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twofish.h
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twofish.h
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/*
* Fast, portable, and easy-to-use Twofish implementation,
* Version 0.3.
* Copyright (c) 2002 by Niels Ferguson.
*
* See the twofish.c file for the details of the how and why of this code.
*
* 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.
*/
#ifndef _twofish_h
#define _twofish_h
/*
* PLATFORM FIXES
* ==============
*
* 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.
*
* The defaults provided here should work on most PC compilers.
*/
/*
* A Twofish_Byte must be an unsigned 8-bit integer.
* It must also be the elementary data size of your C platform,
* i.e. sizeof( Twofish_Byte ) == 1.
*/
typedef unsigned char Twofish_Byte;
/*
* A Twofish_UInt32 must be an unsigned integer of at least 32 bits.
*
* This type is used only internally in the implementation, so ideally it
* would not appear in the header file, but it is used inside the
* Twofish_key structure which means it has to be included here.
*/
typedef unsigned int Twofish_UInt32;
/*
* END OF PLATFORM FIXES
* =====================
*
* You should not have to touch the rest of this file, but the code
* in twofish.c has a few things you need to fix too.
*/
/*
* Structure that contains a prepared Twofish key.
* A cipher key is used in two stages. In the first stage it is converted
* form the original form to an internal representation.
* This internal form is then used to encrypt and decrypt data.
* This structure contains the internal form. It is rather large: 4256 bytes
* on a platform with 32-bit unsigned values.
*
* Treat this as an opague structure, and don't try to manipulate the
* elements in it. I wish I could hide the inside of the structure,
* but C doesn't allow that.
*/
typedef
struct
{
Twofish_UInt32 s[4][256]; /* pre-computed S-boxes */
Twofish_UInt32 K[40]; /* Round key words */
}
Twofish_key;
/*
* Initialise and test the Twofish implementation.
*
* This function MUST be called before any other function in the
* Twofish implementation is called.
* It only needs to be called once.
*
* Apart from initialising the implementation it performs a self test.
* If the Twofish_fatal function is not called, the code passed the test.
* (See the twofish.c file for details on the Twofish_fatal function.)
*/
extern void Twofish_initialise(void);
/*
* Convert a cipher key to the internal form used for
* encryption and decryption.
*
* The cipher key is an array of bytes; the Twofish_Byte type is
* defined above to a type suitable on your platform.
*
* Any key must be converted to an internal form in the Twofisk_key structure
* before it can be used.
* The encryption and decryption functions only work with the internal form.
* The conversion to internal form need only be done once for each key value.
*
* Be sure to wipe all key storage, including the Twofish_key structure,
* once you are done with the key data.
* A simple memset( TwofishKey, 0, sizeof( TwofishKey ) ) will do just fine.
*
* Unlike most implementations, this one allows any key size from 0 bytes
* to 32 bytes. According to the Twofish specifications,
* irregular key sizes are handled by padding the key with zeroes at the end
* until the key size is 16, 24, or 32 bytes, whichever
* comes first. Note that each key of irregular size is equivalent to exactly
* one key of 16, 24, or 32 bytes.
*
* WARNING: Short keys have low entropy, and result in low security.
* Anything less than 8 bytes is utterly insecure. For good security
* use at least 16 bytes. I prefer to use 32-byte keys to prevent
* any collision attacks on the key.
*
* The key length argument key_len must be in the proper range.
* If key_len is not in the range 0,...,32 this routine attempts to generate
* a fatal error (depending on the code environment),
* and at best (or worst) returns without having done anything.
*
* Arguments:
* key Array of key bytes
* key_len Number of key bytes, must be in the range 0,1,...,32.
* xkey Pointer to an Twofish_key structure that will be filled
* with the internal form of the cipher key.
*/
extern void Twofish_prepare_key(
Twofish_Byte key[],
int key_len,
Twofish_key * xkey
);
/*
* Encrypt a single block of data.
*
* This function encrypts a single block of 16 bytes of data.
* If you want to encrypt a larger or variable-length message,
* you will have to use a cipher mode, such as CBC or CTR.
* These are outside the scope of this implementation.
*
* The xkey structure is not modified by this routine, and can be
* used for further encryption and decryption operations.
*
* Arguments:
* xkey pointer to Twofish_key, internal form of the key
* produces by Twofish_prepare_key()
* p Plaintext to be encrypted
* c Place to store the ciphertext
*/
extern void Twofish_encrypt(
Twofish_key * xkey,
Twofish_Byte p[16],
Twofish_Byte c[16]
);
/*
* Decrypt a single block of data.
*
* This function decrypts a single block of 16 bytes of data.
* If you want to decrypt a larger or variable-length message,
* you will have to use a cipher mode, such as CBC or CTR.
* These are outside the scope of this implementation.
*
* The xkey structure is not modified by this routine, and can be
* used for further encryption and decryption operations.
*
* Arguments:
* xkey pointer to Twofish_key, internal form of the key
* produces by Twofish_prepare_key()
* c Ciphertext to be decrypted
* p Place to store the plaintext
*/
extern void Twofish_decrypt(
Twofish_key * xkey,
Twofish_Byte c[16],
Twofish_Byte p[16]
);
#endif // _twofish_h