143 lines
3.8 KiB
Go
143 lines
3.8 KiB
Go
// Package certificate provides utility functions for TLS certificates.
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package certificate
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import (
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"crypto"
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"crypto/ecdsa"
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"crypto/ed25519"
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"crypto/elliptic"
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"crypto/rand"
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"crypto/tls"
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"crypto/x509"
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"crypto/x509/pkix"
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"encoding/pem"
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"math/big"
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"net"
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"os"
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"time"
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)
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// CreateOptions configures the creation of a TLS certificate.
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type CreateOptions struct {
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// Subject Alternate Name values.
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// Should contain the DNS names that this certificate is valid for.
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// E.g. example.com, *.example.com
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DNSNames []string
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// Subject Alternate Name values.
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// Should contain the IP addresses that the certificate is valid for.
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IPAddresses []net.IP
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// Subject specifies the certificate Subject.
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//
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// Subject.CommonName can contain the DNS name that this certificate
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// is valid for. Server certificates should specify both a Subject
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// and a Subject Alternate Name.
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Subject pkix.Name
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// Duration specifies the amount of time that the certificate is valid for.
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Duration time.Duration
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// Ed25519 specifies whether to generate an Ed25519 key pair.
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// If false, an ECDSA key will be generated instead.
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// Ed25519 is not as widely supported as ECDSA.
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Ed25519 bool
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}
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// Create creates a new TLS certificate.
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func Create(options CreateOptions) (tls.Certificate, error) {
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crt, priv, err := newX509KeyPair(options)
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if err != nil {
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return tls.Certificate{}, err
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}
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var cert tls.Certificate
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cert.Leaf = crt
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cert.Certificate = append(cert.Certificate, crt.Raw)
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cert.PrivateKey = priv
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return cert, nil
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}
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// newX509KeyPair creates and returns a new certificate and private key.
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func newX509KeyPair(options CreateOptions) (*x509.Certificate, crypto.PrivateKey, error) {
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var pub crypto.PublicKey
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var priv crypto.PrivateKey
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if options.Ed25519 {
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// Generate an Ed25519 private key
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var err error
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pub, priv, err = ed25519.GenerateKey(rand.Reader)
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if err != nil {
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return nil, nil, err
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}
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} else {
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// Generate an ECDSA private key
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private, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
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if err != nil {
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return nil, nil, err
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}
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priv = private
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pub = &private.PublicKey
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}
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// ECDSA and Ed25519 keys should have the DigitalSignature KeyUsage bits
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// set in the x509.Certificate template
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keyUsage := x509.KeyUsageDigitalSignature
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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, nil, err
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}
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notBefore := time.Now()
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notAfter := notBefore.Add(options.Duration)
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template := x509.Certificate{
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SerialNumber: serialNumber,
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NotBefore: notBefore,
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NotAfter: notAfter,
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KeyUsage: keyUsage,
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ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
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BasicConstraintsValid: true,
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IPAddresses: options.IPAddresses,
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DNSNames: options.DNSNames,
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Subject: options.Subject,
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}
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crt, err := x509.CreateCertificate(rand.Reader, &template, &template, pub, priv)
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if err != nil {
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return nil, nil, err
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}
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cert, err := x509.ParseCertificate(crt)
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if err != nil {
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return nil, nil, err
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}
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return cert, priv, nil
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}
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// Write writes the provided certificate and its private key
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// to certPath and keyPath respectively.
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func Write(cert tls.Certificate, certPath, keyPath string) error {
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certOut, err := os.OpenFile(certPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
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if err != nil {
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return err
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}
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defer certOut.Close()
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if err := pem.Encode(certOut, &pem.Block{
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Type: "CERTIFICATE",
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Bytes: cert.Leaf.Raw,
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}); err != nil {
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return err
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}
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keyOut, err := os.OpenFile(keyPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
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if err != nil {
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return err
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}
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defer keyOut.Close()
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privBytes, err := x509.MarshalPKCS8PrivateKey(cert.PrivateKey)
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if err != nil {
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return err
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}
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return pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes})
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}
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