core/internal/consensus/ca/compat.go

// Copyright 2020 The Monogon Project Authors.
//
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// I've fixed this upstream, compat is going away once
// https://go-review.googlesource.com/c/go/+/204046 hits stable
package ca

import (
	"crypto"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/asn1"
	"errors"
	"io"
	"time"
)

// Workaround for Go not supporting Ed25519 CRLs
type CompatCertificate x509.Certificate

var oidExtensionAuthorityKeyId = []int{2, 5, 29, 35}
var oidSignatureEd25519 = asn1.ObjectIdentifier{1, 3, 101, 112}

func signingParamsForPublicKey(pub interface{}, requestedSigAlgo x509.SignatureAlgorithm) (hashFunc crypto.Hash, sigAlgo pkix.AlgorithmIdentifier, err error) {
	sigAlgo.Algorithm = oidSignatureEd25519
	return
}

// RFC 5280,  4.2.1.1
type authKeyId struct {
	Id []byte `asn1:"optional,tag:0"`
}

// CreateCRL returns a DER encoded CRL, signed by this Certificate, that
// contains the given list of revoked certificates.
func (c *CompatCertificate) CreateCRL(rand io.Reader, priv interface{}, revokedCerts []pkix.RevokedCertificate, now, expiry time.Time) (crlBytes []byte, err error) {
	key, ok := priv.(crypto.Signer)
	if !ok {
		return nil, errors.New("x509: certificate private key does not implement crypto.Signer")
	}

	hashFunc, signatureAlgorithm, err := signingParamsForPublicKey(key.Public(), 0)
	if err != nil {
		return nil, err
	}

	// Force revocation times to UTC per RFC 5280.
	revokedCertsUTC := make([]pkix.RevokedCertificate, len(revokedCerts))
	for i, rc := range revokedCerts {
		rc.RevocationTime = rc.RevocationTime.UTC()
		revokedCertsUTC[i] = rc
	}

	tbsCertList := pkix.TBSCertificateList{
		Version:             1,
		Signature:           signatureAlgorithm,
		Issuer:              c.Subject.ToRDNSequence(),
		ThisUpdate:          now.UTC(),
		NextUpdate:          expiry.UTC(),
		RevokedCertificates: revokedCertsUTC,
	}

	// Authority Key Id
	if len(c.SubjectKeyId) > 0 {
		var aki pkix.Extension
		aki.Id = oidExtensionAuthorityKeyId
		aki.Value, err = asn1.Marshal(authKeyId{Id: c.SubjectKeyId})
		if err != nil {
			return
		}
		tbsCertList.Extensions = append(tbsCertList.Extensions, aki)
	}

	tbsCertListContents, err := asn1.Marshal(tbsCertList)
	if err != nil {
		return
	}

	signed := tbsCertListContents
	if hashFunc != 0 {
		h := hashFunc.New()
		h.Write(signed)
		signed = h.Sum(nil)
	}

	var signature []byte
	signature, err = key.Sign(rand, signed, hashFunc)
	if err != nil {
		return
	}

	return asn1.Marshal(pkix.CertificateList{
		TBSCertList:        tbsCertList,
		SignatureAlgorithm: signatureAlgorithm,
		SignatureValue:     asn1.BitString{Bytes: signature, BitLength: len(signature) * 8},
	})
}