mirror of
https://github.com/cheat/cheat.git
synced 2024-11-26 16:01:35 +01:00
48 lines
1.1 KiB
Go
48 lines
1.1 KiB
Go
package x25519
|
|
|
|
import (
|
|
"crypto/subtle"
|
|
|
|
fp "github.com/cloudflare/circl/math/fp25519"
|
|
)
|
|
|
|
// Size is the length in bytes of a X25519 key.
|
|
const Size = 32
|
|
|
|
// Key represents a X25519 key.
|
|
type Key [Size]byte
|
|
|
|
func (k *Key) clamp(in *Key) *Key {
|
|
*k = *in
|
|
k[0] &= 248
|
|
k[31] = (k[31] & 127) | 64
|
|
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
|
|
validPk[31] &= (1 << (255 % 8)) - 1
|
|
ok := validPk.isValidPubKey()
|
|
ladderMontgomery(shared.clamp(secret), &validPk)
|
|
return ok
|
|
}
|