diff options
| -rw-r--r-- | dsa-sign.c | 116 | ||||
| -rw-r--r-- | dsa-verify.c | 100 | ||||
| -rw-r--r-- | dsa.c | 93 | ||||
| -rw-r--r-- | dsa.h | 158 |
4 files changed, 467 insertions, 0 deletions
diff --git a/dsa-sign.c b/dsa-sign.c new file mode 100644 index 00000000..a22b0a52 --- /dev/null +++ b/dsa-sign.c @@ -0,0 +1,116 @@ +/* dsa-sign.c + * + * The DSA publickey algorithm. + */ + +/* nettle, low-level cryptographics library + * + * Copyright (C) 2002 Niels Möller + * + * The nettle library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or (at your + * option) any later version. + * + * The nettle library is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with the nettle library; see the file COPYING.LIB. If not, write to + * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +#if HAVE_CONFIG_H +#include "config.h" +#endif + +#if WITH_PUBLIC_KEY + +#include "dsa.h" + +#include "bignum.h" + +#include <stdlib.h> + +/* Returns a number x, almost uniformly random in the range + * 0 <= x < n. */ +static void +nettle_mpz_random(mpz_t x, const mpz_t n, + void *ctx, nettle_random_func random) +{ + /* FIXME: This leaves some bias, which may be bad for DSA. A better + * way might to generate a random number of mpz_sizeinbase(n, 2) + * bits, and loop until one smaller than n is found. */ + + /* From Daniel Bleichenbacher (via coderpunks): + * + * There is still a theoretical attack possible with 8 extra bits. + * But, the attack would need about 2^66 signatures 2^66 memory and + * 2^66 time (if I remember that correctly). Compare that to DSA, + * where the attack requires 2^22 signatures 2^40 memory and 2^64 + * time. And of course, the numbers above are not a real threat for + * PGP. Using 16 extra bits (i.e. generating a 176 bit random number + * and reducing it modulo q) will defeat even this theoretical + * attack. + * + * More generally log_2(q)/8 extra bits are enough to defeat my + * attack. NIST also plans to update the standard. + */ + + /* Add a few bits extra, to decrease the bias from the final modulo + * operation. */ + unsigned ndigits = (mpz_sizeinbase(n, 2) + 7) / 8 + 2; + uint8_t *digits = alloca(ndigits); + + random(ctx, ndigits, digits); + nettle_mpz_set_str_256(x, ndigits, digits); + + mpz_fdiv_r(x, x, n); +} + +void +dsa_sign(struct dsa_private_key *key, + void *random_ctx, nettle_random_func random, + struct sha1_ctx *hash, + struct dsa_signature *signature) +{ + mpz_t k; + mpz_t h; + mpz_t tmp; + + /* Select k, 0<k<q, randomly */ + mpz_init_set(tmp, key->pub.q); + mpz_sub_ui(tmp, tmp, 1); + + mpz_init(k); + nettle_mpz_random(k, tmp, random_ctx, random); + mpz_add_ui(k, k, 1); + + /* Compute r = (g^k (mod p)) (mod q) */ + mpz_powm(tmp, key->pub.g, k, key->pub.p); + mpz_fdiv_r(signature->r, tmp, key->pub.q); + + /* Compute hash */ + _dsa_hash(h, hash); + + /* Compute k^-1 (mod q) */ + if (!mpz_invert(k, k, key->pub.q)) + /* What do we do now? The key is invalid. */ + abort(); + + /* Compute signature s = k^-1(h + xr) (mod q) */ + mpz_mul(tmp, signature->r, key->x); + mpz_fdiv_r(tmp, tmp, key->pub.q); + mpz_add(tmp, tmp, h); + mpz_mul(tmp, tmp, k); + mpz_fdiv_r(signature->s, tmp, key->pub.q); + + mpz_clear(k); + mpz_clear(h); + mpz_clear(tmp); +} + +#endif /* WITH_PUBLIC_KEY */ diff --git a/dsa-verify.c b/dsa-verify.c new file mode 100644 index 00000000..ba73d344 --- /dev/null +++ b/dsa-verify.c @@ -0,0 +1,100 @@ +/* dsa-verify.c + * + * The DSA publickey algorithm. + */ + +/* nettle, low-level cryptographics library + * + * Copyright (C) 2002 Niels Möller + * + * The nettle library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or (at your + * option) any later version. + * + * The nettle library is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with the nettle library; see the file COPYING.LIB. If not, write to + * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +#if HAVE_CONFIG_H +#include "config.h" +#endif + +#if WITH_PUBLIC_KEY + +#include "dsa.h" + +#include <stdlib.h> + +int +dsa_verify(struct dsa_public_key *key, + struct sha1_ctx *hash, + const struct dsa_signature *signature) +{ + mpz_t w; + mpz_t tmp; + mpz_t v; + + int res; + + /* Check that r and s are in the proper range */ + if (mpz_sgn(signature->r) <= 0 || mpz_cmp(signature->r, key->q) >= 0) + return 0; + + if (mpz_sgn(signature->s) <= 0 || mpz_cmp(signature->s, key->q) >= 0) + return 0; + + mpz_init(w); + + /* Compute w = s^-1 (mod q) */ + + /* NOTE: In gmp-2, mpz_invert sometimes generates negative inverses, + * so we need gmp-3 or better. */ + if (!mpz_invert(w, signature->s, key->q)) + { + mpz_clear(w); + return 0; + } + + mpz_init(tmp); + mpz_init(v); + + /* Compute hash */ + _dsa_hash(tmp, hash); + + /* v = g^{w * h (mod q)} (mod p) */ + + mpz_mul(tmp, tmp, w); + mpz_fdiv_r(tmp, tmp, key->q); + + mpz_powm(v, key->g, tmp, key->p); + + /* y^{w * r (mod q) } (mod p) */ + mpz_mul(tmp, signature->r, w); + mpz_fdiv_r(tmp, tmp, key->q); + + mpz_powm(tmp, key->y, tmp, key->p); + + /* v = (g^{w * h} * y^{w * r} (mod p) ) (mod q) */ + mpz_mul(v, v, tmp); + mpz_fdiv_r(v, v, key->p); + + mpz_fdiv_r(v, v, key->q); + + res = !mpz_cmp(v, signature->r); + + mpz_clear(w); + mpz_clear(tmp); + mpz_clear(v); + + return res; +} + +#endif /* WITH_PUBLIC_KEY */ @@ -0,0 +1,93 @@ +/* dsa.h + * + * The DSA publickey algorithm. + */ + +/* nettle, low-level cryptographics library + * + * Copyright (C) 2002 Niels Möller + * + * The nettle library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or (at your + * option) any later version. + * + * The nettle library is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with the nettle library; see the file COPYING.LIB. If not, write to + * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +#if HAVE_CONFIG_H +#include "config.h" +#endif + +#if WITH_PUBLIC_KEY + +#include "dsa.h" + +#include "bignum.h" + +void +dsa_public_key_init(struct dsa_public_key *key) +{ + mpz_init(key->p); + mpz_init(key->q); + mpz_init(key->g); + mpz_init(key->y); +} + +void +dsa_public_key_clear(struct dsa_public_key *key) +{ + mpz_clear(key->p); + mpz_clear(key->q); + mpz_clear(key->g); + mpz_clear(key->y); +} + + +void +dsa_private_key_init(struct dsa_private_key *key) +{ + dsa_public_key_init(&key->pub); + mpz_init(key->x); +} + +void +dsa_private_key_clear(struct dsa_private_key *key) +{ + dsa_public_key_clear(&key->pub); + mpz_clear(key->x); +} + + +void +dsa_signature_init(struct dsa_signature *signature) +{ + mpz_init(signature->r); + mpz_init(signature->s); +} + +void +dsa_signature_clear(struct dsa_signature *signature) +{ + mpz_clear(signature->r); + mpz_clear(signature->s); +} + +void +_dsa_hash(mpz_t x, struct sha1_ctx *hash) +{ + uint8_t digest[SHA1_DIGEST_SIZE]; + sha1_digest(hash, sizeof(digest), digest); + + nettle_mpz_set_str_256(x, sizeof(digest), digest); +} + +#endif /* WITH_PUBLIC_KEY */ @@ -0,0 +1,158 @@ +/* dsa.h + * + * The DSA publickey algorithm. + */ + +/* nettle, low-level cryptographics library + * + * Copyright (C) 2002 Niels Möller + * + * The nettle library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or (at your + * option) any later version. + * + * The nettle library is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with the nettle library; see the file COPYING.LIB. If not, write to + * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +#ifndef NETTLE_DSA_H_INCLUDED +#define NETTLE_DSA_H_INCLUDED + +#include <inttypes.h> +#include <gmp.h> + +#include "sha.h" + +/* For nettle_random_func */ +#include "nettle-meta.h" + + +struct dsa_public_key +{ + /* Modulo */ + mpz_t p; + + /* Group order */ + mpz_t q; + + /* Generator */ + mpz_t g; + + /* Public value */ + mpz_t y; +}; + +struct dsa_private_key +{ + /* Unlike an rsa public key, all the public information is needed, + * in addition to the private information. */ + struct dsa_public_key pub; + mpz_t x; +}; + +struct dsa_signature +{ + mpz_t r; + mpz_t s; +}; + +/* Signing a message works as follows: + * + * Store the private key in a dsa_private_key struct. + * + * Initialize a hashing context, by callling + * sha1_init + * + * Hash the message by calling + * sha1_update + * + * Create the signature by calling + * dsa_sign + * + * The signature is represented as two mpz_t bignums. This call also + * resets the hashing context. + * + * When done with the key and signature, don't forget to call + * mpz_clear. + */ + +/* Calls mpz_init to initialize bignum storage. */ +void +dsa_public_key_init(struct dsa_public_key *key); + +/* Calls mpz_clear to deallocate bignum storage. */ +void +dsa_public_key_clear(struct dsa_public_key *key); + + +/* Calls mpz_init to initialize bignum storage. */ +void +dsa_private_key_init(struct dsa_private_key *key); + +/* Calls mpz_clear to deallocate bignum storage. */ +void +dsa_private_key_clear(struct dsa_private_key *key); + +/* Calls mpz_init to initialize bignum storage. */ +void +dsa_signature_init(struct dsa_signature *signature); + +/* Calls mpz_clear to deallocate bignum storage. */ +void +dsa_signature_clear(struct dsa_signature *signature); + + +void +_dsa_hash(mpz_t x, struct sha1_ctx *hash); + +void +dsa_sign(struct dsa_private_key *key, + void *random_ctx, nettle_random_func random, + struct sha1_ctx *hash, + struct dsa_signature *signature); + + +int +dsa_verify(struct dsa_public_key *key, + struct sha1_ctx *hash, + const struct dsa_signature *signature); + +/* Key generation */ + +#if 0 +/* Note that the key structs must be initialized first. */ +int +dsa_generate_keypair(struct dsa_public_key *pub, + struct dsa_private_key *key, + + void *random_ctx, nettle_random_func random, + void *progress_ctx, nettle_progress_func progress, + + /* Desired size of modulo, in bits */ + unsigned n_size, + + /* Desired size of public exponent, in bits. If + * zero, the passed in value pub->e is used. */ + unsigned e_size); + + +#define DSA_SIGN(key, algorithm, ctx, length, data, signature) ( \ + algorithm##_update(ctx, length, data), \ + dsa_##algorithm##_sign(key, ctx, signature) \ +) + +#define DSA_VERIFY(key, algorithm, ctx, length, data, signature) ( \ + algorithm##_update(ctx, length, data), \ + dsa_##algorithm##_verify(key, ctx, signature) \ +) +#endif + +#endif /* NETTLE_DSA_H_INCLUDED */ |