From 315caaba7e83eb6680a0407ea13e04b5f7739788 Mon Sep 17 00:00:00 2001
From: Mark Haines <mark.haines@matrix.org>
Date: Tue, 3 Mar 2015 11:18:07 +0000
Subject: Add functions for signing and verifying messages using curve25519
 keys

---
 lib/ed25519/src/fe.c    |  4 +++-
 lib/ed25519/src/sc.c    |  5 +++++
 lib/ed25519_additions.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 lib/ed25519_additions.c

(limited to 'lib')

diff --git a/lib/ed25519/src/fe.c b/lib/ed25519/src/fe.c
index 448e3e9..07f9f05 100644
--- a/lib/ed25519/src/fe.c
+++ b/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
diff --git a/lib/ed25519/src/sc.c b/lib/ed25519/src/sc.c
index ca5bad2..a883907 100644
--- a/lib/ed25519/src/sc.c
+++ b/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
diff --git a/lib/ed25519_additions.c b/lib/ed25519_additions.c
new file mode 100644
index 0000000..5fa0c68
--- /dev/null
+++ b/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);
+}
-- 
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