/*
* Fast, portable, and easy-to-use Twofish implementation,
* Version 0.3.
* Copyright (c) 2002 by Niels Ferguson.
* (See further down for the almost-unrestricted licensing terms.)
*
* --------------------------------------------------------------------------
* There are two files for this implementation:
* - twofish.h, the header file.
* - twofish.c, the code file.
*
* To incorporate this code into your program you should:
* - Check the licensing terms further down in this comment.
* - Fix the two type definitions in twofish.h to suit your platform.
* - Fix a few definitions in twofish.c in the section marked
* PLATFORM FIXES. There is one important ones that affects
* functionality, and then a few definitions that you can optimise
* for efficiency but those have no effect on the functionality.
* Don't change anything else.
* - Put the code in your project and compile it.
*
* To use this library you should:
* - Call Twofish_initialise() in your program before any other function in
* this library.
* - Use Twofish_prepare_key(...) to convert a key to internal form.
* - Use Twofish_encrypt(...) and Twofish_decrypt(...) to encrypt and decrypt
* data.
* See the comments in the header file for details on these functions.
* --------------------------------------------------------------------------
*
* There are many Twofish implementation available for free on the web.
* Most of them are hard to integrate into your own program.
* As we like people to use our cipher, I thought I would make it easier.
* Here is a free and easy-to-integrate Twofish implementation in C.
* The latest version is always available from my personal home page at
* http://niels.ferguson.net/
*
* Integrating library code into a project is difficult because the library
* header files interfere with the project's header files and code.
* And of course the project's header files interfere with the library code.
* I've tried to resolve these problems here.
* The header file of this implementation is very light-weight.
* It contains two typedefs, a structure, and a few function declarations.
* All names it defines start with "Twofish_".
* The header file is therefore unlikely to cause problems in your project.
* The code file of this implementation doesn't need to include the header
* files of the project. There is thus no danger of the project interfering
* with all the definitions and macros of the Twofish code.
* In most situations, all you need to do is fill in a few platform-specific
* definitions in the header file and code file,
* and you should be able to run the Twofish code in your project.
* I estimate it should take you less than an hour to integrate this code
* into your project, most of it spent reading the comments telling you what
* to do.
*
* For people using C++: it is very easy to wrap this library into a
* TwofishKey class. One of the big advantages is that you can automate the
* wiping of the key material in the destructor. I have not provided a C++
* class because the interface depends too much on the abstract base class
* you use for block ciphers in your program, which I don't know about.
*
* This implementation is designed for use on PC-class machines. It uses the
* Twofish 'full' keying option which uses large tables. Total table size is
* around 5-6 kB for static tables plus 4.5 kB for each pre-processed key.
* If you need an implementation that uses less memory,
* take a look at Brian Gladman's code on his web site:
* http://fp.gladman.plus.com/cryptography_technology/aes/
* He has code for all AES candidates.
* His Twofish code has lots of options trading off table size vs. speed.
* You can also take a look at the optimised code by Doug Whiting on the
* Twofish web site
* http://www.counterpane.com/twofish.html
* which has loads of options.
* I believe these existing implementations are harder to re-use because they
* are not clean libraries and they impose requirements on the environment.
* This implementation is very careful to minimise those,
* and should be easier to integrate into any larger program.
*
* The default mode of this implementation is fully portable as it uses no
* behaviour not defined in the C standard. (This is harder than you think.)
* If you have any problems porting the default mode, please let me know
* so that I can fix the problem. (But only if this code is at fault, I
* don't fix compilers.)
* Most of the platform fixes are related to non-portable but faster ways
* of implementing certain functions.
*
* In general I've tried to make the code as fast as possible, at the expense
* of memory and code size. However, C does impose limits, and this
* implementation will be slower than an optimised assembler implementation.
* But beware of assembler implementations: a good Pentium implementation
* uses completely different code than a good Pentium II implementation.
* You basically have to re-write the assembly code for every generation of
* processor. Unless you are severely pressed for speed, stick with C.
*
* The initialisation routine of this implementation contains a self-test.
* If initialisation succeeds without calling the fatal routine, then
* the implementation works. I don't think you can break the implementation
* in such a way that it still passes the tests, unless you are malicious.
* In other words: if the initialisation routine returns,
* you have successfully ported the implementation.
* (Or not implemented the fatal routine properly, but that is your problem.)
*
* I'm indebted to many people who helped me in one way or another to write
* this code. During the design of Twofish and the AES process I had very
* extensive discussions of all implementation issues with various people.
* Doug Whiting in particular provided a wealth of information. The Twofish
* team spent untold hours discussion various cipher features, and their
* implementation. Brian Gladman implemented all AES candidates in C,
* and we had some fruitful discussions on how to implement Twofish in C.
* Jan Nieuwenhuizen tested this code on Linux using GCC.
*
* Now for the license:
* The author hereby grants a perpetual license to everybody to
* use this code for any purpose as long as the copyright message is included
* in the source code of this or any derived work.
*
* Yes, this means that you, your company, your club, and anyone else
* can use this code anywhere you want. You can change it and distribute it
* under the GPL, include it in your commercial product without releasing
* the source code, put it on the web, etc.
* The only thing you cannot do is remove my copyright message,
* or distribute any source code based on this implementation that does not
* include my copyright message.
*
* I appreciate a mention in the documentation or credits,
* but I understand if that is difficult to do.
* I also appreciate it if you tell me where and why you used my code.
*
* Please send any questions or comments to niels@ferguson.net
*
* Have Fun!
*
* Niels
*/
/*
* DISCLAIMER: As I'm giving away my work for free, I'm of course not going
* to accept any liability of any form. This code, or the Twofish cipher,
* might very well be flawed; you have been warned.
* This software is provided as-is, without any kind of warrenty or
* guarantee. And that is really all you can expect when you download
* code for free from the Internet.
*
* I think it is really sad that disclaimers like this seem to be necessary.
* If people only had a little bit more common sense, and didn't come
* whining like little children every time something happens....
*/
/*
* Version history:
* Version 0.0, 2002-08-30
* First written.
* Version 0.1, 2002-09-03
* Added disclaimer. Improved self-tests.
* Version 0.2, 2002-09-09
* Removed last non-portabilities. Default now works completely within
* the C standard. UInt32 can be larger than 32 bits without problems.
* Version 0.3, 2002-09-28
* Bugfix: use <string.h> instead of <memory.h> to adhere to ANSI/ISO.
* Rename BIG_ENDIAN macro to CPU_IS_BIG_ENDIAN. The gcc library
* header <string.h> already defines BIG_ENDIAN, even though it is not
* supposed to.
*/
/*
* Minimum set of include files.
* You should not need any application-specific include files for this code.
* In fact, adding you own header files could break one of the many macros or
* functions in this file. Be very careful.
* Standard include files will probably be ok.
*/
#include <qstring.h> /* for memset(), memcpy(), and memcmp() */
#include "twofish.h"
/*
* PLATFORM FIXES
* ==============
*
* Fix the type definitions in twofish.h first!
*
* The following definitions have to be fixed for each particular platform
* you work on. If you have a multi-platform program, you no doubt have
* portable definitions that you can substitute here without changing the
* rest of the code.
*/
/*
* Function called if something is fatally wrong with the implementation.
* This fatal function is called when a coding error is detected in the
* Twofish implementation, or when somebody passes an obviously erroneous
* parameter to this implementation. There is not much you can do when
* the code contains bugs, so we just stop.
*
* The argument is a string. Ideally the fatal function prints this string
* as an error message. Whatever else this function does, it should never
* return. A typical implementation would stop the program completely after
* printing the error message.
*
* This default implementation is not very useful,
* but does not assume anything about your environment.
* It will at least let you know something is wrong....
* I didn't want to include any libraries to print and error or so,
* as this makes the code much harder to integrate in a project.
*
* Note that the Twofish_fatal function may not return to the caller.
* Unfortunately this is not something the self-test can test for,
* so you have to make sure of this yourself.
*
* If you want to call an external function, be careful about including
* your own header files here. This code uses a lot of macros, and your
* header file could easily break it. Maybe the best solution is to use
* a separate extern statement for your fatal function.
*/
//#define Twofish_fatal(pmsgx) { MessageBox(GetDesktopWindow(), _T(pmsgx), _T("Twofish Fatal Error"), MB_OK); }
/*
* The rest of the settings are not important for the functionality
* of this Twofish implementation. That is, their default settings
* work on all platforms. You can change them to improve the
* speed of the implementation on your platform. Erroneous settings
* will result in erroneous implementations, but the self-test should
* catch those.
*/
/*
* Macros to rotate a Twofish_UInt32 value left or right by the
* specified number of bits. This should be a 32-bit rotation,
* and not rotation of, say, 64-bit values.
*
* Every encryption or decryption operation uses 32 of these rotations,
* so it is a good idea to make these macros efficient.
*
* This fully portable definition has one piece of tricky stuff.
* The UInt32 might be larger than 32 bits, so we have to mask
* any higher bits off. The simplest way to do this is to 'and' the
* value first with 0xffffffff and then shift it right. An optimising
* compiler that has a 32-bit type can optimise this 'and' away.
*
* Unfortunately there is no portable way of writing the constant
* 0xffffffff. You don't know which suffix to use (U, or UL?)
* The quint32_MASK definition uses a bit of trickery. Shift-left
* is only defined if the shift amount is strictly less than the size
* of the UInt32, so we can't use (1<<32). The answer it to take the value
* 2, cast it to a UInt32, shift it left 31 positions, and subtract one.
* Another example of how to make something very simple extremely difficult.
* I hate C.
*
* The rotation macros are straightforward.
* They are only applied to UInt32 values, which are _unsigned_
* so the >> operator must do a logical shift that brings in zeroes.
* On most platforms you will only need to optimise the ROL32 macro; the
* ROR32 macro is not inefficient on an optimising compiler as all rotation
* amounts in this code are known at compile time.
*
* On many platforms there is a faster solution.
* For example, MS compilers have the __rotl and __rotr functions
* that generate x86 rotation instructions.
*/
#define quint32_MASK ( (((Twofish_UInt32)2)<<31) - 1 )
#ifndef _MSC_VER
#define ROL32(x,n) ( (x)<<(n) | ((x) & quint32_MASK) >> (32-(n)) )
#define ROR32(x,n) ( (x)>>(n) | ((x) & quint32_MASK) << (32-(n)) )
#else
#define ROL32(x,n) (_lrotl((x), (n)))
#define ROR32(x,n) (_lrotr((x), (n)))
#endif
/*
* Select data type for q-table entries.
*
* Larger entry types cost more memory (1.5 kB), and might be faster
* or slower depending on the CPU and compiler details.
*
* This choice only affects the static data size and the key setup speed.
* Functionality, expanded key size, or encryption speed are not affected.
* Define to 1 to get large q-table entries.
*/
#define LARGE_Q_TABLE 0 /* default = 0 */
/*
* Method to select a single byte from a UInt32.
* WARNING: non-portable code if set; might not work on all platforms.
*
* Inside the inner loop of Twofish it is necessary to access the 4
* individual bytes of a UInt32. This can be done using either shifts
* and masks, or memory accesses.
*
* Set to 0 to use shift and mask operations for the byte selection.
* This is more ALU intensive. It is also fully portable.
*
* Set to 1 to use memory accesses. The UInt32 is stored in memory and
* the individual bytes are read from memory one at a time.
* This solution is more memory-intensive, and not fully portable.
* It might be faster on your platform, or not. If you use this option,
* make sure you set the CPU_IS_BIG_ENDIAN flag appropriately.
*
* This macro does not affect the conversion of the inputs and outputs
* of the cipher. See the CONVERT_USING_CASTS macro for that.
*/
#define SELECT_BYTE_FROM_quint32_IN_MEMORY 0 /* default = 0 */
/*
* Method used to read the input and write the output.
* WARNING: non-portable code if set; might not work on all platforms.
*
* Twofish operates on 32-bit words. The input to the cipher is
* a byte array, as is the output. The portable method of doing the
* conversion is a bunch of rotate and mask operations, but on many
* platforms it can be done faster using a cast.
* This only works if your CPU allows UInt32 accesses to arbitrary Byte
* addresses.
*
* Set to 0 to use the shift and mask operations. This is fully
* portable. .
*
* Set to 1 to use a cast. The Byte * is cast to a UInt32 *, and a
* UInt32 is read. If necessary (as indicated by the CPU_IS_BIG_ENDIAN
* macro) the byte order in the UInt32 is swapped. The reverse is done
* to write the output of the encryption/decryption. Make sure you set
* the CPU_IS_BIG_ENDIAN flag appropriately.
* This option does not work unless a UInt32 is exactly 32 bits.
*
* This macro only changes the reading/writing of the plaintext/ciphertext.
* See the SELECT_BYTE_FROM_quint32_IN_MEMORY to affect the way in which
* a UInt32 is split into 4 bytes for the S-box selection.
*/
#define CONVERT_USING_CASTS 0 /* default = 0 */
/*
* Endianness switch.
* Only relevant if SELECT_BYTE_FROM_quint32_IN_MEMORY or
* CONVERT_USING_CASTS is set.
*
* Set to 1 on a big-endian machine, and to 0 on a little-endian machine.
* Twofish uses the little-endian convention (least significant byte first)
* and big-endian machines (using most significant byte first)
* have to do a few conversions.
*
* CAUTION: This code has never been tested on a big-endian machine,
* because I don't have access to one. Feedback appreciated.
*/
#define CPU_IS_BIG_ENDIAN 0
/*
* Macro to reverse the order of the bytes in a UInt32.
* Used to convert to little-endian on big-endian machines.
* This macro is always tested, but only used in the encryption and
* decryption if CONVERT_USING_CASTS, and CPU_IS_BIG_ENDIAN
* are both set. In other words: this macro is only speed-critical if
* both these flags have been set.
*
* This default definition of SWAP works, but on many platforms there is a
* more efficient implementation.
*/
#define BSWAP(x) (ROL32((x),8)&0x00ff00ff | ROR32((x),8) & 0xff00ff00)
/*
* END OF PLATFORM FIXES
* =====================
*
* You should not have to touch the rest of this file.
*/
/*
* Convert the external type names to some that are easier to use inside
* this file. I didn't want to use the names Byte and UInt32 in the
* header file, because many programs already define them and using two
* conventions at once can be very difficult.
* Don't change these definitions! Change the originals
* in twofish.h instead.
*/
/* A Byte must be an unsigned integer, 8 bits long. */
// typedef Twofish_Byte Byte;
/* A UInt32 must be an unsigned integer at least 32 bits long. */
// typedef Twofish_UInt32 UInt32;
/*
* Define a macro ENDIAN_CONVERT.
*
* We define a macro ENDIAN_CONVERT that performs a BSWAP on big-endian
* machines, and is the identity function on little-endian machines.
* The code then uses this macro without considering the endianness.
*/
#if CPU_IS_BIG_ENDIAN
#define ENDIAN_CONVERT(x) BSWAP(x)
#else
#define ENDIAN_CONVERT(x) (x)
#endif
/*
* Compute byte offset within a UInt32 stored in memory.
*
* This is only used when SELECT_BYTE_FROM_quint32_IN_MEMORY is set.
*
* The input is the byte number 0..3, 0 for least significant.
* Note the use of sizeof() to support UInt32 types that are larger
* than 4 bytes.
*/
#if CPU_IS_BIG_ENDIAN
#define BYTE_OFFSET( n ) (sizeof(Twofish_UInt32) - 1 - (n) )
#else
#define BYTE_OFFSET( n ) (n)
#endif
/*
* Macro to get Byte no. b from UInt32 value X.
* We use two different definition, depending on the settings.
*/
#if SELECT_BYTE_FROM_quint32_IN_MEMORY
/* Pick the byte from the memory in which X is stored. */
#define SELECT_BYTE( X, b ) (((Twofish_Byte *)(&(X)))[BYTE_OFFSET(b)])
#else
/* Portable solution: Pick the byte directly from the X value. */
#define SELECT_BYTE( X, b ) (((X) >> (8*(b))) & 0xff)
#endif
/* Some shorthands because we use byte selection in large formulae. */
#define b0(X) SELECT_BYTE((X),0)
#define b1(X) SELECT_BYTE((X),1)
#define b2(X) SELECT_BYTE((X),2)
#define b3(X) SELECT_BYTE((X),3)
/*
* We need macros to load and store UInt32 from/to byte arrays
* using the least-significant-byte-first convention.
*
* GET32( p ) gets a UInt32 in lsb-first form from four bytes pointed to
* by p.
* PUT32( v, p ) writes the UInt32 value v at address p in lsb-first form.
*/
#if CONVERT_USING_CASTS
/* Get UInt32 from four bytes pointed to by p. */
#define GET32( p ) ENDIAN_CONVERT( *((Twofish_UInt32 *)(p)) )
/* Put UInt32 into four bytes pointed to by p */
#define PUT32( v, p ) *((Twofish_UInt32 *)(p)) = ENDIAN_CONVERT(v)
#else
/* Get UInt32 from four bytes pointed to by p. */
#define GET32( p ) \
( \
(Twofish_UInt32)((p)[0]) \
| (Twofish_UInt32)((p)[1])<< 8 \
| (Twofish_UInt32)((p)[2])<<16 \
| (Twofish_UInt32)((p)[3])<<24 \
)
/* Put UInt32 into four bytes pointed to by p */
#define PUT32( v, p ) \
(p)[0] = (Twofish_Byte)(((v) ) & 0xff); \
(p)[1] = (Twofish_Byte)(((v) >> 8) & 0xff); \
(p)[2] = (Twofish_Byte)(((v) >> 16) & 0xff); \
(p)[3] = (Twofish_Byte)(((v) >> 24) & 0xff)
#endif
void Twofish_fatal(char* msg){
qCritical("Twofish: Fatal Error");
exit(1);
}
/*
* Test the platform-specific macros.
* This function tests the macros defined so far to make sure the
* definitions are appropriate for this platform.
* If you make any mistake in the platform configuration, this should detect
* that and inform you what went wrong.
* Somewhere, someday, this is going to save somebody a lot of time,
* because misbehaving macros are hard to debug.
*/
static void test_platform()
{
/* Buffer with test values. */
Twofish_Byte buf[] = {0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0};
Twofish_UInt32 C;
Twofish_UInt32 x,y;
int i;
/*
* Some sanity checks on the types that can't be done in compile time.
* A smart compiler will just optimise these tests away.
* The pre-processor doesn't understand different types, so we cannot
* do these checks in compile-time.
*
* I hate C.
*
* The first check in each case is to make sure the size is correct.
* The second check is to ensure that it is an unsigned type.
*/
if( ((Twofish_UInt32)((Twofish_UInt32)1 << 31) == 0) || ((Twofish_UInt32)-1 < 0 ))
{
Twofish_fatal( "Twofish code: Twofish_UInt32 type not suitable" );
}
if( (sizeof( Twofish_Byte ) != 1) || (((Twofish_Byte)-1) < 0) )
{
Twofish_fatal( "Twofish code: Twofish_Byte type not suitable" );
}
/*
* Sanity-check the endianness conversions.
* This is just an aid to find problems. If you do the endianness
* conversion macros wrong you will fail the full cipher test,
* but that does not help you find the error.
* Always make it easy to find the bugs!
*
* Detail: There is no fully portable way of writing UInt32 constants,
* as you don't know whether to use the U or UL suffix. Using only U you
* might only be allowed 16-bit constants. Using UL you might get 64-bit
* constants which cannot be stored in a UInt32 without warnings, and
* which generally behave subtly different from a true UInt32.
* As long as we're just comparing with the constant,
* we can always use the UL suffix and at worst lose some efficiency.
* I use a separate '32-bit constant' macro in most of my other code.
*
* I hate C.
*
* Start with testing GET32. We test it on all positions modulo 4
* to make sure we can handly any position of inputs. (Some CPUs
* do not allow non-aligned accesses which we would do if you used
* the CONVERT_USING_CASTS option.
*/
if( (GET32( buf ) != 0x78563412UL) || (GET32(buf+1) != 0x9a785634UL)
|| (GET32( buf+2 ) != 0xbc9a7856UL) || (GET32(buf+3) != 0xdebc9a78UL) )
{
Twofish_fatal( "Twofish code: GET32 not implemented properly" );
}
/*
* We can now use GET32 to test PUT32.
* We don't test the shifted versions. If GET32 can do that then
* so should PUT32.
*/
C = GET32( buf );
PUT32( 3*C, buf );
if( GET32( buf ) != 0x69029c36UL )
{
Twofish_fatal( "Twofish code: PUT32 not implemented properly" );
}
/* Test ROL and ROR */
for( i=1; i<32; i++ )
{
/* Just a simple test. */
x = ROR32( C, i );
y = ROL32( C, i );
x ^= (C>>i) ^ (C<<(32-i));
y ^= (C<<i) ^ (C>>(32-i));
x |= y;
/*
* Now all we check is that x is zero in the least significant
* 32 bits. Using the UL suffix is safe here, as it doesn't matter
* if we get a larger type.
*/
if( (x & 0xffffffffUL) != 0 )
{
Twofish_fatal( "Twofish ROL or ROR not properly defined." );
}
}
/* Test the BSWAP macro */
if( BSWAP(C) != 0x12345678UL )
{
/*
* The BSWAP macro should always work, even if you are not using it.
* A smart optimising compiler will just remove this entire test.
*/
Twofish_fatal( "BSWAP not properly defined." );
}
/* And we can test the b<i> macros which use SELECT_BYTE. */
if( (b0(C)!=0x12) || (b1(C) != 0x34) || (b2(C) != 0x56) || (b3(C) != 0x78) )
{
/*
* There are many reasons why this could fail.
* Most likely is that CPU_IS_BIG_ENDIAN has the wrong value.
*/
Twofish_fatal( "Twofish code: SELECT_BYTE not implemented properly" );
}
}
/*
* Finally, we can start on the Twofish-related code.
* You really need the Twofish specifications to understand this code. The
* best source is the Twofish book:
* "The Twofish Encryption Algorithm", by Bruce Schneier, John Kelsey,
* Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson.
* you can also use the AES submission document of Twofish, which is
* available from my list of publications on my personal web site at
* http://niels.ferguson.net/.
*
* The first thing we do is write the testing routines. This is what the
* implementation has to satisfy in the end. We only test the external
* behaviour of the implementation of course.
*/
/*
* Perform a single self test on a (plaintext,ciphertext,key) triple.
* Arguments:
* key array of key bytes
* key_len length of key in bytes
* p plaintext
* c ciphertext
*/
static void test_vector( Twofish_Byte key[], int key_len, Twofish_Byte p[16], Twofish_Byte c[16] )
{
Twofish_Byte tmp[16]; /* scratch pad. */
Twofish_key xkey; /* The expanded key */
int i;
/* Prepare the key */
Twofish_prepare_key( key, key_len, &xkey );
/*
* We run the test twice to ensure that the xkey structure
* is not damaged by the first encryption.
* Those are hideous bugs to find if you get them in an application.
*/
for( i=0; i<2; i++ )
{
/* Encrypt and test */
Twofish_encrypt( &xkey, p, tmp );
if( memcmp( c, tmp, 16 ) != 0 )
{
Twofish_fatal( "Twofish encryption failure" );
}
/* Decrypt and test */
Twofish_decrypt( &xkey, c, tmp );
if( memcmp( p, tmp, 16 ) != 0 )
{
Twofish_fatal( "Twofish decryption failure" );
}
}
/* The test keys are not secret, so we don't need to wipe xkey. */
}
/*
* Check implementation using three (key,plaintext,ciphertext)
* test vectors, one for each major key length.
*
* This is an absolutely minimal self-test.
* This routine does not test odd-sized keys.
*/
static void test_vectors()
{
/*
* We run three tests, one for each major key length.
* These test vectors come from the Twofish specification.
* One encryption and one decryption using randomish data and key
* will detect almost any error, especially since we generate the
* tables ourselves, so we don't have the problem of a single
* damaged table entry in the source.
*/
/* 128-bit test is the I=3 case of section B.2 of the Twofish book. */
static Twofish_Byte k128[] = {
0x9F, 0x58, 0x9F, 0x5C, 0xF6, 0x12, 0x2C, 0x32,
0xB6, 0xBF, 0xEC, 0x2F, 0x2A, 0xE8, 0xC3, 0x5A,
};
static Twofish_Byte p128[] = {
0xD4, 0x91, 0xDB, 0x16, 0xE7, 0xB1, 0xC3, 0x9E,
0x86, 0xCB, 0x08, 0x6B, 0x78, 0x9F, 0x54, 0x19
};
static Twofish_Byte c128[] = {
0x01, 0x9F, 0x98, 0x09, 0xDE, 0x17, 0x11, 0x85,
0x8F, 0xAA, 0xC3, 0xA3, 0xBA, 0x20, 0xFB, 0xC3
};
/* 192-bit test is the I=4 case of section B.2 of the Twofish book. */
static Twofish_Byte k192[] = {
0x88, 0xB2, 0xB2, 0x70, 0x6B, 0x10, 0x5E, 0x36,
0xB4, 0x46, 0xBB, 0x6D, 0x73, 0x1A, 0x1E, 0x88,
0xEF, 0xA7, 0x1F, 0x78, 0x89, 0x65, 0xBD, 0x44
};
static Twofish_Byte p192[] = {
0x39, 0xDA, 0x69, 0xD6, 0xBA, 0x49, 0x97, 0xD5,
0x85, 0xB6, 0xDC, 0x07, 0x3C, 0xA3, 0x41, 0xB2
};
static Twofish_Byte c192[] = {
0x18, 0x2B, 0x02, 0xD8, 0x14, 0x97, 0xEA, 0x45,
0xF9, 0xDA, 0xAC, 0xDC, 0x29, 0x19, 0x3A, 0x65
};
/* 256-bit test is the I=4 case of section B.2 of the Twofish book. */
static Twofish_Byte k256[] = {
0xD4, 0x3B, 0xB7, 0x55, 0x6E, 0xA3, 0x2E, 0x46,
0xF2, 0xA2, 0x82, 0xB7, 0xD4, 0x5B, 0x4E, 0x0D,
0x57, 0xFF, 0x73, 0x9D, 0x4D, 0xC9, 0x2C, 0x1B,
0xD7, 0xFC, 0x01, 0x70, 0x0C, 0xC8, 0x21, 0x6F
};
static Twofish_Byte p256[] = {
0x90, 0xAF, 0xE9, 0x1B, 0xB2, 0x88, 0x54, 0x4F,
0x2C, 0x32, 0xDC, 0x23, 0x9B, 0x26, 0x35, 0xE6
};
static Twofish_Byte c256[] = {
0x6C, 0xB4, 0x56, 0x1C, 0x40, 0xBF, 0x0A, 0x97,
0x05, 0x93, 0x1C, 0xB6, 0xD4, 0x08, 0xE7, 0xFA
};
/* Run the actual tests. */
test_vector( k128, 16, p128, c128 );
test_vector( k192, 24, p192, c192 );
test_vector( k256, 32, p256, c256 );
}
/*
* Perform extensive test for a single key size.
*
* Test a single key size against the test vectors from section
* B.2 in the Twofish book. This is a sequence of 49 encryptions
* and decryptions. Each plaintext is equal to the ciphertext of
* the previous encryption. The key is made up from the ciphertext
* two and three encryptions ago. Both plaintext and key start
* at the zero value.
* We should have designed a cleaner recurrence relation for
* these tests, but it is too late for that now. At least we learned
* how to do it better next time.
* For details see appendix B of the book.
*
* Arguments:
* key_len Number of bytes of key
* final_value Final plaintext value after 49 iterations
*/
static void test_sequence( int key_len, Twofish_Byte final_value[] )
{
Twofish_Byte buf[ (50+3)*16 ]; /* Buffer to hold our computation values. */
Twofish_Byte tmp[16]; /* Temp for testing the decryption. */
Twofish_key xkey; /* The expanded key */
int i;
Twofish_Byte * p;
/* Wipe the buffer */
memset( buf, 0, sizeof( buf ) );
/*
* Because the recurrence relation is done in an inconvenient manner
* we end up looping backwards over the buffer.
*/
/* Pointer in buffer points to current plaintext. */
p = &buf[50*16];
for( i=1; i<50; i++ )
{
/*
* Prepare a key.
* This automatically checks that key_len is valid.
*/
Twofish_prepare_key( p+16, key_len, &xkey );
/* Compute the next 16 bytes in the buffer */
Twofish_encrypt( &xkey, p, p-16 );
/* Check that the decryption is correct. */
Twofish_decrypt( &xkey, p-16, tmp );
if( memcmp( tmp, p, 16 ) != 0 )
{
Twofish_fatal( "Twofish decryption failure in sequence" );
}
/* Move on to next 16 bytes in the buffer. */
p -= 16;
}
/* And check the final value. */
if( memcmp( p, final_value, 16 ) != 0 )
{
Twofish_fatal( "Twofish encryption failure in sequence" );
}
/* None of the data was secret, so there is no need to wipe anything. */
}
/*
* Run all three sequence tests from the Twofish test vectors.
*
* This checks the most extensive test vectors currently available
* for Twofish. The data is from the Twofish book, appendix B.2.
*/
static void test_sequences()
{
static Twofish_Byte r128[] = {
0x5D, 0x9D, 0x4E, 0xEF, 0xFA, 0x91, 0x51, 0x57,
0x55, 0x24, 0xF1, 0x15, 0x81, 0x5A, 0x12, 0xE0
};
static Twofish_Byte r192[] = {
0xE7, 0x54, 0x49, 0x21, 0x2B, 0xEE, 0xF9, 0xF4,
0xA3, 0x90, 0xBD, 0x86, 0x0A, 0x64, 0x09, 0x41
};
static Twofish_Byte r256[] = {
0x37, 0xFE, 0x26, 0xFF, 0x1C, 0xF6, 0x61, 0x75,
0xF5, 0xDD, 0xF4, 0xC3, 0x3B, 0x97, 0xA2, 0x05
};
/* Run the three sequence test vectors */
test_sequence( 16, r128 );
test_sequence( 24, r192 );
test_sequence( 32, r256 );
}
/*
* Test the odd-sized keys.
*
* Every odd-sized key is equivalent to a one of 128, 192, or 256 bits.
* The equivalent key is found by padding at the end with zero bytes
* until a regular key size is reached.
*
* We just test that the key expansion routine behaves properly.
* If the expanded keys are identical, then the encryptions and decryptions
* will behave the same.
*/
static void test_odd_sized_keys()
{
Twofish_Byte buf[32];
Twofish_key xkey;
Twofish_key xkey_two;
int i;
/*
* We first create an all-zero key to use as PRNG key.
* Normally we would not have to fill the buffer with zeroes, as we could
* just pass a zero key length to the Twofish_prepare_key function.
* However, this relies on using odd-sized keys, and those are just the
* ones we are testing here. We can't use an untested function to test
* itself.
*/
memset( buf, 0, sizeof( buf ) );
Twofish_prepare_key( buf, 16, &xkey );
/* Fill buffer with pseudo-random data derived from two encryptions */
Twofish_encrypt( &xkey, buf, buf );
Twofish_encrypt( &xkey, buf, buf+16 );
/* Create all possible shorter keys that are prefixes of the buffer. */
for( i=31; i>=0; i-- )
{
/* Set a byte to zero. This is the new padding byte */
buf[i] = 0;
/* Expand the key with only i bytes of length */
Twofish_prepare_key( buf, i, &xkey );
/* Expand the corresponding padded key of regular length */
Twofish_prepare_key( buf, i<=16 ? 16 : (i<= 24 ? 24 : 32), &xkey_two );
/* Compare the two */
if( memcmp( &xkey, &xkey_two, sizeof( xkey ) ) != 0 )
{
Twofish_fatal( "Odd sized keys do not expand properly" );
}
}
/* None of the key values are secret, so we don't need to wipe them. */
}
/*
* Test the Twofish implementation.
*
* This routine runs all the self tests, in order of importance.
* It is called by the Twofish_initialise routine.
*
* In almost all applications the cost of running the self tests during
* initialisation is insignificant, especially
* compared to the time it takes to load the application from disk.
* If you are very pressed for initialisation performance,
* you could remove some of the tests. Make sure you did run them
* once in the software and hardware configuration you are using.
*/
static void self_test()
{
/* The three test vectors form an absolute minimal test set. */
test_vectors();
/*
* If at all possible you should run these tests too. They take
* more time, but provide a more thorough coverage.
*/
test_sequences();
/* Test the odd-sized keys. */
test_odd_sized_keys();
}
/*
* And now, the actual Twofish implementation.
*
* This implementation generates all the tables during initialisation.
* I don't like large tables in the code, especially since they are easily
* damaged in the source without anyone noticing it. You need code to
* generate them anyway, and this way all the code is close together.
* Generating them in the application leads to a smaller executable
* (the code is smaller than the tables it generates) and a
* larger static memory footprint.
*
* Twofish can be implemented in many ways. I have chosen to
* use large tables with a relatively long key setup time.
* If you encrypt more than a few blocks of data it pays to pre-compute
* as much as possible. This implementation is relatively inefficient for
* applications that need to re-key every block or so.
*/
/*
* We start with the t-tables, directly from the Twofish definition.
* These are nibble-tables, but merging them and putting them two nibbles
* in one byte is more work than it is worth.
*/
static Twofish_Byte t_table[2][4][16] = {
{
{0x8,0x1,0x7,0xD,0x6,0xF,0x3,0x2,0x0,0xB,0x5,0x9,0xE,0xC,0xA,0x4},
{0xE,0xC,0xB,0x8,0x1,0x2,0x3,0x5,0xF,0x4,0xA,0x6,0x7,0x0,0x9,0xD},
{0xB,0xA,0x5,0xE,0x6,0xD,0x9,0x0,0xC,0x8,0xF,0x3,0x2,0x4,0x7,0x1},
{0xD,0x7,0xF,0x4,0x1,0x2,0x6,0xE,0x9,0xB,0x3,0x0,0x8,0x5,0xC,0xA}
},
{
{0x2,0x8,0xB,0xD,0xF,0x7,0x6,0xE,0x3,0x1,0x9,0x4,0x0,0xA,0xC,0x5},
{0x1,0xE,0x2,0xB,0x4,0xC,0x3,0x7,0x6,0xD,0xA,0x5,0xF,0x9,0x0,0x8},
{0x4,0xC,0x7,0x5,0x1,0x6,0x9,0xA,0x0,0xE,0xD,0x8,0x2,0xB,0x3,0xF},
{0xB,0x9,0x5,0x1,0xC,0x3,0xD,0xE,0x6,0x4,0x7,0xF,0x2,0x0,0x8,0xA}
}
};
/* A 1-bit rotation of 4-bit values. Input must be in range 0..15 */
#define ROR4BY1( x ) (((x)>>1) | (((x)<<3) & 0x8) )
/*
* The q-boxes are only used during the key schedule computations.
* These are 8->8 bit lookup tables. Some CPUs prefer to have 8->32 bit
* lookup tables as it is faster to load a 32-bit value than to load an
* 8-bit value and zero the rest of the register.
* The LARGE_Q_TABLE switch allows you to choose 32-bit entries in
* the q-tables. Here we just define the Qtype which is used to store
* the entries of the q-tables.
*/
#if LARGE_Q_TABLE
typedef Twofish_UInt32 Qtype;
#else
typedef Twofish_Byte Qtype;
#endif
/*
* The actual q-box tables.
* There are two q-boxes, each having 256 entries.
*/
static Qtype q_table[2][256];
/*
* Now the function that converts a single t-table into a q-table.
*
* Arguments:
* t[4][16] : four 4->4bit lookup tables that define the q-box
* q[256] : output parameter: the resulting q-box as a lookup table.
*/
static void make_q_table( Twofish_Byte t[4][16], Qtype q[256] )
{
int ae,be,ao,bo; /* Some temporaries. */
int i;
/* Loop over all input values and compute the q-box result. */
for( i=0; i<256; i++ ) {
/*
* This is straight from the Twofish specifications.
*
* The ae variable is used for the a_i values from the specs
* with even i, and ao for the odd i's. Similarly for the b's.
*/
ae = i>>4; be = i&0xf;
ao = ae ^ be; bo = ae ^ ROR4BY1(be) ^ ((ae<<3)&8);
ae = t[0][ao]; be = t[1][bo];
ao = ae ^ be; bo = ae ^ ROR4BY1(be) ^ ((ae<<3)&8);
ae = t[2][ao]; be = t[3][bo];
/* Store the result in the q-box table, the cast avoids a warning. */
q[i] = (Qtype) ((be<<4) | ae);
}
}
/*
* Initialise both q-box tables.
*/
static void initialise_q_boxes() {
/* Initialise each of the q-boxes using the t-tables */
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.
*/