--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/pk/dh/dh_sys.c	Wed Mar 08 12:58:00 2006 +0000
@@ -0,0 +1,499 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://libtomcrypt.org
+ */
+
+/**
+  @file dh_sys.c
+  DH Crypto, Tom St Denis
+*/
+  
+/**
+  Encrypt a short symmetric key with a public DH key
+  @param in        The symmetric key to encrypt
+  @param inlen     The length of the key (octets)
+  @param out       [out] The ciphertext
+  @param outlen    [in/out]  The max size and resulting size of the ciphertext
+  @param prng      An active PRNG state
+  @param wprng     The index of the PRNG desired
+  @param hash      The index of the hash desired (must produce a digest of size >= the size of the plaintext)
+  @param key       The public key you wish to encrypt with.
+  @return CRYPT_OK if successful
+*/
+int dh_encrypt_key(const unsigned char *in,   unsigned long inlen,
+                         unsigned char *out,  unsigned long *outlen,
+                         prng_state *prng, int wprng, int hash,
+                         dh_key *key)
+{
+    unsigned char *pub_expt, *dh_shared, *skey;
+    dh_key        pubkey;
+    unsigned long x, y, z, hashsize, pubkeysize;
+    int           err;
+
+    LTC_ARGCHK(in != NULL);
+    LTC_ARGCHK(out   != NULL);
+    LTC_ARGCHK(outlen   != NULL);
+    LTC_ARGCHK(key   != NULL);
+
+    /* check that wprng/hash are not invalid */
+    if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
+       return err;
+    }
+
+    if ((err = hash_is_valid(hash)) != CRYPT_OK) {
+       return err;
+    }
+
+    if (inlen > hash_descriptor[hash].hashsize)  {
+        return CRYPT_INVALID_HASH;
+    }
+
+    /* allocate memory */
+    pub_expt  = XMALLOC(DH_BUF_SIZE);
+    dh_shared = XMALLOC(DH_BUF_SIZE);
+    skey      = XMALLOC(MAXBLOCKSIZE);
+    if (pub_expt == NULL || dh_shared == NULL || skey == NULL) {
+       if (pub_expt != NULL) {
+          XFREE(pub_expt);
+       }
+       if (dh_shared != NULL) {
+          XFREE(dh_shared);
+       }
+       if (skey != NULL) {
+          XFREE(skey);
+       }
+       return CRYPT_MEM;
+    }
+
+    /* make a random key and export the public copy */
+    if ((err = dh_make_key(prng, wprng, dh_get_size(key), &pubkey)) != CRYPT_OK) {
+       goto LBL_ERR;
+    }
+
+    pubkeysize = DH_BUF_SIZE;
+    if ((err = dh_export(pub_expt, &pubkeysize, PK_PUBLIC, &pubkey)) != CRYPT_OK) {
+       dh_free(&pubkey);
+       goto LBL_ERR;
+    }
+
+    /* now check if the out buffer is big enough */
+    if (*outlen < (1 + 4 + 4 + PACKET_SIZE + pubkeysize + inlen)) {
+       dh_free(&pubkey);
+       err = CRYPT_BUFFER_OVERFLOW;
+       goto LBL_ERR;
+    }
+
+    /* make random key */
+    hashsize  = hash_descriptor[hash].hashsize;
+
+    x = DH_BUF_SIZE;
+    if ((err = dh_shared_secret(&pubkey, key, dh_shared, &x)) != CRYPT_OK) {
+       dh_free(&pubkey);
+       goto LBL_ERR;
+    }
+    dh_free(&pubkey);
+
+    z = MAXBLOCKSIZE;
+    if ((err = hash_memory(hash, dh_shared, x, skey, &z)) != CRYPT_OK) {
+       goto LBL_ERR;
+    }
+
+    /* store header */
+    packet_store_header(out, PACKET_SECT_DH, PACKET_SUB_ENC_KEY);
+
+    /* output header */
+    y = PACKET_SIZE;
+
+    /* size of hash name and the name itself */
+    out[y++] = hash_descriptor[hash].ID;
+
+    /* length of DH pubkey and the key itself */
+    STORE32L(pubkeysize, out+y);
+    y += 4;
+    for (x = 0; x < pubkeysize; x++, y++) {
+        out[y] = pub_expt[x];
+    }
+
+    /* Store the encrypted key */
+    STORE32L(inlen, out+y);
+    y += 4;
+
+    for (x = 0; x < inlen; x++, y++) {
+      out[y] = skey[x] ^ in[x];
+    }
+    *outlen = y;
+
+    err = CRYPT_OK;
+LBL_ERR:
+#ifdef LTC_CLEAN_STACK
+    /* clean up */
+    zeromem(pub_expt,  DH_BUF_SIZE);
+    zeromem(dh_shared, DH_BUF_SIZE);
+    zeromem(skey,      MAXBLOCKSIZE);
+#endif
+    XFREE(skey);
+    XFREE(dh_shared);
+    XFREE(pub_expt);
+
+    return err;
+}
+
+/**
+   Decrypt a DH encrypted symmetric key
+   @param in       The DH encrypted packet
+   @param inlen    The length of the DH encrypted packet
+   @param out      The plaintext
+   @param outlen   [in/out]  The max size and resulting size of the plaintext
+   @param key      The private DH key corresponding to the public key that encrypted the plaintext
+   @return CRYPT_OK if successful
+*/
+int dh_decrypt_key(const unsigned char *in, unsigned long inlen,
+                         unsigned char *out, unsigned long *outlen, 
+                         dh_key *key)
+{
+   unsigned char *shared_secret, *skey;
+   unsigned long  x, y, z, hashsize, keysize;
+   int            hash, err;
+   dh_key         pubkey;
+
+   LTC_ARGCHK(in     != NULL);
+   LTC_ARGCHK(out != NULL);
+   LTC_ARGCHK(outlen != NULL);
+   LTC_ARGCHK(key    != NULL);
+
+   /* right key type? */
+   if (key->type != PK_PRIVATE) {
+      return CRYPT_PK_NOT_PRIVATE;
+   }
+
+   /* allocate ram */
+   shared_secret = XMALLOC(DH_BUF_SIZE);
+   skey          = XMALLOC(MAXBLOCKSIZE);
+   if (shared_secret == NULL || skey == NULL) {
+      if (shared_secret != NULL) {
+         XFREE(shared_secret);
+      }
+      if (skey != NULL) {
+         XFREE(skey);
+      }
+      return CRYPT_MEM;
+   }
+
+   /* check if initial header should fit */
+   if (inlen < PACKET_SIZE+1+4+4) {
+      err =  CRYPT_INVALID_PACKET;
+      goto LBL_ERR;
+   } else {
+      inlen -= PACKET_SIZE+1+4+4;
+   }
+
+   /* is header correct? */
+   if ((err = packet_valid_header((unsigned char *)in, PACKET_SECT_DH, PACKET_SUB_ENC_KEY)) != CRYPT_OK)  {
+      goto LBL_ERR;
+   }
+
+   /* now lets get the hash name */
+   y = PACKET_SIZE;
+   hash = find_hash_id(in[y++]);
+   if (hash == -1) {
+      err = CRYPT_INVALID_HASH;
+      goto LBL_ERR;
+   }
+
+   /* common values */
+   hashsize  = hash_descriptor[hash].hashsize;
+
+   /* get public key */
+   LOAD32L(x, in+y);
+   
+   /* now check if the imported key will fit */
+   if (inlen < x) {
+      err = CRYPT_INVALID_PACKET;
+      goto LBL_ERR;
+   } else {
+      inlen -= x;
+   }
+   
+   y += 4;
+   if ((err = dh_import(in+y, x, &pubkey)) != CRYPT_OK) {
+      goto LBL_ERR;
+   }
+   y += x;
+
+   /* make shared key */
+   x = DH_BUF_SIZE;
+   if ((err = dh_shared_secret(key, &pubkey, shared_secret, &x)) != CRYPT_OK) {
+      dh_free(&pubkey);
+      goto LBL_ERR;
+   }
+   dh_free(&pubkey);
+
+   z = MAXBLOCKSIZE;
+   if ((err = hash_memory(hash, shared_secret, x, skey, &z)) != CRYPT_OK) {
+      goto LBL_ERR;
+   }
+
+   /* load in the encrypted key */
+   LOAD32L(keysize, in+y);
+   
+   /* will the out fit as part of the input */
+   if (inlen < keysize) {
+      err = CRYPT_INVALID_PACKET;
+      goto LBL_ERR;
+   } else {
+      inlen -= keysize;
+   }
+   
+   if (keysize > *outlen) {
+       err = CRYPT_BUFFER_OVERFLOW;
+       goto LBL_ERR;
+   }
+   y += 4;
+
+   *outlen = keysize;
+
+   for (x = 0; x < keysize; x++, y++) {
+      out[x] = skey[x] ^ in[y];
+   }
+
+   err = CRYPT_OK;
+LBL_ERR:
+#ifdef LTC_CLEAN_STACK
+   zeromem(shared_secret, DH_BUF_SIZE);
+   zeromem(skey,          MAXBLOCKSIZE);
+#endif
+
+   XFREE(skey);
+   XFREE(shared_secret);
+
+   return err;
+}
+
+/* perform an ElGamal Signature of a hash 
+ *
+ * The math works as follows.  x is the private key, M is the message to sign
+ 
+ 1.  pick a random k
+ 2.  compute a = g^k mod p
+ 3.  compute b = (M - xa)/k mod p
+ 4.  Send (a,b)
+ 
+ Now to verify with y=g^x mod p, a and b
+ 
+ 1.  compute y^a * a^b = g^(xa) * g^(k*(M-xa)/k)
+                       = g^(xa + (M - xa))
+                       = g^M [all mod p]
+                       
+ 2.  Compare against g^M mod p [based on input hash].
+ 3.  If result of #2 == result of #1 then signature valid 
+*/
+
+/**
+  Sign a message digest using a DH private key 
+  @param in      The data to sign
+  @param inlen   The length of the input (octets)
+  @param out     [out] The destination of the signature
+  @param outlen  [in/out] The max size and resulting size of the output
+  @param prng    An active PRNG state
+  @param wprng   The index of the PRNG desired
+  @param key     A private DH key
+  @return CRYPT_OK if successful
+*/
+int dh_sign_hash(const unsigned char *in,  unsigned long inlen,
+                       unsigned char *out, unsigned long *outlen,
+                       prng_state *prng, int wprng, dh_key *key)
+{
+   mp_int         a, b, k, m, g, p, p1, tmp;
+   unsigned char *buf;
+   unsigned long  x, y;
+   int            err;
+
+   LTC_ARGCHK(in     != NULL);
+   LTC_ARGCHK(out    != NULL);
+   LTC_ARGCHK(outlen != NULL);
+   LTC_ARGCHK(key    != NULL);
+
+   /* check parameters */
+   if (key->type != PK_PRIVATE) {
+      return CRYPT_PK_NOT_PRIVATE;
+   }
+
+   if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* is the IDX valid ?  */
+   if (is_valid_idx(key->idx) != 1) {
+      return CRYPT_PK_INVALID_TYPE;
+   }
+
+   /* allocate ram for buf */
+   buf = XMALLOC(520);
+
+   /* make up a random value k,
+    * since the order of the group is prime
+    * we need not check if gcd(k, r) is 1 
+    */
+   if (prng_descriptor[wprng].read(buf, sets[key->idx].size, prng) != 
+       (unsigned long)(sets[key->idx].size)) {
+      err = CRYPT_ERROR_READPRNG;
+      goto LBL_ERR;
+   }
+
+   /* init bignums */
+   if ((err = mp_init_multi(&a, &b, &k, &m, &p, &g, &p1, &tmp, NULL)) != MP_OKAY) { 
+      err = mpi_to_ltc_error(err);
+      goto LBL_ERR;
+   }
+
+   /* load k and m */
+   if ((err = mp_read_unsigned_bin(&m, (unsigned char *)in, inlen)) != MP_OKAY)        { goto error; }
+   if ((err = mp_read_unsigned_bin(&k, buf, sets[key->idx].size)) != MP_OKAY)          { goto error; }
+
+   /* load g, p and p1 */
+   if ((err = mp_read_radix(&g, sets[key->idx].base, 64)) != MP_OKAY)               { goto error; }
+   if ((err = mp_read_radix(&p, sets[key->idx].prime, 64)) != MP_OKAY)              { goto error; }
+   if ((err = mp_sub_d(&p, 1, &p1)) != MP_OKAY)                                     { goto error; }
+   if ((err = mp_div_2(&p1, &p1)) != MP_OKAY)                                       { goto error; } /* p1 = (p-1)/2 */
+
+   /* now get a = g^k mod p */
+   if ((err = mp_exptmod(&g, &k, &p, &a)) != MP_OKAY)                               { goto error; }
+
+   /* now find M = xa + kb mod p1 or just b = (M - xa)/k mod p1 */
+   if ((err = mp_invmod(&k, &p1, &k)) != MP_OKAY)                                   { goto error; } /* k = 1/k mod p1 */
+   if ((err = mp_mulmod(&a, &key->x, &p1, &tmp)) != MP_OKAY)                        { goto error; } /* tmp = xa */
+   if ((err = mp_submod(&m, &tmp, &p1, &tmp)) != MP_OKAY)                           { goto error; } /* tmp = M - xa */
+   if ((err = mp_mulmod(&k, &tmp, &p1, &b)) != MP_OKAY)                             { goto error; } /* b = (M - xa)/k */
+   
+   /* check for overflow */
+   if ((unsigned long)(PACKET_SIZE + 4 + 4 + mp_unsigned_bin_size(&a) + mp_unsigned_bin_size(&b)) > *outlen) {
+      err = CRYPT_BUFFER_OVERFLOW;
+      goto LBL_ERR;
+   }
+   
+   /* store header  */
+   y = PACKET_SIZE;
+
+   /* now store them both (a,b) */
+   x = (unsigned long)mp_unsigned_bin_size(&a);
+   STORE32L(x, out+y);  y += 4;
+   if ((err = mp_to_unsigned_bin(&a, out+y)) != MP_OKAY)                            { goto error; }
+   y += x;
+
+   x = (unsigned long)mp_unsigned_bin_size(&b);
+   STORE32L(x, out+y);  y += 4;
+   if ((err = mp_to_unsigned_bin(&b, out+y)) != MP_OKAY)                            { goto error; }
+   y += x;
+
+   /* check if size too big */
+   if (*outlen < y) {
+      err = CRYPT_BUFFER_OVERFLOW;
+      goto LBL_ERR;
+   }
+
+   /* store header */
+   packet_store_header(out, PACKET_SECT_DH, PACKET_SUB_SIGNED);
+   *outlen = y;
+
+   err = CRYPT_OK;
+   goto LBL_ERR;
+error:
+   err = mpi_to_ltc_error(err);
+LBL_ERR:
+   mp_clear_multi(&tmp, &p1, &g, &p, &m, &k, &b, &a, NULL);
+
+   XFREE(buf);
+
+   return err;
+}
+
+
+/**
+   Verify the signature given
+   @param sig        The signature
+   @param siglen     The length of the signature (octets)
+   @param hash       The hash that was signed
+   @param hashlen    The length of the hash (octets)
+   @param stat       [out] Result of signature comparison, 1==valid, 0==invalid
+   @param key        The public DH key that signed the hash
+   @return CRYPT_OK if succsessful (even if signature is invalid)
+*/
+int dh_verify_hash(const unsigned char *sig, unsigned long siglen,
+                   const unsigned char *hash, unsigned long hashlen, 
+                         int *stat, dh_key *key)
+{
+   mp_int        a, b, p, g, m, tmp;
+   unsigned long x, y;
+   int           err;
+
+   LTC_ARGCHK(sig  != NULL);
+   LTC_ARGCHK(hash != NULL);
+   LTC_ARGCHK(stat != NULL);
+   LTC_ARGCHK(key  != NULL);
+
+   /* default to invalid */
+   *stat = 0;
+
+   /* check initial input length */
+   if (siglen < PACKET_SIZE+4+4) {
+      return CRYPT_INVALID_PACKET;
+   } 
+
+   /* header ok? */
+   if ((err = packet_valid_header((unsigned char *)sig, PACKET_SECT_DH, PACKET_SUB_SIGNED)) != CRYPT_OK) {
+      return err;
+   }
+   
+   /* get hash out of packet */
+   y = PACKET_SIZE;
+
+   /* init all bignums */
+   if ((err = mp_init_multi(&a, &p, &b, &g, &m, &tmp, NULL)) != MP_OKAY) { 
+      return mpi_to_ltc_error(err);
+   }
+
+   /* load a and b */
+   INPUT_BIGNUM(&a, sig, x, y, siglen);
+   INPUT_BIGNUM(&b, sig, x, y, siglen);
+
+   /* load p and g */
+   if ((err = mp_read_radix(&p, sets[key->idx].prime, 64)) != MP_OKAY)              { goto error1; }
+   if ((err = mp_read_radix(&g, sets[key->idx].base, 64)) != MP_OKAY)               { goto error1; }
+
+   /* load m */
+   if ((err = mp_read_unsigned_bin(&m, (unsigned char *)hash, hashlen)) != MP_OKAY) { goto error1; }
+
+   /* find g^m mod p */
+   if ((err = mp_exptmod(&g, &m, &p, &m)) != MP_OKAY)                { goto error1; } /* m = g^m mod p */
+
+   /* find y^a * a^b */
+   if ((err = mp_exptmod(&key->y, &a, &p, &tmp)) != MP_OKAY)         { goto error1; } /* tmp = y^a mod p */
+   if ((err = mp_exptmod(&a, &b, &p, &a)) != MP_OKAY)                { goto error1; } /* a = a^b mod p */
+   if ((err = mp_mulmod(&a, &tmp, &p, &a)) != MP_OKAY)               { goto error1; } /* a = y^a * a^b mod p */
+
+   /* y^a * a^b == g^m ??? */
+   if (mp_cmp(&a, &m) == 0) {
+      *stat = 1;
+   }
+
+   /* clean up */
+   err = CRYPT_OK;
+   goto done;
+error1:
+   err = mpi_to_ltc_error(err);
+error:
+done:
+   mp_clear_multi(&tmp, &m, &g, &p, &b, &a, NULL);
+   return err;
+}
+
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/dh/dh_sys.c,v $ */
+/* $Revision: 1.3 $ */
+/* $Date: 2005/05/05 14:35:59 $ */