+ let k3 = Hmac::from_engine(hmac).to_byte_array();
+
+ let mut hmac = HmacEngine::<Sha256>::new(&prk[..]);
+ hmac.input(&k3);
+ hmac.input(&[4; 1]);
+ let k4 = Hmac::from_engine(hmac).to_byte_array();
+
+ let mut hmac = HmacEngine::<Sha256>::new(&prk[..]);
+ hmac.input(&k4);
+ hmac.input(&[5; 1]);
+ let k5 = Hmac::from_engine(hmac).to_byte_array();
+
+ (k1, k2, k3, k4, k5)