AES modes extravaganza. CTS

crypto/aes-modes/aes-cts.c

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+/* aes-cts.c
+ *
+ * Copyright (C) 2006-2025 wolfSSL Inc.
+ *
+ * This file is part of wolfSSL.
+ *
+ * wolfSSL is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * wolfSSL is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
+ */
+
+/* AES-CTS Example
+ * This example demonstrates:
+ * - One-shot encryption using wc_AesCtsEncrypt()
+ * - One-shot decryption using wc_AesCtsDecrypt()
+ * Note: CTS (Ciphertext Stealing) allows encryption of data that is not
+ *       a multiple of the block size without padding expansion
+ *       Requires minimum 16 bytes input
+ * Note: CTS streaming API (Update/Final) requires careful handling of
+ *       internal buffering and is not demonstrated in this example.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifndef WOLFSSL_USER_SETTINGS
+    #include <wolfssl/options.h>
+#endif
+#include <wolfssl/wolfcrypt/settings.h>
+#include <wolfssl/wolfcrypt/aes.h>
+#include <wolfssl/wolfcrypt/random.h>
+#include <wolfssl/wolfcrypt/error-crypt.h>
+
+#if !defined(NO_AES) && defined(WOLFSSL_AES_CTS)
+
+#define AES_KEY_SIZE    AES_256_KEY_SIZE
+
+static int read_file(const char* filename, byte** data, word32* dataSz)
+{
+    FILE* fp;
+    long fileSz;
+
+    fp = fopen(filename, "rb");
+    if (fp == NULL) {
+        printf("Error: Cannot open file %s\n", filename);
+        return -1;
+    }
+
+    fseek(fp, 0, SEEK_END);
+    fileSz = ftell(fp);
+    fseek(fp, 0, SEEK_SET);
+
+    *data = (byte*)malloc(fileSz);
+    if (*data == NULL) {
+        fclose(fp);
+        printf("Error: Memory allocation failed\n");
+        return -1;
+    }
+
+    *dataSz = (word32)fread(*data, 1, fileSz, fp);
+    fclose(fp);
+
+    return 0;
+}
+
+static int write_file(const char* filename, const byte* data, word32 dataSz)
+{
+    FILE* fp;
+
+    fp = fopen(filename, "wb");
+    if (fp == NULL) {
+        printf("Error: Cannot create file %s\n", filename);
+        return -1;
+    }
+
+    fwrite(data, 1, dataSz, fp);
+    fclose(fp);
+
+    return 0;
+}
+
+/* One-shot encryption */
+static int encrypt_file(const char* inFile, const char* outFile,
+                        const byte* key, word32 keySz)
+{
+    WC_RNG rng;
+    byte   iv[AES_BLOCK_SIZE];
+    byte*  plaintext = NULL;
+    byte*  output = NULL;
+    word32 plaintextSz;
+    word32 outputSz;
+    int    ret;
+
+    ret = read_file(inFile, &plaintext, &plaintextSz);
+    if (ret != 0) return ret;
+
+    /* CTS requires minimum 16 bytes */
+    if (plaintextSz < AES_BLOCK_SIZE) {
+        printf("Error: Input must be at least %d bytes for CTS\n",
+               AES_BLOCK_SIZE);
+        free(plaintext);
+        return -1;
+    }
+
+    /* Output: IV + ciphertext (same size as plaintext with CTS) */
+    outputSz = AES_BLOCK_SIZE + plaintextSz;
+    output = (byte*)malloc(outputSz);
+    if (output == NULL) {
+        free(plaintext);
+        return -1;
+    }
+
+    /* Generate random IV */
+    ret = wc_InitRng(&rng);
+    if (ret != 0) {
+        free(plaintext);
+        free(output);
+        return ret;
+    }
+
+    ret = wc_RNG_GenerateBlock(&rng, iv, AES_BLOCK_SIZE);
+    wc_FreeRng(&rng);
+    if (ret != 0) {
+        free(plaintext);
+        free(output);
+        return ret;
+    }
+
+    /* One-shot encrypt */
+    ret = wc_AesCtsEncrypt(key, keySz, output + AES_BLOCK_SIZE,
+                           plaintext, plaintextSz, iv);
+
+    if (ret != 0) {
+        free(plaintext);
+        free(output);
+        return ret;
+    }
+
+    /* Prepend IV to output */
+    memcpy(output, iv, AES_BLOCK_SIZE);
+
+    ret = write_file(outFile, output, outputSz);
+
+    free(plaintext);
+    free(output);
+
+    printf("AES-CTS encryption complete (one-shot)\n");
+    return ret;
+}
+
+/* One-shot decryption (CTS streaming API requires complex buffering) */
+static int decrypt_file(const char* inFile, const char* outFile,
+                        const byte* key, word32 keySz)
+{
+    byte   iv[AES_BLOCK_SIZE];
+    byte*  input = NULL;
+    byte*  plaintext = NULL;
+    word32 inputSz;
+    word32 ciphertextSz;
+    int    ret;
+
+    ret = read_file(inFile, &input, &inputSz);
+    if (ret != 0) return ret;
+
+    if (inputSz < AES_BLOCK_SIZE * 2) {
+        free(input);
+        printf("Error: File too small\n");
+        return -1;
+    }
+
+    /* Extract IV from beginning */
+    memcpy(iv, input, AES_BLOCK_SIZE);
+
+    ciphertextSz = inputSz - AES_BLOCK_SIZE;
+    plaintext = (byte*)malloc(ciphertextSz);
+    if (plaintext == NULL) {
+        free(input);
+        return -1;
+    }
+
+    /* One-shot decrypt */
+    ret = wc_AesCtsDecrypt(key, keySz, plaintext,
+                           input + AES_BLOCK_SIZE, ciphertextSz, iv);
+
+    if (ret != 0) {
+        free(input);
+        free(plaintext);
+        return ret;
+    }
+
+    ret = write_file(outFile, plaintext, ciphertextSz);
+
+    free(input);
+    free(plaintext);
+
+    printf("AES-CTS decryption complete (one-shot, no streaming API "
+           "available)\n");
+    return ret;
+}
+
+int main(int argc, char** argv)
+{
+    byte key[AES_KEY_SIZE];
+    int  ret;
+
+    if (argc != 3) {
+        printf("Usage: %s <input file> <output file>\n", argv[0]);
+        printf("Encrypts input file (one-shot), then decrypts to output file "
+               "(streaming)\n");
+        printf("Note: Input must be at least 16 bytes\n");
+        return 1;
+    }
+
+    wolfCrypt_Init();
+
+    /* Use a fixed key for demonstration */
+    memset(key, 0x10, AES_KEY_SIZE);
+
+    /* Encrypt to temporary file */
+    ret = encrypt_file(argv[1], "temp_encrypted.bin", key, AES_KEY_SIZE);
+    if (ret != 0) {
+        printf("Encryption failed: %d\n", ret);
+        wolfCrypt_Cleanup();
+        return 1;
+    }
+
+    /* Decrypt to output file */
+    ret = decrypt_file("temp_encrypted.bin", argv[2], key, AES_KEY_SIZE);
+    if (ret != 0) {
+        printf("Decryption failed: %d\n", ret);
+        wolfCrypt_Cleanup();
+        return 1;
+    }
+
+    /* Clean up temp file */
+    remove("temp_encrypted.bin");
+
+    printf("Success! Decrypted file written to %s\n", argv[2]);
+
+    wolfCrypt_Cleanup();
+    return 0;
+}
+
+#else
+
+int main(int argc, char** argv)
+{
+    (void)argc;
+    (void)argv;
+    printf("AES-CTS not compiled in. Enable with WOLFSSL_AES_CTS\n");
+    return 0;
+}
+
+#endif