Problems with AES-CFB1

[Ananthasayanan Kandiah]

Hi,

I'm trying to use AES-CFB1 through the "low-level" calls. Here's the
example program I have come up with:

#include <stdio.h>
#include <string.h>
#include <openssl/aes.h>
#include <openssl/bio.h>

#define  KEY_SIZE 16

int main(void)
{
    int            i;
    AES_KEY        key;
    BIO*        bio_out;

    unsigned char key_data[KEY_SIZE] = {
        0xfe, 0xec, 0x82, 0x17, 0xb5, 0x1, 0x98, 0x6b,
        0x5e, 0xf1, 0xb8, 0x6, 0x52, 0x74, 0x2e, 0x52
    };

    unsigned char iv[AES_BLOCK_SIZE];

    unsigned char const iv_data[AES_BLOCK_SIZE] = {
        0x10, 0x8a, 0xc9, 0x30, 0xb7, 0xf2, 0x35, 0x21,
        0xfb, 0xac, 0x6b, 0xdf, 0x80, 0x95, 0xeb, 0x1e
    };

    char*   data    = "Internet is a wonderful mechanism for making a fool
"
                      "of yourself in front of a very large audience";


    int     length  = (int) strlen(data);

    int     num = 0;

    /* Allocate some space for the ciphertext and plaintext */
    char*    ciphertext = (char*) malloc(sizeof(char) * length);
    char*    plaintext  = (char*) malloc(sizeof(char) * length);

    /* Copy the IV data to the IV array */
    memcpy(iv, iv_data, AES_BLOCK_SIZE);

    /* Set the encrypt key structure using the predefined key */
    AES_set_encrypt_key(key_data, KEY_SIZE * 8, &key);

    /* Carry out the encryption */
    AES_cfb1_encrypt(data, ciphertext, length, &key, iv, &num, AES_ENCRYPT);

    /* Setup output */
    bio_out = BIO_new_fp(stdout, BIO_NOCLOSE);

    BIO_printf(bio_out, "Original plaintext: %s\n\n", data);

    BIO_printf(bio_out, "Ciphertext: ");

    /* Print out the ciphertext */
    for (i = 0; i < length; i++)
        BIO_printf(bio_out, "%02x", ((unsigned char*)ciphertext)[i]);

    BIO_printf(bio_out, "\n\n");

    /* Start the decryption process */

    /* First, copy the original IV data back to the IV array - as it was
overwritten
     * during the encryption process
     */
    memcpy(iv, iv_data, AES_BLOCK_SIZE);

    /* Reset how far we've gone through the IV */
    num = 0;

    /* Carry out the decryption */
    AES_cfb1_encrypt(ciphertext, plaintext, length, &key, iv, &num,
AES_DECRYPT);

    BIO_printf(bio_out, "Recovered plaintext: ");

    /* print out the plaintext */
    for (i = 0; i < length; i++)
        BIO_printf(bio_out, "%c", ((unsigned char*)plaintext)[i]);

    BIO_printf(bio_out, "\n\n");

    BIO_free(bio_out);

    free(ciphertext);
    free(plaintext);


    return 0;
}

When I run it, the output which I receive is:

Original plaintext: Internet is a wonderful mechanism for making a foolof
yourself in front of a very large audience

Ciphertext:
92c0883c54eb8df072b43278000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Recovered plaintext: Internet is


d:\ananthasayanan\stuff\projects\programming\openssl\openssl-1.0.0d\demos\crypto\low_level\ciphers\symmetric\aes\aes_cfb
1_128\x64\Release>aes_cfb1_128.exe
Original plaintext: Internet is a wonderful mechanism for making a fool of
yourself in front of a very large audience

Ciphertext:
92c0883c54eb8df072b43278000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Recovered plaintext: Internet is

As you can see, the ciphertext that is produced is only 12 bytes in length.
Hence, the recovered plaintext has only 12 characters. I have had a
look atthe source-code for AES_cfb1_encrypt
and the comment says that the input should be "packed". What does this
mean? Am I doing something wrong or is there a bug with AES-CFB1?


Thanks,
Anantha