i2pd/libi2pd/Elligator.cpp

#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;
	std::unique_ptr<Elligator2>& GetElligator ()
	{
		if (!g_Elligator)
		{
			auto el = new Elligator2();
			if (!g_Elligator) // make sure it was not created already
				g_Elligator.reset (el);
			else
				delete el;
		}
		return g_Elligator;
	}
}
}