vendor.github.com.cloudflare.circl.dh.x448.key.go Maven / Gradle / Ivy
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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
}