Hello, I'm having problems with the EVP_Encrypt/Decrypt interface.
The following program doesn't work as expected. It does simple
data->encrypt->decrypt->in. Specifically, I get some garbage mixed with
the plaintext in the final buffer.
It seems like the EVP_DncryptUpdate decrypts (n-1) blocks of 8 bytes,
which is OK, but the EVP_DncryptFinal doesn't decrypt the remaining
block and returns `bad_decrypt' error - everything is in the comments
below. What am I doing wrong?
======= t_evp.c =============
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/err.h>
int main(void)
{
BIO *bio_err=NULL;
EVP_CIPHER_CTX ectx;
u_char enckey[EVP_MAX_KEY_LENGTH];
u_char password[]="sample password";
u_char data[]="abcdefghijklmnopqrstuvwxyz1234567890";
int outl, inl;
u_char *out, *in;
int toutl;
int ret;
OpenSSL_add_all_algorithms();
ERR_load_crypto_strings();
bio_err = BIO_new_fp(stderr,BIO_NOCLOSE);
/* Make 3DES key out of password */
EVP_BytesToKey(EVP_des_ede3_cbc(), EVP_sha1(),
NULL, password, strlen(password), 1, enckey, NULL);
/* Initialize encryption */
EVP_CIPHER_CTX_init(&ectx);
EVP_EncryptInit( &ectx, EVP_des_ede3_cbc(), enckey, NULL);
/* Make room for encrypted output and decrypted input */
out = malloc( strlen(data) + 2*EVP_CIPHER_CTX_block_size(&ectx));
in = malloc( strlen(data) + 2*EVP_CIPHER_CTX_block_size(&ectx));
/* Encrypt from data to out */
/* Length of the data is 36 */
EVP_EncryptUpdate( &ectx, out, &outl, data, strlen(data));
toutl = outl; /* Now outl is 32 */
EVP_EncryptFinal( &ectx, out, &outl);
toutl += outl; /* Now outl is 8 */
/* Clean up and reinitialize */
EVP_CIPHER_CTX_cleanup(&ectx);
EVP_DecryptInit( &ectx, EVP_des_ede3_cbc(), enckey, NULL );
/* Decrypt from out to in */
/* toutl is 40 */
EVP_DecryptUpdate( &ectx, in, &inl, out, toutl);
/* inl is 32 - correct, but the result in `in' is garbage,
* and then some plaintext (starting with `qrst...'
*/
ret = EVP_DecryptFinal( &ectx, in, &inl);
/* This fails, inl is 0 and error `bad_decrypt' is set */
if (ret != 1)
{
ERR_print_errors(bio_err);
}
return 0;
}
======= end t_evp.c =============
--
Paweł Krawczyk <http://ceti.pl/~kravietz/>
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