crypter.h

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// Copyright (c) 2009-2012 The Bitcoin Developers
// Distributed under the MIT/X11 software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef __CRYPTER_H__
#define __CRYPTER_H__

#include "allocators.h" /* for SecureString */
#include "key.h"
#include "serialize.h"

const unsigned int WALLET_CRYPTO_KEY_SIZE = 32;
const unsigned int WALLET_CRYPTO_SALT_SIZE = 8;

/*
Private key encryption is done based on a CMasterKey,
which holds a salt and random encryption key.

CMasterKeys are encrypted using AES-256-CBC using a key
derived using derivation method nDerivationMethod
(0 == EVP_sha512()) and derivation iterations nDeriveIterations.
vchOtherDerivationParameters is provided for alternative algorithms
which may require more parameters (such as scrypt).

Wallet Private Keys are then encrypted using AES-256-CBC
with the double-sha256 of the public key as the IV, and the
master key's key as the encryption key (see keystore.[ch]).
*/

class CMasterKey
{
public:
    std::vector<unsigned char> vchCryptedKey;
    std::vector<unsigned char> vchSalt;
    // 0 = EVP_sha512()
    // 1 = scrypt()
    unsigned int nDerivationMethod;
    unsigned int nDeriveIterations;
    // Use this for more parameters to key derivation,
    // such as the various parameters to scrypt
    std::vector<unsigned char> vchOtherDerivationParameters;

    IMPLEMENT_SERIALIZE
    (
        READWRITE(vchCryptedKey);
        READWRITE(vchSalt);
        READWRITE(nDerivationMethod);
        READWRITE(nDeriveIterations);
        READWRITE(vchOtherDerivationParameters);
    )
    CMasterKey()
    {
        // 25000 rounds is just under 0.1 seconds on a 1.86 GHz Pentium M
        // ie slightly lower than the lowest hardware we need bother supporting
        nDeriveIterations = 25000;
        nDerivationMethod = 0;
        vchOtherDerivationParameters = std::vector<unsigned char>(0);
    }
};

typedef std::vector<unsigned char, secure_allocator<unsigned char> > CKeyingMaterial;

class CCrypter
{
private:
    unsigned char chKey[WALLET_CRYPTO_KEY_SIZE];
    unsigned char chIV[WALLET_CRYPTO_KEY_SIZE];
    bool fKeySet;

public:
    bool SetKeyFromPassphrase(const SecureString &strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod);
    bool Encrypt(const CKeyingMaterial& vchPlaintext, std::vector<unsigned char> &vchCiphertext);
    bool Decrypt(const std::vector<unsigned char>& vchCiphertext, CKeyingMaterial& vchPlaintext);
    bool SetKey(const CKeyingMaterial& chNewKey, const std::vector<unsigned char>& chNewIV);

    void CleanKey()
    {
        OPENSSL_cleanse(chKey, sizeof(chKey));
        OPENSSL_cleanse(chIV, sizeof(chIV));
        fKeySet = false;
    }

    CCrypter()
    {
        fKeySet = false;

        // Try to keep the key data out of swap (and be a bit over-careful to keep the IV that we don't even use out of swap)
        // Note that this does nothing about suspend-to-disk (which will put all our key data on disk)
        // Note as well that at no point in this program is any attempt made to prevent stealing of keys by reading the memory of the running process.
        LockedPageManager::instance.LockRange(&chKey[0], sizeof chKey);
        LockedPageManager::instance.LockRange(&chIV[0], sizeof chIV);
    }

    ~CCrypter()
    {
        CleanKey();

        LockedPageManager::instance.UnlockRange(&chKey[0], sizeof chKey);
        LockedPageManager::instance.UnlockRange(&chIV[0], sizeof chIV);
    }
};

bool EncryptSecret(const CKeyingMaterial& vMasterKey, const CKeyingMaterial &vchPlaintext, const uint256& nIV, std::vector<unsigned char> &vchCiphertext);
bool DecryptSecret(const CKeyingMaterial& vMasterKey, const std::vector<unsigned char>& vchCiphertext, const uint256& nIV, CKeyingMaterial& vchPlaintext);

#endif