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/*
This file is part of cpp-ethereum.
cpp-ethereum 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.
cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
*/
/** @file ECDHE.h
* @author Alex Leverington <nessence@gmail.com>
* @date 2014
*
* Elliptic curve Diffie-Hellman ephemeral key exchange
*/
#pragma once
#include "AES.h"
namespace dev
{
namespace crypto
{
/// Public key of remote and corresponding shared secret.
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typedef std::pair<Public,h256> AliasSession;
/**
* @brief An addressable EC key pair.
*/
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class Alias
{
friend class ECDHEKeyExchange; // todo: remove
public:
Alias(Secret _s): m_secret(_s) {};
AliasSession session(Address _a) { return m_sessions.count(_a) ? m_sessions.find(_a)->second : AliasSession(); }
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private:
std::map<Address,AliasSession> m_sessions;
Secret m_secret;
};
/**
* @brief Derive DH shared secret from EC keypairs.
* As ephemeral keys are single-use, agreement is limited to a single occurence.
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*/
class ECDHE
{
public:
/// Constructor (pass public key for ingress exchange).
ECDHE(): m_ephemeral(KeyPair::create()) {};
/// Public key sent to remote.
Public pubkey() { return m_ephemeral.pub(); }
/// Input public key for dh agreement, output generated shared secret.
void agree(Public const& _remoteEphemeral, Secret& o_sharedSecret);
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protected:
KeyPair m_ephemeral; ///< Ephemeral keypair; generated.
Public m_remoteEphemeral; ///< Public key of remote; parameter.
};
/**
* @brief Secure exchange of static keys.
* Key exchange is encrypted with public key of remote and then encrypted by block cipher. For a blind remote the ecdhe public key is used to encrypt exchange, and for a known remote the known public key is used. The block cipher key is derived from ecdhe shared secret.
*
* Usage: Agree -> Exchange -> Authenticate
*/
class ECDHEKeyExchange: private ECDHE
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{
public:
/// Exchange with unknown remote (pass public key for ingress exchange)
ECDHEKeyExchange(Alias& _k): m_alias(_k) {};
/// Exchange with known remote
ECDHEKeyExchange(Alias& _k, AliasSession _known): m_alias(_k), m_known(_known) {};
/// Provide public key for dh agreement to generate shared secret.
void agree(Public const& _remoteEphemeral);
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/// @returns encrypted payload of key exchange
void exchange(bytes& o_exchange);
/// Decrypt payload, check mac, check trust, decrypt exchange, authenticate exchange, verify version, verify signature, and if no failure occurs, update or creats trust and derive session-shared-secret.
bool authenticate(bytes _exchangeIn);
private:
Secret m_ephemeralSecret;
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Alias m_alias;
AliasSession m_known;
Secret m_sharedAliasSecret;
FixedHash<16> m_sharedC;
FixedHash<16> m_sharedM;
};
}
}