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cfkem.go
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cfkem.go
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// Copyright 2022 Cloudflare, Inc. All rights reserved. Use of this source code
// is governed by a BSD-style license that can be found in the LICENSE file.
//
// Glue to add Circl's (post-quantum) hybrid KEMs.
//
// To enable set CurvePreferences with the desired scheme as the first element:
//
// import (
// "crypto/tls"
//
// [...]
//
// config.CurvePreferences = []tls.CurveID{
// tls.X25519Kyber768Draft00,
// tls.X25519,
// tls.P256,
// }
package tls
import (
"fmt"
"io"
"crypto/ecdh"
"github.com/cloudflare/circl/kem"
"github.com/cloudflare/circl/kem/hybrid"
)
// Either *ecdh.PrivateKey or *kemPrivateKey
type clientKeySharePrivate interface{}
type kemPrivateKey struct {
secretKey kem.PrivateKey
curveID CurveID
}
var (
X25519Kyber512Draft00 = CurveID(0xfe30)
X25519Kyber768Draft00 = CurveID(0x6399)
X25519Kyber768Draft00Old = CurveID(0xfe31)
P256Kyber768Draft00 = CurveID(0xfe32)
invalidCurveID = CurveID(0)
)
// Extract CurveID from clientKeySharePrivate
func clientKeySharePrivateCurveID(ks clientKeySharePrivate) CurveID {
switch v := ks.(type) {
case *kemPrivateKey:
return v.curveID
case *ecdh.PrivateKey:
ret, ok := curveIDForCurve(v.Curve())
if !ok {
panic("cfkem: internal error: unknown curve")
}
return ret
default:
panic("cfkem: internal error: unknown clientKeySharePrivate")
}
}
// Returns scheme by CurveID if supported by Circl
func curveIdToCirclScheme(id CurveID) kem.Scheme {
switch id {
case X25519Kyber512Draft00:
return hybrid.Kyber512X25519()
case X25519Kyber768Draft00, X25519Kyber768Draft00Old:
return hybrid.Kyber768X25519()
case P256Kyber768Draft00:
return hybrid.P256Kyber768Draft00()
}
return nil
}
// Generate a new shared secret and encapsulates it for the packed
// public key in ppk using randomness from rnd.
func encapsulateForKem(scheme kem.Scheme, rnd io.Reader, ppk []byte) (
ct, ss []byte, alert alert, err error) {
pk, err := scheme.UnmarshalBinaryPublicKey(ppk)
if err != nil {
return nil, nil, alertIllegalParameter, fmt.Errorf("unpack pk: %w", err)
}
seed := make([]byte, scheme.EncapsulationSeedSize())
if _, err := io.ReadFull(rnd, seed); err != nil {
return nil, nil, alertInternalError, fmt.Errorf("random: %w", err)
}
ct, ss, err = scheme.EncapsulateDeterministically(pk, seed)
return ct, ss, alertIllegalParameter, err
}
// Generate a new keypair using randomness from rnd.
func generateKemKeyPair(scheme kem.Scheme, curveID CurveID, rnd io.Reader) (
kem.PublicKey, *kemPrivateKey, error) {
seed := make([]byte, scheme.SeedSize())
if _, err := io.ReadFull(rnd, seed); err != nil {
return nil, nil, err
}
pk, sk := scheme.DeriveKeyPair(seed)
return pk, &kemPrivateKey{sk, curveID}, nil
}