DES_ofb_encrypt
void DES_ofb_encrypt(const unsigned char *in, unsigned char *out, int numbits,
DES_ofb_encrypt(plain, ofb_buf1, 64, sizeof(plain) / 8, &ks, &ofb_tmp);
DES_ofb_encrypt(ofb_buf1, ofb_buf2, 64, sizeof(ofb_buf1) / 8, &ks,