--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/dsa/dsa_decrypt_key.c	Sat Feb 03 08:20:30 2007 +0000
@@ -0,0 +1,139 @@
+/* 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.com
+ */
+#include "tomcrypt.h"
+
+/**
+  @file dsa_decrypt_key.c
+  DSA Crypto, Tom St Denis
+*/  
+
+#ifdef MDSA
+
+/**
+  Decrypt an DSA encrypted key
+  @param in       The ciphertext
+  @param inlen    The length of the ciphertext (octets)
+  @param out      [out] The plaintext
+  @param outlen   [in/out] The max size and resulting size of the plaintext
+  @param key      The corresponding private DSA key
+  @return CRYPT_OK if successful
+*/
+int dsa_decrypt_key(const unsigned char *in,  unsigned long  inlen,
+                          unsigned char *out, unsigned long *outlen, 
+                          dsa_key *key)
+{
+   unsigned char  *skey, *expt;
+   void           *g_pub;
+   unsigned long  x, y, hashOID[32];
+   int            hash, err;
+   ltc_asn1_list  decode[3];
+
+   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;
+   }
+   
+   /* decode to find out hash */
+   LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0]));
+ 
+   if ((err = der_decode_sequence(in, inlen, decode, 1)) != CRYPT_OK) {
+      return err;
+   }
+
+   hash = find_hash_oid(hashOID, decode[0].size);                   
+   if (hash_is_valid(hash) != CRYPT_OK) {
+      return CRYPT_INVALID_PACKET;
+   }
+
+   /* we now have the hash! */
+   
+   if ((err = mp_init(&g_pub)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* allocate memory */
+   expt   = XMALLOC(mp_unsigned_bin_size(key->p) + 1);
+   skey   = XMALLOC(MAXBLOCKSIZE);
+   if (expt == NULL || skey == NULL) {
+      if (expt != NULL) {
+         XFREE(expt);
+      }
+      if (skey != NULL) {
+         XFREE(skey);
+      }
+      mp_clear(g_pub);
+      return CRYPT_MEM;
+   }
+   
+   LTC_SET_ASN1(decode, 1, LTC_ASN1_INTEGER,          g_pub,      1UL);
+   LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING,      skey,      MAXBLOCKSIZE);
+
+   /* read the structure in now */
+   if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) {
+      goto LBL_ERR;
+   }
+
+   /* make shared key */
+   x = mp_unsigned_bin_size(key->p) + 1;
+   if ((err = dsa_shared_secret(key->x, g_pub, key, expt, &x)) != CRYPT_OK) {
+      goto LBL_ERR;
+   }
+
+   y = MIN(mp_unsigned_bin_size(key->p) + 1, MAXBLOCKSIZE);
+   if ((err = hash_memory(hash, expt, x, expt, &y)) != CRYPT_OK) {
+      goto LBL_ERR;
+   }
+
+   /* ensure the hash of the shared secret is at least as big as the encrypt itself */
+   if (decode[2].size > y) {
+      err = CRYPT_INVALID_PACKET;
+      goto LBL_ERR;
+   }
+
+   /* avoid buffer overflow */
+   if (*outlen < decode[2].size) {
+      *outlen = decode[2].size;
+      err = CRYPT_BUFFER_OVERFLOW;
+      goto LBL_ERR;
+   }
+
+   /* Decrypt the key */
+   for (x = 0; x < decode[2].size; x++) {
+     out[x] = expt[x] ^ skey[x];
+   }
+   *outlen = x;
+
+   err = CRYPT_OK;
+LBL_ERR:
+#ifdef LTC_CLEAN_STACK
+   zeromem(expt,   mp_unsigned_bin_size(key->p) + 1);
+   zeromem(skey,   MAXBLOCKSIZE);
+#endif
+
+   XFREE(expt);
+   XFREE(skey);
+  
+   mp_clear(g_pub);
+
+   return err;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_decrypt_key.c,v $ */
+/* $Revision: 1.9 $ */
+/* $Date: 2006/12/04 03:18:43 $ */
+