AES modes extravaganza. CTS
Anthony Hu
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123d562214
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482ade5848
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/* aes-cts.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-CTS Example
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* This example demonstrates:
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* - One-shot encryption using wc_AesCtsEncrypt()
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* - One-shot decryption using wc_AesCtsDecrypt()
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* Note: CTS (Ciphertext Stealing) allows encryption of data that is not
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* a multiple of the block size without padding expansion
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* Requires minimum 16 bytes input
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* Note: CTS streaming API (Update/Final) requires careful handling of
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* internal buffering and is not demonstrated in this example.
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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_CTS)
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#define AES_KEY_SIZE AES_256_KEY_SIZE
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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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WC_RNG rng;
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byte iv[AES_BLOCK_SIZE];
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byte* plaintext = NULL;
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byte* output = NULL;
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word32 plaintextSz;
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word32 outputSz;
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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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/* CTS requires minimum 16 bytes */
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if (plaintextSz < AES_BLOCK_SIZE) {
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printf("Error: Input must be at least %d bytes for CTS\n",
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AES_BLOCK_SIZE);
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free(plaintext);
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return -1;
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}
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/* Output: IV + ciphertext (same size as plaintext with CTS) */
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outputSz = AES_BLOCK_SIZE + plaintextSz;
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output = (byte*)malloc(outputSz);
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if (output == 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(output);
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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(output);
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return ret;
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}
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/* One-shot encrypt */
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ret = wc_AesCtsEncrypt(key, keySz, output + AES_BLOCK_SIZE,
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plaintext, plaintextSz, iv);
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if (ret != 0) {
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free(plaintext);
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free(output);
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return ret;
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}
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/* Prepend IV to output */
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memcpy(output, iv, AES_BLOCK_SIZE);
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ret = write_file(outFile, output, outputSz);
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free(plaintext);
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free(output);
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printf("AES-CTS encryption complete (one-shot)\n");
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return ret;
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}
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/* One-shot decryption (CTS streaming API requires complex buffering) */
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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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byte iv[AES_BLOCK_SIZE];
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byte* input = NULL;
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byte* plaintext = NULL;
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word32 inputSz;
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word32 ciphertextSz;
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int ret;
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ret = read_file(inFile, &input, &inputSz);
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if (ret != 0) return ret;
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if (inputSz < AES_BLOCK_SIZE * 2) {
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free(input);
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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, input, AES_BLOCK_SIZE);
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ciphertextSz = inputSz - AES_BLOCK_SIZE;
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plaintext = (byte*)malloc(ciphertextSz);
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if (plaintext == NULL) {
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free(input);
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return -1;
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}
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/* One-shot decrypt */
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ret = wc_AesCtsDecrypt(key, keySz, plaintext,
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input + AES_BLOCK_SIZE, ciphertextSz, iv);
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if (ret != 0) {
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free(input);
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free(plaintext);
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return ret;
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}
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ret = write_file(outFile, plaintext, ciphertextSz);
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free(input);
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free(plaintext);
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printf("AES-CTS decryption complete (one-shot, no streaming API "
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"available)\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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printf("Note: Input must be at least 16 bytes\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, 0x10, 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-CTS not compiled in. Enable with WOLFSSL_AES_CTS\n");
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return 0;
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}
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#endif
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