[SOLVED]OpenSSL encryption in Qt sometimes return zero length on decryption.

[antonyprojr]

I'm trying this code to encrypt and decrypt some data. The problem is sometimes the result length of decrypted data is zero. I don't understand why.

@AES* aes = new AES;

void MainWindow::on_pushButton_2_clicked()
{
QByteArray source = ui->lineEdit->text().toLatin1();
QString password = QString::number(qrand());
QByteArray enc = aes->Encrypt(source, password);
QByteArray dec = aes->Decrypt(enc, password);
QString text(dec);
}
QByteArray AES::Encrypt(QByteArray source, QString password)
{
EVP_CIPHER_CTX en;

unsigned int salt[] = {12345, 54321};
unsigned char *key_data;
int key_data_len;

QByteArray ba = password.toLatin1();
key_data = (unsigned char*)ba.data();
key_data_len = strlen((char*)key_data);

int i, nrounds = 5;
unsigned char key[32], iv[32];

i = EVP_BytesToKey(EVP_aes_256_cbc(), EVP_sha1(), (unsigned char )salt, key_data, key_data_len, nrounds, key, iv);
if (i != 32) {
qDebug() << "Key size is " + QString::number(i8) + " bits - should be 256 bits";
}

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

char *input = source.data();
char *out;
int len;

len = strlen(input);

int c_len = len + AES_BLOCK_SIZE, f_len = 0;
unsigned char *ciphertext = (unsigned char *)malloc(c_len);

EVP_EncryptInit_ex(&en, NULL, NULL, NULL, NULL);
EVP_EncryptUpdate(&en, ciphertext, &c_len, (unsigned char *)input, len);
EVP_EncryptFinal_ex(&en, ciphertext+c_len, &f_len);

len = c_len + f_len;

out = (char*)ciphertext;

qDebug() << QString::number(len);

EVP_CIPHER_CTX_cleanup(&en);

return QByteArray(out, len);
}

QByteArray AES::Decrypt(QByteArray source, QString password)
{
EVP_CIPHER_CTX de;

unsigned int salt[] = {12345, 54321};
unsigned char *key_data;
int key_data_len;

QByteArray ba = password.toLatin1();
key_data = (unsigned char*)ba.data();
key_data_len = strlen((char*)key_data);

int i, nrounds = 5;
unsigned char key[32], iv[32];

i = EVP_BytesToKey(EVP_aes_256_cbc(), EVP_sha1(), (unsigned char )salt, key_data, key_data_len, nrounds, key, iv);
if (i != 32) {
qDebug() << "Key size is " + QString::number(i8) + " bits - should be 256 bits";
}

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

char *input = source.data();
char *out;
int len;

len = strlen(input);

int p_len = len, f_len = 0;
unsigned char *plaintext = (unsigned char *)malloc(p_len + AES_BLOCK_SIZE);

EVP_DecryptInit_ex(&de, NULL, NULL, NULL, NULL);
EVP_DecryptUpdate(&de, plaintext, &p_len, (unsigned char *)input, len);
EVP_DecryptFinal_ex(&de, plaintext+p_len, &f_len);

len = p_len + f_len;

out = (char*)plaintext;

qDebug() << QString::number(len);

EVP_CIPHER_CTX_cleanup(&de);

return QByteArray(out, len);
}@

[antonyprojr]

Now i'm using botan and i have no trouble.

[oyefremov]

Following code fragment is incorrect:
@
char *input = source.data();
char *out;
int len;

len = strlen(input);
@

it must be replaced with:

@
char *input = source.data();
char *out;
int len = source.size();
@

data in input array can include zero bytes and strlen can not be used to measure it.