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// Copyright (C) 2022 Andrew Ayer
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
// OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
// Except as contained in this notice, the name(s) of the above copyright
// holders shall not be used in advertising or otherwise to promote the
// sale, use or other dealings in this Software without prior written
// authorization.
// Package cert provides helper functions for working with TLS certificates.
package cert // import "src.agwa.name/go-listener/cert"
import (
"crypto"
"crypto/tls"
"crypto/x509"
"encoding/pem"
"errors"
"fmt"
"os"
)
// A function that returns a [tls.Certificate] based on the given [tls.ClientHelloInfo]
type GetCertificateFunc func(*tls.ClientHelloInfo) (*tls.Certificate, error)
// Load a [tls.Certificate] from the given PEM-encoded file. The file must contain
// the following blocks:
// - Exactly one PRIVATE KEY, containing the private key in PKCS#8 format.
// - At least one CERTIFICATE, comprising the certificate chain, leaf certificate first and root certificate omitted.
// - Up to one OCSP RESPONSE, containing a stapled OCSP response.
// - Any number of SIGNED CERTIFICATE TIMESTAMP, containing stapled SCTs.
func LoadCertificate(filename string) (*tls.Certificate, error) {
data, err := os.ReadFile(filename)
if err != nil {
return nil, err
}
cert := new(tls.Certificate)
for {
block, rest := pem.Decode(data)
if block == nil {
break
}
switch block.Type {
case "PRIVATE KEY", "RSA PRIVATE KEY", "EC PRIVATE KEY":
if cert.PrivateKey != nil {
return nil, errors.New("contains more than one private key")
}
cert.PrivateKey, err = makePrivateKey(block)
if err != nil {
return nil, fmt.Errorf("contains invalid private key: %w", err)
}
case "CERTIFICATE":
cert.Certificate = append(cert.Certificate, block.Bytes)
case "OCSP RESPONSE":
if cert.OCSPStaple != nil {
return nil, errors.New("contains more than one OCSP response")
}
cert.OCSPStaple = block.Bytes
case "SIGNED CERTIFICATE TIMESTAMP":
cert.SignedCertificateTimestamps = append(cert.SignedCertificateTimestamps, block.Bytes)
default:
return nil, errors.New("contains unrecognized PEM block `" + block.Type + "'")
}
data = rest
}
if cert.PrivateKey == nil {
return nil, errors.New("doesn't contain any private key")
}
if len(cert.Certificate) == 0 {
return nil, errors.New("doesn't contain any certificates")
}
cert.Leaf, err = x509.ParseCertificate(cert.Certificate[0])
if err != nil {
return nil, fmt.Errorf("contains invalid leaf certificate: %w", err)
}
return cert, nil
}
func parsePrivateKey(block *pem.Block) (crypto.PrivateKey, error) {
switch block.Type {
case "PRIVATE KEY":
return x509.ParsePKCS8PrivateKey(block.Bytes)
case "RSA PRIVATE KEY":
return x509.ParsePKCS1PrivateKey(block.Bytes)
case "EC PRIVATE KEY":
return x509.ParseECPrivateKey(block.Bytes)
default:
return nil, errors.New("unrecognized private key type `" + block.Type + "'")
}
}
func makePrivateKey(block *pem.Block) (crypto.PrivateKey, error) {
key, err := parsePrivateKey(block)
if err != nil {
return nil, err
}
usage := block.Headers["Usage"]
switch usage {
case "":
return key, nil
case "decrypt":
decrypter, ok := key.(crypto.Decrypter)
if !ok {
return nil, fmt.Errorf("this key type does not support decryption")
}
return struct{ crypto.Decrypter }{decrypter}, nil
case "sign":
signer, ok := key.(crypto.Signer)
if !ok {
return nil, fmt.Errorf("this key type does not support signing")
}
return struct{ crypto.Signer }{signer}, nil
default:
return nil, errors.New("unrecognized usage `" + usage + "'")
}
}
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