--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/ecc/ecc_decrypt_key.c	Thu Jan 11 02:41:05 2007 +0000
@@ -0,0 +1,150 @@
+/* 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
+ */
+
+/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
+ *
+ * All curves taken from NIST recommendation paper of July 1999
+ * Available at http://csrc.nist.gov/cryptval/dss.htm
+ */
+#include "tomcrypt.h"
+
+/**
+  @file ecc_decrypt_key.c
+  ECC Crypto, Tom St Denis
+*/  
+
+#ifdef MECC
+
+/**
+  Decrypt an ECC 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 ECC key
+  @return CRYPT_OK if successful
+*/
+int ecc_decrypt_key(const unsigned char *in,  unsigned long  inlen,
+                          unsigned char *out, unsigned long *outlen, 
+                          ecc_key *key)
+{
+   unsigned char *ecc_shared, *skey, *pub_expt;
+   unsigned long  x, y, hashOID[32];
+   int            hash, err;
+   ecc_key        pubkey;
+   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! */
+
+   /* allocate memory */
+   pub_expt   = XMALLOC(ECC_BUF_SIZE);
+   ecc_shared = XMALLOC(ECC_BUF_SIZE);
+   skey       = XMALLOC(MAXBLOCKSIZE);
+   if (pub_expt == NULL || ecc_shared == NULL || skey == NULL) {
+      if (pub_expt != NULL) {
+         XFREE(pub_expt);
+      }
+      if (ecc_shared != NULL) {
+         XFREE(ecc_shared);
+      }
+      if (skey != NULL) {
+         XFREE(skey);
+      }
+      return CRYPT_MEM;
+   }
+   LTC_SET_ASN1(decode, 1, LTC_ASN1_OCTET_STRING,      pub_expt,  ECC_BUF_SIZE);
+   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;
+   }
+
+   /* import ECC key from packet */
+   if ((err = ecc_import(decode[1].data, decode[1].size, &pubkey)) != CRYPT_OK) {
+      goto LBL_ERR;
+   }
+
+   /* make shared key */
+   x = ECC_BUF_SIZE;
+   if ((err = ecc_shared_secret(key, &pubkey, ecc_shared, &x)) != CRYPT_OK) {
+      ecc_free(&pubkey);
+      goto LBL_ERR;
+   }
+   ecc_free(&pubkey);
+
+   y = MIN(ECC_BUF_SIZE, MAXBLOCKSIZE);
+   if ((err = hash_memory(hash, ecc_shared, x, ecc_shared, &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] = skey[x] ^ ecc_shared[x];
+   }
+   *outlen = x;
+
+   err = CRYPT_OK;
+LBL_ERR:
+#ifdef LTC_CLEAN_STACK
+   zeromem(pub_expt,   ECC_BUF_SIZE);
+   zeromem(ecc_shared, ECC_BUF_SIZE);
+   zeromem(skey,       MAXBLOCKSIZE);
+#endif
+
+   XFREE(pub_expt);
+   XFREE(ecc_shared);
+   XFREE(skey);
+
+   return err;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_decrypt_key.c,v $ */
+/* $Revision: 1.5 $ */
+/* $Date: 2006/06/16 21:53:41 $ */
+