/** * @file aes_api.c * * @brief	interface for NIST AES implementation, OFB decryption only * * @date @(#) Sep 21 2004, 09:28:38 * * @author Reinhard Wobst */#include "aes_ref_encr.h"#include "aes_api.h"/* help function */static void encrypt_one_block(unsigned char *block);/* static data */static unsigned char *Iv;static int Counter;static ROUNDKEYS *roundkeys;/** * @brief initialize AES OFB decryption * * @param key	the 128 bit key * @param iv	the 128 bit initialization vector * @param rky	pointer to workspace for round keys */void decrypt_aes_init(unsigned char key[], unsigned char *iv,		      ROUNDKEYS * rky){    unsigned char keytab[4][MAXBC];    int i;    roundkeys = rky;    for (i = 4 * 4; i--;)	keytab[i % 4][i / 4] = key[i];    rijndaelKeySched(keytab, 128, 128, *roundkeys);    Counter = 0;    Iv = iv;    encrypt_one_block(Iv);}/** * @brief decrypt piece of AES OFB enciphered text * * @param block	[in,out] the ciphertext, will be overwritten by * 		plaintext * @param len	number of bytes to decrypt */void decrypt_aes_ofb(unsigned char *block, int len){    register int i;    register unsigned char *piv = Iv + Counter;    if (Counter) {	while (Counter < 16 && len > 0) {	    *block++ ^= *piv++;	    ++Counter;	    --len;	}	if (!len)	    return;	encrypt_one_block(Iv);	piv = Iv;	Counter = 0;    }    /* now counter == 0 */    while (len >= 16) {	for (i = 16; i--;)	    *block++ ^= *piv++;	piv = Iv;	encrypt_one_block(Iv);	len -= 16;    }    /* still Counter == 0, len < 16 */    while (len) {	*block++ ^= *piv++;	--len;	++Counter;    }}/** * @brief	encrypt one AES block * * @param block	the block */static void encrypt_one_block(unsigned char *block){    register int j, t;    unsigned char table[4][MAXBC];    /* parse input stream into rectangular array */    for (j = 0; j < 4; j++)	for (t = 0; t < 4; t++)	    table[t][j] = block[4 * j + t] & 0xFF;    rijndaelEncrypt(table, 128, 128, *roundkeys);    /* parse rectangular array into output ciphertext bytes */    for (j = 0; j < 4; j++)	for (t = 0; t < 4; t++)	    block[4 * j + t] = table[t][j];}