ZeroTierOne/node/C25519.hpp

/*
 * ZeroTier One - Network Virtualization Everywhere
 * Copyright (C) 2011-2019  ZeroTier, Inc.  https://www.zerotier.com/
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 *
 * --
 *
 * You can be released from the requirements of the license by purchasing
 * a commercial license. Buying such a license is mandatory as soon as you
 * develop commercial closed-source software that incorporates or links
 * directly against ZeroTier software without disclosing the source code
 * of your own application.
 */

#ifndef ZT_C25519_HPP
#define ZT_C25519_HPP

#include "Utils.hpp"

namespace ZeroTier {

#define ZT_C25519_PUBLIC_KEY_LEN 64
#define ZT_C25519_PRIVATE_KEY_LEN 64
#define ZT_C25519_SIGNATURE_LEN 96

/**
 * A combined Curve25519 ECDH and Ed25519 signature engine
 */
class C25519
{
public:
	struct Public { uint8_t data[ZT_C25519_PUBLIC_KEY_LEN]; };
	struct Private { uint8_t data[ZT_C25519_PRIVATE_KEY_LEN]; };
	struct Signature { uint8_t data[ZT_C25519_SIGNATURE_LEN]; };
	struct Pair { Public pub; Private priv; };

	/**
	 * Generate a C25519 elliptic curve key pair
	 */
	static inline Pair generate()
	{
		Pair kp;
		Utils::getSecureRandom(kp.priv.data,ZT_C25519_PRIVATE_KEY_LEN);
		_calcPubDH(kp);
		_calcPubED(kp);
		return kp;
	}

	/**
	 * Generate a key pair satisfying a condition
	 *
	 * This begins with a random keypair from a random secret key and then
	 * iteratively increments the random secret until cond(kp) returns true.
	 * This is used to compute key pairs in which the public key, its hash
	 * or some other aspect of it satisfies some condition, such as for a
	 * hashcash criteria.
	 *
	 * @param cond Condition function or function object
	 * @return Key pair where cond(kp) returns true
	 * @tparam F Type of 'cond'
	 */
	template<typename F>
	static inline Pair generateSatisfying(F cond)
	{
		Pair kp;
		void *const priv = (void *)kp.priv.data;
		Utils::getSecureRandom(priv,ZT_C25519_PRIVATE_KEY_LEN);
		_calcPubED(kp); // do Ed25519 key -- bytes 32-63 of pub and priv
		do {
			++(((uint64_t *)priv)[1]);
			--(((uint64_t *)priv)[2]);
			_calcPubDH(kp); // keep regenerating bytes 0-31 until satisfied
		} while (!cond(kp));
		return kp;
	}

	/**
	 * Perform C25519 ECC key agreement
	 *
	 * Actual key bytes are generated from one or more SHA-512 digests of
	 * the raw result of key agreement.
	 *
	 * @param mine My private key
	 * @param their Their public key
	 * @param keybuf Buffer to fill
	 * @param keylen Number of key bytes to generate
	 */
	static void agree(const Private &mine,const Public &their,void *keybuf,unsigned int keylen);

	/**
	 * Sign a message with a sender's key pair
	 *
	 * This takes the SHA-521 of msg[] and then signs the first 32 bytes of this
	 * digest, returning it and the 64-byte ed25519 signature in signature[].
	 * This results in a signature that verifies both the signer's authenticity
	 * and the integrity of the message.
	 *
	 * This is based on the original ed25519 code from NaCl and the SUPERCOP
	 * cipher benchmark suite, but with the modification that it always
	 * produces a signature of fixed 96-byte length based on the hash of an
	 * arbitrary-length message.
	 *
	 * @param myPrivate My private key
	 * @param myPublic My public key
	 * @param msg Message to sign
	 * @param len Length of message in bytes
	 * @param signature Buffer to fill with signature -- MUST be 96 bytes in length
	 */
	static void sign(const Private &myPrivate,const Public &myPublic,const void *msg,unsigned int len,void *signature);

	/**
	 * Sign a message with a sender's key pair
	 *
	 * Note that this generates a 96-byte signature that contains an extra 32 bytes
	 * of hash data. This data is included for historical reasons and is optional. The
	 * verify function here will take the first 64 bytes only (normal ed25519 signature)
	 * or a 96-byte length signature with the extra input hash data.
	 * 
	 * @param myPrivate My private key
	 * @param myPublic My public key
	 * @param msg Message to sign
	 * @param len Length of message in bytes
	 * @return Signature
	 */
	static inline Signature sign(const Private &myPrivate,const Public &myPublic,const void *msg,unsigned int len)
	{
		Signature sig;
		sign(myPrivate,myPublic,msg,len,sig.data);
		return sig;
	}
	static inline Signature sign(const Pair &mine,const void *msg,unsigned int len)
	{
		Signature sig;
		sign(mine.priv,mine.pub,msg,len,sig.data);
		return sig;
	}

	/**
	 * Verify a message's signature
	 *
	 * @param their Public key to verify against
	 * @param msg Message to verify signature integrity against
	 * @param len Length of message in bytes
	 * @param signature Signature bytes
	 * @param siglen Length of signature in bytes
	 * @return True if signature is valid and the message is authentic and unmodified
	 */
	static bool verify(const Public &their,const void *msg,unsigned int len,const void *signature,const unsigned int siglen);

	/**
	 * Verify a message's signature
	 *
	 * @param their Public key to verify against
	 * @param msg Message to verify signature integrity against
	 * @param len Length of message in bytes
	 * @param signature 96-byte signature
	 * @return True if signature is valid and the message is authentic and unmodified
	 */
	static inline bool verify(const Public &their,const void *msg,unsigned int len,const Signature &signature) { return verify(their,msg,len,signature.data,96); }

private:
	// derive first 32 bytes of kp.pub from first 32 bytes of kp.priv
	// this is the ECDH key
	static void _calcPubDH(Pair &kp);

	// derive 2nd 32 bytes of kp.pub from 2nd 32 bytes of kp.priv
	// this is the Ed25519 sign/verify key
	static void _calcPubED(Pair &kp);
};

} // namespace ZeroTier

#endif