aesxam.c

aes算法的加密解密

            // encrypt the block (now in b1)
            aes_encrypt(b1, b1, ctx);

            if(len != 0 && len != BLOCK_LEN)    // use ciphertext stealing
            {
                // set the length of the last block
                wlen = len;

                // xor ciphertext into last block
                for(i = 0; i < len; ++i)
                    b3[i] ^= b1[i];

                // move 'stolen' ciphertext into last block
                for(i = len; i < BLOCK_LEN; ++i)
                    b3[i] = b1[i];

                // encrypt this block
                aes_encrypt(b3, b3, ctx);

                // and write it as the second to last encrypted block
                if(fwrite((char*)b3, 1, BLOCK_LEN, fout) != BLOCK_LEN)
                    return WRITE_ERROR;
            }

            // write the encrypted block
            if(fwrite((char*)b1, 1, wlen, fout) != wlen)
                return WRITE_ERROR;

            if(len != BLOCK_LEN)
                return OK;

            // advance the buffer pointers
            bt = b3, b3 = b2, b2 = b1, b1 = bt;
        }
    }
}

int decfile(FILE *fin, FILE *fout, aes_decrypt_ctx ctx[1])
{   unsigned char dbuf[3 * BLOCK_LEN], buf[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.

    len = (unsigned long)fread((char*)dbuf, 1, 2 * BLOCK_LEN, fin);

    if(len < 2 * BLOCK_LEN) // the original file is less than one block in length
    {
        len -= BLOCK_LEN;
        // decrypt from position len to position len + BLOCK_LEN
        aes_decrypt(dbuf + len, dbuf + len, ctx);

        // undo the CBC chaining
        for(i = 0; i < len; ++i)
            dbuf[i] ^= dbuf[i + BLOCK_LEN];

        // output the decrypted bytes
        if(fwrite((char*)dbuf, 1, len, fout) != len)
            return WRITE_ERROR;

        return OK;
    }
    else
    {   unsigned char *b1 = dbuf, *b2 = b1 + BLOCK_LEN, *b3 = b2 + BLOCK_LEN, *bt;

        for( ; ; )  // while some ciphertext remains, prepare to decrypt block b2
        {
            // read in the next block to see if ciphertext stealing is needed
            len = fread((char*)b3, 1, BLOCK_LEN, fin);

            // decrypt the b2 block
            aes_decrypt(b2, buf, ctx);

            if(len == 0 || len == BLOCK_LEN)    // no ciphertext stealing
            {
                // unchain CBC using the previous ciphertext block in b1
                for(i = 0; i < BLOCK_LEN; ++i)
                    buf[i] ^= b1[i];
            }
            else    // partial last block - use ciphertext stealing
            {
                wlen = len;

                // produce last 'len' bytes of plaintext by xoring with
                // the lowest 'len' bytes of next block b3 - C[N-1]
                for(i = 0; i < len; ++i)
                    buf[i] ^= b3[i];

                // reconstruct the C[N-1] block in b3 by adding in the
                // last (BLOCK_LEN - len) bytes of C[N-2] in b2
                for(i = len; i < BLOCK_LEN; ++i)
                    b3[i] = buf[i];

                // decrypt the C[N-1] block in b3
                aes_decrypt(b3, b3, ctx);

                // produce the last but one plaintext block by xoring with
                // the last but two ciphertext block
                for(i = 0; i < BLOCK_LEN; ++i)
                    b3[i] ^= b1[i];

                // write decrypted plaintext blocks
                if(fwrite((char*)b3, 1, BLOCK_LEN, fout) != BLOCK_LEN)
                    return WRITE_ERROR;
            }

            // write the decrypted plaintext block
            if(fwrite((char*)buf, 1, wlen, fout) != wlen)
                return WRITE_ERROR;

            if(len != BLOCK_LEN)
                return OK;

            // advance the buffer pointers
            bt = b1, b1 = b2, b2 = b3, b3 = bt;
        }
    }
}

int main(int argc, char *argv[])
{   FILE            *fin = 0, *fout = 0;
    char            *cp, ch, key[32];
    int             i, by = 0, key_len, err = 0;

    if(argc != 5 || toupper(*argv[3]) != 'D' && toupper(*argv[3]) != 'E')
    {
        printf("usage: aesxam in_filename out_filename [d/e] key_in_hex\n");
        err = -1; goto exit;
    }

    aes_init();     // in case dynamic AES tables are being used

    cp = argv[4];   // this is a pointer to the hexadecimal key digits
    i = 0;          // this is a count for the input digits processed

    while(i < 64 && *cp)        // the maximum key length is 32 bytes and
    {                           // hence at most 64 hexadecimal digits
        ch = toupper(*cp++);    // process a hexadecimal digit
        if(ch >= '0' && ch <= '9')
            by = (by << 4) + ch - '0';
        else if(ch >= 'A' && ch <= 'F')
            by = (by << 4) + ch - 'A' + 10;
        else                    // error if not hexadecimal
        {
            printf("key must be in hexadecimal notation\n");
            err = -2; goto exit;
        }

        // store a key byte for each pair of hexadecimal digits
        if(i++ & 1)
            key[i / 2 - 1] = by & 0xff;
    }

    if(*cp)
    {
        printf("The key value is too long\n");
        err = -3; goto exit;
    }
    else if(i < 32 || (i & 15))
    {
        printf("The key length must be 32, 48 or 64 hexadecimal digits\n");
        err = -4; goto exit;
    }

    key_len = i / 2;

    if(!(fin = fopen(argv[1], "rb")))   // try to open the input file
    {
        printf("The input file: %s could not be opened\n", argv[1]);
        err = -5; goto exit;
    }

    if(!(fout = fopen(argv[2], "wb")))  // try to open the output file
    {
        printf("The output file: %s could not be opened\n", argv[2]);
        err = -6; goto exit;
    }

    if(toupper(*argv[3]) == 'E') // encryption in Cipher Block Chaining mode
    {   aes_encrypt_ctx ctx[1];

        aes_encrypt_key((unsigned char*)key, key_len, ctx);

        err = encfile(fin, fout, ctx);
    }
    else                         // decryption in Cipher Block Chaining mode
    {   aes_decrypt_ctx ctx[1];

        aes_decrypt_key((unsigned char*)key, key_len, ctx);

        err = decfile(fin, fout, ctx);
    }
exit:
    if(err == READ_ERROR)
        printf("Error reading from input file: %s\n", argv[1]);

    if(err == WRITE_ERROR)
        printf("Error writing to output file: %s\n", argv[2]);

    if(fout)
        fclose(fout);

    if(fin)
        fclose(fin);

    return err;
}