diff options
Diffstat (limited to 'crypto/openssh/schnorr.c')
| -rw-r--r-- | crypto/openssh/schnorr.c | 376 |
1 files changed, 308 insertions, 68 deletions
diff --git a/crypto/openssh/schnorr.c b/crypto/openssh/schnorr.c index 61ba68a..daeec06 100644 --- a/crypto/openssh/schnorr.c +++ b/crypto/openssh/schnorr.c @@ -1,4 +1,4 @@ -/* $OpenBSD: schnorr.c,v 1.2 2009/02/18 04:31:21 djm Exp $ */ +/* $OpenBSD: schnorr.c,v 1.3 2009/03/05 07:18:19 djm Exp $ */ /* $FreeBSD$ */ /* * Copyright (c) 2008 Damien Miller. All rights reserved. @@ -41,38 +41,36 @@ #include "buffer.h" #include "log.h" -#include "jpake.h" +#include "schnorr.h" #ifdef JPAKE +#include "openbsd-compat/openssl-compat.h" + /* #define SCHNORR_DEBUG */ /* Privacy-violating debugging */ /* #define SCHNORR_MAIN */ /* Include main() selftest */ -/* XXX */ -/* Parametise signature hash? (sha256, sha1, etc.) */ -/* Signature format - include type name, hash type, group params? */ - #ifndef SCHNORR_DEBUG # define SCHNORR_DEBUG_BN(a) # define SCHNORR_DEBUG_BUF(a) #else -# define SCHNORR_DEBUG_BN(a) jpake_debug3_bn a -# define SCHNORR_DEBUG_BUF(a) jpake_debug3_buf a +# define SCHNORR_DEBUG_BN(a) debug3_bn a +# define SCHNORR_DEBUG_BUF(a) debug3_buf a #endif /* SCHNORR_DEBUG */ /* * Calculate hash component of Schnorr signature H(g || g^v || g^x || id) - * using SHA1. Returns signature as bignum or NULL on error. + * using the hash function defined by "evp_md". Returns signature as + * bignum or NULL on error. */ static BIGNUM * schnorr_hash(const BIGNUM *p, const BIGNUM *q, const BIGNUM *g, - const BIGNUM *g_v, const BIGNUM *g_x, + const EVP_MD *evp_md, const BIGNUM *g_v, const BIGNUM *g_x, const u_char *id, u_int idlen) { u_char *digest; u_int digest_len; BIGNUM *h; - EVP_MD_CTX evp_md_ctx; Buffer b; int success = -1; @@ -82,7 +80,6 @@ schnorr_hash(const BIGNUM *p, const BIGNUM *q, const BIGNUM *g, } buffer_init(&b); - EVP_MD_CTX_init(&evp_md_ctx); /* h = H(g || p || q || g^v || g^x || id) */ buffer_put_bignum2(&b, g); @@ -94,7 +91,7 @@ schnorr_hash(const BIGNUM *p, const BIGNUM *q, const BIGNUM *g, SCHNORR_DEBUG_BUF((buffer_ptr(&b), buffer_len(&b), "%s: hashblob", __func__)); - if (hash_buffer(buffer_ptr(&b), buffer_len(&b), EVP_sha256(), + if (hash_buffer(buffer_ptr(&b), buffer_len(&b), evp_md, &digest, &digest_len) != 0) { error("%s: hash_buffer", __func__); goto out; @@ -107,7 +104,6 @@ schnorr_hash(const BIGNUM *p, const BIGNUM *q, const BIGNUM *g, SCHNORR_DEBUG_BN((h, "%s: h = ", __func__)); out: buffer_free(&b); - EVP_MD_CTX_cleanup(&evp_md_ctx); bzero(digest, digest_len); xfree(digest); digest_len = 0; @@ -120,18 +116,20 @@ schnorr_hash(const BIGNUM *p, const BIGNUM *q, const BIGNUM *g, /* * Generate Schnorr signature to prove knowledge of private value 'x' used * in public exponent g^x, under group defined by 'grp_p', 'grp_q' and 'grp_g' + * using the hash function "evp_md". * 'idlen' bytes from 'id' will be included in the signature hash as an anti- * replay salt. - * On success, 0 is returned and *siglen bytes of signature are returned in - * *sig (caller to free). Returns -1 on failure. + * + * On success, 0 is returned. The signature values are returned as *e_p + * (g^v mod p) and *r_p (v - xh mod q). The caller must free these values. + * On failure, -1 is returned. */ int schnorr_sign(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, - const BIGNUM *x, const BIGNUM *g_x, const u_char *id, u_int idlen, - u_char **sig, u_int *siglen) + const EVP_MD *evp_md, const BIGNUM *x, const BIGNUM *g_x, + const u_char *id, u_int idlen, BIGNUM **r_p, BIGNUM **e_p) { int success = -1; - Buffer b; BIGNUM *h, *tmp, *v, *g_v, *r; BN_CTX *bn_ctx; @@ -174,7 +172,7 @@ schnorr_sign(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, SCHNORR_DEBUG_BN((g_v, "%s: g_v = ", __func__)); /* h = H(g || g^v || g^x || id) */ - if ((h = schnorr_hash(grp_p, grp_q, grp_g, g_v, g_x, + if ((h = schnorr_hash(grp_p, grp_q, grp_g, evp_md, g_v, g_x, id, idlen)) == NULL) { error("%s: schnorr_hash failed", __func__); goto out; @@ -189,12 +187,49 @@ schnorr_sign(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, error("%s: BN_mod_mul (r = v - tmp)", __func__); goto out; } + SCHNORR_DEBUG_BN((g_v, "%s: e = ", __func__)); SCHNORR_DEBUG_BN((r, "%s: r = ", __func__)); - /* Signature is (g_v, r) */ + *e_p = g_v; + *r_p = r; + + success = 0; + out: + BN_CTX_free(bn_ctx); + if (h != NULL) + BN_clear_free(h); + if (v != NULL) + BN_clear_free(v); + BN_clear_free(tmp); + + return success; +} + +/* + * Generate Schnorr signature to prove knowledge of private value 'x' used + * in public exponent g^x, under group defined by 'grp_p', 'grp_q' and 'grp_g' + * using a SHA256 hash. + * 'idlen' bytes from 'id' will be included in the signature hash as an anti- + * replay salt. + * On success, 0 is returned and *siglen bytes of signature are returned in + * *sig (caller to free). Returns -1 on failure. + */ +int +schnorr_sign_buf(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, + const BIGNUM *x, const BIGNUM *g_x, const u_char *id, u_int idlen, + u_char **sig, u_int *siglen) +{ + Buffer b; + BIGNUM *r, *e; + + if (schnorr_sign(grp_p, grp_q, grp_g, EVP_sha256(), + x, g_x, id, idlen, &r, &e) != 0) + return -1; + + /* Signature is (e, r) */ buffer_init(&b); /* XXX sigtype-hash as string? */ - buffer_put_bignum2(&b, g_v); + buffer_put_bignum2(&b, e); buffer_put_bignum2(&b, r); *siglen = buffer_len(&b); *sig = xmalloc(*siglen); @@ -202,36 +237,28 @@ schnorr_sign(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, SCHNORR_DEBUG_BUF((buffer_ptr(&b), buffer_len(&b), "%s: sigblob", __func__)); buffer_free(&b); - success = 0; - out: - BN_CTX_free(bn_ctx); - if (h != NULL) - BN_clear_free(h); - if (v != NULL) - BN_clear_free(v); + BN_clear_free(r); - BN_clear_free(g_v); - BN_clear_free(tmp); + BN_clear_free(e); - return success; + return 0; } /* - * Verify Schnorr signature 'sig' of length 'siglen' against public exponent - * g_x (g^x) under group defined by 'grp_p', 'grp_q' and 'grp_g'. + * Verify Schnorr signature { r (v - xh mod q), e (g^v mod p) } against + * public exponent g_x (g^x) under group defined by 'grp_p', 'grp_q' and + * 'grp_g' using hash "evp_md". * Signature hash will be salted with 'idlen' bytes from 'id'. * Returns -1 on failure, 0 on incorrect signature or 1 on matching signature. */ int schnorr_verify(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, - const BIGNUM *g_x, const u_char *id, u_int idlen, - const u_char *sig, u_int siglen) + const EVP_MD *evp_md, const BIGNUM *g_x, const u_char *id, u_int idlen, + const BIGNUM *r, const BIGNUM *e) { int success = -1; - Buffer b; - BIGNUM *g_v, *h, *r, *g_xh, *g_r, *expected; + BIGNUM *h, *g_xh, *g_r, *expected; BN_CTX *bn_ctx; - u_int rlen; SCHNORR_DEBUG_BN((g_x, "%s: g_x = ", __func__)); @@ -241,39 +268,23 @@ schnorr_verify(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, return -1; } - g_v = h = r = g_xh = g_r = expected = NULL; + h = g_xh = g_r = expected = NULL; if ((bn_ctx = BN_CTX_new()) == NULL) { error("%s: BN_CTX_new", __func__); goto out; } - if ((g_v = BN_new()) == NULL || - (r = BN_new()) == NULL || - (g_xh = BN_new()) == NULL || + if ((g_xh = BN_new()) == NULL || (g_r = BN_new()) == NULL || (expected = BN_new()) == NULL) { error("%s: BN_new", __func__); goto out; } - /* Extract g^v and r from signature blob */ - buffer_init(&b); - buffer_append(&b, sig, siglen); - SCHNORR_DEBUG_BUF((buffer_ptr(&b), buffer_len(&b), - "%s: sigblob", __func__)); - buffer_get_bignum2(&b, g_v); - buffer_get_bignum2(&b, r); - rlen = buffer_len(&b); - buffer_free(&b); - if (rlen != 0) { - error("%s: remaining bytes in signature %d", __func__, rlen); - goto out; - } - buffer_free(&b); - SCHNORR_DEBUG_BN((g_v, "%s: g_v = ", __func__)); + SCHNORR_DEBUG_BN((e, "%s: e = ", __func__)); SCHNORR_DEBUG_BN((r, "%s: r = ", __func__)); /* h = H(g || g^v || g^x || id) */ - if ((h = schnorr_hash(grp_p, grp_q, grp_g, g_v, g_x, + if ((h = schnorr_hash(grp_p, grp_q, grp_g, evp_md, e, g_x, id, idlen)) == NULL) { error("%s: schnorr_hash failed", __func__); goto out; @@ -300,20 +311,248 @@ schnorr_verify(const BIGNUM *grp_p, const BIGNUM *grp_q, const BIGNUM *grp_g, } SCHNORR_DEBUG_BN((expected, "%s: expected = ", __func__)); - /* Check g_v == expected */ - success = BN_cmp(expected, g_v) == 0; + /* Check e == expected */ + success = BN_cmp(expected, e) == 0; out: BN_CTX_free(bn_ctx); if (h != NULL) BN_clear_free(h); - BN_clear_free(g_v); - BN_clear_free(r); BN_clear_free(g_xh); BN_clear_free(g_r); BN_clear_free(expected); return success; } +/* + * Verify Schnorr signature 'sig' of length 'siglen' against public exponent + * g_x (g^x) under group defined by 'grp_p', 'grp_q' and 'grp_g' using a + * SHA256 hash. + * Signature hash will be salted with 'idlen' bytes from 'id'. + * Returns -1 on failure, 0 on incorrect signature or 1 on matching signature. + */ +int +schnorr_verify_buf(const BIGNUM *grp_p, const BIGNUM *grp_q, + const BIGNUM *grp_g, + const BIGNUM *g_x, const u_char *id, u_int idlen, + const u_char *sig, u_int siglen) +{ + Buffer b; + int ret = -1; + u_int rlen; + BIGNUM *r, *e; + + e = r = NULL; + if ((e = BN_new()) == NULL || + (r = BN_new()) == NULL) { + error("%s: BN_new", __func__); + goto out; + } + + /* Extract g^v and r from signature blob */ + buffer_init(&b); + buffer_append(&b, sig, siglen); + SCHNORR_DEBUG_BUF((buffer_ptr(&b), buffer_len(&b), + "%s: sigblob", __func__)); + buffer_get_bignum2(&b, e); + buffer_get_bignum2(&b, r); + rlen = buffer_len(&b); + buffer_free(&b); + if (rlen != 0) { + error("%s: remaining bytes in signature %d", __func__, rlen); + goto out; + } + + ret = schnorr_verify(grp_p, grp_q, grp_g, EVP_sha256(), + g_x, id, idlen, r, e); + out: + BN_clear_free(e); + BN_clear_free(r); + + return ret; +} + +/* Helper functions */ + +/* + * 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 +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 +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; + } + } +} + +/* + * Construct a MODP group from hex strings p (which must be a safe + * prime) and g, automatically calculating subgroup q as (p / 2) + */ +struct modp_group * +modp_group_from_g_and_safe_p(const char *grp_g, const char *grp_p) +{ + struct modp_group *ret; + + ret = xmalloc(sizeof(*ret)); + ret->p = ret->q = ret->g = NULL; + if (BN_hex2bn(&ret->p, grp_p) == 0 || + BN_hex2bn(&ret->g, grp_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; +} + +void +modp_group_free(struct modp_group *grp) +{ + if (grp->g != NULL) + BN_clear_free(grp->g); + if (grp->p != NULL) + BN_clear_free(grp->p); + if (grp->q != NULL) + BN_clear_free(grp->q); + bzero(grp, sizeof(*grp)); + xfree(grp); +} + +/* main() function for self-test */ + #ifdef SCHNORR_MAIN static void schnorr_selftest_one(const BIGNUM *grp_p, const BIGNUM *grp_q, @@ -331,16 +570,17 @@ schnorr_selftest_one(const BIGNUM *grp_p, const BIGNUM *grp_q, if (BN_mod_exp(g_x, grp_g, x, grp_p, bn_ctx) == -1) fatal("%s: g_x", __func__); - if (schnorr_sign(grp_p, grp_q, grp_g, x, g_x, "junk", 4, &sig, &siglen)) + 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(grp_p, grp_q, grp_g, g_x, "junk", 4, + 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(grp_p, grp_q, grp_g, g_x, "JUNK", 4, + 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(grp_p, grp_q, grp_g, g_x, "junk", 4, + 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__); xfree(sig); @@ -352,7 +592,7 @@ static void schnorr_selftest(void) { BIGNUM *x; - struct jpake_group *grp; + struct modp_group *grp; u_int i; char *hh; |
