/* * 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 /* for memset(), memcpy(), and memcmp() */ #include #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(const char* msg){ qCritical("Twofish: Fatal Error: %s",msg); 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<>(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 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 */ 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" ); return 0; } } /* * 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 void 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" ); } } /* 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. */ void Twofish_initialise() { /* First test the various platform-specific definitions. */ test_platform(); /* 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. */ 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. */ void 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." ); /* * 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 encryption function still * 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" ); /* * 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; } /* 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 ) ); } /* * 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. */