99 lines
3.1 KiB
Go
99 lines
3.1 KiB
Go
// Copyright 2020 Matthew Holt
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package acmez
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import (
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"crypto/ecdsa"
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"crypto/elliptic"
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"crypto/rand"
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"crypto/sha256"
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"crypto/tls"
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"crypto/x509"
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"crypto/x509/pkix"
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"encoding/asn1"
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"encoding/pem"
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"math/big"
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"time"
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"github.com/mholt/acmez/acme"
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)
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// TLSALPN01ChallengeCert creates a certificate that can be used for
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// handshakes while solving the tls-alpn-01 challenge. See RFC 8737 §3.
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func TLSALPN01ChallengeCert(challenge acme.Challenge) (*tls.Certificate, error) {
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keyAuthSum := sha256.Sum256([]byte(challenge.KeyAuthorization))
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keyAuthSumASN1, err := asn1.Marshal(keyAuthSum[:sha256.Size])
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if err != nil {
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return nil, err
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}
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certKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
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if err != nil {
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return nil, err
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}
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challengeKeyASN1, err := x509.MarshalECPrivateKey(certKey)
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if err != nil {
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return nil, err
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}
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serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
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serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
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if err != nil {
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return nil, err
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}
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template := x509.Certificate{
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SerialNumber: serialNumber,
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Subject: pkix.Name{CommonName: "ACME challenge"},
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NotBefore: time.Now(),
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NotAfter: time.Now().Add(24 * time.Hour * 365),
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ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
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BasicConstraintsValid: true,
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DNSNames: []string{challenge.Identifier.Value},
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// add key authentication digest as the acmeValidation-v1 extension
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// (marked as critical such that it won't be used by non-ACME software).
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// Reference: https://www.rfc-editor.org/rfc/rfc8737.html#section-3
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ExtraExtensions: []pkix.Extension{
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{
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Id: idPEACMEIdentifierV1,
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Critical: true,
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Value: keyAuthSumASN1,
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},
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},
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}
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challengeCertDER, err := x509.CreateCertificate(rand.Reader, &template, &template, &certKey.PublicKey, certKey)
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if err != nil {
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return nil, err
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}
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challengeCertPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: challengeCertDER})
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challengeKeyPEM := pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: challengeKeyASN1})
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cert, err := tls.X509KeyPair(challengeCertPEM, challengeKeyPEM)
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if err != nil {
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return nil, err
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}
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return &cert, nil
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}
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// ACMETLS1Protocol is the ALPN value for the TLS-ALPN challenge
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// handshake. See RFC 8737 §6.2.
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const ACMETLS1Protocol = "acme-tls/1"
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// idPEACMEIdentifierV1 is the SMI Security for PKIX Certification Extension OID referencing the ACME extension.
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// See RFC 8737 §6.1. https://www.rfc-editor.org/rfc/rfc8737.html#section-6.1
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var idPEACMEIdentifierV1 = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 31}
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