default.cpp

// default.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "default.h"
#include "queue.h"
#include <time.h>
#include <memory>

NAMESPACE_BEGIN(CryptoPP)

static const unsigned int MASH_ITERATIONS = 200;
static const unsigned int SALTLENGTH = 8;
static const unsigned int BLOCKSIZE = Default_BlockCipher::Encryption::BLOCKSIZE;
static const unsigned int KEYLENGTH = Default_BlockCipher::Encryption::DEFAULT_KEYLENGTH;

// The purpose of this function Mash() is to take an arbitrary length input
// string and *deterministicly* produce an arbitrary length output string such
// that (1) it looks random, (2) no information about the input is
// deducible from it, and (3) it contains as much entropy as it can hold, or
// the amount of entropy in the input string, whichever is smaller.

static void Mash(const byte *in, size_t inLen, byte *out, size_t outLen, int iterations)
{
        if (BytePrecision(outLen) > 2)
                throw InvalidArgument("Mash: output legnth too large");

        size_t bufSize = RoundUpToMultipleOf(outLen, (size_t)DefaultHashModule::DIGESTSIZE);
        byte b[2];
        SecByteBlock buf(bufSize);
        SecByteBlock outBuf(bufSize);
        DefaultHashModule hash;

        unsigned int i;
        for(i=0; i<outLen; i+=DefaultHashModule::DIGESTSIZE)
        {
                b[0] = (byte) (i >> 8);
                b[1] = (byte) i;
                hash.Update(b, 2);
                hash.Update(in, inLen);
                hash.Final(outBuf+i);
        }

        while (iterations-- > 1)
        {
                memcpy(buf, outBuf, bufSize);
                for (i=0; i<bufSize; i+=DefaultHashModule::DIGESTSIZE)
                {
                        b[0] = (byte) (i >> 8);
                        b[1] = (byte) i;
                        hash.Update(b, 2);
                        hash.Update(buf, bufSize);
                        hash.Final(outBuf+i);
                }
        }

        memcpy(out, outBuf, outLen);
}

static void GenerateKeyIV(const byte *passphrase, size_t passphraseLength, const byte *salt, size_t saltLength, byte *key, byte *IV)
{
        SecByteBlock temp(passphraseLength+saltLength);
        memcpy(temp, passphrase, passphraseLength);
        memcpy(temp+passphraseLength, salt, saltLength);
        SecByteBlock keyIV(KEYLENGTH+BLOCKSIZE);
        Mash(temp, passphraseLength + saltLength, keyIV, KEYLENGTH+BLOCKSIZE, MASH_ITERATIONS);
        memcpy(key, keyIV, KEYLENGTH);
        memcpy(IV, keyIV+KEYLENGTH, BLOCKSIZE);
}

// ********************************************************

DefaultEncryptor::DefaultEncryptor(const char *passphrase, BufferedTransformation *attachment)
        : ProxyFilter(NULL, 0, 0, attachment), m_passphrase((const byte *)passphrase, strlen(passphrase))
{
}

DefaultEncryptor::DefaultEncryptor(const byte *passphrase, size_t passphraseLength, BufferedTransformation *attachment)
        : ProxyFilter(NULL, 0, 0, attachment), m_passphrase(passphrase, passphraseLength)
{
}


void DefaultEncryptor::FirstPut(const byte *)
{
        // VC60 workaround: __LINE__ expansion bug
        CRYPTOPP_COMPILE_ASSERT_INSTANCE(SALTLENGTH <= DefaultHashModule::DIGESTSIZE, 1);
        CRYPTOPP_COMPILE_ASSERT_INSTANCE(BLOCKSIZE <= DefaultHashModule::DIGESTSIZE, 2);

        SecByteBlock salt(DefaultHashModule::DIGESTSIZE), keyCheck(DefaultHashModule::DIGESTSIZE);
        DefaultHashModule hash;

        // use hash(passphrase | time | clock) as salt
        hash.Update(m_passphrase, m_passphrase.size());
        time_t t=time(0);
        hash.Update((byte *)&t, sizeof(t));
        clock_t c=clock();
        hash.Update((byte *)&c, sizeof(c));
        hash.Final(salt);

        // use hash(passphrase | salt) as key check
        hash.Update(m_passphrase, m_passphrase.size());
        hash.Update(salt, SALTLENGTH);
        hash.Final(keyCheck);

        AttachedTransformation()->Put(salt, SALTLENGTH);

        // mash passphrase and salt together into key and IV
        SecByteBlock key(KEYLENGTH);
        SecByteBlock IV(BLOCKSIZE);
        GenerateKeyIV(m_passphrase, m_passphrase.size(), salt, SALTLENGTH, key, IV);

        m_cipher.SetKeyWithIV(key, key.size(), IV);
        SetFilter(new StreamTransformationFilter(m_cipher));

        m_filter->Put(keyCheck, BLOCKSIZE);
}

void DefaultEncryptor::LastPut(const byte *inString, size_t length)
{
        m_filter->MessageEnd();
}

// ********************************************************

DefaultDecryptor::DefaultDecryptor(const char *p, BufferedTransformation *attachment, bool throwException)
        : ProxyFilter(NULL, SALTLENGTH+BLOCKSIZE, 0, attachment)
        , m_state(WAITING_FOR_KEYCHECK)
        , m_passphrase((const byte *)p, strlen(p))
        , m_throwException(throwException)
{
}

DefaultDecryptor::DefaultDecryptor(const byte *passphrase, size_t passphraseLength, BufferedTransformation *attachment, bool throwException)
        : ProxyFilter(NULL, SALTLENGTH+BLOCKSIZE, 0, attachment)
        , m_state(WAITING_FOR_KEYCHECK)
        , m_passphrase(passphrase, passphraseLength)
        , m_throwException(throwException)
{
}

void DefaultDecryptor::FirstPut(const byte *inString)
{
        CheckKey(inString, inString+SALTLENGTH);
}

void DefaultDecryptor::LastPut(const byte *inString, size_t length)
{
        if (m_filter.get() == NULL)
        {
                m_state = KEY_BAD;
                if (m_throwException)
                        throw KeyBadErr();
        }
        else
        {
                m_filter->MessageEnd();
                m_state = WAITING_FOR_KEYCHECK;
        }
}

void DefaultDecryptor::CheckKey(const byte *salt, const byte *keyCheck)
{
        SecByteBlock check(STDMAX((unsigned int)2*BLOCKSIZE, (unsigned int)DefaultHashModule::DIGESTSIZE));

        DefaultHashModule hash;
        hash.Update(m_passphrase, m_passphrase.size());
        hash.Update(salt, SALTLENGTH);
        hash.Final(check);

        SecByteBlock key(KEYLENGTH);
        SecByteBlock IV(BLOCKSIZE);
        GenerateKeyIV(m_passphrase, m_passphrase.size(), salt, SALTLENGTH, key, IV);

        m_cipher.SetKeyWithIV(key, key.size(), IV);
        std::auto_ptr<StreamTransformationFilter> decryptor(new StreamTransformationFilter(m_cipher));

        decryptor->Put(keyCheck, BLOCKSIZE);
        decryptor->ForceNextPut();
        decryptor->Get(check+BLOCKSIZE, BLOCKSIZE);

        SetFilter(decryptor.release());

        if (memcmp(check, check+BLOCKSIZE, BLOCKSIZE))
        {
                m_state = KEY_BAD;
                if (m_throwException)
                        throw KeyBadErr();
        }
        else
                m_state = KEY_GOOD;
}

// ********************************************************

static DefaultMAC * NewDefaultEncryptorMAC(const byte *passphrase, size_t passphraseLength)
{
        size_t macKeyLength = DefaultMAC::StaticGetValidKeyLength(16);
        SecByteBlock macKey(macKeyLength);
        // since the MAC is encrypted there is no reason to mash the passphrase for many iterations
        Mash(passphrase, passphraseLength, macKey, macKeyLength, 1);
        return new DefaultMAC(macKey, macKeyLength);
}

DefaultEncryptorWithMAC::DefaultEncryptorWithMAC(const char *passphrase, BufferedTransformation *attachment)
        : ProxyFilter(NULL, 0, 0, attachment)
        , m_mac(NewDefaultEncryptorMAC((const byte *)passphrase, strlen(passphrase)))
{
        SetFilter(new HashFilter(*m_mac, new DefaultEncryptor(passphrase), true));
}

DefaultEncryptorWithMAC::DefaultEncryptorWithMAC(const byte *passphrase, size_t passphraseLength, BufferedTransformation *attachment)
        : ProxyFilter(NULL, 0, 0, attachment)
        , m_mac(NewDefaultEncryptorMAC(passphrase, passphraseLength))
{
        SetFilter(new HashFilter(*m_mac, new DefaultEncryptor(passphrase, passphraseLength), true));
}

void DefaultEncryptorWithMAC::LastPut(const byte *inString, size_t length)
{
        m_filter->MessageEnd();
}

// ********************************************************

DefaultDecryptorWithMAC::DefaultDecryptorWithMAC(const char *passphrase, BufferedTransformation *attachment, bool throwException)
        : ProxyFilter(NULL, 0, 0, attachment)
        , m_mac(NewDefaultEncryptorMAC((const byte *)passphrase, strlen(passphrase)))
        , m_throwException(throwException)
{
        SetFilter(new DefaultDecryptor(passphrase, m_hashVerifier=new HashVerifier(*m_mac, NULL, HashVerifier::PUT_MESSAGE), throwException));
}

DefaultDecryptorWithMAC::DefaultDecryptorWithMAC(const byte *passphrase, size_t passphraseLength, BufferedTransformation *attachment, bool throwException)
        : ProxyFilter(NULL, 0, 0, attachment)
        , m_mac(NewDefaultEncryptorMAC(passphrase, passphraseLength))
        , m_throwException(throwException)
{
        SetFilter(new DefaultDecryptor(passphrase, passphraseLength, m_hashVerifier=new HashVerifier(*m_mac, NULL, HashVerifier::PUT_MESSAGE), throwException));
}

DefaultDecryptor::State DefaultDecryptorWithMAC::CurrentState() const
{
        return static_cast<const DefaultDecryptor *>(m_filter.get())->CurrentState();
}

bool DefaultDecryptorWithMAC::CheckLastMAC() const
{
        return m_hashVerifier->GetLastResult();
}

void DefaultDecryptorWithMAC::LastPut(const byte *inString, size_t length)
{
        m_filter->MessageEnd();
        if (m_throwException && !CheckLastMAC())
                throw MACBadErr();
}

NAMESPACE_END

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