[c] Implemented the cfich_aes_ctr.c file
Reads passphrase from stdin Encrypt stores salt+iv+ciphertext in the output Decrypt reads the salt,iv,and ciphertext and uses those values
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SHA256:JiuxZNdA5bRWXPMUJChI0AQ75yC+cXY4xM0IaVwEVys
1 changed files with 247 additions and 0 deletions
247
TPs/TP02/c/src/cfich_aes_ctr.c
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247
TPs/TP02/c/src/cfich_aes_ctr.c
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#include <openssl/err.h>
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#include <openssl/evp.h>
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#include <openssl/rand.h>
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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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#define KEY_SIZE 32
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#define SALT_SIZE 16
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#define ITERATIONS 10000
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int aes_ctr(const char *input_file, const char *output_file, const unsigned char *key, int enc) {
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int BUF_SIZE = 1024;
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int cipher_block_size = EVP_CIPHER_block_size(EVP_aes_256_ctr());
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int input_size = BUF_SIZE;
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int output_size = input_size + (cipher_block_size - 1);
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int u_len = 0, f_len = 0;
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unsigned char input_buf[input_size], output_buf[output_size];
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FILE *finput = fopen(input_file, "rb");
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if (finput == NULL) {
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fprintf(stderr, "Error opening input file\n");
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return 1;
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}
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// Open output file
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FILE *foutput = fopen(output_file, "ab");
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if (foutput == NULL) {
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fprintf(stderr, "Error opening output file\n");
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fclose(finput);
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return 1;
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}
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EVP_CIPHER_CTX *ctx = NULL;
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if (!(ctx = EVP_CIPHER_CTX_new())) {
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fprintf(stderr, "Error creating context\n");
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fclose(finput);
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fclose(foutput);
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return 1;
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}
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// If enc is 1, then we are encrypting, else we are decrypting
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// If we are encrypting, we need to generate an IV
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// If we are decrypting, we need to read the IV from the file
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unsigned char iv[16];
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if (enc) {
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if (RAND_bytes(iv, 16) != 1) {
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fprintf(stderr, "Error generating IV\n");
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return 1;
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}
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if (fwrite(iv, 1, 16, foutput) != 16) {
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fprintf(stderr, "Error writing IV to file\n");
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return 1;
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}
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} else {
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// Seek forward by 16 bytes to ignore the salt
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if (fseek(finput, 16, SEEK_SET) != 0) {
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fprintf(stderr, "Error seeking to IV position in input file\n");
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return 1;
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}
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if (fread(iv, 1, 16, finput) != 16) {
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fprintf(stderr, "Error reading IV from file\n");
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return 1;
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}
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}
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if (EVP_CipherInit_ex(ctx, EVP_aes_256_ctr(), NULL, key, iv, enc) != 1) {
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fprintf(stderr, "ERROR: EVP_CipherInit_ex failed. OpenSSL error: %s\n",
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ERR_error_string(ERR_get_error(), NULL));
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EVP_CIPHER_CTX_free(ctx);
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return 1;
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}
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int read_size, len;
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while ((read_size = fread(input_buf, 1, BUF_SIZE, finput)) > 0) {
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printf("Read %d bytes, passing through CipherUpdate...\n", read_size);
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if (EVP_CipherUpdate(ctx, output_buf, &len, input_buf, read_size) != 1) {
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fprintf(stderr, "ERROR: EVP_CipherUpdate failed. OpenSSL error: %s\n",
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ERR_error_string(ERR_get_error(), NULL));
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fclose(finput);
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fclose(foutput);
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return 1;
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}
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printf("\tGot back %d bytes from CipherUpdate...\n", len);
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printf("Writing %d bytes to %s...\n", len, output_file);
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if (fwrite(output_buf, 1, len, foutput) != len) {
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fprintf(stderr, "Error writing to output file\n");
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return 1;
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}
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printf("\tWrote %d bytes\n", len);
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u_len += len;
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}
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if (read_size == -1) {
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fprintf(stderr, "ERROR: Reading from the file %s failed.\n", input_file);
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}
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if (EVP_CipherFinal_ex(ctx, output_buf, &f_len) != 1) {
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fprintf(stderr, "ERROR: EVP_CipherFinal_ex failed. OpenSSL error: %s\n",
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ERR_error_string(ERR_get_error(), NULL));
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fclose(finput);
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fclose(foutput);
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return 1;
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}
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printf("u_len: %d, f_len: %d\n", u_len, f_len);
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if (f_len) {
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printf("Writing final %d bytes to %s...\n", f_len, output_file);
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if (fwrite(output_buf, 1, f_len, foutput) != f_len) {
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fprintf(stderr, "Error writing to output file\n");
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fclose(finput);
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fclose(foutput);
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return 1;
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}
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}
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printf("\tWrote last %d bytes\n", f_len);
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fclose(finput);
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fclose(foutput);
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return 0;
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}
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int encrypt(char *input_file, const char *passphrase) {
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unsigned char key[KEY_SIZE];
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unsigned char salt[SALT_SIZE];
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// Derive key from passphrase using PBKDF2
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char *output_file = malloc(strlen(input_file) + 5);
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strcpy(output_file, input_file);
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strcat(output_file, ".enc");
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if (RAND_bytes(salt, SALT_SIZE) != 1) {
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fprintf(stderr, "Error generating salt\n");
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return 1;
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}
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// Write salt to output file
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FILE *foutput = fopen(output_file, "wb");
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if (foutput == NULL) {
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fprintf(stderr, "Error opening output file\n");
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return 1;
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}
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if (fwrite(salt, 1, 16, foutput) != 16) {
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fprintf(stderr, "Error writing salt to file\n");
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return 1;
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}
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fclose(foutput);
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// Derive key from passphrase using PBKDF2
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if (PKCS5_PBKDF2_HMAC(passphrase, strlen(passphrase), salt, SALT_SIZE, ITERATIONS, EVP_sha256(),
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KEY_SIZE, key) != 1) {
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fprintf(stderr, "Error deriving key from passphrase\n");
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return 1;
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}
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// Print salt and key
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printf("Salt: ");
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for (int i = 0; i < SALT_SIZE; i++) {
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printf("%02x", salt[i]);
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}
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printf("\n");
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printf("Key: ");
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for (int i = 0; i < KEY_SIZE; i++) {
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printf("%02x", key[i]);
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}
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printf("\n");
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aes_ctr(input_file, output_file, key, 1);
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return 0;
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}
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int decrypt(char *input_file, const char *passphrase) {
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unsigned char key[KEY_SIZE];
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unsigned char salt[SALT_SIZE];
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// Derive key from passphrase using PBKDF2
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char *output_file = malloc(strlen(input_file) + 5);
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strcpy(output_file, input_file);
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strcat(output_file, ".dec");
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// Read salt from input file
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FILE *finput = fopen(input_file, "rb");
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if (finput == NULL) {
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fprintf(stderr, "Error opening input file\n");
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return 1;
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}
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if (fread(salt, 1, 16, finput) != 16) {
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fprintf(stderr, "Error reading salt from file\n");
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return 1;
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}
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fclose(finput);
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// Derive key from passphrase using PBKDF2
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if (PKCS5_PBKDF2_HMAC(passphrase, strlen(passphrase), salt, SALT_SIZE, ITERATIONS, EVP_sha256(),
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KEY_SIZE, key) != 1) {
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fprintf(stderr, "Error deriving key from passphrase\n");
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return 1;
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}
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// Print salt and key
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printf("Salt: ");
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for (int i = 0; i < SALT_SIZE; i++) {
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printf("%02x", salt[i]);
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}
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printf("\n");
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printf("Key: ");
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for (int i = 0; i < KEY_SIZE; i++) {
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printf("%02x", key[i]);
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}
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printf("\n");
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aes_ctr(input_file, output_file, key, 0);
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return 0;
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}
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int main(int argc, char *argv[]) {
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if (argc < 3) {
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fprintf(stderr, "Usage: %s {enc|dec} [file_path]\n", argv[0]);
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return 1;
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}
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char *mode = argv[1];
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char *input_file = argv[2];
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if (!(strcmp(mode, "enc") == 0 || strcmp(mode, "dec") == 0)) {
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fprintf(stderr, "Invalid mode. Use 'enc' or 'dec'.\n");
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}
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if (argc != 3) {
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fprintf(stderr, "Usage: %s {enc|dec} [file_path]\n", argv[0]);
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return 1;
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}
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input_file = argv[2];
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char passphrase[256]; // Assuming maximum passphrase length of 255 characters
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printf("Enter passphrase: ");
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if (fgets(passphrase, sizeof(passphrase), stdin) == NULL) {
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fprintf(stderr, "Error reading passphrase from stdin\n");
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return 1;
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}
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passphrase[strcspn(passphrase, "\n")] = '\0'; // Remove trailing newline
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if (strcmp(mode, "enc") == 0) {
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encrypt(input_file, passphrase);
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} else {
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decrypt(input_file, passphrase);
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}
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return 0;
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}
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