New files.

Rev: src/nettle/dsa-sign.c:1.1
Rev: src/nettle/dsa-verify.c:1.1
Rev: src/nettle/dsa.c:1.1
Rev: src/nettle/dsa.h:1.1

dsa-sign.c

+/* dsa-sign.c
+ *
+ * The DSA publickey algorithm.
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2002 Niels Mller
+ *  
+ * 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 */

dsa-verify.c

+/* dsa-verify.c
+ *
+ * The DSA publickey algorithm.
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2002 Niels Mller
+ *  
+ * 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 */

dsa.c

+/* dsa.h
+ *
+ * The DSA publickey algorithm.
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2002 Niels Mller
+ *  
+ * 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 */

dsa.h

+/* dsa.h
+ *
+ * The DSA publickey algorithm.
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2002 Niels Mller
+ *  
+ * 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 */