1 files changed, 72 insertions, 0 deletions
diff --git a/src/pk/dsa/dsa_shared_secret.c b/src/pk/dsa/dsa_shared_secret.c
new file mode 100644
index 0000000..570d637
--- /dev/null
+++ b/src/pk/dsa/dsa_shared_secret.c
@@ -0,0 +1,72 @@
+/* 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, tomstdenis@gmail.com, http://libtomcrypt.com
+ */
+#include "tomcrypt.h"
+
+/**
+  @file dsa_shared_secret.c
+  DSA Crypto, Tom St Denis
+*/  
+
+#ifdef MDSA
+
+/**
+  Create a DSA shared secret between two keys
+  @param private_key      The private DSA key (the exponent)
+  @param base             The base of the exponentiation (allows this to be used for both encrypt and decrypt) 
+  @param public_key       The public key
+  @param out              [out] Destination of the shared secret
+  @param outlen           [in/out] The max size and resulting size of the shared secret
+  @return CRYPT_OK if successful
+*/
+int dsa_shared_secret(void          *private_key, void *base,
+                      dsa_key       *public_key,
+                      unsigned char *out,         unsigned long *outlen)
+{
+   unsigned long  x;
+   void          *res;
+   int            err;
+
+   LTC_ARGCHK(private_key != NULL);
+   LTC_ARGCHK(public_key  != NULL);
+   LTC_ARGCHK(out         != NULL);
+   LTC_ARGCHK(outlen      != NULL);
+
+   /* make new point */
+   if ((err = mp_init(&res)) != CRYPT_OK) {
+      return err;
+   }
+
+   if ((err = mp_exptmod(base, private_key, public_key->p, res)) != CRYPT_OK) {
+      mp_clear(res);
+      return err;
+   }
+   
+   x = (unsigned long)mp_unsigned_bin_size(res);
+   if (*outlen < x) {
+      *outlen = x;
+      err = CRYPT_BUFFER_OVERFLOW;
+      goto done;
+   }
+   zeromem(out, x);
+   if ((err = mp_to_unsigned_bin(res, out + (x - mp_unsigned_bin_size(res))))   != CRYPT_OK)          { goto done; }
+
+   err     = CRYPT_OK;
+   *outlen = x;
+done:
+   mp_clear(res);
+   return err;
+}
+
+#endif
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_shared_secret.c,v $ */
+/* $Revision: 1.7 $ */
+/* $Date: 2006/12/04 03:18:43 $ */
+