Add functions for signing and verifying messages using curve25519 keys

include/axolotl/crypto.hh

@@ -48,6 +48,25 @@ void curve25519_shared_secret(
 );
 
 
+/** Signs the message using our private key.
+ * The output buffer must be at least 64 bytes long. */
+void curve25519_sign(
+    Curve25519KeyPair const & our_key,
+    std::uint8_t const * message, std::size_t message_length,
+    std::uint8_t * output
+);
+
+
+/** Verify thei message using their public key.
+ * The signature input buffer must be 64 bytes long.
+ * Returns true if the signature is valid. */
+bool curve25519_verify(
+    Curve25519PublicKey const & their_key,
+    std::uint8_t const * message, std::size_t message_length,
+    std::uint8_t const * signature
+);
+
+
 struct Aes256Key {
     static const int LENGTH = 32;
     std::uint8_t key[32];

lib/ed25519/src/fe.c

@@ -1,6 +1,8 @@
 #include "fixedint.h"
 #include "fe.h"
 
+#ifndef ED25519_LOAD_BYTES
+#define ED25519_LOAD_BYTES
 
 /*
     helper functions
@@ -26,7 +28,7 @@ static uint64_t load_4(const unsigned char *in) {
     return result;
 }
 
-
+#endif
 
 /*
     h = 0

lib/ed25519/src/sc.c

@@ -1,6 +1,9 @@
 #include "fixedint.h"
 #include "sc.h"
 
+#ifndef ED25519_LOAD_BYTES
+#define ED25519_LOAD_BYTES
+
 static uint64_t load_3(const unsigned char *in) {
     uint64_t result;
 
@@ -22,6 +25,8 @@ static uint64_t load_4(const unsigned char *in) {
     return result;
 }
 
+#endif
+
 /*
 Input:
   s[0]+256*s[1]+...+256^63*s[63] = s

lib/ed25519_additions.c

@@ -0,0 +1,43 @@
+void convert_curve25519_to_ed25519(
+    unsigned char * public_key,
+    unsigned char * signature
+) {
+    fe mont_x, mont_x_minus_one, mont_x_plus_one, inv_mont_x_plus_one;
+    fe one;
+    fe ed_y;
+
+    fe_frombytes(mont_x, public_key);
+    fe_1(one);
+    fe_sub(mont_x_minus_one, mont_x, one);
+    fe_add(mont_x_plus_one, mont_x, one);
+    fe_invert(inv_mont_x_plus_one, mont_x_plus_one);
+    fe_mul(ed_y, mont_x_minus_one, inv_mont_x_plus_one);
+    fe_tobytes(public_key, ed_y);
+
+    public_key[31] &= 0x7F;
+    public_key[31] |= (signature[63] & 0x80);
+    signature[63] &= 0x7F;
+}
+
+
+void convert_ed25519_to_curve25519(
+    unsigned char const * public_key,
+    unsigned char * signature
+) {
+    unsigned char sign_bit = public_key[31] & 0x80;
+    signature[63] &= 0x7F;
+    signature[63] |= sign_bit;
+}
+
+
+void ed25519_keypair(
+    unsigned char * private_key,
+    unsigned char * public_key
+) {
+    ge_p3 A;
+    private_key[0] &= 248;
+    private_key[31] &= 63;
+    private_key[31] |= 64;
+    ge_scalarmult_base(&A, private_key);
+    ge_p3_tobytes(public_key, &A);
+}

src/crypto.cpp

@@ -28,6 +28,38 @@ int curve25519_donna(
 #include "crypto-algorithms/aes.h"
 #include "crypto-algorithms/sha256.h"
 
+int ed25519_sign(
+    unsigned char *signature,
+    const unsigned char *message, size_t message_len,
+    const unsigned char *public_key,
+    const unsigned char *private_key
+);
+
+
+int ed25519_verify(
+    const unsigned char *signature,
+    const unsigned char *message, size_t message_len,
+    const unsigned char *public_key
+);
+
+
+void convert_curve25519_to_ed25519(
+    unsigned char * public_key,
+    unsigned char * signature
+);
+
+
+void convert_ed25519_to_curve25519(
+    unsigned char const * public_key,
+    unsigned char * signature
+);
+
+
+void ed25519_keypair(
+    unsigned char * private_key,
+    unsigned char * public_key
+);
+
 }
 
 
@@ -124,6 +156,41 @@ void axolotl::curve25519_shared_secret(
 }
 
 
+void axolotl::curve25519_sign(
+    axolotl::Curve25519KeyPair const & our_key,
+    std::uint8_t const * message, std::size_t message_length,
+    std::uint8_t * output
+) {
+    std::uint8_t private_key[32];
+    std::uint8_t public_key[32];
+    std::memcpy(private_key, our_key.private_key, 32);
+    ::ed25519_keypair(private_key, public_key);
+    ::ed25519_sign(
+        output,
+        message, message_length,
+        public_key, private_key
+    );
+    ::convert_ed25519_to_curve25519(public_key, output);
+}
+
+
+bool axolotl::curve25519_verify(
+    axolotl::Curve25519PublicKey const & their_key,
+    std::uint8_t const * message, std::size_t message_length,
+    std::uint8_t const * signature
+) {
+    std::uint8_t public_key[32];
+    std::uint8_t signature_buffer[64];
+    std::memcpy(public_key, their_key.public_key, 32);
+    std::memcpy(signature_buffer, signature, 64);
+    ::convert_curve25519_to_ed25519(public_key, signature_buffer);
+    return 0 != ::ed25519_verify(
+        signature,
+        message, message_length,
+        public_key
+    );
+}
+
 std::size_t axolotl::aes_encrypt_cbc_length(
     std::size_t input_length
 ) {

src/libs.cpp

@@ -16,4 +16,12 @@ extern "C" {
 #include "crypto-algorithms/sha256.c"
 #include "crypto-algorithms/aes.c"
 #include "curve25519-donna/curve25519-donna.c"
+#define select ed25519_select
+#include "ed25519/src/fe.c"
+#include "ed25519/src/sc.c"
+#include "ed25519/src/ge.c"
+#include "ed25519/src/sha512.c"
+#include "ed25519/src/verify.c"
+#include "ed25519/src/sign.c"
+#include "ed25519_additions.c"
 }

test.py

@@ -23,10 +23,10 @@ if not os.path.exists("build"):
 test_files = glob.glob("tests/test_*.cpp")
 source_files = glob.glob("src/*.cpp")
 
-compile_args = "g++ -Itests/include -Iinclude -Ilib --std=c++11".split()
+compile_args = "g++ -g -O0 -Itests/include -Iinclude -Ilib --std=c++11".split()
 compile_args += source_files
 
 for test_file in test_files:
-    exe_file = "build/" + test_file[:4]
+    exe_file = "build/" + test_file[5:-4]
     subprocess.check_call(compile_args + [test_file, "-o", exe_file])
     subprocess.check_call([exe_file])

tests/test_crypto.cpp

@@ -83,6 +83,35 @@ assert_equals(expected_agreement, actual_agreement, 32);
 } /* Curve25529 Test Case 1 */
 
 
+{ /* Signature Test Cast 1 */
+TestCase test_case("Signature Test Case 1");
+
+std::uint8_t private_key[33] = "This key is a string of 32 bytes";
+std::uint8_t message[] = "message";
+std::size_t message_length = sizeof(message) - 1;
+
+axolotl::Curve25519KeyPair key_pair;
+axolotl::generate_key(private_key, key_pair);
+
+std::uint8_t signature[64];
+
+axolotl::curve25519_sign(
+    key_pair, message, message_length, signature
+);
+
+bool result = axolotl::curve25519_verify(
+    key_pair, message, message_length, signature
+);
+assert_equals(true, result);
+
+message[0] = 'n';
+result = axolotl::curve25519_verify(
+    key_pair, message, message_length, signature
+);
+assert_equals(false, result);
+
+} /* Signature Test Cast 1 */
+
 { /* AES Test Case 1 */
 
 TestCase test_case("AES Test Case 1");