C-具有AES-256和CFB模式的OpenSSL

Question

I am working on Ubuntu 14.10 and I am trying to get the same output using C and OpenSSL that I would get using the command:

openssl enc -aes-256-cfb8 -in test -out test.enc -K $key -iv $iv

I have been working on this for two days and not getting it, the encryption works but it is not the one I am supposed to get.

My code is:

int outlen, inlen;  

unsigned char inbuf[BUFSIZE] , outbuf[BUFSIZE];  

strcpy(inbuf,text);

EVP_CIPHER_CTX ctx;   
EVP_CIPHER_CTX_init(&ctx);   

EVP_EncryptInit_ex(&ctx, EVP_aes_256_cfb8(), NULL, key, iv);

int i =0;
int n = strlen(text);
for(i; i < n; i++) {    

    if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, inbuf, 1)) 
        return 0;  
}    

if(!EVP_EncryptFinal(&ctx, outbuf, &outlen)) 
    return 0;  

EVP_CIPHER_CTX_cleanup(&ctx); P_EncryptFinal(&ctx, outbuf, &outlen)) 
    return 0;  

EVP_CIPHER_CTX_cleanup(&ctx);  i < n; i++) {    

    if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, inbuf, 1)) 
        return 0;  
}    

if(!EVP_EncryptFinal(&ctx, outbuf, &outlen)) 
    return 0;  

EVP_CIPHER_CTX_cleanup(&ctx); 

Thank You!

Answer 1

You are encrypting the same byte over and over again. In EVP_EncryptUpdate, you have to move the inbuf pointer along across each input byte, and you have to move the outbuf pointer along to fresh memory. I made minor changes to your code (and completed it enough to run):

#include <stdio.h>
#include <openssl/ssl.h>

#define BUFSIZE 256

int doit(char* text, char* key, char* iv)
{
    int outlen, inlen;  

    unsigned char inbuf[BUFSIZE] , outbuf[BUFSIZE];  

    strcpy(inbuf,text);

    EVP_CIPHER_CTX ctx;   
    EVP_CIPHER_CTX_init(&ctx);   

    EVP_EncryptInit_ex(&ctx, EVP_aes_256_cfb8(), NULL, key, iv);

    int i =0;
    int n = strlen(text);
    unsigned char* p = outbuf;
    for(i; i < n; i++) {    

        if(!EVP_EncryptUpdate(&ctx, p, &outlen, &inbuf[i], 1)) 
            return 0;  
        p += outlen;
    }    

    if(!EVP_EncryptFinal(&ctx, p, &outlen)) 
        return 0;  
    p += outlen;

    EVP_CIPHER_CTX_cleanup(&ctx);

    outlen = p - outbuf;
    for (n = 0; n < outlen; n++)
        printf("%c", outbuf[n] & 0xff);
}

int main()
{
    char* key = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
    char* iv = "BBBBBBBBBBBBBBBB";
    doit("hello world", key, iv);
}

The C code wants bytes for key and IV, but the openssl command line wants hex chars. This command line will get you the same result as the above C code:

openssl enc -aes-256-cfb8 -in test -out test.enc -K 4141414141414141414141414141414141414141414141414141414141414141 -iv 42424242424242424242424242424242

Of course, you need to set up the exact same plaintext:

$ echo "hello world" > test
$ truncate --size 11 test # remove newline at end