Add Curve25519 based on curve25519-donna by Adam Langley.

This uses only the c64 version from curve25519-donna; on systems that
don't have a native uint128_t type, a donna128 type stands in for just
enough 128-bit operations to satisfy donna.cpp

13 files changed, 1015 insertions, 0 deletions

diff --git a/src/cmd/keygen.cpp b/src/cmd/keygen.cpp
index 3054b98ee..ae23ce45e 100644
--- a/src/cmd/keygen.cpp
+++ b/src/cmd/keygen.cpp
@@ -17,6 +17,10 @@
 #include <botan/ecdsa.h>
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+#include <botan/curve25519.h>
+#endif
+
 using namespace Botan;
 
 namespace {
@@ -55,6 +59,11 @@ Private_Key* gen_key(RandomNumberGenerator& rng, const std::string& algo, size_t
       }
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+   if(algo == "curve25519")
+      return new Curve25519_PrivateKey(rng);
+#endif
+
    throw std::runtime_error("Unknown algorithm " + algo);
    }
 
diff --git a/src/cmd/speed_pk.cpp b/src/cmd/speed_pk.cpp
index 6d20065cc..d978cde9d 100644
--- a/src/cmd/speed_pk.cpp
+++ b/src/cmd/speed_pk.cpp
@@ -32,6 +32,10 @@
   #include <botan/dh.h>
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+  #include <botan/curve25519.h>
+#endif
+
 #if defined(BOTAN_HAS_NYBERG_RUEPPEL)
   #include <botan/nr.h>
 #endif
@@ -507,6 +511,53 @@ void benchmark_dsa_nr(RandomNumberGenerator& rng,
 #endif
    }
 
+#if defined(BOTAN_HAS_CURVE_25519)
+void benchmark_curve25519(RandomNumberGenerator& rng,
+                          double seconds,
+                          Benchmark_Report& report)
+   {
+   Timer keygen_timer("keygen");
+   Timer kex_timer("key exchange");
+
+   while(kex_timer.seconds() < seconds)
+      {
+      keygen_timer.start();
+      Curve25519_PrivateKey key1(rng);
+      keygen_timer.stop();
+
+      keygen_timer.start();
+      Curve25519_PrivateKey key2(rng);
+      keygen_timer.stop();
+
+      PK_Key_Agreement ka1(key1, "KDF2(SHA-256)");
+      PK_Key_Agreement ka2(key2, "KDF2(SHA-256)");
+
+      SymmetricKey secret1, secret2;
+
+      for(size_t i = 0; i != 1000; ++i)
+         {
+         if(kex_timer.seconds() > seconds)
+            break;
+
+         kex_timer.start();
+         secret1 = ka1.derive_key(32, key2.public_value());
+         kex_timer.stop();
+
+         kex_timer.start();
+         secret2 = ka2.derive_key(32, key1.public_value());
+         kex_timer.stop();
+
+         if(secret1 != secret2)
+            std::cerr << "Curve25519 secrets did not match\n";
+         }
+      }
+
+   const std::string nm = "Curve25519";
+   report.report(nm, keygen_timer);
+   report.report(nm, kex_timer);
+   }
+#endif
+
 #ifdef BOTAN_HAS_DIFFIE_HELLMAN
 void benchmark_dh(RandomNumberGenerator& rng,
                   double seconds,
@@ -793,6 +844,11 @@ void bench_pk(RandomNumberGenerator& rng,
       benchmark_gost_3410(rng, seconds, report);
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+   if(algo == "All" || algo == "Curve25519")
+      benchmark_curve25519(rng, seconds, report);
+#endif
+
 #if defined(BOTAN_HAS_DIFFIE_HELLMAN)
    if(algo == "All" || algo == "DH")
       benchmark_dh(rng, seconds, report);
diff --git a/src/lib/engine/core_engine/def_pk_ops.cpp b/src/lib/engine/core_engine/def_pk_ops.cpp
index b21877b16..cbe7d27fc 100644
--- a/src/lib/engine/core_engine/def_pk_ops.cpp
+++ b/src/lib/engine/core_engine/def_pk_ops.cpp
@@ -43,6 +43,10 @@
   #include <botan/ecdh.h>
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+  #include <botan/curve25519.h>
+#endif
+
 namespace Botan {
 
 PK_Ops::Encryption*
@@ -90,6 +94,11 @@ Core_Engine::get_key_agreement_op(const Private_Key& key, RandomNumberGenerator&
       return new ECDH_KA_Operation(*ecdh);
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+   if(const Curve25519_PrivateKey* c25519 = dynamic_cast<const Curve25519_PrivateKey*>(&key))
+      return new Curve25519_KA_Operation(*c25519);
+#endif
+
    return nullptr;
    }
 
diff --git a/src/lib/pubkey/curve25519/curve25519.cpp b/src/lib/pubkey/curve25519/curve25519.cpp
new file mode 100644
index 000000000..fe30e37d9
--- /dev/null
+++ b/src/lib/pubkey/curve25519/curve25519.cpp
@@ -0,0 +1,115 @@
+/*
+* Curve25519
+* (C) 2014 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/curve25519.h>
+#include <botan/ber_dec.h>
+#include <botan/der_enc.h>
+
+namespace Botan {
+
+namespace {
+
+void size_check(size_t size, const char* thing)
+   {
+   if(size != 32)
+      throw Decoding_Error("Invalid size " + std::to_string(size) + " for Curve25519 " + thing);
+   }
+
+secure_vector<byte> curve25519(const secure_vector<byte>& secret,
+                               const byte pubval[32])
+   {
+   secure_vector<byte> out(32);
+   const int rc = curve25519_donna(&out[0], &secret[0], &pubval[0]);
+   BOTAN_ASSERT_EQUAL(rc, 0, "Return value of curve25519_donna is ok");
+   return out;
+   }
+
+secure_vector<byte> curve25519_basepoint(const secure_vector<byte>& secret)
+   {
+   const byte basepoint[32] = { 9 };
+   return curve25519(secret, basepoint);
+   }
+
+}
+
+AlgorithmIdentifier Curve25519_PublicKey::algorithm_identifier() const
+   {
+   return AlgorithmIdentifier(get_oid(), AlgorithmIdentifier::USE_NULL_PARAM);
+   }
+
+bool Curve25519_PublicKey::check_key(RandomNumberGenerator&, bool) const
+   {
+   return true; // no tests possible?
+   }
+
+Curve25519_PublicKey::Curve25519_PublicKey(const AlgorithmIdentifier&,
+                                           const secure_vector<byte>& key_bits)
+   {
+   BER_Decoder(key_bits)
+      .start_cons(SEQUENCE)
+      .decode(m_public, OCTET_STRING)
+      .verify_end()
+   .end_cons();
+
+   size_check(m_public.size(), "public key");
+   }
+
+std::vector<byte> Curve25519_PublicKey::x509_subject_public_key() const
+   {
+   return DER_Encoder()
+      .start_cons(SEQUENCE)
+        .encode(m_public, OCTET_STRING)
+      .end_cons()
+      .get_contents_unlocked();
+   }
+
+Curve25519_PrivateKey::Curve25519_PrivateKey(RandomNumberGenerator& rng)
+   {
+   m_private = rng.random_vec(32);
+   m_public = curve25519_basepoint(m_private);
+   }
+
+Curve25519_PrivateKey::Curve25519_PrivateKey(const AlgorithmIdentifier&,
+                                             const secure_vector<byte>& key_bits,
+                                             RandomNumberGenerator& rng)
+   {
+   BER_Decoder(key_bits)
+      .start_cons(SEQUENCE)
+      .decode(m_public, OCTET_STRING)
+      .decode(m_private, OCTET_STRING)
+      .verify_end()
+   .end_cons();
+
+   size_check(m_public.size(), "public key");
+   size_check(m_private.size(), "private key");
+
+   load_check(rng);
+   }
+
+secure_vector<byte> Curve25519_PrivateKey::pkcs8_private_key() const
+   {
+   return DER_Encoder()
+      .start_cons(SEQUENCE)
+        .encode(m_public, OCTET_STRING)
+        .encode(m_private, OCTET_STRING)
+      .end_cons()
+      .get_contents();
+   }
+
+bool Curve25519_PrivateKey::check_key(RandomNumberGenerator&, bool) const
+   {
+   return curve25519_basepoint(m_private) == m_public;
+   }
+
+secure_vector<byte> Curve25519_PrivateKey::agree(const byte w[], size_t w_len) const
+   {
+   size_check(w_len, "public value");
+
+   return curve25519(m_private, w);
+   }
+
+}
diff --git a/src/lib/pubkey/curve25519/curve25519.h b/src/lib/pubkey/curve25519/curve25519.h
new file mode 100644
index 000000000..718ebf05d
--- /dev/null
+++ b/src/lib/pubkey/curve25519/curve25519.h
@@ -0,0 +1,94 @@
+/*
+* Curve25519
+* (C) 2014 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_CURVE_25519_H__
+#define BOTAN_CURVE_25519_H__
+
+#include <botan/pk_keys.h>
+#include <botan/pk_ops.h>
+
+namespace Botan {
+
+class BOTAN_DLL Curve25519_PublicKey : public virtual Public_Key
+   {
+   public:
+      std::string algo_name() const override { return "Curve25519"; }
+
+      size_t estimated_strength() const override { return 128; }
+
+      size_t max_input_bits() const { return 256; }
+
+      bool check_key(RandomNumberGenerator& rng, bool strong) const override;
+
+      AlgorithmIdentifier algorithm_identifier() const override;
+
+      std::vector<byte> x509_subject_public_key() const override;
+
+      std::vector<byte> public_value() const { return unlock(m_public); }
+
+      Curve25519_PublicKey(const AlgorithmIdentifier& alg_id,
+                           const secure_vector<byte>& key_bits);
+
+      Curve25519_PublicKey(const secure_vector<byte>& pub) : m_public(pub) {}
+   protected:
+      Curve25519_PublicKey() {}
+      secure_vector<byte> m_public;
+   };
+
+class BOTAN_DLL Curve25519_PrivateKey : public Curve25519_PublicKey,
+                                        public virtual Private_Key,
+                                        public virtual PK_Key_Agreement_Key
+   {
+   public:
+      Curve25519_PrivateKey(const AlgorithmIdentifier& alg_id,
+                            const secure_vector<byte>& key_bits,
+                            RandomNumberGenerator& rng);
+
+      Curve25519_PrivateKey(RandomNumberGenerator& rng);
+
+      Curve25519_PrivateKey(const secure_vector<byte>& secret_key);
+
+      std::vector<byte> public_value() const override { return Curve25519_PublicKey::public_value(); }
+
+      secure_vector<byte> agree(const byte w[], size_t w_len) const;
+
+      const secure_vector<byte>& get_x() const { return m_private; }
+
+      secure_vector<byte> pkcs8_private_key() const override;
+
+      bool check_key(RandomNumberGenerator& rng, bool strong) const override;
+   private:
+      secure_vector<byte> m_private;
+   };
+
+/**
+* Curve25519 operation
+*/
+class BOTAN_DLL Curve25519_KA_Operation : public PK_Ops::Key_Agreement
+   {
+   public:
+      Curve25519_KA_Operation(const Curve25519_PrivateKey& key) : m_key(key) {}
+
+      secure_vector<byte> agree(const byte w[], size_t w_len)
+         {
+         return m_key.agree(w, w_len);
+         }
+   private:
+      const Curve25519_PrivateKey& m_key;
+   };
+
+/*
+* The types above are just wrappers for curve25519_donna, plus defining
+* encodings for public and private keys.
+*/
+int BOTAN_DLL curve25519_donna(uint8_t mypublic[32],
+                               const uint8_t secret[32],
+                               const uint8_t basepoint[32]);
+
+}
+
+#endif
diff --git a/src/lib/pubkey/curve25519/donna.cpp b/src/lib/pubkey/curve25519/donna.cpp
new file mode 100644
index 000000000..29d40ce13
--- /dev/null
+++ b/src/lib/pubkey/curve25519/donna.cpp
@@ -0,0 +1,456 @@
+/*
+* curve25519-donna-c64.c from github.com/agl/curve25519-donna
+* revision 80ad9b9930c9baef5829dd2a235b6b7646d32a8e
+*/
+
+/* Copyright 2008, Google Inc.
+ * All rights reserved.
+ *
+ * Code released into the public domain.
+ *
+ * curve25519-donna: Curve25519 elliptic curve, public key function
+ *
+ * http://code.google.com/p/curve25519-donna/
+ *
+ * Adam Langley <[email protected]>
+ *
+ * Derived from public domain C code by Daniel J. Bernstein <[email protected]>
+ *
+ * More information about curve25519 can be found here
+ *   http://cr.yp.to/ecdh.html
+ *
+ * djb's sample implementation of curve25519 is written in a special assembly
+ * language called qhasm and uses the floating point registers.
+ *
+ * This is, almost, a clean room reimplementation from the curve25519 paper. It
+ * uses many of the tricks described therein. Only the crecip function is taken
+ * from the sample implementation.
+ */
+
+#include <botan/curve25519.h>
+#include <botan/mul128.h>
+#include <botan/loadstor.h>
+#include <string.h>
+
+#if !defined(BOTAN_TARGET_HAS_NATIVE_UINT128)
+  #include <botan/internal/donna128.h>
+#endif
+
+namespace Botan {
+
+typedef byte u8;
+typedef u64bit limb;
+typedef limb felem[5];
+
+#if !defined(BOTAN_TARGET_HAS_NATIVE_UINT128)
+typedef donna128 uint128_t;
+
+#else
+
+inline u64bit carry_shift(const uint128_t a, size_t shift)
+   {
+   return static_cast<u64bit>(a >> shift);
+   }
+
+inline u64bit combine_lower(const uint128_t a, size_t s1,
+                            const uint128_t b, size_t s2)
+   {
+   return static_cast<u64bit>((a >> s1) | (b << s2));
+   }
+
+#endif
+
+/* Sum two numbers: output += in */
+static inline void
+fsum(limb *output, const limb *in) {
+  output[0] += in[0];
+  output[1] += in[1];
+  output[2] += in[2];
+  output[3] += in[3];
+  output[4] += in[4];
+}
+
+/* Find the difference of two numbers: output = in - output
+ * (note the order of the arguments!)
+ *
+ * Assumes that out[i] < 2**52
+ * On return, out[i] < 2**55
+ */
+static inline void
+fdifference_backwards(felem out, const felem in) {
+  /* 152 is 19 << 3 */
+  static const limb two54m152 = (static_cast<limb>(1) << 54) - 152;
+  static const limb two54m8 = (static_cast<limb>(1) << 54) - 8;
+
+  out[0] = in[0] + two54m152 - out[0];
+  out[1] = in[1] + two54m8 - out[1];
+  out[2] = in[2] + two54m8 - out[2];
+  out[3] = in[3] + two54m8 - out[3];
+  out[4] = in[4] + two54m8 - out[4];
+}
+
+/* Multiply a number by a scalar: output = in * scalar */
+static inline void
+fscalar_product(felem output, const felem in, const limb scalar) {
+  uint128_t a = uint128_t(in[0]) * scalar;
+  output[0] = a & 0x7ffffffffffff;
+
+  a = uint128_t(in[1]) * scalar + carry_shift(a, 51);
+  output[1] = a & 0x7ffffffffffff;
+
+  a = uint128_t(in[2]) * scalar + carry_shift(a, 51);
+  output[2] = a & 0x7ffffffffffff;
+
+  a = uint128_t(in[3]) * scalar + carry_shift(a, 51);
+  output[3] = a & 0x7ffffffffffff;
+
+  a = uint128_t(in[4]) * scalar + carry_shift(a, 51);
+  output[4] = a & 0x7ffffffffffff;
+
+  output[0] += carry_shift(a, 51) * 19;
+}
+
+/* Multiply two numbers: output = in2 * in
+ *
+ * output must be distinct to both inputs. The inputs are reduced coefficient
+ * form, the output is not.
+ *
+ * Assumes that in[i] < 2**55 and likewise for in2.
+ * On return, output[i] < 2**52
+ */
+static inline void
+fmul(felem output, const felem in2, const felem in) {
+  uint128_t t[5];
+  limb r0,r1,r2,r3,r4,s0,s1,s2,s3,s4,c;
+
+  r0 = in[0];
+  r1 = in[1];
+  r2 = in[2];
+  r3 = in[3];
+  r4 = in[4];
+
+  s0 = in2[0];
+  s1 = in2[1];
+  s2 = in2[2];
+  s3 = in2[3];
+  s4 = in2[4];
+
+  t[0]  =  uint128_t(r0) * s0;
+  t[1]  =  uint128_t(r0) * s1 + uint128_t(r1) * s0;
+  t[2]  =  uint128_t(r0) * s2 + uint128_t(r2) * s0 + uint128_t(r1) * s1;
+  t[3]  =  uint128_t(r0) * s3 + uint128_t(r3) * s0 + uint128_t(r1) * s2 + uint128_t(r2) * s1;
+  t[4]  =  uint128_t(r0) * s4 + uint128_t(r4) * s0 + uint128_t(r3) * s1 + uint128_t(r1) * s3 + uint128_t(r2) * s2;
+
+  r4 *= 19;
+  r1 *= 19;
+  r2 *= 19;
+  r3 *= 19;
+
+  t[0] += uint128_t(r4) * s1 + uint128_t(r1) * s4 + uint128_t(r2) * s3 + uint128_t(r3) * s2;
+  t[1] += uint128_t(r4) * s2 + uint128_t(r2) * s4 + uint128_t(r3) * s3;
+  t[2] += uint128_t(r4) * s3 + uint128_t(r3) * s4;
+  t[3] += uint128_t(r4) * s4;
+
+                  r0 = t[0] & 0x7ffffffffffff; c = carry_shift(t[0], 51);
+  t[1] += c;      r1 = t[1] & 0x7ffffffffffff; c = carry_shift(t[1], 51);
+  t[2] += c;      r2 = t[2] & 0x7ffffffffffff; c = carry_shift(t[2], 51);
+  t[3] += c;      r3 = t[3] & 0x7ffffffffffff; c = carry_shift(t[3], 51);
+  t[4] += c;      r4 = t[4] & 0x7ffffffffffff; c = carry_shift(t[4], 51);
+  r0 +=   c * 19; c = carry_shift(r0, 51); r0 = r0 & 0x7ffffffffffff;
+  r1 +=   c;      c = carry_shift(r1, 51); r1 = r1 & 0x7ffffffffffff;
+  r2 +=   c;
+
+  output[0] = r0;
+  output[1] = r1;
+  output[2] = r2;
+  output[3] = r3;
+  output[4] = r4;
+}
+
+static inline void fsquare_times(felem output, const felem in, limb count) {
+  uint128_t t[5];
+  limb r0,r1,r2,r3,r4,c;
+  limb d0,d1,d2,d4,d419;
+
+  r0 = in[0];
+  r1 = in[1];
+  r2 = in[2];
+  r3 = in[3];
+  r4 = in[4];
+
+  do {
+    d0 = r0 * 2;
+    d1 = r1 * 2;
+    d2 = r2 * 2 * 19;
+    d419 = r4 * 19;
+    d4 = d419 * 2;
+
+    t[0] = uint128_t(r0) * r0 + uint128_t(d4) * r1 + uint128_t(d2) * (r3     );
+    t[1] = uint128_t(d0) * r1 + uint128_t(d4) * r2 + uint128_t(r3) * (r3 * 19);
+    t[2] = uint128_t(d0) * r2 + uint128_t(r1) * r1 + uint128_t(d4) * (r3     );
+    t[3] = uint128_t(d0) * r3 + uint128_t(d1) * r2 + uint128_t(r4) * (d419   );
+    t[4] = uint128_t(d0) * r4 + uint128_t(d1) * r3 + uint128_t(r2) * (r2     );
+
+                    r0 = t[0] & 0x7ffffffffffff; c = carry_shift(t[0], 51);
+    t[1] += c;      r1 = t[1] & 0x7ffffffffffff; c = carry_shift(t[1], 51);
+    t[2] += c;      r2 = t[2] & 0x7ffffffffffff; c = carry_shift(t[2], 51);
+    t[3] += c;      r3 = t[3] & 0x7ffffffffffff; c = carry_shift(t[3], 51);
+    t[4] += c;      r4 = t[4] & 0x7ffffffffffff; c = carry_shift(t[4], 51);
+    r0 +=   c * 19; c = r0 >> 51; r0 = r0 & 0x7ffffffffffff;
+    r1 +=   c;      c = r1 >> 51; r1 = r1 & 0x7ffffffffffff;
+    r2 +=   c;
+  } while(--count);
+
+  output[0] = r0;
+  output[1] = r1;
+  output[2] = r2;
+  output[3] = r3;
+  output[4] = r4;
+}
+
+/* Load a little-endian 64-bit number  */
+static limb
+load_limb(const u8 *in) {
+  return load_le<u64bit>(in, 0);
+}
+
+static void
+store_limb(u8 *out, limb in) {
+  store_le(in, out);
+}
+
+/* Take a little-endian, 32-byte number and expand it into polynomial form */
+static void
+fexpand(limb *output, const u8 *in) {
+  output[0] = load_limb(in) & 0x7ffffffffffff;
+  output[1] = (load_limb(in+6) >> 3) & 0x7ffffffffffff;
+  output[2] = (load_limb(in+12) >> 6) & 0x7ffffffffffff;
+  output[3] = (load_limb(in+19) >> 1) & 0x7ffffffffffff;
+  output[4] = (load_limb(in+24) >> 12) & 0x7ffffffffffff;
+}
+
+/* Take a fully reduced polynomial form number and contract it into a
+ * little-endian, 32-byte array
+ */
+static void
+fcontract(u8 *output, const felem input) {
+  uint128_t t[5];
+
+  t[0] = input[0];
+  t[1] = input[1];
+  t[2] = input[2];
+  t[3] = input[3];
+  t[4] = input[4];
+
+  t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+  t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+  t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+  t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+  t[0] += (t[4] >> 51) * 19; t[4] &= 0x7ffffffffffff;
+
+  t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+  t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+  t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+  t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+  t[0] += (t[4] >> 51) * 19; t[4] &= 0x7ffffffffffff;
+
+  /* now t is between 0 and 2^255-1, properly carried. */
+  /* case 1: between 0 and 2^255-20. case 2: between 2^255-19 and 2^255-1. */
+
+  t[0] += 19;
+
+  t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+  t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+  t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+  t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+  t[0] += (t[4] >> 51) * 19; t[4] &= 0x7ffffffffffff;
+
+  /* now between 19 and 2^255-1 in both cases, and offset by 19. */
+
+  t[0] += 0x8000000000000 - 19;
+  t[1] += 0x8000000000000 - 1;
+  t[2] += 0x8000000000000 - 1;
+  t[3] += 0x8000000000000 - 1;
+  t[4] += 0x8000000000000 - 1;
+
+  /* now between 2^255 and 2^256-20, and offset by 2^255. */
+
+  t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+  t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+  t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+  t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+  t[4] &= 0x7ffffffffffff;
+
+  store_limb(output,    combine_lower(t[0], 0, t[1], 51));
+  store_limb(output+8,  combine_lower(t[1], 13, t[2], 38));
+  store_limb(output+16, combine_lower(t[2], 26, t[3], 25));
+  store_limb(output+24, combine_lower(t[3], 39, t[4], 12));
+}
+
+/* Input: Q, Q', Q-Q'
+ * Output: 2Q, Q+Q'
+ *
+ *   x2 z3: long form
+ *   x3 z3: long form
+ *   x z: short form, destroyed
+ *   xprime zprime: short form, destroyed
+ *   qmqp: short form, preserved
+ */
+static void
+fmonty(limb *x2, limb *z2, /* output 2Q */
+       limb *x3, limb *z3, /* output Q + Q' */
+       limb *x, limb *z,   /* input Q */
+       limb *xprime, limb *zprime, /* input Q' */
+       const limb *qmqp /* input Q - Q' */) {
+  limb origx[5], origxprime[5], zzz[5], xx[5], zz[5], xxprime[5],
+        zzprime[5], zzzprime[5];
+
+  memcpy(origx, x, 5 * sizeof(limb));
+  fsum(x, z);
+  fdifference_backwards(z, origx);  // does x - z
+
+  memcpy(origxprime, xprime, sizeof(limb) * 5);
+  fsum(xprime, zprime);
+  fdifference_backwards(zprime, origxprime);
+  fmul(xxprime, xprime, z);
+  fmul(zzprime, x, zprime);
+  memcpy(origxprime, xxprime, sizeof(limb) * 5);
+  fsum(xxprime, zzprime);
+  fdifference_backwards(zzprime, origxprime);
+  fsquare_times(x3, xxprime, 1);
+  fsquare_times(zzzprime, zzprime, 1);
+  fmul(z3, zzzprime, qmqp);
+
+  fsquare_times(xx, x, 1);
+  fsquare_times(zz, z, 1);
+  fmul(x2, xx, zz);
+  fdifference_backwards(zz, xx);  // does zz = xx - zz
+  fscalar_product(zzz, zz, 121665);
+  fsum(zzz, xx);
+  fmul(z2, zz, zzz);
+}
+
+// -----------------------------------------------------------------------------
+// Maybe swap the contents of two limb arrays (@a and @b), each @len elements
+// long. Perform the swap iff @swap is non-zero.
+//
+// This function performs the swap without leaking any side-channel
+// information.
+// -----------------------------------------------------------------------------
+static void
+swap_conditional(limb a[5], limb b[5], limb iswap) {
+  unsigned i;
+  const limb swap = -iswap;
+
+  for (i = 0; i < 5; ++i) {
+    const limb x = swap & (a[i] ^ b[i]);
+    a[i] ^= x;
+    b[i] ^= x;
+  }
+}
+
+/* Calculates nQ where Q is the x-coordinate of a point on the curve
+ *
+ *   resultx/resultz: the x coordinate of the resulting curve point (short form)
+ *   n: a little endian, 32-byte number
+ *   q: a point of the curve (short form)
+ */
+static void
+cmult(limb *resultx, limb *resultz, const u8 *n, const limb *q) {
+  limb a[5] = {0}, b[5] = {1}, c[5] = {1}, d[5] = {0};
+  limb *nqpqx = a, *nqpqz = b, *nqx = c, *nqz = d, *t;
+  limb e[5] = {0}, f[5] = {1}, g[5] = {0}, h[5] = {1};
+  limb *nqpqx2 = e, *nqpqz2 = f, *nqx2 = g, *nqz2 = h;
+
+  unsigned i, j;
+
+  memcpy(nqpqx, q, sizeof(limb) * 5);
+
+  for (i = 0; i < 32; ++i) {
+    u8 byte = n[31 - i];
+    for (j = 0; j < 8; ++j) {
+      const limb bit = byte >> 7;
+
+      swap_conditional(nqx, nqpqx, bit);
+      swap_conditional(nqz, nqpqz, bit);
+      fmonty(nqx2, nqz2,
+             nqpqx2, nqpqz2,
+             nqx, nqz,
+             nqpqx, nqpqz,
+             q);
+      swap_conditional(nqx2, nqpqx2, bit);
+      swap_conditional(nqz2, nqpqz2, bit);
+
+      t = nqx;
+      nqx = nqx2;
+      nqx2 = t;
+      t = nqz;
+      nqz = nqz2;
+      nqz2 = t;
+      t = nqpqx;
+      nqpqx = nqpqx2;
+      nqpqx2 = t;
+      t = nqpqz;
+      nqpqz = nqpqz2;
+      nqpqz2 = t;
+
+      byte <<= 1;
+    }
+  }
+
+  memcpy(resultx, nqx, sizeof(limb) * 5);
+  memcpy(resultz, nqz, sizeof(limb) * 5);
+}
+
+
+// -----------------------------------------------------------------------------
+// Shamelessly copied from djb's code, tightened a little
+// -----------------------------------------------------------------------------
+static void
+crecip(felem out, const felem z) {
+  felem a,t0,b,c;
+
+  /* 2 */ fsquare_times(a, z, 1); // a = 2
+  /* 8 */ fsquare_times(t0, a, 2);
+  /* 9 */ fmul(b, t0, z); // b = 9
+  /* 11 */ fmul(a, b, a); // a = 11
+  /* 22 */ fsquare_times(t0, a, 1);
+  /* 2^5 - 2^0 = 31 */ fmul(b, t0, b);
+  /* 2^10 - 2^5 */ fsquare_times(t0, b, 5);
+  /* 2^10 - 2^0 */ fmul(b, t0, b);
+  /* 2^20 - 2^10 */ fsquare_times(t0, b, 10);
+  /* 2^20 - 2^0 */ fmul(c, t0, b);
+  /* 2^40 - 2^20 */ fsquare_times(t0, c, 20);
+  /* 2^40 - 2^0 */ fmul(t0, t0, c);
+  /* 2^50 - 2^10 */ fsquare_times(t0, t0, 10);
+  /* 2^50 - 2^0 */ fmul(b, t0, b);
+  /* 2^100 - 2^50 */ fsquare_times(t0, b, 50);
+  /* 2^100 - 2^0 */ fmul(c, t0, b);
+  /* 2^200 - 2^100 */ fsquare_times(t0, c, 100);
+  /* 2^200 - 2^0 */ fmul(t0, t0, c);
+  /* 2^250 - 2^50 */ fsquare_times(t0, t0, 50);
+  /* 2^250 - 2^0 */ fmul(t0, t0, b);
+  /* 2^255 - 2^5 */ fsquare_times(t0, t0, 5);
+  /* 2^255 - 21 */ fmul(out, t0, a);
+}
+
+int
+curve25519_donna(u8 *mypublic, const u8 *secret, const u8 *basepoint) {
+  limb bp[5], x[5], z[5], zmone[5];
+  uint8_t e[32];
+  int i;
+
+  for (i = 0;i < 32;++i) e[i] = secret[i];
+  e[0] &= 248;
+  e[31] &= 127;
+  e[31] |= 64;
+
+  fexpand(bp, basepoint);
+  cmult(x, z, e, bp);
+  crecip(zmone, z);
+  fmul(z, x, zmone);
+  fcontract(mypublic, z);
+  return 0;
+}
+
+}
diff --git a/src/lib/pubkey/curve25519/donna128.h b/src/lib/pubkey/curve25519/donna128.h
new file mode 100644
index 000000000..f2b2d88ea
--- /dev/null
+++ b/src/lib/pubkey/curve25519/donna128.h
@@ -0,0 +1,116 @@
+/*
+* A minimal 128-bit integer type for curve25519-donna
+* (C) 2014 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_CURVE25519_DONNA128_H__
+#define BOTAN_CURVE25519_DONNA128_H__
+
+#include <botan/mul128.h>
+
+namespace Botan {
+
+class donna128
+   {
+   public:
+      donna128(u64bit ll = 0, u64bit hh = 0) { l = ll; h = hh; }
+
+      donna128(const donna128&) = default;
+      donna128& operator=(const donna128&) = default;
+
+      friend donna128 operator>>(const donna128& x, size_t shift)
+         {
+         donna128 z = x;
+         const u64bit carry = z.h << (64 - shift);
+         z.h = (z.h >> shift);
+         z.l = (z.l >> shift) | carry;
+         return z;
+         }
+
+      friend donna128 operator<<(const donna128& x, size_t shift)
+         {
+         donna128 z = x;
+         const u64bit carry = z.l >> (64 - shift);
+         z.l = (z.l << shift);
+         z.h = (z.h << shift) | carry;
+         return z;
+         }
+
+      friend u64bit operator&(const donna128& x, u64bit mask)
+         {
+         return x.l & mask;
+         }
+
+      u64bit operator&=(u64bit mask)
+         {
+         h = 0;
+         l &= mask;
+         return l;
+         }
+
+      donna128& operator+=(const donna128& x)
+         {
+         l += x.l;
+         h += (l < x.l);
+         h += x.h;
+         return *this;
+         }
+
+      donna128& operator+=(u64bit x)
+         {
+         l += x;
+         h += (l < x);
+         return *this;
+         }
+
+      u64bit lo() const { return l; }
+      u64bit hi() const { return h; }
+   private:
+      u64bit h = 0, l = 0;
+   };
+
+inline donna128 operator*(const donna128& x, u64bit y)
+   {
+   BOTAN_ASSERT(x.hi() == 0, "High 64 bits of donna128 set to zero during multiply");
+
+   u64bit lo = 0, hi = 0;
+   mul64x64_128(x.lo(), y, &lo, &hi);
+   return donna128(lo, hi);
+   }
+
+inline donna128 operator+(const donna128& x, const donna128& y)
+   {
+   donna128 z = x;
+   z += y;
+   return z;
+   }
+
+inline donna128 operator+(const donna128& x, u64bit y)
+   {
+   donna128 z = x;
+   z += y;
+   return z;
+   }
+
+inline donna128 operator|(const donna128& x, const donna128& y)
+   {
+   return donna128(x.lo() | y.lo(), x.hi() | y.hi());
+   }
+
+inline u64bit carry_shift(const donna128& a, size_t shift)
+   {
+   return (a >> shift).lo();
+   }
+
+inline u64bit combine_lower(const donna128 a, size_t s1,
+                            const donna128 b, size_t s2)
+   {
+   donna128 z = (a >> s1) | (b << s2);
+   return z.lo();
+   }
+
+}
+
+#endif
diff --git a/src/lib/pubkey/curve25519/info.txt b/src/lib/pubkey/curve25519/info.txt
new file mode 100644
index 000000000..68c417056
--- /dev/null
+++ b/src/lib/pubkey/curve25519/info.txt
@@ -0,0 +1,9 @@
+define CURVE_25519 20141227
+
+<header:public>
+curve25519.h
+</header:public>
+
+<header:internal>
+donna128.h
+</header:internal>
diff --git a/src/lib/pubkey/pk_algs.cpp b/src/lib/pubkey/pk_algs.cpp
index 9673199e0..e1784dd9f 100644
--- a/src/lib/pubkey/pk_algs.cpp
+++ b/src/lib/pubkey/pk_algs.cpp
@@ -44,6 +44,10 @@
   #include <botan/ecdh.h>
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+  #include <botan/curve25519.h>
+#endif
+
 namespace Botan {
 
 Public_Key* make_public_key(const AlgorithmIdentifier& alg_id,
@@ -98,6 +102,11 @@ Public_Key* make_public_key(const AlgorithmIdentifier& alg_id,
       return new ECDH_PublicKey(alg_id, key_bits);
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+   if(alg_name == "Curve25519")
+      return new Curve25519_PublicKey(alg_id, key_bits);
+#endif
+
    return nullptr;
    }
 
@@ -154,6 +163,11 @@ Private_Key* make_private_key(const AlgorithmIdentifier& alg_id,
       return new ECDH_PrivateKey(alg_id, key_bits);
 #endif
 
+#if defined(BOTAN_HAS_CURVE_25519)
+   if(alg_name == "Curve25519")
+      return new Curve25519_PrivateKey(alg_id, key_bits, rng);
+#endif
+
    return nullptr;
    }
 
diff --git a/src/tests/data/pubkey/c25519_scalar.vec b/src/tests/data/pubkey/c25519_scalar.vec
new file mode 100644
index 000000000..0b8f7e72b
--- /dev/null
+++ b/src/tests/data/pubkey/c25519_scalar.vec
@@ -0,0 +1,79 @@
+
+# scalarmult1 from libsodium
+Secret    = 77076D0A7318A57D3C16C17251B26645DF4C2F87EBC0992AB177FBA51DB92C2A
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out       = 8520F0098930A754748B7DDCB43EF75A0DBF3A0D26381AF4EBA4A98EAA9B4E6A
+
+# scalarmult2
+Secret = 5DAB087E624A8A4B79E17F8B83800EE66F3BB1292618B6FD1C2F8B27FF88E0EB
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = DE9EDB7D7B7DC1B4D35B61C2ECE435373F8343C85B78674DADFC7E146F882B4F
+
+# scalarmult5
+Secret = 77076D0A7318A57D3C16C17251B26645DF4C2F87EBC0992AB177FBA51DB92C2A
+Basepoint = DE9EDB7D7B7DC1B4D35B61C2ECE435373F8343C85B78674DADFC7E146F882B4F
+Out = 4A5D9D5BA4CE2DE1728E3BF480350F25E07E21C947D19E3376F09B3C1E161742
+
+# scalarmult6
+Secret = 5DAB087E624A8A4B79E17F8B83800EE66F3BB1292618B6FD1C2F8B27FF88E0EB
+Basepoint = 8520F0098930A754748B7DDCB43EF75A0DBF3A0D26381AF4EBA4A98EAA9B4E6A
+Out = 4A5D9D5BA4CE2DE1728E3BF480350F25E07E21C947D19E3376F09B3C1E161742
+
+# test-noncanon from donna
+Secret = 0100000000000000000000000000000000000000000000000000000000000000
+Basepoint = 2500000000000000000000000000000000000000000000000000000000000000
+Out = 3C7777CAF997B264416077665B4E229D0B9548DC0CD81998DDCDC5C8533C797F
+
+Secret    = 0100000000000000000000000000000000000000000000000000000000000000
+Basepoint = FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+Out = B32D1362C248D62FE62619CFF04DD43DB73FFC1B6308EDE30B78D87380F1E834
+
+# Following values generated at random by curve25519-donna
+
+Secret = D55FF01DA1262795A4E50E607F87B80DCCD447A6EE0F6CD8D25177F79575744D
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = D5BDC7055ABA7855692CC861009E3AE6B6339329826B11F8B92E5ADAEB85335E
+
+Secret = 0224D9367436089D81B1150DFC748EC851F9A41389E21C8C1181E01BA1760C23
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = AD7E1E41C6AC0544F949EB76D71C75120ADD345C44384BDD830974D2DD329644
+
+Secret = D55FF01DA1262795A4E50E607F87B80DCCD447A6EE0F6CD8D25177F79575744D
+Basepoint = AD7E1E41C6AC0544F949EB76D71C75120ADD345C44384BDD830974D2DD329644
+Out = FC343E1965225D8666F4AE8E70E04039D21C603F7CE7F17C0CC8440C62C03575
+
+Secret = 0224D9367436089D81B1150DFC748EC851F9A41389E21C8C1181E01BA1760C23
+Basepoint = D5BDC7055ABA7855692CC861009E3AE6B6339329826B11F8B92E5ADAEB85335E
+Out = FC343E1965225D8666F4AE8E70E04039D21C603F7CE7F17C0CC8440C62C03575
+
+Secret = 65A06F749B010EA5738CDEBE3EF65F38C17A13F8CCC5B0AE51B5091D845C6DEB
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = B84AEDDA6C2CD17CCB62D94E3238E7093BA77D15BE4C563D1B11EA3C2EECA87F
+
+Secret = 92B158501611EF8521C101E28629130427B42D2DA65E9EC9387B94BC2F08B806
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = 06479EC3C771D635F54787DEA334149E07E20957127C816E3059258428C17970
+
+Secret = 65A06F749B010EA5738CDEBE3EF65F38C17A13F8CCC5B0AE51B5091D845C6DEB
+Basepoint = 06479EC3C771D635F54787DEA334149E07E20957127C816E3059258428C17970
+Out = 47C69389596EA49AEE14F4259250808385C37F4EBBD6AA176779BFEB8042D834
+
+Secret = 92B158501611EF8521C101E28629130427B42D2DA65E9EC9387B94BC2F08B806
+Basepoint = B84AEDDA6C2CD17CCB62D94E3238E7093BA77D15BE4C563D1B11EA3C2EECA87F
+Out = 47C69389596EA49AEE14F4259250808385C37F4EBBD6AA176779BFEB8042D834
+
+Secret = 2D7B885AA77351153994425725F35AFB84D9729DECA3D9D832570569C973566E
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = 93928FCC20DFEA2AF6CA8B1268192B68D87FDA744FD67FCFAEF84165C504597C
+
+Secret = E3B07D96E4B5F3D265ACFE950707B62B053F2FD5CCF20D662F62AB09ED2AC325
+Basepoint = 0900000000000000000000000000000000000000000000000000000000000000
+Out = 68B7894FF03386C8C1907847866CD771519163D002FA7C3360650186A22F7263
+
+Secret = 2D7B885AA77351153994425725F35AFB84D9729DECA3D9D832570569C973566E
+Basepoint = 68B7894FF03386C8C1907847866CD771519163D002FA7C3360650186A22F7263
+Out = 0BE4BB615F362A21A28A404631F6832DD1019A7145C020031614D8B6F697983A
+
+Secret = E3B07D96E4B5F3D265ACFE950707B62B053F2FD5CCF20D662F62AB09ED2AC325
+Basepoint = 93928FCC20DFEA2AF6CA8B1268192B68D87FDA744FD67FCFAEF84165C504597C
+Out = 0BE4BB615F362A21A28A404631F6832DD1019A7145C020031614D8B6F697983A
diff --git a/src/tests/test_c25519.cpp b/src/tests/test_c25519.cpp
new file mode 100644
index 000000000..cb03ebf69
--- /dev/null
+++ b/src/tests/test_c25519.cpp
@@ -0,0 +1,56 @@
+#include "tests.h"
+#include "test_pubkey.h"
+
+#if defined(BOTAN_HAS_CURVE_25519)
+#include <botan/curve25519.h>
+#include <botan/hex.h>
+#include <iostream>
+#include <fstream>
+#endif
+
+using namespace Botan;
+
+#if defined(BOTAN_HAS_CURVE_25519)
+
+namespace {
+
+size_t curve25519_scalar_kat(const std::string& secret_h,
+                             const std::string& basepoint_h,
+                             const std::string& out_h)
+   {
+   const std::vector<byte> secret = hex_decode(secret_h);
+   const std::vector<byte> basepoint = hex_decode(basepoint_h);
+   const std::vector<byte> out = hex_decode(out_h);
+
+   std::vector<byte> got(32);
+   curve25519_donna(&got[0], &secret[0], &basepoint[0]);
+
+   if(got != out)
+      {
+      std::cout << "Got " << hex_encode(got) << " exp " << hex_encode(out) << "\n";
+      return 1;
+      }
+
+   return 0;
+   }
+
+}
+#endif
+
+size_t test_curve25519()
+   {
+   size_t fails = 0;
+
+#if defined(BOTAN_HAS_CURVE_25519)
+   std::ifstream c25519_scalar(PK_TEST_DATA_DIR "/c25519_scalar.vec");
+
+   fails += run_tests_bb(c25519_scalar, "Curve25519 ScalarMult", "Out", true,
+             [](std::map<std::string, std::string> m) -> size_t
+             {
+             return curve25519_scalar_kat(m["Secret"], m["Basepoint"], m["Out"]);
+             });
+#endif
+
+   return fails;
+   }
+
diff --git a/src/tests/tests.cpp b/src/tests/tests.cpp
index 3ec904c02..99a4d8e3a 100644
--- a/src/tests/tests.cpp
+++ b/src/tests/tests.cpp
@@ -261,6 +261,7 @@ int main(int argc, char* argv[])
    DEF_TEST(ecc_pointmul);
    DEF_TEST(ecdsa);
    DEF_TEST(gost_3410);
+   DEF_TEST(curve25519);
    DEF_TEST(mceliece);
 
    DEF_TEST(ecc_unit);
diff --git a/src/tests/tests.h b/src/tests/tests.h
index d4ccf91c1..61cc405a0 100644
--- a/src/tests/tests.h
+++ b/src/tests/tests.h
@@ -67,6 +67,7 @@ size_t test_elgamal();
 size_t test_ecc_pointmul();
 size_t test_ecdsa();
 size_t test_gost_3410();
+size_t test_curve25519();
 size_t test_mceliece();
 
 // One off tests