Add wallet privkey encryption.

This commit adds support for ckeys, or enCrypted private keys, to the wallet.
All keys are stored in memory in their encrypted form and thus the passphrase
is required from the user to spend coins, or to create new addresses.

Keys are encrypted with AES-256-CBC using OpenSSL's EVP library. The key is
calculated via EVP_BytesToKey using SHA512 with (by default) 25000 rounds and
a random salt.

By default, the user's wallet remains unencrypted until they call the RPC
command encryptwallet <passphrase> or, from the GUI menu, Options->
Encrypt Wallet.

When the user is attempting to call RPC functions which require the password
to unlock the wallet, an error will be returned unless they call
walletpassphrase <passphrase> <time to keep key in memory> first.

A keypoolrefill command has been added which tops up the users keypool
(requiring the passphrase via walletpassphrase first).
keypoolsize has been added to the output of getinfo to show the user the
number of keys left before they need to specify their passphrase (and call
keypoolrefill).

Note that walletpassphrase will automatically fill keypool in a separate
thread which it spawns when the passphrase is set. This could cause some
delays in other threads waiting for locks on the wallet passphrase, including
one which could cause the passphrase to be stored longer than expected,
however it will not allow the passphrase to be used longer than expected as
ThreadCleanWalletPassphrase will attempt to get a lock on the key as soon
as the specified lock time has arrived.

When the keypool runs out (and wallet is locked) GetOrReuseKeyFromPool
returns vchDefaultKey, meaning miners may start to generate many blocks to
vchDefaultKey instead of a new key each time.

A walletpassphrasechange <oldpassphrase> <newpassphrase> has been added to
allow the user to change their password via RPC.

Whenever keying material (unencrypted private keys, the user's passphrase,
the wallet's AES key) is stored unencrypted in memory, any reasonable attempt
is made to mlock/VirtualLock that memory before storing the keying material.
This is not true in several (commented) cases where mlock/VirtualLocking the
memory is not possible.

Although encryption of private keys in memory can be very useful on desktop
systems (as some small amount of protection against stupid viruses), on an
RPC server, the password is entered fairly insecurely. Thus, the only main
advantage encryption has for RPC servers is for RPC servers that do not spend
coins, except in rare cases, eg. a webserver of a merchant which only receives
payment except for cases of manual intervention.

Thanks to jgarzik for the original patch and sipa, gmaxwell and many others
for all their input.

Conflicts:

	src/wallet.cpp

1 files changed, 96 insertions, 0 deletions

diff --git a/src/crypter.h b/src/crypter.h
new file mode 100644
index 0000000000..5b95ea415e
--- /dev/null
+++ b/src/crypter.h
@@ -0,0 +1,96 @@
+// Copyright (c) 2011 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 "key.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 is 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 private key as the IV, and the
+master key's key as the encryption key.
+*/
+
+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 std::string &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()
+    {
+        memset(&chKey, 0, sizeof chKey);
+        memset(&chIV, 0, sizeof chIV);
+        munlock(&chKey, sizeof chKey);
+        munlock(&chIV, sizeof chIV);
+        fKeySet = false;
+    }
+
+    CCrypter()
+    {
+        fKeySet = false;
+    }
+
+    ~CCrypter()
+    {
+        CleanKey();
+    }
+};
+
+bool EncryptSecret(CKeyingMaterial& vMasterKey, const CSecret &vchPlaintext, const uint256& nIV, std::vector<unsigned char> &vchCiphertext);
+bool DecryptSecret(const CKeyingMaterial& vMasterKey, const std::vector<unsigned char> &vchCiphertext, const uint256& nIV, CSecret &vchPlaintext);
+
+#endif