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anhuanhu
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AES modes extravaganza. ofb, siv, xts
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‎crypto/aes-modes/aes-ofb.c‎

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/* aes-ofb.c
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*
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* Copyright (C) 2006-2025 wolfSSL Inc.
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*
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* This file is part of wolfSSL.
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*
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* wolfSSL is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* wolfSSL is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
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*/
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/* AES-OFB Example
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* This example demonstrates:
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* - One-shot encryption using wc_AesOfbEncrypt()
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* - Streaming decryption using wc_AesOfbDecrypt() in chunks
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* Note: OFB mode inherently supports streaming (no padding required)
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#ifndef WOLFSSL_USER_SETTINGS
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#include <wolfssl/options.h>
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#endif
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#include <wolfssl/wolfcrypt/settings.h>
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#include <wolfssl/wolfcrypt/aes.h>
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#include <wolfssl/wolfcrypt/random.h>
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#include <wolfssl/wolfcrypt/error-crypt.h>
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#if !defined(NO_AES) && defined(WOLFSSL_AES_OFB)
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#define AES_KEY_SIZE AES_256_KEY_SIZE
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/* Small chunk size to demonstrate streaming */
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#define CHUNK_SIZE 64
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static int read_file(const char* filename, byte** data, word32* dataSz)
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{
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FILE* fp;
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long fileSz;
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fp = fopen(filename, "rb");
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if (fp == NULL) {
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printf("Error: Cannot open file %s\n", filename);
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return -1;
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}
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fseek(fp, 0, SEEK_END);
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fileSz = ftell(fp);
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fseek(fp, 0, SEEK_SET);
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*data = (byte*)malloc(fileSz);
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if (*data == NULL) {
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fclose(fp);
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printf("Error: Memory allocation failed\n");
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return -1;
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}
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*dataSz = (word32)fread(*data, 1, fileSz, fp);
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fclose(fp);
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return 0;
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}
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static int write_file(const char* filename, const byte* data, word32 dataSz)
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{
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FILE* fp;
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fp = fopen(filename, "wb");
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if (fp == NULL) {
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printf("Error: Cannot create file %s\n", filename);
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return -1;
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}
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fwrite(data, 1, dataSz, fp);
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fclose(fp);
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return 0;
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}
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/* One-shot encryption */
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static int encrypt_file(const char* inFile, const char* outFile,
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const byte* key, word32 keySz)
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{
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Aes aes;
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WC_RNG rng;
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byte iv[AES_BLOCK_SIZE];
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byte* plaintext = NULL;
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byte* ciphertext = NULL;
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word32 plaintextSz;
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int ret;
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ret = read_file(inFile, &plaintext, &plaintextSz);
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if (ret != 0) return ret;
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/* IV + ciphertext */
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ciphertext = (byte*)malloc(plaintextSz + AES_BLOCK_SIZE);
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if (ciphertext == NULL) {
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free(plaintext);
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return -1;
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}
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/* Generate random IV */
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ret = wc_InitRng(&rng);
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if (ret != 0) {
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free(plaintext);
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free(ciphertext);
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return ret;
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}
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ret = wc_RNG_GenerateBlock(&rng, iv, AES_BLOCK_SIZE);
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wc_FreeRng(&rng);
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if (ret != 0) {
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free(plaintext);
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free(ciphertext);
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return ret;
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}
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/* Initialize AES */
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ret = wc_AesInit(&aes, NULL, INVALID_DEVID);
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if (ret != 0) {
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free(plaintext);
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free(ciphertext);
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return ret;
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}
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ret = wc_AesSetKey(&aes, key, keySz, iv, AES_ENCRYPTION);
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if (ret != 0) {
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wc_AesFree(&aes);
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free(plaintext);
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free(ciphertext);
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return ret;
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}
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/* One-shot encrypt */
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ret = wc_AesOfbEncrypt(&aes, ciphertext + AES_BLOCK_SIZE, plaintext,
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plaintextSz);
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wc_AesFree(&aes);
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if (ret != 0) {
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free(plaintext);
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free(ciphertext);
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return ret;
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}
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/* Prepend IV to output */
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memcpy(ciphertext, iv, AES_BLOCK_SIZE);
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ret = write_file(outFile, ciphertext, plaintextSz + AES_BLOCK_SIZE);
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free(plaintext);
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free(ciphertext);
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printf("AES-OFB encryption complete (one-shot)\n");
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return ret;
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}
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/* Streaming decryption - process in chunks */
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static int decrypt_file(const char* inFile, const char* outFile,
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const byte* key, word32 keySz)
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{
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Aes aes;
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byte iv[AES_BLOCK_SIZE];
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byte* ciphertext = NULL;
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byte* plaintext = NULL;
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word32 ciphertextSz;
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word32 plaintextSz;
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word32 offset;
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word32 chunkSz;
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int ret;
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ret = read_file(inFile, &ciphertext, &ciphertextSz);
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if (ret != 0) return ret;
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if (ciphertextSz < AES_BLOCK_SIZE) {
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free(ciphertext);
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printf("Error: File too small\n");
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return -1;
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}
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/* Extract IV from beginning */
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memcpy(iv, ciphertext, AES_BLOCK_SIZE);
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plaintextSz = ciphertextSz - AES_BLOCK_SIZE;
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plaintext = (byte*)malloc(plaintextSz);
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if (plaintext == NULL) {
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free(ciphertext);
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return -1;
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}
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/* Initialize AES */
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ret = wc_AesInit(&aes, NULL, INVALID_DEVID);
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if (ret != 0) {
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free(ciphertext);
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free(plaintext);
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return ret;
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}
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ret = wc_AesSetKey(&aes, key, keySz, iv, AES_ENCRYPTION);
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if (ret != 0) {
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wc_AesFree(&aes);
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free(ciphertext);
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free(plaintext);
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return ret;
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}
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/* Streaming decrypt - process in chunks */
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printf("AES-OFB streaming decryption:\n");
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offset = 0;
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while (offset < plaintextSz) {
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chunkSz = plaintextSz - offset;
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if (chunkSz > CHUNK_SIZE) {
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chunkSz = CHUNK_SIZE;
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}
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ret = wc_AesOfbDecrypt(&aes, plaintext + offset,
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ciphertext + AES_BLOCK_SIZE + offset, chunkSz);
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if (ret != 0) {
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wc_AesFree(&aes);
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free(ciphertext);
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free(plaintext);
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return ret;
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}
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printf(" Decrypted chunk: offset=%u, size=%u\n", offset, chunkSz);
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offset += chunkSz;
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}
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wc_AesFree(&aes);
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ret = write_file(outFile, plaintext, plaintextSz);
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free(ciphertext);
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free(plaintext);
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printf("AES-OFB decryption complete (streaming)\n");
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return ret;
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}
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int main(int argc, char** argv)
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{
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byte key[AES_KEY_SIZE];
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int ret;
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if (argc != 3) {
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printf("Usage: %s <input file> <output file>\n", argv[0]);
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printf("Encrypts input file (one-shot), then decrypts to output file "
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"(streaming)\n");
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return 1;
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}
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wolfCrypt_Init();
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/* Use a fixed key for demonstration */
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memset(key, 0x05, AES_KEY_SIZE);
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/* Encrypt to temporary file */
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ret = encrypt_file(argv[1], "temp_encrypted.bin", key, AES_KEY_SIZE);
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if (ret != 0) {
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printf("Encryption failed: %d\n", ret);
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wolfCrypt_Cleanup();
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return 1;
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}
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/* Decrypt to output file */
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ret = decrypt_file("temp_encrypted.bin", argv[2], key, AES_KEY_SIZE);
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if (ret != 0) {
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printf("Decryption failed: %d\n", ret);
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wolfCrypt_Cleanup();
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return 1;
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}
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/* Clean up temp file */
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remove("temp_encrypted.bin");
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printf("Success! Decrypted file written to %s\n", argv[2]);
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wolfCrypt_Cleanup();
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return 0;
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}
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#else
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int main(int argc, char** argv)
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{
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(void)argc;
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(void)argv;
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printf("AES-OFB not compiled in. Enable with WOLFSSL_AES_OFB\n");
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return 0;
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}
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#endif

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