From df1aa52e087135a25602ed2935fe8a785ff7cd21 Mon Sep 17 00:00:00 2001
From: orignal <i2porignal@yandex.ru>
Date: Thu, 5 Dec 2019 16:03:11 -0500
Subject: [PATCH] Elligator's encode

---
 libi2pd/Elligator.cpp | 68 +++++++++++++++++++++++++++++++++++++++++++
 libi2pd/Elligator.h   |  8 +++++
 2 files changed, 76 insertions(+)

diff --git a/libi2pd/Elligator.cpp b/libi2pd/Elligator.cpp
index cc49adbf..cc38672a 100644
--- a/libi2pd/Elligator.cpp
+++ b/libi2pd/Elligator.cpp
@@ -1,15 +1,83 @@
+#include "Crypto.h"
 #include "Elligator.h"
 
 namespace i2p
 {
 namespace crypto
 {
+	static const uint8_t p_[32]= 
+	{
+		0xed, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
+	};
+
+	static const uint8_t n1_[32] = 
+	{
+		0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
+	};
+
+	static const uint8_t n2_[32] = 
+	{
+		0xeb, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
+	};
+
+	static const uint8_t A_[32] = 
+	{
+		0x06, 0x6d, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+	};
+
+	static const uint8_t u_[32] = 
+	{
+		0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+	};
+
+	#define decode_bytes(x) { x = BN_new (); BN_bin2bn (x##_, 32, x); }
 	Elligator2::Elligator2 ()
 	{
+		decode_bytes (p);
+		decode_bytes (n1);
+		decode_bytes (n2);
+		decode_bytes (A);	
+		decode_bytes (u);
+		
+		BN_CTX * ctx = BN_CTX_new ();
+		BN_mod_inverse (iu, u, p, ctx);	
+		BN_CTX_free (ctx);
 	}
 
 	Elligator2::~Elligator2 ()
 	{
+		BN_free (p);
+		BN_free (n1);
+		BN_free (n2);
+		BN_free (A);
+	}
+
+	void Elligator2::Encode (const uint8_t * key, uint8_t * encoded) const
+	{
+		BN_CTX * ctx = BN_CTX_new ();
+		BN_CTX_start (ctx);
+
+		BIGNUM * a = BN_CTX_get (ctx); BN_bin2bn (key, 32, a);
+		BIGNUM * b = BN_CTX_get (ctx);
+		BN_add (a, A, b);
+		BIGNUM * c = BN_CTX_get (ctx);
+		BN_mod_exp (c, b, n2, p, ctx);		
+		BN_mod_mul (b, c, a, p, ctx);
+		BN_sub (b, p, b);
+
+		//BN_mod_exp (c, b, n2, p, ctx);	
+		
+		BN_mod_mul (c, b, iu, p, ctx);
+		// TODO:
+		bn2buf (b, encoded, 32);
+
+		BN_CTX_end (ctx);	
+		BN_CTX_free (ctx);
 	}
 
 	static std::unique_ptr<Elligator2> g_Elligator;
diff --git a/libi2pd/Elligator.h b/libi2pd/Elligator.h
index 7993ccb9..09f46888 100644
--- a/libi2pd/Elligator.h
+++ b/libi2pd/Elligator.h
@@ -1,7 +1,9 @@
 #ifndef ELLIGATOR_H__
 #define ELLIGATOR_H__
 
+#include <inttypes.h>
 #include <memory>
+#include <openssl/bn.h>
 
 namespace i2p
 {
@@ -14,6 +16,12 @@ namespace crypto
 
 			Elligator2 ();
 			~Elligator2 ();
+
+			void Encode (const uint8_t * key, uint8_t * encoded) const;
+
+		private:
+
+			BIGNUM * p, * n1, * n2, * A, * u, * iu;
 	};
 
 	std::unique_ptr<Elligator2>& GetElligator ();