/* Encryption and decryption are symmetric */
#define stream_decrypt stream_encrypt
static void stream_encrypt(stream_state *self, unsigned char *block,
                           int len)
{
        int i, j = self->last_pos;
        for(i=0; i<len; i++, j=(j+1) % self->keylen)
        {
                block[i] ^= self->key[j];
        }
        self->last_pos = j;
}