derive CA from pre-shared key (#3815)

pkg/derivecert/pem.go

@@ -0,0 +1,55 @@
+package derivecert
+
+import (
+	"crypto/ecdsa"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+)
+
+// PEM representation of certificate authority data, serializable to JSON
+type PEM struct {
+	Cert []byte
+	Key  []byte
+}
+
+// ToPEM converts private key and certificate into PEM representation
+func ToPEM(key *ecdsa.PrivateKey, certDer []byte) (*PEM, error) {
+	b, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return nil, fmt.Errorf("unable to marshal ECDSA private key: %w", err)
+	}
+	return &PEM{
+		Key:  pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: b}),
+		Cert: pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDer}),
+	}, nil
+}
+
+// TLS parses PEM and returns TLS certificate
+func (p *PEM) TLS() (tls.Certificate, error) {
+	return tls.X509KeyPair(p.Cert, p.Key)
+}
+
+// KeyCert parses private key and cert from PEM encoded format
+func (p *PEM) KeyCert() (*ecdsa.PrivateKey, *x509.Certificate, error) {
+	certDer, _ := pem.Decode(p.Cert)
+	if certDer == nil {
+		return nil, nil, fmt.Errorf("parse PEM cert")
+	}
+	keyDer, _ := pem.Decode(p.Key)
+	if keyDer == nil {
+		return nil, nil, fmt.Errorf("parse PEM key")
+	}
+
+	cert, err := x509.ParseCertificate(certDer.Bytes)
+	if err != nil {
+		return nil, nil, fmt.Errorf("parse cert: %w", err)
+	}
+	key, err := x509.ParseECPrivateKey(keyDer.Bytes)
+	if err != nil {
+		return nil, nil, fmt.Errorf("parse key: %w", err)
+	}
+
+	return key, cert, nil
+}