP, JPAKE_R_ZKP_VERIFY_FAILED);
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// cleanup
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BN_free(t3);
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BN_free(t2);
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BN_free(t1);
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BN_free(h);
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return ret;
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}
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static void generate_step_part(JPAKE_STEP_PART *p, const BIGNUM *x,
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const BIGNUM *g, JPAKE_CTX *ctx)
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{
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BN_mod_exp(p->gx, g, x, ctx->p.p, ctx->ctx);
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generate_zkp(p, x, g, ctx);
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}
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// Generate each party's random numbers. xa is in [0, q), xb is in [1, q).
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static void genrand(JPAKE_CTX *ctx)
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{
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BIGNUM *qm1;
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// xa in [0, q)
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BN_rand_range(ctx->xa, ctx->p.q);
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// q-1
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qm1 = BN_new();
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BN_copy(qm1, ctx->p.q);
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BN_sub_word(qm1, 1);
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// ... and xb in [0, q-1)
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BN_rand_range(ctx->xb, qm1);
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// [1, q)
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BN_add_word(ctx->xb, 1);
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// cleanup
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BN_free(qm1);
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}
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int JPAKE_STEP1_generate(JPAKE_STEP1 *send, JPAKE_CTX *ctx)
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{
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genrand(ctx);
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generate_step_part(&send->p1, ctx->xa, ctx->p.g, ctx);
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generate_step_part(&send->p2, ctx->xb, ctx->p.g, ctx);
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return 1;
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}
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int JPAKE_STEP1_process(JPAKE_CTX *ctx, const JPAKE_STEP1 *received)
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{
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// verify their ZKP(xc)
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if(!verify_zkp(&received->p1, ctx->p.g, ctx))
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{
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JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_VERIFY_X3_FAILED);
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return 0;
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}
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// verify their ZKP(xd)
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if(!verify_zkp(&received->p2, ctx->p.g, ctx))
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{
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JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_VERIFY_X4_FAILED);
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return 0;
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}
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// g^xd != 1
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if(BN_is_one(received->p2.gx))
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{
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JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_G_TO_THE_X4_IS_ONE);
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return 0;
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}
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// Save the bits we need for later
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BN_copy(ctx->p.gxc, received->p1.gx);
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BN_copy(ctx->p.gxd, received->p2.gx);
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return 1;
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}
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int JPAKE_STEP2_generate(JPAKE_STEP2 *send, JPAKE_CTX *ctx)
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{
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BIGNUM *t1 = BN_new();
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BIGNUM *t2 = BN_new();
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// X = g^{(xa + xc + xd) * xb * s}
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// t1 = g^xa
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BN_mod_exp(t1, ctx->p.g, ctx->xa, ctx->p.p, ctx->ctx);
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// t2 = t1 * g^{xc} = g^{xa} * g^{xc} = g^{xa + xc}
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BN_mod_mul(t2, t1, ctx->p.gxc, ctx->p.p, ctx->ctx);
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// t1 = t2 * g^{xd} = g^{xa + xc + xd}
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BN_mod_mul(t1, t2, ctx->p.gxd, ctx->p.p, ctx->ctx);
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// t2 = xb * s
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BN_mod_mul(t2, ctx->xb, ctx->secret, ctx->p.q, ctx->ctx);
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// ZKP(xb * s)
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// XXX: this is kinda funky, because we're using
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//
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// g' = g^{xa + xc + xd}
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//
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// as the generator, which means X is g'^{xb * s}
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// X = t1^{t2} = t1^{xb * s} = g^{(xa + xc + xd) * xb * s}
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generate_step_part(send, t2, t1, ctx);
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// cleanup
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BN_free(t1);
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BN_free(t2);
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return 1;
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}
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// gx = g^{xc + xa + xb} * xd * s
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static int compute_key(JPAKE_CTX *ctx, const BIGNUM *gx)
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{
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BIGNUM *t1 = BN_new();
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BIGNUM *t2 = BN_new();
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BIGNUM *t3 = BN_new();
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// K = (gx/g^{xb * xd * s})^{xb}
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// = (g^{(xc + xa + xb) * xd * s - xb * xd *s})^{xb}
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// = (g^{(xa + xc) * xd * s})^{xb}
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// = g^{(xa + xc) * xb * xd * s}
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// [which is the same regardless of who calculates it]
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// t1 = (g^{xd})^{xb} = g^{xb * xd}
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BN_mod_exp(t1, ctx->p.gxd, ctx->xb, ctx->p.p, ctx->ctx);
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// t2 = -s = q-s
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BN_sub(t2, ctx->p.q, ctx->secret);
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// t3 = t1^t2 = g^{-xb * xd * s}
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BN_mod_exp(t3, t1, t2, ctx->p.p, ctx->ctx);
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// t1 = gx * t3 = X/g^{xb * xd * s}
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BN_mod_mul(t1, gx, t3, ctx->p.p, ctx->ctx);
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// K = t1^{xb}
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BN_mod_exp(ctx->key, t1, ctx->xb, ctx->p.p, ctx->ctx);
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// cleanup
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BN_free(t3);
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BN_free(t2);
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BN_free(t1);
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return 1;
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}
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int JPAKE_STEP2_process(JPAKE_CTX *ctx, const JPAKE_STEP2 *received)
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{
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BIGNUM *t1 = BN_new();
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BIGNUM *t2 = BN_new();
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int ret = 0;
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// g' = g^{xc + xa + xb} [from our POV]
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// t1 = xa + xb
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BN_mod_add(t1, ctx->xa, ctx->xb, ctx->p.q, ctx->ctx);
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// t2 = g^{t1} = g^{xa+xb}
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BN_mod_exp(t2, ctx->p.g, t1, ctx->p.p, ctx->ctx);
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// t1 = g^{xc} * t2 = g^{xc + xa + xb}
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BN_mod_mul(t1, ctx->p.gxc, t2, ctx->p.p, ctx->ctx);
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if(verify_zkp(received, t1, ctx))
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ret = 1;
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else
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JPAKEerr(JPAKE_F_JPAKE_STEP2_PROCESS, JPAKE_R_VERIFY_B_FAILED);
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compute_key(ctx, received->gx);
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// cleanup
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BN_free(t2);
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BN_free(t1);
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return ret;
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}
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static void quickhashbn(unsigned char *md, const BIGNUM *bn)
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{
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SHA_CTX sha;
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SHA1_Init(&sha);
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hashbn(&sha, bn);
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SHA1_Final(md, &sha);
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}
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void JPAKE_STEP3A_init(JPAKE_STEP3A *s3a)
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{}
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int JPAKE_STEP3A_generate(JPAKE_STEP3A *send, JPAKE_CTX *ctx)
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{
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quickhashbn(send->hhk, ctx->key);
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SHA1(send->hhk, sizeof send->hhk, send->hhk);
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return 1;
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}
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int JPAKE_STEP3A_process(JPAKE_CTX *ctx, const JPAKE_STEP3A *received)
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{
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unsigned char hhk[SHA_DIGEST_LENGTH];
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quickhashbn(hhk, ctx->key);
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SHA1(hhk, sizeof hhk, hhk);
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if(memcmp(hhk, received->hhk, sizeof hhk))
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{
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JPAKEerr(JPAKE_F_JPAKE_STEP3A_PROCESS, JPAKE_R_HASH_OF_HASH_OF_KEY_MISMATCH);
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return 0;
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}
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return 1;
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}
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void JPAKE_STEP3A_release(JPAKE_STEP3A *s3a)
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{}
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void JPAKE_STEP3B_init(JPAKE_STEP3B *s3b)
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{}
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int JPAKE_STEP3B_generate(JPAKE_STEP3B *send, JPAKE_CTX *ctx)
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{
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quickhashbn(send->hk, ctx->key);
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return 1;
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}
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int JPAKE_STEP3B_process(JPAKE_CTX *ctx, const JPAKE_STEP3B *received)
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{
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unsigned char hk[SHA_DIGEST_LENGTH];
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quickhashbn(hk, ctx->key);
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if(memcmp(hk, received->hk, sizeof hk))
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{
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JPAKEerr(JPAKE_F_JPAKE_STEP3B_PROCESS, JPAKE_R_HASH_OF_KEY_MISMATCH);
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return 0;
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}
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return 1;
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}
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void JPAKE_STEP3B_release(JPAKE_STEP3B *s3b)
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{}
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const BIGNUM *JPAKE_get_shared_key(JPAKE_CTX *ctx)
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{
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return ctx->key;
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}
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