aesxam.c

aes算法的加密解密

/*
 ---------------------------------------------------------------------------
 Copyright (c) 1998-2007, Brian Gladman, Worcester, UK. All rights reserved.

 LICENSE TERMS

 The free distribution and use of this software is allowed (with or without
 changes) provided that:

  1. source code distributions include the above copyright notice, this
     list of conditions and the following disclaimer;

  2. binary distributions include the above copyright notice, this list
     of conditions and the following disclaimer in their documentation;

  3. the name of the copyright holder is not used to endorse products
     built using this software without specific written permission.

 DISCLAIMER

 This software is provided 'as is' with no explicit or implied warranties
 in respect of its properties, including, but not limited to, correctness
 and/or fitness for purpose.
 ---------------------------------------------------------------------------
 Issue Date: 20/12/2007
*/

//  An example of the use of AES (Rijndael) for file encryption.  This code
//  implements AES in CBC mode with ciphertext stealing when the file length
//  is greater than one block (16 bytes).  This code is an example of how to
//  use AES and is not intended for real use since it does not provide any
//  file integrity checking.
//
//  The Command line is:
//
//      aesxam input_file_name output_file_name [D|E] hexadecimalkey
//
//  where E gives encryption and D decryption of the input file into the
//  output file using the given hexadecimal key string.  The later is a
//  hexadecimal sequence of 32, 48 or 64 digits.  Examples to encrypt or
//  decrypt aes.c into aes.enc are:
//
//      aesxam file.c file.enc E 0123456789abcdeffedcba9876543210
//
//      aesxam file.enc file2.c D 0123456789abcdeffedcba9876543210
//
//  which should return a file 'file2.c' identical to 'file.c'
//
//  CIPHERTEXT STEALING
//
//  Ciphertext stealing modifies the encryption of the last two CBC
//  blocks. It can be applied invariably to the last two plaintext
//  blocks or only applied when the last block is a partial one. In
//  this code it is only applied if there is a partial block.  For
//  a plaintext consisting of N blocks, with the last block possibly
//  a partial one, ciphertext stealing works as shown below (note the
//  reversal of the last two ciphertext blocks).  During decryption
//  the part of the C:N-1 block that is not transmitted (X) can be
//  obtained from the decryption of the penultimate ciphertext block
//  since the bytes in X are xored with the zero padding appended to
//  the last plaintext block.
//
//  This is a picture of the processing of the last
//  plaintext blocks during encryption:
//
//    +---------+   +---------+   +---------+   +-------+-+
//    |  P:N-4  |   |  P:N-3  |   |  P:N-2  |   | P:N-1 |0|
//    +---------+   +---------+   +---------+   +-------+-+
//         |             |             |             |
//         v             v             v             v
//  +----->x      +----->x      +----->x      +----->x   x = xor
//  |      |      |      |      |      |      |      |
//  |      v      |      v      |      v      |      v
//  |    +---+    |    +---+    |    +---+    |    +---+
//  |    | E |    |    | E |    |    | E |    |    | E |
//  |    +---+    |    +---+    |    +---+    |    +---+
//  |      |      |      |      |      |      |      |
//  |      |      |      |      |      v      |  +---+
//  |      |      |      |      | +-------+-+ |  |
//  |      |      |      |      | | C:N-1 |X| |  |
//  |      |      |      |      | +-------+-+ ^  |
//  |      |      |      |      |     ||      |  |
//  |      |      |      |      |     |+------+  |
//  |      |      |      |      |     +----------|--+
//  |      |      |      |      |                |  |
//  |      |      |      |      |      +---------+  |
//  |      |      |      |      |      |            |
//  |      v      |      v      |      v            v
//  | +---------+ | +---------+ | +---------+   +-------+
// -+ |  C:N-4  |-+ |  C:N-3  |-+ |  C:N-2  |   | C:N-1 |
//    +---------+   +---------+   +---------+   +-------+
//
//  And this is a picture of the processing of the last
//  ciphertext blocks during decryption:
//
//    +---------+   +---------+   +---------+   +-------+
// -+ |  C:N-4  |-+ |  C:N-3  |-+ |  C:N-2  |   | C:N-1 |
//  | +---------+ | +---------+ | +---------+   +-------+
//  |      |      |      |      |      |            |
//  |      v      |      v      |      v   +--------|----+
//  |    +---+    |    +---+    |    +---+ |  +--<--+    |
//  |    | D |    |    | D |    |    | D | |  |     |    |
//  |    +---+    |    +---+    |    +---+ |  |     v    v
//  |      |      |      |      |      |   ^  | +-------+-+
//  |      v      |      v      |      v   |  | | C:N-1 |X|
//  +----->x      +----->x      | +-------+-+ | +-------+-+
//         |             |      | |       |X| |      |
//         |             |      | +-------+-+ |      v
//         |             |      |     |       |    +---+
//         |             |      |     |       v    | D |
//         |             |      |     +------>x    +---+
//         |             |      |             |      |
//         |             |      +----->x<-----|------+   x = xor
//         |             |             |      +-----+
//         |             |             |            |
//         v             v             v            v
//    +---------+   +---------+   +---------+   +-------+
//    |  P:N-4  |   |  P:N-3  |   |  P:N-2  |   | P:N-1 |
//    +---------+   +---------+   +---------+   +-------+

#include <stdio.h>
#include <ctype.h>

#include "aes.h"
#include "rdtsc.h"

#define BLOCK_LEN   16

#define OK           0
#define READ_ERROR  -7
#define WRITE_ERROR -8

//  A Pseudo Random Number Generator (PRNG) used for the
//  Initialisation Vector. The PRNG is George Marsaglia's
//  Multiply-With-Carry (MWC) PRNG that concatenates two
//  16-bit MWC generators:
//      x(n)=36969 * x(n-1) + carry mod 2^16
//      y(n)=18000 * y(n-1) + carry mod 2^16
//  to produce a combined PRNG with a period of about 2^60.
//  The Pentium cycle counter is used to initialise it. This
//  is crude but the IV does not really need to be secret.

#define RAND(a,b) (((a = 36969 * (a & 65535) + (a >> 16)) << 16) + \
                    (b = 18000 * (b & 65535) + (b >> 16))  )

void fillrand(unsigned char *buf, const int len)
{   static unsigned long a[2], mt = 1, count = 4;
    static unsigned char r[4];
    int                  i;

    if(mt) { mt = 0; *(unsigned long long*)a = read_tsc(); }

    for(i = 0; i < len; ++i)
    {
        if(count == 4)
        {
            *(unsigned long*)r = RAND(a[0], a[1]);
            count = 0;
        }

        buf[i] = r[count++];
    }
}

int encfile(FILE *fin, FILE *fout, aes_encrypt_ctx ctx[1])
{   unsigned char dbuf[3 * BLOCK_LEN];
    unsigned long i, len, wlen = BLOCK_LEN;

    // When ciphertext stealing is used, we three ciphertext blocks so
    // we use a buffer that is three times the block length.  The buffer
    // pointers b1, b2 and b3 point to the buffer positions of three
    // ciphertext blocks, b3 being the most recent and b1 being the
    // oldest. We start with the IV in b1 and the block to be decrypted
    // in b2.

    // set a random IV

    fillrand(dbuf, BLOCK_LEN);

    // read the first file block
    len = (unsigned long) fread((char*)dbuf + BLOCK_LEN, 1, BLOCK_LEN, fin);

    if(len < BLOCK_LEN)
    {   // if the file length is less than one block

        // xor the file bytes with the IV bytes
        for(i = 0; i < len; ++i)
            dbuf[i + BLOCK_LEN] ^= dbuf[i];

        // encrypt the top 16 bytes of the buffer
        aes_encrypt(dbuf + len, dbuf + len, ctx);

        len += BLOCK_LEN;
        // write the IV and the encrypted file bytes
        if(fwrite((char*)dbuf, 1, len, fout) != len)
            return WRITE_ERROR;

        return OK;
    }
    else    // if the file length is more 16 bytes
    {   unsigned char *b1 = dbuf, *b2 = b1 + BLOCK_LEN, *b3 = b2 + BLOCK_LEN, *bt;

        // write the IV
        if(fwrite((char*)dbuf, 1, BLOCK_LEN, fout) != BLOCK_LEN)
            return WRITE_ERROR;

        for( ; ; )
        {
            // read the next block to see if ciphertext stealing is needed
            len = (unsigned long)fread((char*)b3, 1, BLOCK_LEN, fin);

            // do CBC chaining prior to encryption for current block (in b2)
            for(i = 0; i < BLOCK_LEN; ++i)
                b1[i] ^= b2[i];