package x448 import ( "crypto/subtle" fp "github.com/cloudflare/circl/math/fp448" ) // Size is the length in bytes of a X448 key. const Size = 56 // Key represents a X448 key. type Key [Size]byte func (k *Key) clamp(in *Key) *Key { *k = *in k[0] &= 252 k[55] |= 128 return k } // isValidPubKey verifies if the public key is not a low-order point. func (k *Key) isValidPubKey() bool { fp.Modp((*fp.Elt)(k)) var isLowOrder int for _, P := range lowOrderPoints { isLowOrder |= subtle.ConstantTimeCompare(P[:], k[:]) } return isLowOrder == 0 } // KeyGen obtains a public key given a secret key. func KeyGen(public, secret *Key) { ladderJoye(public.clamp(secret)) } // Shared calculates Alice's shared key from Alice's secret key and Bob's // public key returning true on success. A failure case happens when the public // key is a low-order point, thus the shared key is all-zeros and the function // returns false. func Shared(shared, secret, public *Key) bool { validPk := *public ok := validPk.isValidPubKey() ladderMontgomery(shared.clamp(secret), &validPk) return ok }