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+/*
+ * 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 instead of to adhere to ANSI/ISO.
+ * Rename BIG_ENDIAN macro to CPU_IS_BIG_ENDIAN. The gcc library
+ * header 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 <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+/* #include * 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) { fprintf(stderr, pmsgx); exit(1); } */
+#define Twofish_fatal(pmsgx, code) { return(code); }
+
+
+/*
+ * 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 UINT32_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 UINT32_MASK ( (((Twofish_UInt32)2)<<31) - 1 )
+
+#ifndef _MSC_VER
+#define ROL32(x,n) ( (x)<<(n) | ((x) & UINT32_MASK) >> (32-(n)) )
+#define ROR32(x,n) ( (x)>>(n) | ((x) & UINT32_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_UINT32_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_UINT32_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_UINT32_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_UINT32_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_UINT32_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
+
+
+/*
+ * 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 int 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", ERR_UINT32 );
+ }
+ if( (sizeof( Twofish_Byte ) != 1) || (((Twofish_Byte)-1) < 0) )
+ {
+ Twofish_fatal( "Twofish code: Twofish_Byte type not suitable", ERR_BYTE );
+ }
+
+ /*
+ * 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", ERR_GET32 );
+ }
+
+ /*
+ * 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", ERR_PUT32 );
+ }
+
+
+ /* 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<>(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.", ERR_ROLR );
+ }
+ }
+
+ /* 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.", ERR_BSWAP );
+ }
+
+ /* And we can test the b 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", ERR_SELECTB );
+ }
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 int 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 */
+ if ((i = Twofish_prepare_key( key, key_len, &xkey)) < 0)
+ return i;
+
+ /*
+ * 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", ERR_TEST_ENC );
+ }
+
+ /* Decrypt and test */
+ Twofish_decrypt( &xkey, c, tmp );
+ if( memcmp( p, tmp, 16 ) != 0 )
+ {
+ Twofish_fatal( "Twofish decryption failure", ERR_TEST_DEC );
+ }
+ }
+
+ /* The test keys are not secret, so we don't need to wipe xkey. */
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 int 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
+ };
+
+ int ret;
+
+ /* Run the actual tests. */
+ if ((ret = test_vector( k128, 16, p128, c128 )) < 0)
+ return ret;
+ if ((ret = test_vector( k192, 24, p192, c192 )) < 0)
+ return ret;
+ if ((ret = test_vector( k256, 32, p256, c256 )) < 0)
+ return ret;
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 int 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, ret;
+ 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.
+ */
+ if ((ret = Twofish_prepare_key( p+16, key_len, &xkey)) < 0)
+ return ret;
+
+ /* 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", ERR_SEQ_DEC );
+ }
+ /* 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", ERR_SEQ_ENC );
+ }
+
+ /* None of the data was secret, so there is no need to wipe anything. */
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 int 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 */
+ int ret;
+ if ((ret = test_sequence( 16, r128)) < 0)
+ return ret;
+ if ((ret = test_sequence( 24, r192)) < 0)
+ return ret;
+ if ((ret = test_sequence( 32, r256)) < 0)
+ return ret;
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 int test_odd_sized_keys()
+ {
+ Twofish_Byte buf[32];
+ Twofish_key xkey;
+ Twofish_key xkey_two;
+ int i, ret;
+
+ /*
+ * 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 ) );
+ if ((ret = Twofish_prepare_key( buf, 16, &xkey)) < 0)
+ return ret;
+
+ /* 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 */
+ if ((ret = Twofish_prepare_key( buf, i, &xkey)) < 0)
+ return ret;
+
+ /* Expand the corresponding padded key of regular length */
+ if ((ret = Twofish_prepare_key( buf, i<=16 ? 16 : (i<= 24 ? 24 : 32), &xkey_two )) < 0)
+ return ret;
+
+ /* Compare the two */
+ if( memcmp( &xkey, &xkey_two, sizeof( xkey ) ) != 0 )
+ {
+ Twofish_fatal( "Odd sized keys do not expand properly", ERR_ODD_KEY );
+ }
+ }
+
+ /* None of the key values are secret, so we don't need to wipe them. */
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 int self_test()
+ {
+ int ret;
+ /* The three test vectors form an absolute minimal test set. */
+ if ((ret = test_vectors()) < 0)
+ return ret;
+
+ /*
+ * If at all possible you should run these tests too. They take
+ * more time, but provide a more thorough coverage.
+ */
+ if ((ret = test_sequences()) < 0)
+ return ret;
+
+ /* Test the odd-sized keys. */
+ if ((ret = test_odd_sized_keys()) < 0)
+ return ret;
+ return SUCCESS;
+ }
+
+
+/*
+ * 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 */
+ make_q_table( t_table[0], q_table[0] );
+ make_q_table( t_table[1], q_table[1] );
+ }
+
+
+/*
+ * Next up is the MDS matrix multiplication.
+ * The MDS matrix multiplication operates in the field
+ * GF(2)[x]/p(x) with p(x)=x^8+x^6+x^5+x^3+1.
+ * If you don't understand this, read a book on finite fields. You cannot
+ * follow the finite-field computations without some background.
+ *
+ * In this field, multiplication by x is easy: shift left one bit
+ * and if bit 8 is set then xor the result with 0x169.
+ *
+ * The MDS coefficients use a multiplication by 1/x,
+ * or rather a division by x. This is easy too: first make the
+ * value 'even' (i.e. bit 0 is zero) by xorring with 0x169 if necessary,
+ * and then shift right one position.
+ * Even easier: shift right and xor with 0xb4 if the lsbit was set.
+ *
+ * The MDS coefficients are 1, EF, and 5B, and we use the fact that
+ * EF = 1 + 1/x + 1/x^2
+ * 5B = 1 + 1/x^2
+ * in this field. This makes multiplication by EF and 5B relatively easy.
+ *
+ * This property is no accident, the MDS matrix was designed to allow
+ * this implementation technique to be used.
+ *
+ * We have four MDS tables, each mapping 8 bits to 32 bits.
+ * Each table performs one column of the matrix multiplication.
+ * As the MDS is always preceded by q-boxes, each of these tables
+ * also implements the q-box just previous to that column.
+ */
+
+/* The actual MDS tables. */
+static Twofish_UInt32 MDS_table[4][256];
+
+/* A small table to get easy conditional access to the 0xb4 constant. */
+static Twofish_UInt32 mds_poly_divx_const[] = {0,0xb4};
+
+/* Function to initialise the MDS tables. */
+static void initialise_mds_tables()
+ {
+ int i;
+ Twofish_UInt32 q,qef,q5b; /* Temporary variables. */
+
+ /* Loop over all 8-bit input values */
+ for( i=0; i<256; i++ )
+ {
+ /*
+ * To save some work during the key expansion we include the last
+ * of the q-box layers from the h() function in these MDS tables.
+ */
+
+ /* We first do the inputs that are mapped through the q0 table. */
+ q = q_table[0][i];
+ /*
+ * Here we divide by x, note the table to get 0xb4 only if the
+ * lsbit is set.
+ * This sets qef = (1/x)*q in the finite field
+ */
+ qef = (q >> 1) ^ mds_poly_divx_const[ q & 1 ];
+ /*
+ * Divide by x again, and add q to get (1+1/x^2)*q.
+ * Note that (1+1/x^2) = 5B in the field, and addition in the field
+ * is exclusive or on the bits.
+ */
+ q5b = (qef >> 1) ^ mds_poly_divx_const[ qef & 1 ] ^ q;
+ /*
+ * Add q5b to qef to set qef = (1+1/x+1/x^2)*q.
+ * Again, (1+1/x+1/x^2) = EF in the field.
+ */
+ qef ^= q5b;
+
+ /*
+ * Now that we have q5b = 5B * q and qef = EF * q
+ * we can fill two of the entries in the MDS matrix table.
+ * See the Twofish specifications for the order of the constants.
+ */
+ MDS_table[1][i] = (q <<24) | (q5b<<16) | (qef<<8) | qef;
+ MDS_table[3][i] = (q5b<<24) | (qef<<16) | (q <<8) | q5b;
+
+ /* Now we do it all again for the two columns that have a q1 box. */
+ q = q_table[1][i];
+ qef = (q >> 1) ^ mds_poly_divx_const[ q & 1 ];
+ q5b = (qef >> 1) ^ mds_poly_divx_const[ qef & 1 ] ^ q;
+ qef ^= q5b;
+
+ /* The other two columns use the coefficient in a different order. */
+ MDS_table[0][i] = (qef<<24) | (qef<<16) | (q5b<<8) | q ;
+ MDS_table[2][i] = (qef<<24) | (q <<16) | (qef<<8) | q5b;
+ }
+ }
+
+
+/*
+ * The h() function is the heart of the Twofish cipher.
+ * It is a complicated sequence of q-box lookups, key material xors,
+ * and finally the MDS matrix.
+ * We use lots of macros to make this reasonably fast.
+ */
+
+/* First a shorthand for the two q-tables */
+#define q0 q_table[0]
+#define q1 q_table[1]
+
+/*
+ * Each macro computes one column of the h for either 2, 3, or 4 stages.
+ * As there are 4 columns, we have 12 macros in all.
+ *
+ * The key bytes are stored in the Byte array L at offset
+ * 0,1,2,3, 8,9,10,11, [16,17,18,19, [24,25,26,27]] as this is the
+ * order we get the bytes from the user. If you look at the Twofish
+ * specs, you'll see that h() is applied to the even key words or the
+ * odd key words. The bytes of the even words appear in this spacing,
+ * and those of the odd key words too.
+ *
+ * These macros are the only place where the q-boxes and the MDS table
+ * are used.
+ */
+#define H02( y, L ) MDS_table[0][q0[q0[y]^L[ 8]]^L[0]]
+#define H12( y, L ) MDS_table[1][q0[q1[y]^L[ 9]]^L[1]]
+#define H22( y, L ) MDS_table[2][q1[q0[y]^L[10]]^L[2]]
+#define H32( y, L ) MDS_table[3][q1[q1[y]^L[11]]^L[3]]
+#define H03( y, L ) H02( q1[y]^L[16], L )
+#define H13( y, L ) H12( q1[y]^L[17], L )
+#define H23( y, L ) H22( q0[y]^L[18], L )
+#define H33( y, L ) H32( q0[y]^L[19], L )
+#define H04( y, L ) H03( q1[y]^L[24], L )
+#define H14( y, L ) H13( q0[y]^L[25], L )
+#define H24( y, L ) H23( q0[y]^L[26], L )
+#define H34( y, L ) H33( q1[y]^L[27], L )
+
+/*
+ * Now we can define the h() function given an array of key bytes.
+ * This function is only used in the key schedule, and not to pre-compute
+ * the keyed S-boxes.
+ *
+ * In the key schedule, the input is always of the form k*(1+2^8+2^16+2^24)
+ * so we only provide k as an argument.
+ *
+ * Arguments:
+ * k input to the h() function.
+ * L pointer to array of key bytes at
+ * offsets 0,1,2,3, ... 8,9,10,11, [16,17,18,19, [24,25,26,27]]
+ * kCycles # key cycles, 2, 3, or 4.
+ */
+static Twofish_UInt32 h( int k, Twofish_Byte L[], int kCycles )
+ {
+ switch( kCycles ) {
+ /* We code all 3 cases separately for speed reasons. */
+ case 2:
+ return H02(k,L) ^ H12(k,L) ^ H22(k,L) ^ H32(k,L);
+ case 3:
+ return H03(k,L) ^ H13(k,L) ^ H23(k,L) ^ H33(k,L);
+ case 4:
+ return H04(k,L) ^ H14(k,L) ^ H24(k,L) ^ H34(k,L);
+ default:
+ /* This is always a coding error, which is fatal. */
+ Twofish_fatal( "Twofish h(): Illegal argument", ERR_ILL_ARG );
+ return ERR_ILL_ARG;
+ }
+ }
+
+
+/*
+ * Pre-compute the keyed S-boxes.
+ * Fill the pre-computed S-box array in the expanded key structure.
+ * Each pre-computed S-box maps 8 bits to 32 bits.
+ *
+ * The S argument contains half the number of bytes of the full key, but is
+ * derived from the full key. (See Twofish specifications for details.)
+ * S has the weird byte input order used by the Hxx macros.
+ *
+ * This function takes most of the time of a key expansion.
+ *
+ * Arguments:
+ * S pointer to array of 8*kCycles Bytes containing the S vector.
+ * kCycles number of key words, must be in the set {2,3,4}
+ * xkey pointer to Twofish_key structure that will contain the S-boxes.
+ */
+static int fill_keyed_sboxes( Twofish_Byte S[], int kCycles, Twofish_key * xkey )
+ {
+ int i;
+ switch( kCycles ) {
+ /* We code all 3 cases separately for speed reasons. */
+ case 2:
+ for( i=0; i<256; i++ )
+ {
+ xkey->s[0][i]= H02( i, S );
+ xkey->s[1][i]= H12( i, S );
+ xkey->s[2][i]= H22( i, S );
+ xkey->s[3][i]= H32( i, S );
+ }
+ break;
+ case 3:
+ for( i=0; i<256; i++ )
+ {
+ xkey->s[0][i]= H03( i, S );
+ xkey->s[1][i]= H13( i, S );
+ xkey->s[2][i]= H23( i, S );
+ xkey->s[3][i]= H33( i, S );
+ }
+ break;
+ case 4:
+ for( i=0; i<256; i++ )
+ {
+ xkey->s[0][i]= H04( i, S );
+ xkey->s[1][i]= H14( i, S );
+ xkey->s[2][i]= H24( i, S );
+ xkey->s[3][i]= H34( i, S );
+ }
+ break;
+ default:
+ /* This is always a coding error, which is fatal. */
+ Twofish_fatal( "Twofish fill_keyed_sboxes(): Illegal argument", ERR_ILL_ARG );
+ }
+ return SUCCESS;
+ }
+
+
+/* A flag to keep track of whether we have been initialised or not. */
+static int Twofish_initialised = 0;
+
+/*
+ * Initialise the Twofish implementation.
+ * This function must be called before any other function in the
+ * Twofish implementation is called.
+ * This routine also does some sanity checks, to make sure that
+ * all the macros behave, and it tests the whole cipher.
+ */
+int Twofish_initialise()
+ {
+ int ret;
+ /* First test the various platform-specific definitions. */
+ if ((ret = test_platform()) < 0)
+ return ret;
+
+ /* We can now generate our tables, in the right order of course. */
+ initialise_q_boxes();
+ initialise_mds_tables();
+
+ /* We're finished with the initialisation itself. */
+ Twofish_initialised = 1;
+
+ /*
+ * And run some tests on the whole cipher.
+ * Yes, you need to do this every time you start your program.
+ * It is called assurance; you have to be certain that your program
+ * still works properly.
+ */
+ return self_test();
+ }
+
+
+/*
+ * The Twofish key schedule uses an Reed-Solomon code matrix multiply.
+ * Just like the MDS matrix, the RS-matrix is designed to be easy
+ * to implement. Details are below in the code.
+ *
+ * These constants make it easy to compute in the finite field used
+ * for the RS code.
+ *
+ * We use Bytes for the RS computation, but these are automatically
+ * widened to unsigned integers in the expressions. Having unsigned
+ * ints in these tables therefore provides the fastest access.
+ */
+static unsigned int rs_poly_const[] = {0, 0x14d};
+static unsigned int rs_poly_div_const[] = {0, 0xa6 };
+
+
+/*
+ * Prepare a key for use in encryption and decryption.
+ * Like most block ciphers, Twofish allows the key schedule
+ * to be pre-computed given only the key.
+ * Twofish has a fairly 'heavy' key schedule that takes a lot of time
+ * to compute. The main work is pre-computing the S-boxes used in the
+ * encryption and decryption. We feel that this makes the cipher much
+ * harder to attack. The attacker doesn't even know what the S-boxes
+ * contain without including the entire key schedule in the analysis.
+ *
+ * Unlike most Twofish implementations, this one allows any key size from
+ * 0 to 32 bytes. Odd key sizes are defined for Twofish (see the
+ * specifications); the key is simply padded with zeroes to the next real
+ * key size of 16, 24, or 32 bytes.
+ * Each odd-sized key is thus equivalent to a single normal-sized key.
+ *
+ * Arguments:
+ * key array of key bytes
+ * key_len number of bytes in the key, must be in the range 0,...,32.
+ * xkey Pointer to an Twofish_key structure that will be filled
+ * with the internal form of the cipher key.
+ */
+int Twofish_prepare_key( Twofish_Byte key[], int key_len, Twofish_key * xkey )
+ {
+ /* We use a single array to store all key material in,
+ * to simplify the wiping of the key material at the end.
+ * The first 32 bytes contain the actual (padded) cipher key.
+ * The next 32 bytes contain the S-vector in its weird format,
+ * and we have 4 bytes of overrun necessary for the RS-reduction.
+ */
+ Twofish_Byte K[32+32+4];
+
+ int kCycles; /* # key cycles, 2,3, or 4. */
+
+ int i;
+ Twofish_UInt32 A, B; /* Used to compute the round keys. */
+
+ Twofish_Byte * kptr; /* Three pointers for the RS computation. */
+ Twofish_Byte * sptr;
+ Twofish_Byte * t;
+
+ Twofish_Byte b,bx,bxx; /* Some more temporaries for the RS computation. */
+
+ /* Check that the Twofish implementation was initialised. */
+ if( Twofish_initialised == 0 )
+ {
+ /*
+ * You didn't call Twofish_initialise before calling this routine.
+ * This is a programming error, and therefore we call the fatal
+ * routine.
+ *
+ * I could of course call the initialisation routine here,
+ * but there are a few reasons why I don't. First of all, the
+ * self-tests have to be done at startup. It is no good to inform
+ * the user that the cipher implementation fails when he wants to
+ * write his data to disk in encrypted form. You have to warn him
+ * before he spends time typing his data. Second, the initialisation
+ * and self test are much slower than a single key expansion.
+ * Calling the initialisation here makes the performance of the
+ * cipher unpredictable. This can lead to really weird problems
+ * if you use the cipher for a real-time task. Suddenly it fails
+ * once in a while the first time you try to use it. Things like
+ * that are almost impossible to debug.
+ */
+ /* Twofish_fatal( "Twofish implementation was not initialised.", ERR_INIT ); */
+
+ /*
+ * There is always a danger that the Twofish_fatal routine returns,
+ * in spite of the specifications that it should not.
+ * (A good programming rule: don't trust the rest of the code.)
+ * This would be disasterous. If the q-tables and MDS-tables have
+ * not been initialised, they are probably still filled with zeroes.
+ * Suppose the MDS-tables are all zero. The key expansion would then
+ * generate all-zero round keys, and all-zero s-boxes. The danger
+ * is that nobody would notice as the encry
+ * mangles the input, and the decryption still 'decrypts' it,
+ * but now in a completely key-independent manner.
+ * To stop such security disasters, we use blunt force.
+ * If your program hangs here: fix the fatal routine!
+ */
+ for(;;); /* Infinite loop, which beats being insecure. */
+ }
+
+ /* Check for valid key length. */
+ if( key_len < 0 || key_len > 32 )
+ {
+ /*
+ * This can only happen if a programmer didn't read the limitations
+ * on the key size.
+ */
+ Twofish_fatal( "Twofish_prepare_key: illegal key length", ERR_KEY_LEN );
+ /*
+ * A return statement just in case the fatal macro returns.
+ * The rest of the code assumes that key_len is in range, and would
+ * buffer-overflow if it wasn't.
+ *
+ * Why do we still use a programming language that has problems like
+ * buffer overflows, when these problems were solved in 1960 with
+ * the development of Algol? Have we not leared anything?
+ */
+ return ERR_KEY_LEN;
+ }
+
+ /* Pad the key with zeroes to the next suitable key length. */
+ memcpy( K, key, key_len );
+ memset( K+key_len, 0, sizeof(K)-key_len );
+
+ /*
+ * Compute kCycles: the number of key cycles used in the cipher.
+ * 2 for 128-bit keys, 3 for 192-bit keys, and 4 for 256-bit keys.
+ */
+ kCycles = (key_len + 7) >> 3;
+ /* Handle the special case of very short keys: minimum 2 cycles. */
+ if( kCycles < 2 )
+ {
+ kCycles = 2;
+ }
+
+ /*
+ * From now on we just pretend to have 8*kCycles bytes of
+ * key material in K. This handles all the key size cases.
+ */
+
+ /*
+ * We first compute the 40 expanded key words,
+ * formulas straight from the Twofish specifications.
+ */
+ for( i=0; i<40; i+=2 )
+ {
+ /*
+ * Due to the byte spacing expected by the h() function
+ * we can pick the bytes directly from the key K.
+ * As we use bytes, we never have the little/big endian
+ * problem.
+ *
+ * Note that we apply the rotation function only to simple
+ * variables, as the rotation macro might evaluate its argument
+ * more than once.
+ */
+ A = h( i , K , kCycles );
+ B = h( i+1, K+4, kCycles );
+ B = ROL32( B, 8 );
+
+ /* Compute and store the round keys. */
+ A += B;
+ B += A;
+ xkey->K[i] = A;
+ xkey->K[i+1] = ROL32( B, 9 );
+ }
+
+ /* Wipe variables that contained key material. */
+ A=B=0;
+
+ /*
+ * And now the dreaded RS multiplication that few seem to understand.
+ * The RS matrix is not random, and is specially designed to compute the
+ * RS matrix multiplication in a simple way.
+ *
+ * We work in the field GF(2)[x]/x^8+x^6+x^3+x^2+1. Note that this is a
+ * different field than used for the MDS matrix.
+ * (At least, it is a different representation because all GF(2^8)
+ * representations are equivalent in some form.)
+ *
+ * We take 8 consecutive bytes of the key and interpret them as
+ * a polynomial k_0 + k_1 y + k_2 y^2 + ... + k_7 y^7 where
+ * the k_i bytes are the key bytes and are elements of the finite field.
+ * We multiply this polynomial by y^4 and reduce it modulo
+ * y^4 + (x + 1/x)y^3 + (x)y^2 + (x + 1/x)y + 1.
+ * using straightforward polynomial modulo reduction.
+ * The coefficients of the result are the result of the RS
+ * matrix multiplication. When we wrote the Twofish specification,
+ * the original RS definition used the polynomials,
+ * but that requires much more mathematical knowledge.
+ * We were already using matrix multiplication in a finite field for
+ * the MDS matrix, so I re-wrote the RS operation as a matrix
+ * multiplication to reduce the difficulty of understanding it.
+ * Some implementors have not picked up on this simpler method of
+ * computing the RS operation, even though it is mentioned in the
+ * specifications.
+ *
+ * It is possible to perform these computations faster by using 32-bit
+ * word operations, but that is not portable and this is not a speed-
+ * critical area.
+ *
+ * We explained the 1/x computation when we did the MDS matrix.
+ *
+ * The S vector is stored in K[32..64].
+ * The S vector has to be reversed, so we loop cross-wise.
+ *
+ * Note the weird byte spacing of the S-vector, to match the even
+ * or odd key words arrays. See the discussion at the Hxx macros for
+ * details.
+ */
+ kptr = K + 8*kCycles; /* Start at end of key */
+ sptr = K + 32; /* Start at start of S */
+
+ /* Loop over all key material */
+ while( kptr > K )
+ {
+ kptr -= 8;
+ /*
+ * Initialise the polynimial in sptr[0..12]
+ * The first four coefficients are 0 as we have to multiply by y^4.
+ * The next 8 coefficients are from the key material.
+ */
+ memset( sptr, 0, 4 );
+ memcpy( sptr+4, kptr, 8 );
+
+ /*
+ * The 12 bytes starting at sptr are now the coefficients of
+ * the polynomial we need to reduce.
+ */
+
+ /* Loop over the polynomial coefficients from high to low */
+ t = sptr+11;
+ /* Keep looping until polynomial is degree 3; */
+ while( t > sptr+3 )
+ {
+ /* Pick up the highest coefficient of the poly. */
+ b = *t;
+
+ /*
+ * Compute x and (x+1/x) times this coefficient.
+ * See the MDS matrix implementation for a discussion of
+ * multiplication by x and 1/x. We just use different
+ * constants here as we are in a
+ * different finite field representation.
+ *
+ * These two statements set
+ * bx = (x) * b
+ * bxx= (x + 1/x) * b
+ */
+ bx = (Twofish_Byte)((b<<1) ^ rs_poly_const[ b>>7 ]);
+ bxx= (Twofish_Byte)((b>>1) ^ rs_poly_div_const[ b&1 ] ^ bx);
+
+ /*
+ * Subtract suitable multiple of
+ * y^4 + (x + 1/x)y^3 + (x)y^2 + (x + 1/x)y + 1
+ * from the polynomial, except that we don't bother
+ * updating t[0] as it will become zero anyway.
+ */
+ t[-1] ^= bxx;
+ t[-2] ^= bx;
+ t[-3] ^= bxx;
+ t[-4] ^= b;
+
+ /* Go to the next coefficient. */
+ t--;
+ }
+
+ /* Go to next S-vector word, obeying the weird spacing rules. */
+ sptr += 8;
+ }
+
+ /* Wipe variables that contained key material. */
+ b = bx = bxx = 0;
+
+ /* And finally, we can compute the key-dependent S-boxes. */
+ fill_keyed_sboxes( &K[32], kCycles, xkey );
+
+ /* Wipe array that contained key material. */
+ memset( K, 0, sizeof( K ) );
+ return SUCCESS;
+ }
+
+
+/*
+ * We can now start on the actual encryption and decryption code.
+ * As these are often speed-critical we will use a lot of macros.
+ */
+
+/*
+ * The g() function is the heart of the round function.
+ * We have two versions of the g() function, one without an input
+ * rotation and one with.
+ * The pre-computed S-boxes make this pretty simple.
+ */
+#define g0(X,xkey) \
+ (xkey->s[0][b0(X)]^xkey->s[1][b1(X)]^xkey->s[2][b2(X)]^xkey->s[3][b3(X)])
+
+#define g1(X,xkey) \
+ (xkey->s[0][b3(X)]^xkey->s[1][b0(X)]^xkey->s[2][b1(X)]^xkey->s[3][b2(X)])
+
+/*
+ * A single round of Twofish. The A,B,C,D are the four state variables,
+ * T0 and T1 are temporaries, xkey is the expanded key, and r the
+ * round number.
+ *
+ * Note that this macro does not implement the swap at the end of the round.
+ */
+#define ENCRYPT_RND( A,B,C,D, T0, T1, xkey, r ) \
+ T0 = g0(A,xkey); T1 = g1(B,xkey);\
+ C ^= T0+T1+xkey->K[8+2*(r)]; C = ROR32(C,1);\
+ D = ROL32(D,1); D ^= T0+2*T1+xkey->K[8+2*(r)+1]
+
+/*
+ * Encrypt a single cycle, consisting of two rounds.
+ * This avoids the swapping of the two halves.
+ * Parameter r is now the cycle number.
+ */
+#define ENCRYPT_CYCLE( A, B, C, D, T0, T1, xkey, r ) \
+ ENCRYPT_RND( A,B,C,D,T0,T1,xkey,2*(r) );\
+ ENCRYPT_RND( C,D,A,B,T0,T1,xkey,2*(r)+1 )
+
+/* Full 16-round encryption */
+#define ENCRYPT( A,B,C,D,T0,T1,xkey ) \
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 0 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 1 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 2 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 3 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 4 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 5 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 6 );\
+ ENCRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 7 )
+
+/*
+ * A single round of Twofish for decryption. It differs from
+ * ENCRYTP_RND only because of the 1-bit rotations.
+ */
+#define DECRYPT_RND( A,B,C,D, T0, T1, xkey, r ) \
+ T0 = g0(A,xkey); T1 = g1(B,xkey);\
+ C = ROL32(C,1); C ^= T0+T1+xkey->K[8+2*(r)];\
+ D ^= T0+2*T1+xkey->K[8+2*(r)+1]; D = ROR32(D,1)
+
+/*
+ * Decrypt a single cycle, consisting of two rounds.
+ * This avoids the swapping of the two halves.
+ * Parameter r is now the cycle number.
+ */
+#define DECRYPT_CYCLE( A, B, C, D, T0, T1, xkey, r ) \
+ DECRYPT_RND( A,B,C,D,T0,T1,xkey,2*(r)+1 );\
+ DECRYPT_RND( C,D,A,B,T0,T1,xkey,2*(r) )
+
+/* Full 16-round decryption. */
+#define DECRYPT( A,B,C,D,T0,T1, xkey ) \
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 7 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 6 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 5 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 4 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 3 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 2 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 1 );\
+ DECRYPT_CYCLE( A,B,C,D,T0,T1,xkey, 0 )
+
+/*
+ * A macro to read the state from the plaintext and do the initial key xors.
+ * The koff argument allows us to use the same macro
+ * for the decryption which uses different key words at the start.
+ */
+#define GET_INPUT( src, A,B,C,D, xkey, koff ) \
+ A = GET32(src )^xkey->K[ koff]; B = GET32(src+ 4)^xkey->K[1+koff]; \
+ C = GET32(src+ 8)^xkey->K[2+koff]; D = GET32(src+12)^xkey->K[3+koff]
+
+/*
+ * Similar macro to put the ciphertext in the output buffer.
+ * We xor the keys into the state variables before we use the PUT32
+ * macro as the macro might use its argument multiple times.
+ */
+#define PUT_OUTPUT( A,B,C,D, dst, xkey, koff ) \
+ A ^= xkey->K[ koff]; B ^= xkey->K[1+koff]; \
+ C ^= xkey->K[2+koff]; D ^= xkey->K[3+koff]; \
+ PUT32( A, dst ); PUT32( B, dst+ 4 ); \
+ PUT32( C, dst+8 ); PUT32( D, dst+12 )
+
+
+/*
+ * Twofish block encryption
+ *
+ * Arguments:
+ * xkey expanded key array
+ * p 16 bytes of plaintext
+ * c 16 bytes in which to store the ciphertext
+ */
+void Twofish_encrypt( Twofish_key * xkey, Twofish_Byte p[16], Twofish_Byte c[16])
+ {
+ Twofish_UInt32 A,B,C,D,T0,T1; /* Working variables */
+
+ /* Get the four plaintext words xorred with the key */
+ GET_INPUT( p, A,B,C,D, xkey, 0 );
+
+ /* Do 8 cycles (= 16 rounds) */
+ ENCRYPT( A,B,C,D,T0,T1,xkey );
+
+ /* Store them with the final swap and the output whitening. */
+ PUT_OUTPUT( C,D,A,B, c, xkey, 4 );
+ }
+
+
+/*
+ * Twofish block decryption.
+ *
+ * Arguments:
+ * xkey expanded key array
+ * p 16 bytes of plaintext
+ * c 16 bytes in which to store the ciphertext
+ */
+void Twofish_decrypt( Twofish_key * xkey, Twofish_Byte c[16], Twofish_Byte p[16])
+ {
+ Twofish_UInt32 A,B,C,D,T0,T1; /* Working variables */
+
+ /* Get the four plaintext words xorred with the key */
+ GET_INPUT( c, A,B,C,D, xkey, 4 );
+
+ /* Do 8 cycles (= 16 rounds) */
+ DECRYPT( A,B,C,D,T0,T1,xkey );
+
+ /* Store them with the final swap and the output whitening. */
+ PUT_OUTPUT( C,D,A,B, p, xkey, 0 );
+ }
+
+/*
+ * Using the macros it is easy to make special routines for
+ * CBC mode, CTR mode etc. The only thing you might want to
+ * add is a XOR_PUT_OUTPUT which xors the outputs into the
+ * destinationa instead of overwriting the data. This requires
+ * a XOR_PUT32 macro as well, but that should all be trivial.
+ *
+ * I thought about including routines for the separate cipher
+ * modes here, but it is unclear which modes should be included,
+ * and each encryption or decryption routine takes up a lot of code space.
+ * Also, I don't have any test vectors for any cipher modes
+ * with Twofish.
+ */
+
+