1 files changed, 90 insertions, 0 deletions
diff --git a/src/libstate/engine/gnump/gmp_elg.cpp b/src/libstate/engine/gnump/gmp_elg.cpp
new file mode 100644
index 000000000..63e9440ff
--- /dev/null
+++ b/src/libstate/engine/gnump/gmp_elg.cpp
@@ -0,0 +1,90 @@
+/*************************************************
+* GMP ElGamal Engine Source File                 *
+* (C) 1999-2007 Jack Lloyd                       *
+*************************************************/
+
+#include <botan/eng_gmp.h>
+#include <botan/gmp_wrap.h>
+#include <gmp.h>
+
+namespace Botan {
+
+#if defined(BOTAN_HAS_ELGAMAL)
+
+namespace {
+
+/*************************************************
+* GMP ElGamal Operation                          *
+*************************************************/
+class GMP_ELG_Op : public ELG_Operation
+   {
+   public:
+      SecureVector<byte> encrypt(const byte[], u32bit, const BigInt&) const;
+      BigInt decrypt(const BigInt&, const BigInt&) const;
+
+      ELG_Operation* clone() const { return new GMP_ELG_Op(*this); }
+
+      GMP_ELG_Op(const DL_Group& group, const BigInt& y1, const BigInt& x1) :
+         x(x1), y(y1), g(group.get_g()), p(group.get_p()) {}
+   private:
+      GMP_MPZ x, y, g, p;
+   };
+
+/*************************************************
+* GMP ElGamal Encrypt Operation                  *
+*************************************************/
+SecureVector<byte> GMP_ELG_Op::encrypt(const byte in[], u32bit length,
+                                       const BigInt& k_bn) const
+   {
+   GMP_MPZ i(in, length);
+
+   if(mpz_cmp(i.value, p.value) >= 0)
+      throw Invalid_Argument("GMP_ELG_Op: Input is too large");
+
+   GMP_MPZ a, b, k(k_bn);
+
+   mpz_powm(a.value, g.value, k.value, p.value);
+   mpz_powm(b.value, y.value, k.value, p.value);
+   mpz_mul(b.value, b.value, i.value);
+   mpz_mod(b.value, b.value, p.value);
+
+   const u32bit p_bytes = p.bytes();
+   SecureVector<byte> output(2*p_bytes);
+   a.encode(output, p_bytes);
+   b.encode(output + p_bytes, p_bytes);
+   return output;
+   }
+
+/*************************************************
+* GMP ElGamal Decrypt Operation                  *
+*************************************************/
+BigInt GMP_ELG_Op::decrypt(const BigInt& a_bn, const BigInt& b_bn) const
+   {
+   if(mpz_cmp_ui(x.value, 0) == 0)
+      throw Internal_Error("GMP_ELG_Op::decrypt: No private key");
+
+   GMP_MPZ a(a_bn), b(b_bn);
+
+   if(mpz_cmp(a.value, p.value) >= 0 || mpz_cmp(b.value, p.value) >= 0)
+      throw Invalid_Argument("GMP_ELG_Op: Invalid message");
+
+   mpz_powm(a.value, a.value, x.value, p.value);
+   mpz_invert(a.value, a.value, p.value);
+   mpz_mul(a.value, a.value, b.value);
+   mpz_mod(a.value, a.value, p.value);
+   return a.to_bigint();
+   }
+
+}
+
+/*************************************************
+* Acquire an ElGamal op                          *
+*************************************************/
+ELG_Operation* GMP_Engine::elg_op(const DL_Group& group, const BigInt& y,
+                                  const BigInt& x) const
+   {
+   return new GMP_ELG_Op(group, y, x);
+   }
+#endif
+
+}