/*
Nastasie Ion Octavian
http://tavi-tech.blogspot.com/2012/04/linux-aes-encryption-c.html
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/evp.h>
#include <openssl/aes.h>

#define FILE_BUFFER AES_BLOCK_SIZE*1024

unsigned char* encrypt_data(unsigned char* data, int *data_len, unsigned char* key, unsigned char* iv)
{
    EVP_CIPHER_CTX enc_cipher;
    unsigned char *enc_data;
    int enc_len = 0, final_len = 0;

    EVP_CIPHER_CTX_init(&enc_cipher);
    EVP_EncryptInit_ex(&enc_cipher, EVP_aes_256_cbc(), NULL, key, iv);

    enc_data = (unsigned char*)malloc(*data_len + AES_BLOCK_SIZE - *data_len % AES_BLOCK_SIZE);
    if(!enc_data)
        return NULL;

    EVP_EncryptUpdate(&enc_cipher, enc_data, &enc_len, data, *data_len);
    EVP_EncryptFinal_ex(&enc_cipher, enc_data + enc_len, &final_len);

    *data_len = enc_len + final_len;
    EVP_CIPHER_CTX_cleanup(&enc_cipher);
    return enc_data;
}

unsigned char* decrypt_data(unsigned char* data, int *data_len, unsigned char* key, unsigned char* iv)
{
    EVP_CIPHER_CTX dec_cipher;
    unsigned char *dec_data;
    int dec_len = 0, fin_len = 0;

    EVP_CIPHER_CTX_init(&dec_cipher);
    EVP_DecryptInit_ex(&dec_cipher, EVP_aes_256_cbc(), NULL, key, iv);

    dec_data = (unsigned char *)malloc(*data_len);
    if(!dec_data)
        return NULL;

    EVP_DecryptUpdate(&dec_cipher, dec_data, &dec_len, data, *data_len);
    EVP_DecryptFinal(&dec_cipher, dec_data + dec_len, &fin_len);

    *data_len = dec_len + fin_len;
    EVP_CIPHER_CTX_cleanup(&dec_cipher);
    return dec_data;
}

int encrypt_file(char* file_in, char* file_out, unsigned char* key, unsigned char* iv)
{
    FILE *fin, *fout;
    EVP_CIPHER_CTX enc_cipher;
    unsigned char buffer[FILE_BUFFER];
    unsigned char aux[FILE_BUFFER];
    int read_len, write_len = 0;

    fin = fopen(file_in,"rb");
    if(!fin)
        return -1;
    fout = fopen(file_out, "wb");
    if(!fout)
        return -2;

    EVP_CIPHER_CTX_init(&enc_cipher);
    EVP_EncryptInit_ex(&enc_cipher, EVP_aes_256_cbc(), NULL, key, iv);

    while((read_len = fread(buffer,1,FILE_BUFFER,fin)) == FILE_BUFFER)
    {
        EVP_EncryptUpdate(&enc_cipher, aux, &write_len, buffer, read_len);
        fwrite(aux,1,write_len, fout);
    }
    EVP_EncryptUpdate(&enc_cipher, aux, &write_len, buffer, read_len);
    read_len = write_len;
    EVP_EncryptFinal_ex(&enc_cipher, aux + write_len, &write_len);
    fwrite(aux,1,read_len + write_len, fout);

    fclose(fin);
    fclose(fout);
    EVP_CIPHER_CTX_cleanup(&enc_cipher);
    return 0;
}

int decrypt_file(char* file_in, char* file_out, unsigned char* key, unsigned char* iv)
{
    FILE *fin, *fout;
    EVP_CIPHER_CTX dec_cipher;
    unsigned char buffer[FILE_BUFFER];
    unsigned char aux[FILE_BUFFER];
    int read_len, write_len = 0;

    fin = fopen(file_in,"rb");
    if(!fin)
        return -1;
    fout = fopen(file_out, "wb");
    if(!fout)
        return -2;


    EVP_CIPHER_CTX_init(&dec_cipher);
    EVP_DecryptInit_ex(&dec_cipher, EVP_aes_256_cbc(), NULL, key, iv);

    while((read_len = fread(buffer,1,FILE_BUFFER,fin)) == FILE_BUFFER)
    {
        EVP_DecryptUpdate(&dec_cipher, aux, &write_len, buffer, read_len);
        fwrite(aux,1,write_len, fout);
    }
    EVP_DecryptUpdate(&dec_cipher, aux, &write_len, buffer, read_len);
    read_len = write_len;
    EVP_DecryptFinal_ex(&dec_cipher, aux + read_len, &write_len);
    fwrite(aux,1, read_len + write_len, fout);

    fclose(fin);
    fclose(fout);
    EVP_CIPHER_CTX_cleanup(&dec_cipher);
    return 0;
}

void cbuff()
{
    int ch;
    while( (ch =(int)getchar()) != EOF && (char)ch != '\n');
}

int main()
{
    unsigned char key[] = "012345678901234a";
    unsigned char iv[] = "012435678901234d";
    char inp[30], enc[30], dec[30];
    int lene;

    printf("input: ");
    scanf("%s",inp);
    cbuff();

    printf("enc: ");
    scanf("%s",enc);
    cbuff();

    printf("dec: ");
    scanf("%s",dec);
    cbuff();

    encrypt_file(inp, enc, key, iv);
    decrypt_file(enc, dec, key, iv);

    return 0;
}