/*
**
** Krishna Puttaswamy: created on 29th May 2006
** description: program to better understand symmetric key encryption
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <fcntl.h>
#include <string.h>

#include <openssl/rand.h>
#include <openssl/evp.h>
#include <openssl/blowfish.h>

#define RAND_SEED_LENGTH 16
#define SYMMETRIC_KEY_LENGTH 16
#define IV_LENGTH 16
#define SYMMETRIC_CYPHER_TYPE "bf-ecb"

void get_data_from_random_file (unsigned char *data, int length)
{
    int i, j, fd;

    if ((fd = open ("/dev/urandom", O_RDONLY)) == -1)
	perror ("Not able to read the /dev/urandom file");

    if ((read (fd, data, length)) == -1)
	perror ("Error reading data from the random file");

    close (fd);
}

void print_in_hex (unsigned char *data, int length)
{
    int i = 0;
    for (i = 0; i < length; i++)
	printf ("%2x", data[i]);
    printf ("\n");
}

unsigned char *symmetric_encrypt (unsigned char *data, int inputlen,
				  unsigned char *key, int keylen,
				  unsigned char *iv, int ivlen, int *outlen)
{
    EVP_CIPHER_CTX ctx;
    const EVP_CIPHER *cipher_type;

    EVP_CIPHER_CTX_init (&ctx);
    OpenSSL_add_all_ciphers ();
    cipher_type = EVP_get_cipherbyname (SYMMETRIC_CYPHER_TYPE);
    if (cipher_type == NULL)
	{
	    fprintf (stderr, "Unknown cipher %s\n", SYMMETRIC_CYPHER_TYPE);
	    return NULL;
	}

    EVP_EncryptInit_ex (&ctx, cipher_type, NULL, key, iv);

    int maxbuffersize = inputlen + EVP_CIPHER_CTX_block_size (&ctx);
    unsigned char *encrypt = (unsigned char *) malloc (maxbuffersize);
    int templen = 0;

    if (EVP_EncryptUpdate (&ctx, encrypt, outlen, data, inputlen) != 1)
	{
	    printf ("encrypt: error in encrypt update\n");
	    return 0;
	}

    if (EVP_EncryptFinal_ex (&ctx, encrypt + *outlen, &templen) != 1)
	{
	    printf ("encrypt: error in encrypt final\n");
	    return 0;
	}
    *outlen += templen;
    printf ("The encrypted length is %d \n", *outlen);
    EVP_CIPHER_CTX_cleanup (&ctx);

    return encrypt;
}

unsigned char *symmetric_decrypt (unsigned char *data, int inputlen,
				  unsigned char *key, int keylen,
				  unsigned char *iv, int ivlen, int *outlen)
{
    EVP_CIPHER_CTX ctx;
    const EVP_CIPHER *cipher_type;

    EVP_CIPHER_CTX_init (&ctx);
    OpenSSL_add_all_ciphers ();
    cipher_type = EVP_get_cipherbyname (SYMMETRIC_CYPHER_TYPE);
    if (cipher_type == NULL)
	{
	    fprintf (stderr, "Unknown cipher %s\n", SYMMETRIC_CYPHER_TYPE);
	    return NULL;
	}

    EVP_DecryptInit_ex (&ctx, cipher_type, NULL, key, iv);

    int maxbuffersize = inputlen + EVP_CIPHER_CTX_block_size (&ctx);
    unsigned char *encrypt = (unsigned char *) malloc (maxbuffersize);
    int templen = 0;

    if (EVP_DecryptUpdate (&ctx, encrypt, outlen, data, inputlen) != 1)
	{
	    printf ("encrypt: error in encrypt update\n");
	    return 0;
	}

    if (EVP_DecryptFinal_ex (&ctx, encrypt + *outlen, &templen) != 1)
	{
	    printf ("encrypt: error in encrypt final\n");
	    return 0;
	}
    *outlen += templen;
    printf ("The decrypted length is %d \n", *outlen);
    EVP_CIPHER_CTX_cleanup (&ctx);

    return encrypt;
}

void generate_symmetric_key (unsigned char *key, int keylen,
			     unsigned char *iv, int ivlen)
{
    RAND_bytes (key, keylen);
    RAND_pseudo_bytes (iv, ivlen);
}

int main ()
{
    unsigned char data[100], key[SYMMETRIC_KEY_LENGTH], iv[IV_LENGTH];

    get_data_from_random_file (data, RAND_SEED_LENGTH);
    RAND_seed (data, RAND_SEED_LENGTH);

    if (RAND_status () == 0)
	printf ("Didn't have enuf randomness \n");

    generate_symmetric_key (key, SYMMETRIC_KEY_LENGTH, iv, IV_LENGTH);
    printf ("The symmetric key is \n");
    print_in_hex (key, SYMMETRIC_KEY_LENGTH);
    printf ("The IV is \n");
    print_in_hex (iv, IV_LENGTH);

    printf ("Enter text to encrypt \n");
    scanf ("%s", data);

    int encryptedlen = 0, decryptedlen = 0;
    unsigned char *encryptedText =
	symmetric_encrypt (data, strlen ((const char *) data) + 1, key,
			   SYMMETRIC_KEY_LENGTH, iv, IV_LENGTH,
			   &encryptedlen);
    unsigned char *decryptedText =
	symmetric_decrypt (encryptedText, encryptedlen, key,
			   SYMMETRIC_KEY_LENGTH, iv, IV_LENGTH,
			   &decryptedlen);
    printf ("Original data is  of len %d\n%s\n", strlen ((char *) data),
	    data);
    printf ("Decrypted data is of len %d\n%s\n",
	    strlen ((char *) decryptedText), decryptedText);

    free (decryptedText);
    free (encryptedText);
}