keepassx1/src/crypto/twofish.cpp

/*
 * Fast, portable, and easy-to-use Twofish implementation, 
 * Version 0.3.
 * Copyright (c) 2002 by Niels Ferguson. 
 * (See further down for the almost-unrestricted licensing terms.)
 *
 * --------------------------------------------------------------------------
 * There are two files for this implementation:
 * - twofish.h, the header file.
 * - twofish.c, the code file.
 *
 * To incorporate this code into your program you should:
 * - Check the licensing terms further down in this comment.
 * - Fix the two type definitions in twofish.h to suit your platform.
 * - Fix a few definitions in twofish.c in the section marked 
 *   PLATFORM FIXES. There is one important ones that affects 
 *   functionality, and then a few definitions that you can optimise 
 *   for efficiency but those have no effect on the functionality. 
 *   Don't change anything else.
 * - Put the code in your project and compile it.
 *
 * To use this library you should:
 * - Call Twofish_initialise() in your program before any other function in
 *   this library.
 * - Use Twofish_prepare_key(...) to convert a key to internal form.
 * - Use Twofish_encrypt(...) and Twofish_decrypt(...) to encrypt and decrypt
 *   data.
 * See the comments in the header file for details on these functions.
 * --------------------------------------------------------------------------
 * 
 * There are many Twofish implementation available for free on the web.
 * Most of them are hard to integrate into your own program.
 * As we like people to use our cipher, I thought I would make it easier. 
 * Here is a free and easy-to-integrate Twofish implementation in C.
 * The latest version is always available from my personal home page at
 *    http://niels.ferguson.net/
 *
 * Integrating library code into a project is difficult because the library
 * header files interfere with the project's header files and code. 
 * And of course the project's header files interfere with the library code.
 * I've tried to resolve these problems here. 
 * The header file of this implementation is very light-weight. 
 * It contains two typedefs, a structure, and a few function declarations.
 * All names it defines start with "Twofish_". 
 * The header file is therefore unlikely to cause problems in your project.
 * The code file of this implementation doesn't need to include the header
 * files of the project. There is thus no danger of the project interfering
 * with all the definitions and macros of the Twofish code.
 * In most situations, all you need to do is fill in a few platform-specific
 * definitions in the header file and code file, 
 * and you should be able to run the Twofish code in your project.
 * I estimate it should take you less than an hour to integrate this code
 * into your project, most of it spent reading the comments telling you what
 * to do.
 *
 * For people using C++: it is very easy to wrap this library into a
 * TwofishKey class. One of the big advantages is that you can automate the
 * wiping of the key material in the destructor. I have not provided a C++
 * class because the interface depends too much on the abstract base class 
 * you use for block ciphers in your program, which I don't know about.
 *
 * This implementation is designed for use on PC-class machines. It uses the 
 * Twofish 'full' keying option which uses large tables. Total table size is 
 * around 5-6 kB for static tables plus 4.5 kB for each pre-processed key.
 * If you need an implementation that uses less memory,
 * take a look at Brian Gladman's code on his web site:
 *     http://fp.gladman.plus.com/cryptography_technology/aes/
 * He has code for all AES candidates.
 * His Twofish code has lots of options trading off table size vs. speed.
 * You can also take a look at the optimised code by Doug Whiting on the
 * Twofish web site
 *      http://www.counterpane.com/twofish.html
 * which has loads of options.
 * I believe these existing implementations are harder to re-use because they
 * are not clean libraries and they impose requirements on the environment. 
 * This implementation is very careful to minimise those, 
 * and should be easier to integrate into any larger program.
 *
 * The default mode of this implementation is fully portable as it uses no
 * behaviour not defined in the C standard. (This is harder than you think.)
 * If you have any problems porting the default mode, please let me know
 * so that I can fix the problem. (But only if this code is at fault, I 
 * don't fix compilers.)
 * Most of the platform fixes are related to non-portable but faster ways 
 * of implementing certain functions.
 *
 * In general I've tried to make the code as fast as possible, at the expense
 * of memory and code size. However, C does impose limits, and this 
 * implementation will be slower than an optimised assembler implementation.
 * But beware of assembler implementations: a good Pentium implementation
 * uses completely different code than a good Pentium II implementation.
 * You basically have to re-write the assembly code for every generation of
 * processor. Unless you are severely pressed for speed, stick with C.
 *
 * The initialisation routine of this implementation contains a self-test.
 * If initialisation succeeds without calling the fatal routine, then
 * the implementation works. I don't think you can break the implementation
 * in such a way that it still passes the tests, unless you are malicious.
 * In other words: if the initialisation routine returns, 
 * you have successfully ported the implementation. 
 * (Or not implemented the fatal routine properly, but that is your problem.)
 *
 * I'm indebted to many people who helped me in one way or another to write
 * this code. During the design of Twofish and the AES process I had very 
 * extensive discussions of all implementation issues with various people.
 * Doug Whiting in particular provided a wealth of information. The Twofish 
 * team spent untold hours discussion various cipher features, and their 
 * implementation. Brian Gladman implemented all AES candidates in C, 
 * and we had some fruitful discussions on how to implement Twofish in C.
 * Jan Nieuwenhuizen tested this code on Linux using GCC.
 *
 * Now for the license:
 * The author hereby grants a perpetual license to everybody to
 * use this code for any purpose as long as the copyright message is included
 * in the source code of this or any derived work.
 * 
 * Yes, this means that you, your company, your club, and anyone else
 * can use this code anywhere you want. You can change it and distribute it
 * under the GPL, include it in your commercial product without releasing
 * the source code, put it on the web, etc. 
 * The only thing you cannot do is remove my copyright message, 
 * or distribute any source code based on this implementation that does not 
 * include my copyright message. 
 * 
 * I appreciate a mention in the documentation or credits, 
 * but I understand if that is difficult to do.
 * I also appreciate it if you tell me where and why you used my code.
 *
 * Please send any questions or comments to niels@ferguson.net
 *
 * Have Fun!
 *
 * Niels
 */

/*
 * DISCLAIMER: As I'm giving away my work for free, I'm of course not going
 * to accept any liability of any form. This code, or the Twofish cipher,
 * might very well be flawed; you have been warned.
 * This software is provided as-is, without any kind of warrenty or
 * guarantee. And that is really all you can expect when you download 
 * code for free from the Internet. 
 *
 * I think it is really sad that disclaimers like this seem to be necessary.
 * If people only had a little bit more common sense, and didn't come
 * whining like little children every time something happens....
 */
 
/*
 * Version history:
 * Version 0.0, 2002-08-30
 *      First written.
 * Version 0.1, 2002-09-03
 *      Added disclaimer. Improved self-tests.
 * Version 0.2, 2002-09-09
 *      Removed last non-portabilities. Default now works completely within
 *      the C standard. UInt32 can be larger than 32 bits without problems.
 * Version 0.3, 2002-09-28
 *      Bugfix: use <string.h> instead of <memory.h> to adhere to ANSI/ISO.
 *      Rename BIG_ENDIAN macro to CPU_IS_BIG_ENDIAN. The gcc library 
 *      header <string.h> already defines BIG_ENDIAN, even though it is not 
 *      supposed to.
 */


/* 
 * Minimum set of include files.
 * You should not need any application-specific include files for this code. 
 * In fact, adding you own header files could break one of the many macros or
 * functions in this file. Be very careful.
 * Standard include files will probably be ok.
 */

#include <qstring.h>     /* for memset(), memcpy(), and memcmp() */
#include "twofish.h"


/*
 * PLATFORM FIXES
 * ==============
 *
 * Fix the type definitions in twofish.h first!
 * 
 * The following definitions have to be fixed for each particular platform 
 * you work on. If you have a multi-platform program, you no doubt have 
 * portable definitions that you can substitute here without changing the 
 * rest of the code.
 */


/* 
 * Function called if something is fatally wrong with the implementation. 
 * This fatal function is called when a coding error is detected in the
 * Twofish implementation, or when somebody passes an obviously erroneous
 * parameter to this implementation. There is not much you can do when
 * the code contains bugs, so we just stop.
 * 
 * The argument is a string. Ideally the fatal function prints this string
 * as an error message. Whatever else this function does, it should never
 * return. A typical implementation would stop the program completely after
 * printing the error message.
 *
 * This default implementation is not very useful, 
 * but does not assume anything about your environment. 
 * It will at least let you know something is wrong....
 * I didn't want to include any libraries to print and error or so,
 * as this makes the code much harder to integrate in a project.
 *
 * Note that the Twofish_fatal function may not return to the caller.
 * Unfortunately this is not something the self-test can test for,
 * so you have to make sure of this yourself.
 *
 * If you want to call an external function, be careful about including
 * your own header files here. This code uses a lot of macros, and your
 * header file could easily break it. Maybe the best solution is to use
 * a separate extern statement for your fatal function.
 */

//#define Twofish_fatal(pmsgx) { MessageBox(GetDesktopWindow(), _T(pmsgx), _T("Twofish Fatal Error"), MB_OK); }


/*
 * The rest of the settings are not important for the functionality
 * of this Twofish implementation. That is, their default settings
 * work on all platforms. You can change them to improve the 
 * speed of the implementation on your platform. Erroneous settings
 * will result in erroneous implementations, but the self-test should
 * catch those.
 */


/* 
 * Macros to rotate a Twofish_UInt32 value left or right by the 
 * specified number of bits. This should be a 32-bit rotation, 
 * and not rotation of, say, 64-bit values.
 *
 * Every encryption or decryption operation uses 32 of these rotations,
 * so it is a good idea to make these macros efficient.
 *
 * This fully portable definition has one piece of tricky stuff.
 * The UInt32 might be larger than 32 bits, so we have to mask
 * any higher bits off. The simplest way to do this is to 'and' the
 * value first with 0xffffffff and then shift it right. An optimising
 * compiler that has a 32-bit type can optimise this 'and' away.
 * 
 * Unfortunately there is no portable way of writing the constant
 * 0xffffffff. You don't know which suffix to use (U, or UL?)
 * The quint32_MASK definition uses a bit of trickery. Shift-left
 * is only defined if the shift amount is strictly less than the size
 * of the UInt32, so we can't use (1<<32). The answer it to take the value
 * 2, cast it to a UInt32, shift it left 31 positions, and subtract one.
 * Another example of how to make something very simple extremely difficult.
 * I hate C.
 * 
 * The rotation macros are straightforward.
 * They are only applied to UInt32 values, which are _unsigned_
 * so the >> operator must do a logical shift that brings in zeroes.
 * On most platforms you will only need to optimise the ROL32 macro; the
 * ROR32 macro is not inefficient on an optimising compiler as all rotation
 * amounts in this code are known at compile time.
 *
 * On many platforms there is a faster solution.
 * For example, MS compilers have the __rotl and __rotr functions
 * that generate x86 rotation instructions.
 */
#define quint32_MASK    ( (((Twofish_UInt32)2)<<31) - 1 )

#ifndef _MSC_VER
#define ROL32(x,n) ( (x)<<(n) | ((x) & quint32_MASK) >> (32-(n)) )
#define ROR32(x,n) ( (x)>>(n) | ((x) & quint32_MASK) << (32-(n)) )
#else
#define ROL32(x,n) (_lrotl((x), (n)))
#define ROR32(x,n) (_lrotr((x), (n)))
#endif

/*
 * Select data type for q-table entries. 
 *
 * Larger entry types cost more memory (1.5 kB), and might be faster 
 * or slower depending on the CPU and compiler details.
 *
 * This choice only affects the static data size and the key setup speed.
 * Functionality, expanded key size, or encryption speed are not affected.
 * Define to 1 to get large q-table entries.
 */
#define LARGE_Q_TABLE   0    /* default = 0 */


/*
 * Method to select a single byte from a UInt32.
 * WARNING: non-portable code if set; might not work on all platforms.
 *
 * Inside the inner loop of Twofish it is necessary to access the 4 
 * individual bytes of a UInt32. This can be done using either shifts
 * and masks, or memory accesses.
 *
 * Set to 0 to use shift and mask operations for the byte selection.
 * This is more ALU intensive. It is also fully portable. 
 * 
 * Set to 1 to use memory accesses. The UInt32 is stored in memory and
 * the individual bytes are read from memory one at a time.
 * This solution is more memory-intensive, and not fully portable.
 * It might be faster on your platform, or not. If you use this option,
 * make sure you set the CPU_IS_BIG_ENDIAN flag appropriately.
 * 
 * This macro does not affect the conversion of the inputs and outputs
 * of the cipher. See the CONVERT_USING_CASTS macro for that.
 */
#define SELECT_BYTE_FROM_quint32_IN_MEMORY    0    /* default = 0 */


/*
 * Method used to read the input and write the output.
 * WARNING: non-portable code if set; might not work on all platforms.
 *
 * Twofish operates on 32-bit words. The input to the cipher is
 * a byte array, as is the output. The portable method of doing the
 * conversion is a bunch of rotate and mask operations, but on many 
 * platforms it can be done faster using a cast.
 * This only works if your CPU allows UInt32 accesses to arbitrary Byte
 * addresses.
 * 
 * Set to 0 to use the shift and mask operations. This is fully
 * portable. .
 *
 * Set to 1 to use a cast. The Byte * is cast to a UInt32 *, and a
 * UInt32 is read. If necessary (as indicated by the CPU_IS_BIG_ENDIAN 
 * macro) the byte order in the UInt32 is swapped. The reverse is done
 * to write the output of the encryption/decryption. Make sure you set
 * the CPU_IS_BIG_ENDIAN flag appropriately.
 * This option does not work unless a UInt32 is exactly 32 bits.
 *
 * This macro only changes the reading/writing of the plaintext/ciphertext.
 * See the SELECT_BYTE_FROM_quint32_IN_MEMORY to affect the way in which
 * a UInt32 is split into 4 bytes for the S-box selection.
 */
#define CONVERT_USING_CASTS    0    /* default = 0 */


/* 
 * Endianness switch.
 * Only relevant if SELECT_BYTE_FROM_quint32_IN_MEMORY or
 * CONVERT_USING_CASTS is set.
 *
 * Set to 1 on a big-endian machine, and to 0 on a little-endian machine. 
 * Twofish uses the little-endian convention (least significant byte first)
 * and big-endian machines (using most significant byte first) 
 * have to do a few conversions. 
 *
 * CAUTION: This code has never been tested on a big-endian machine, 
 * because I don't have access to one. Feedback appreciated.
 */
#define CPU_IS_BIG_ENDIAN    0


/* 
 * Macro to reverse the order of the bytes in a UInt32.
 * Used to convert to little-endian on big-endian machines.
 * This macro is always tested, but only used in the encryption and
 * decryption if CONVERT_USING_CASTS, and CPU_IS_BIG_ENDIAN
 * are both set. In other words: this macro is only speed-critical if
 * both these flags have been set.
 *
 * This default definition of SWAP works, but on many platforms there is a 
 * more efficient implementation. 
 */
#define BSWAP(x) (ROL32((x),8)&0x00ff00ff | ROR32((x),8) & 0xff00ff00)


/*
 * END OF PLATFORM FIXES
 * =====================
 * 
 * You should not have to touch the rest of this file.
 */


/*
 * Convert the external type names to some that are easier to use inside
 * this file. I didn't want to use the names Byte and UInt32 in the
 * header file, because many programs already define them and using two
 * conventions at once can be very difficult.
 * Don't change these definitions! Change the originals 
 * in twofish.h instead. 
 */
/* A Byte must be an unsigned integer, 8 bits long. */
// typedef Twofish_Byte    Byte;
/* A UInt32 must be an unsigned integer at least 32 bits long. */
// typedef Twofish_UInt32  UInt32;


/* 
 * Define a macro ENDIAN_CONVERT.
 *
 * We define a macro ENDIAN_CONVERT that performs a BSWAP on big-endian
 * machines, and is the identity function on little-endian machines.
 * The code then uses this macro without considering the endianness.
 */

#if CPU_IS_BIG_ENDIAN
#define ENDIAN_CONVERT(x)    BSWAP(x)
#else
#define ENDIAN_CONVERT(x)    (x)
#endif


/* 
 * Compute byte offset within a UInt32 stored in memory.
 *
 * This is only used when SELECT_BYTE_FROM_quint32_IN_MEMORY is set.
 * 
 * The input is the byte number 0..3, 0 for least significant.
 * Note the use of sizeof() to support UInt32 types that are larger
 * than 4 bytes.
 */
#if CPU_IS_BIG_ENDIAN
#define BYTE_OFFSET( n )  (sizeof(Twofish_UInt32) - 1 - (n) )
#else
#define BYTE_OFFSET( n )  (n)
#endif


/*
 * Macro to get Byte no. b from UInt32 value X.
 * We use two different definition, depending on the settings.
 */
#if SELECT_BYTE_FROM_quint32_IN_MEMORY
    /* Pick the byte from the memory in which X is stored. */
#define SELECT_BYTE( X, b ) (((Twofish_Byte *)(&(X)))[BYTE_OFFSET(b)])
#else
    /* Portable solution: Pick the byte directly from the X value. */
#define SELECT_BYTE( X, b ) (((X) >> (8*(b))) & 0xff)
#endif


/* Some shorthands because we use byte selection in large formulae. */
#define b0(X)   SELECT_BYTE((X),0)
#define b1(X)   SELECT_BYTE((X),1)
#define b2(X)   SELECT_BYTE((X),2)
#define b3(X)   SELECT_BYTE((X),3)


/*
 * We need macros to load and store UInt32 from/to byte arrays
 * using the least-significant-byte-first convention.
 *
 * GET32( p ) gets a UInt32 in lsb-first form from four bytes pointed to
 * by p.
 * PUT32( v, p ) writes the UInt32 value v at address p in lsb-first form.
 */
#if CONVERT_USING_CASTS

    /* Get UInt32 from four bytes pointed to by p. */
#define GET32( p )    ENDIAN_CONVERT( *((Twofish_UInt32 *)(p)) )
    /* Put UInt32 into four bytes pointed to by p */
#define PUT32( v, p ) *((Twofish_UInt32 *)(p)) = ENDIAN_CONVERT(v)

#else

    /* Get UInt32 from four bytes pointed to by p. */
#define GET32( p ) \
    ( \
      (Twofish_UInt32)((p)[0])     \
    | (Twofish_UInt32)((p)[1])<< 8 \
    | (Twofish_UInt32)((p)[2])<<16 \
    | (Twofish_UInt32)((p)[3])<<24 \
    )
    /* Put UInt32 into four bytes pointed to by p */
#define PUT32( v, p ) \
    (p)[0] = (Twofish_Byte)(((v)      ) & 0xff); \
    (p)[1] = (Twofish_Byte)(((v) >>  8) & 0xff); \
    (p)[2] = (Twofish_Byte)(((v) >> 16) & 0xff); \
    (p)[3] = (Twofish_Byte)(((v) >> 24) & 0xff)

#endif


void Twofish_fatal(char* msg){
	qCritical("Twofish: Fatal Error");
	exit(1);
}



/*
 * Test the platform-specific macros.
 * This function tests the macros defined so far to make sure the 
 * definitions are appropriate for this platform.
 * If you make any mistake in the platform configuration, this should detect
 * that and inform you what went wrong.
 * Somewhere, someday, this is going to save somebody a lot of time,
 * because misbehaving macros are hard to debug.
 */
static void test_platform()
    {
    /* Buffer with test values. */
    Twofish_Byte buf[] = {0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0};
    Twofish_UInt32 C;
    Twofish_UInt32 x,y;
    int i;

    /* 
     * Some sanity checks on the types that can't be done in compile time. 
     * A smart compiler will just optimise these tests away.
     * The pre-processor doesn't understand different types, so we cannot
     * do these checks in compile-time.
     *
     * I hate C.
     *
     * The first check in each case is to make sure the size is correct.
     * The second check is to ensure that it is an unsigned type.
     */
    if( ((Twofish_UInt32)((Twofish_UInt32)1 << 31) == 0) || ((Twofish_UInt32)-1 < 0 )) 
        {
        Twofish_fatal( "Twofish code: Twofish_UInt32 type not suitable" );
        }
    if( (sizeof( Twofish_Byte ) != 1) || (((Twofish_Byte)-1) < 0) ) 
        {
        Twofish_fatal( "Twofish code: Twofish_Byte type not suitable" );
        }

    /* 
     * Sanity-check the endianness conversions. 
     * This is just an aid to find problems. If you do the endianness
     * conversion macros wrong you will fail the full cipher test,
     * but that does not help you find the error.
     * Always make it easy to find the bugs! 
     *
     * Detail: There is no fully portable way of writing UInt32 constants,
     * as you don't know whether to use the U or UL suffix. Using only U you
     * might only be allowed 16-bit constants. Using UL you might get 64-bit
     * constants which cannot be stored in a UInt32 without warnings, and
     * which generally behave subtly different from a true UInt32.
     * As long as we're just comparing with the constant, 
     * we can always use the UL suffix and at worst lose some efficiency. 
     * I use a separate '32-bit constant' macro in most of my other code.
     *
     * I hate C.
     *
     * Start with testing GET32. We test it on all positions modulo 4 
     * to make sure we can handly any position of inputs. (Some CPUs
     * do not allow non-aligned accesses which we would do if you used
     * the CONVERT_USING_CASTS option.
     */
    if( (GET32( buf ) != 0x78563412UL) || (GET32(buf+1) != 0x9a785634UL) 
        || (GET32( buf+2 ) != 0xbc9a7856UL) || (GET32(buf+3) != 0xdebc9a78UL) )
        {
        Twofish_fatal( "Twofish code: GET32 not implemented properly" );
        }

    /* 
     * We can now use GET32 to test PUT32.
     * We don't test the shifted versions. If GET32 can do that then
     * so should PUT32.
     */
    C = GET32( buf );
    PUT32( 3*C, buf );
    if( GET32( buf ) != 0x69029c36UL )
        {
        Twofish_fatal( "Twofish code: PUT32 not implemented properly" );
        }


    /* Test ROL and ROR */
    for( i=1; i<32; i++ ) 
        {
        /* Just a simple test. */
        x = ROR32( C, i );
        y = ROL32( C, i );
        x ^= (C>>i) ^ (C<<(32-i));
        y ^= (C<<i) ^ (C>>(32-i));
        x |= y;
        /* 
         * Now all we check is that x is zero in the least significant
         * 32 bits. Using the UL suffix is safe here, as it doesn't matter
         * if we get a larger type.
         */
        if( (x & 0xffffffffUL) != 0 )
            {
            Twofish_fatal( "Twofish ROL or ROR not properly defined." );
            }
        }

    /* Test the BSWAP macro */
    if( BSWAP(C) != 0x12345678UL )
        {
        /*
         * The BSWAP macro should always work, even if you are not using it.
         * A smart optimising compiler will just remove this entire test.
         */
        Twofish_fatal( "BSWAP not properly defined." );
        }

    /* And we can test the b<i> macros which use SELECT_BYTE. */
    if( (b0(C)!=0x12) || (b1(C) != 0x34) || (b2(C) != 0x56) || (b3(C) != 0x78) )
        {
        /*
         * There are many reasons why this could fail.
         * Most likely is that CPU_IS_BIG_ENDIAN has the wrong value. 
         */
        Twofish_fatal( "Twofish code: SELECT_BYTE not implemented properly" );
        }
    }


/*
 * Finally, we can start on the Twofish-related code.
 * You really need the Twofish specifications to understand this code. The
 * best source is the Twofish book:
 *     "The Twofish Encryption Algorithm", by Bruce Schneier, John Kelsey,
 *     Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson.
 * you can also use the AES submission document of Twofish, which is 
 * available from my list of publications on my personal web site at 
 *    http://niels.ferguson.net/.
 *
 * The first thing we do is write the testing routines. This is what the 
 * implementation has to satisfy in the end. We only test the external
 * behaviour of the implementation of course.
 */


/*
 * Perform a single self test on a (plaintext,ciphertext,key) triple.
 * Arguments:
 *  key     array of key bytes
 *  key_len length of key in bytes
 *  p       plaintext
 *  c       ciphertext
 */
static void test_vector( Twofish_Byte key[], int key_len, Twofish_Byte p[16], Twofish_Byte c[16] )
    {
    Twofish_Byte tmp[16];               /* scratch pad. */
    Twofish_key xkey;           /* The expanded key */
    int i;


    /* Prepare the key */
    Twofish_prepare_key( key, key_len, &xkey );

    /* 
     * We run the test twice to ensure that the xkey structure
     * is not damaged by the first encryption. 
     * Those are hideous bugs to find if you get them in an application.
     */
    for( i=0; i<2; i++ ) 
        {
        /* Encrypt and test */
        Twofish_encrypt( &xkey, p, tmp );
        if( memcmp( c, tmp, 16 ) != 0 ) 
            {
            Twofish_fatal( "Twofish encryption failure" );
            }

        /* Decrypt and test */
        Twofish_decrypt( &xkey, c, tmp );
        if( memcmp( p, tmp, 16 ) != 0 ) 
            {
            Twofish_fatal( "Twofish decryption failure" );
            }
        }

    /* The test keys are not secret, so we don't need to wipe xkey. */
    }


/*
 * Check implementation using three (key,plaintext,ciphertext)
 * test vectors, one for each major key length.
 * 
 * This is an absolutely minimal self-test. 
 * This routine does not test odd-sized keys.
 */
static void test_vectors()
    {
    /*
     * We run three tests, one for each major key length.
     * These test vectors come from the Twofish specification.
     * One encryption and one decryption using randomish data and key
     * will detect almost any error, especially since we generate the
     * tables ourselves, so we don't have the problem of a single
     * damaged table entry in the source.
     */

    /* 128-bit test is the I=3 case of section B.2 of the Twofish book. */
    static Twofish_Byte k128[] = {
        0x9F, 0x58, 0x9F, 0x5C, 0xF6, 0x12, 0x2C, 0x32, 
        0xB6, 0xBF, 0xEC, 0x2F, 0x2A, 0xE8, 0xC3, 0x5A,
        };
    static Twofish_Byte p128[] = {
        0xD4, 0x91, 0xDB, 0x16, 0xE7, 0xB1, 0xC3, 0x9E, 
        0x86, 0xCB, 0x08, 0x6B, 0x78, 0x9F, 0x54, 0x19
        };
    static Twofish_Byte c128[] = {
        0x01, 0x9F, 0x98, 0x09, 0xDE, 0x17, 0x11, 0x85, 
        0x8F, 0xAA, 0xC3, 0xA3, 0xBA, 0x20, 0xFB, 0xC3
        };

    /* 192-bit test is the I=4 case of section B.2 of the Twofish book. */
    static Twofish_Byte k192[] = {
        0x88, 0xB2, 0xB2, 0x70, 0x6B, 0x10, 0x5E, 0x36, 
        0xB4, 0x46, 0xBB, 0x6D, 0x73, 0x1A, 0x1E, 0x88, 
        0xEF, 0xA7, 0x1F, 0x78, 0x89, 0x65, 0xBD, 0x44
        };
    static Twofish_Byte p192[] = {
        0x39, 0xDA, 0x69, 0xD6, 0xBA, 0x49, 0x97, 0xD5,
        0x85, 0xB6, 0xDC, 0x07, 0x3C, 0xA3, 0x41, 0xB2
        };
    static Twofish_Byte c192[] = {
        0x18, 0x2B, 0x02, 0xD8, 0x14, 0x97, 0xEA, 0x45,
        0xF9, 0xDA, 0xAC, 0xDC, 0x29, 0x19, 0x3A, 0x65
        };

    /* 256-bit test is the I=4 case of section B.2 of the Twofish book. */
    static Twofish_Byte k256[] = {
        0xD4, 0x3B, 0xB7, 0x55, 0x6E, 0xA3, 0x2E, 0x46, 
        0xF2, 0xA2, 0x82, 0xB7, 0xD4, 0x5B, 0x4E, 0x0D,
        0x57, 0xFF, 0x73, 0x9D, 0x4D, 0xC9, 0x2C, 0x1B,
        0xD7, 0xFC, 0x01, 0x70, 0x0C, 0xC8, 0x21, 0x6F
        };
    static Twofish_Byte p256[] = {
        0x90, 0xAF, 0xE9, 0x1B, 0xB2, 0x88, 0x54, 0x4F,
        0x2C, 0x32, 0xDC, 0x23, 0x9B, 0x26, 0x35, 0xE6
        };
    static Twofish_Byte c256[] = {
        0x6C, 0xB4, 0x56, 0x1C, 0x40, 0xBF, 0x0A, 0x97,
        0x05, 0x93, 0x1C, 0xB6, 0xD4, 0x08, 0xE7, 0xFA
        };

    /* Run the actual tests. */
    test_vector( k128, 16, p128, c128 );
    test_vector( k192, 24, p192, c192 );
    test_vector( k256, 32, p256, c256 );
    }   


/*
 * Perform extensive test for a single key size.
 * 
 * Test a single key size against the test vectors from section
 * B.2 in the Twofish book. This is a sequence of 49 encryptions
 * and decryptions. Each plaintext is equal to the ciphertext of
 * the previous encryption. The key is made up from the ciphertext
 * two and three encryptions ago. Both plaintext and key start
 * at the zero value. 
 * We should have designed a cleaner recurrence relation for
 * these tests, but it is too late for that now. At least we learned
 * how to do it better next time.
 * For details see appendix B of the book.
 *
 * Arguments:
 * key_len      Number of bytes of key
 * final_value  Final plaintext value after 49 iterations
 */
static void test_sequence( int key_len, Twofish_Byte final_value[] )
    {
    Twofish_Byte buf[ (50+3)*16 ];      /* Buffer to hold our computation values. */
    Twofish_Byte tmp[16];               /* Temp for testing the decryption. */
    Twofish_key xkey;           /* The expanded key */
    int i;                      
    Twofish_Byte * p;

    /* Wipe the buffer */
    memset( buf, 0, sizeof( buf ) );

    /*
     * Because the recurrence relation is done in an inconvenient manner
     * we end up looping backwards over the buffer.
     */

    /* Pointer in buffer points to current plaintext. */
    p = &buf[50*16];
    for( i=1; i<50; i++ )
        {
        /* 
         * Prepare a key.
         * This automatically checks that key_len is valid.
         */
        Twofish_prepare_key( p+16, key_len, &xkey );

        /* Compute the next 16 bytes in the buffer */
        Twofish_encrypt( &xkey, p, p-16 );

        /* Check that the decryption is correct. */
        Twofish_decrypt( &xkey, p-16, tmp );
        if( memcmp( tmp, p, 16 ) != 0 )
            {
            Twofish_fatal( "Twofish decryption failure in sequence" );
            }
        /* Move on to next 16 bytes in the buffer. */
        p -= 16;
        }

    /* And check the final value. */
    if( memcmp( p, final_value, 16 ) != 0 ) 
        {
        Twofish_fatal( "Twofish encryption failure in sequence" );
        }

    /* None of the data was secret, so there is no need to wipe anything. */
    }


/* 
 * Run all three sequence tests from the Twofish test vectors. 
 *
 * This checks the most extensive test vectors currently available 
 * for Twofish. The data is from the Twofish book, appendix B.2.
 */
static void test_sequences()
    {
    static Twofish_Byte r128[] = {
        0x5D, 0x9D, 0x4E, 0xEF, 0xFA, 0x91, 0x51, 0x57,
        0x55, 0x24, 0xF1, 0x15, 0x81, 0x5A, 0x12, 0xE0
        };
    static Twofish_Byte r192[] = {
        0xE7, 0x54, 0x49, 0x21, 0x2B, 0xEE, 0xF9, 0xF4,
        0xA3, 0x90, 0xBD, 0x86, 0x0A, 0x64, 0x09, 0x41
        };
    static Twofish_Byte r256[] = {
        0x37, 0xFE, 0x26, 0xFF, 0x1C, 0xF6, 0x61, 0x75,
        0xF5, 0xDD, 0xF4, 0xC3, 0x3B, 0x97, 0xA2, 0x05
        };

    /* Run the three sequence test vectors */
    test_sequence( 16, r128 );
    test_sequence( 24, r192 );
    test_sequence( 32, r256 );
    }


/*
 * Test the odd-sized keys.
 *
 * Every odd-sized key is equivalent to a one of 128, 192, or 256 bits.
 * The equivalent key is found by padding at the end with zero bytes
 * until a regular key size is reached.
 *
 * We just test that the key expansion routine behaves properly.
 * If the expanded keys are identical, then the encryptions and decryptions
 * will behave the same.
 */
static void test_odd_sized_keys()
    {
    Twofish_Byte buf[32];
    Twofish_key xkey;
    Twofish_key xkey_two;
    int i;

    /* 
     * We first create an all-zero key to use as PRNG key. 
     * Normally we would not have to fill the buffer with zeroes, as we could
     * just pass a zero key length to the Twofish_prepare_key function.
     * However, this relies on using odd-sized keys, and those are just the
     * ones we are testing here. We can't use an untested function to test 
     * itself. 
     */
    memset( buf, 0, sizeof( buf ) );
    Twofish_prepare_key( buf, 16, &xkey );

    /* Fill buffer with pseudo-random data derived from two encryptions */
    Twofish_encrypt( &xkey, buf, buf );
    Twofish_encrypt( &xkey, buf, buf+16 );

    /* Create all possible shorter keys that are prefixes of the buffer. */
    for( i=31; i>=0; i-- )
        {
        /* Set a byte to zero. This is the new padding byte */
        buf[i] = 0;

        /* Expand the key with only i bytes of length */
        Twofish_prepare_key( buf, i, &xkey );

        /* Expand the corresponding padded key of regular length */
        Twofish_prepare_key( buf, i<=16 ? 16 : (i<= 24 ? 24 : 32), &xkey_two );

        /* Compare the two */
        if( memcmp( &xkey, &xkey_two, sizeof( xkey ) ) != 0 )
            {
            Twofish_fatal( "Odd sized keys do not expand properly" );
            }
        }

    /* None of the key values are secret, so we don't need to wipe them. */
    }


/*
 * Test the Twofish implementation.
 *
 * This routine runs all the self tests, in order of importance.
 * It is called by the Twofish_initialise routine.
 * 
 * In almost all applications the cost of running the self tests during
 * initialisation is insignificant, especially
 * compared to the time it takes to load the application from disk. 
 * If you are very pressed for initialisation performance, 
 * you could remove some of the tests. Make sure you did run them
 * once in the software and hardware configuration you are using.
 */
static void self_test()
    {
    /* The three test vectors form an absolute minimal test set. */
    test_vectors();

    /* 
     * If at all possible you should run these tests too. They take
     * more time, but provide a more thorough coverage.
     */
    test_sequences();

    /* Test the odd-sized keys. */
    test_odd_sized_keys();
    }


/*
 * And now, the actual Twofish implementation.
 *
 * This implementation generates all the tables during initialisation. 
 * I don't like large tables in the code, especially since they are easily 
 * damaged in the source without anyone noticing it. You need code to 
 * generate them anyway, and this way all the code is close together.
 * Generating them in the application leads to a smaller executable 
 * (the code is smaller than the tables it generates) and a 
 * larger static memory footprint.
 *
 * Twofish can be implemented in many ways. I have chosen to 
 * use large tables with a relatively long key setup time.
 * If you encrypt more than a few blocks of data it pays to pre-compute 
 * as much as possible. This implementation is relatively inefficient for 
 * applications that need to re-key every block or so.
 */

/* 
 * We start with the t-tables, directly from the Twofish definition. 
 * These are nibble-tables, but merging them and putting them two nibbles 
 * in one byte is more work than it is worth.
 */
static Twofish_Byte t_table[2][4][16] = {
    {
        {0x8,0x1,0x7,0xD,0x6,0xF,0x3,0x2,0x0,0xB,0x5,0x9,0xE,0xC,0xA,0x4},
        {0xE,0xC,0xB,0x8,0x1,0x2,0x3,0x5,0xF,0x4,0xA,0x6,0x7,0x0,0x9,0xD},
        {0xB,0xA,0x5,0xE,0x6,0xD,0x9,0x0,0xC,0x8,0xF,0x3,0x2,0x4,0x7,0x1},
        {0xD,0x7,0xF,0x4,0x1,0x2,0x6,0xE,0x9,0xB,0x3,0x0,0x8,0x5,0xC,0xA}
    },
    {
        {0x2,0x8,0xB,0xD,0xF,0x7,0x6,0xE,0x3,0x1,0x9,0x4,0x0,0xA,0xC,0x5},
        {0x1,0xE,0x2,0xB,0x4,0xC,0x3,0x7,0x6,0xD,0xA,0x5,0xF,0x9,0x0,0x8},
        {0x4,0xC,0x7,0x5,0x1,0x6,0x9,0xA,0x0,0xE,0xD,0x8,0x2,0xB,0x3,0xF},
        {0xB,0x9,0x5,0x1,0xC,0x3,0xD,0xE,0x6,0x4,0x7,0xF,0x2,0x0,0x8,0xA}
    }
};


/* A 1-bit rotation of 4-bit values. Input must be in range 0..15 */
#define ROR4BY1( x ) (((x)>>1) | (((x)<<3) & 0x8) )

/*
 * The q-boxes are only used during the key schedule computations. 
 * These are 8->8 bit lookup tables. Some CPUs prefer to have 8->32 bit 
 * lookup tables as it is faster to load a 32-bit value than to load an 
 * 8-bit value and zero the rest of the register.
 * The LARGE_Q_TABLE switch allows you to choose 32-bit entries in 
 * the q-tables. Here we just define the Qtype which is used to store 
 * the entries of the q-tables.
 */
#if LARGE_Q_TABLE
typedef Twofish_UInt32      Qtype;
#else
typedef Twofish_Byte        Qtype;
#endif

/* 
 * The actual q-box tables. 
 * There are two q-boxes, each having 256 entries.
 */
static Qtype q_table[2][256];


/*
 * Now the function that converts a single t-table into a q-table.
 *
 * Arguments:
 * t[4][16] : four 4->4bit lookup tables that define the q-box
 * q[256]   : output parameter: the resulting q-box as a lookup table.
 */
static void make_q_table( Twofish_Byte t[4][16], Qtype q[256] )
    {
    int ae,be,ao,bo;        /* Some temporaries. */
    int i;
    /* Loop over all input values and compute the q-box result. */
    for( i=0; i<256; i++ ) {
        /* 
         * This is straight from the Twofish specifications. 
         * 
         * The ae variable is used for the a_i values from the specs
         * with even i, and ao for the odd i's. Similarly for the b's.
         */
        ae = i>>4; be = i&0xf;
        ao = ae ^ be; bo = ae ^ ROR4BY1(be) ^ ((ae<<3)&8);
        ae = t[0][ao]; be = t[1][bo];
        ao = ae ^ be; bo = ae ^ ROR4BY1(be) ^ ((ae<<3)&8);
        ae = t[2][ao]; be = t[3][bo];

        /* Store the result in the q-box table, the cast avoids a warning. */
        q[i] = (Qtype) ((be<<4) | ae);
        }
    }


/* 
 * Initialise both q-box tables. 
 */
static void initialise_q_boxes() {
    /* Initialise each of the q-boxes using the t-tables */