Add CRL support to Prometheus

This commit adds support for certificate revocation status by Certificate
Revocation List (CRL) in Prometheus.

New fields 'CRL' and 'CRLFile' have been added to the Prometheus config
('tls_config' section). These enable certificate revocation validation
with the provided CRL.

The Prometheus loads the Certificate Revocation List (CRL) to validate the
revocation status of the peer's certificate chain by invoking the
'verifyPeerCertificate' (https://pkg.go.dev/crypto/tls) function during
a TLS handshake.

Signed-off-by: Ziqi Zhang <[email protected]>

Author: Ziqi Zhang

config/generate.go

@@ -92,7 +92,7 @@ func GenerateCertificateAuthority(commonName string, parentCert *x509.Certificat
 		},
 		NotBefore:             now,
 		NotAfter:              now.Add(validityPeriod),
-		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageCertSign,
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
 		IsCA:                  true,
 		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
 		BasicConstraintsValid: true,
@@ -186,6 +186,51 @@ func writeCertificateAndKey(path string, cert *x509.Certificate, key *rsa.Privat
 	return nil
 }
 
+func GenerateCRL(cert *x509.Certificate, privateKey *rsa.PrivateKey, revokedCerts []pkix.RevokedCertificate, isExpired bool) ([]byte, error) {
+	now := time.Now()
+
+	next := now.AddDate(30, 0, 0)
+	if isExpired {
+		next = now
+	}
+
+	crl := &x509.RevocationList{
+		SignatureAlgorithm:  x509.SHA256WithRSA,
+		ThisUpdate:          now,
+		NextUpdate:          next,
+		RevokedCertificates: revokedCerts,
+		Number:              big.NewInt(1),
+		Issuer:              cert.Subject,
+	}
+
+	crlBytes, err := x509.CreateRevocationList(rand.Reader, crl, cert, privateKey)
+	if err != nil {
+		return nil, fmt.Errorf("cannot create revocation list: %v", err)
+	}
+
+	return crlBytes, nil
+}
+
+func writeCRLs(filename string, crlData [][]byte) error {
+	crlPemBytes := new(bytes.Buffer)
+	for _, data := range crlData {
+		crlPem := &pem.Block{
+			Type:  "X509 CRL",
+			Bytes: data,
+		}
+		err := pem.Encode(crlPemBytes, crlPem)
+		if err != nil {
+			return err
+		}
+	}
+
+	if crlPemBytes == nil {
+		return fmt.Errorf("empty CRL to write")
+	}
+
+	return os.WriteFile(filename, crlPemBytes.Bytes(), 0644)
+}
+
 func main() {
 	log.Println("Generating root CA")
 	rootCert, rootKey, err := GenerateCertificateAuthority("Prometheus Root CA", nil, nil)
@@ -199,6 +244,12 @@ func main() {
 		log.Fatal(err)
 	}
 
+	log.Println("Generating Irrelevant CA")
+	irlvtCert, irlvtKey, err := GenerateCertificateAuthority("Prometheus TLS Irrelevant CA", nil, nil)
+	if err != nil {
+		log.Fatal(err)
+	}
+
 	log.Println("Generating server certificate")
 	cert, key, err := GenerateCertificate(caCert, caKey, true, "localhost", net.IPv4(127, 0, 0, 1), net.IPv4(127, 0, 0, 0))
 	if err != nil {
@@ -209,6 +260,16 @@ func main() {
 		log.Fatal(err)
 	}
 
+	log.Println("Generating revoked server certificate")
+	revokedCert, revokedKey, err := GenerateCertificate(caCert, caKey, true, "localhost", net.IPv4(127, 0, 0, 1), net.IPv4(127, 0, 0, 0))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCertificateAndKey("testdata/server_revoked", revokedCert, revokedKey); err != nil {
+		log.Fatal(err)
+	}
+
 	log.Println("Generating client certificate")
 	cert, key, err = GenerateCertificate(caCert, caKey, false, "localhost")
 	if err != nil {
@@ -235,11 +296,108 @@ func main() {
 		log.Fatal(err)
 	}
 
+	if err := os.WriteFile("testdata/tls-ca-no-root.pem", b.Bytes(), 0644); err != nil {
+		log.Fatal(err)
+	}
+
 	if err := EncodeCertificate(&b, rootCert); err != nil {
 		log.Fatal(err)
 	}
 
 	if err := os.WriteFile("testdata/tls-ca-chain.pem", b.Bytes(), 0644); err != nil {
 		log.Fatal(err)
 	}
+
+	if err := EncodeCertificate(&b, irlvtCert); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := os.WriteFile("testdata/tls-ca-chain-add-irlvt-ca.pem", b.Bytes(), 0644); err != nil {
+		log.Fatal(err)
+	}
+
+	log.Println("Generating CRLs")
+	crlProp_revokedCert := []pkix.RevokedCertificate{
+		{
+			SerialNumber:   revokedCert.SerialNumber,
+			RevocationTime: time.Now(),
+		},
+	}
+
+	crl_RevokedCert, err := GenerateCRL(caCert, caKey, crlProp_revokedCert, false)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_cert_revoked.pem", [][]byte{crl_RevokedCert}); err != nil {
+		log.Fatal(err)
+	}
+
+	crl_RevokedCert_expired, err := GenerateCRL(caCert, caKey, crlProp_revokedCert, true)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_cert_revoked_expired.pem", [][]byte{crl_RevokedCert_expired}); err != nil {
+		log.Fatal(err)
+	}
+
+	crl_irlvtRevokedCert, err := GenerateCRL(irlvtCert, irlvtKey, crlProp_revokedCert, false)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	crlProp_empty := []pkix.RevokedCertificate{
+		{
+			SerialNumber:   big.NewInt(1),
+			RevocationTime: time.Now(),
+		},
+	}
+
+	crl_InterCA_Empty, err := GenerateCRL(caCert, caKey, crlProp_empty, false)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_inter_empty.pem", [][]byte{crl_InterCA_Empty}); err != nil {
+		log.Fatal(err)
+	}
+
+	crlProp_RevokedInterCA := []pkix.RevokedCertificate{
+		{
+			SerialNumber:   caCert.SerialNumber,
+			RevocationTime: time.Now(),
+		},
+	}
+
+	crl_revokedInterCA, err := GenerateCRL(rootCert, rootKey, crlProp_RevokedInterCA, false)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	crl_Root_Empty, err := GenerateCRL(rootCert, rootKey, crlProp_empty, false)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_root_empty.pem", [][]byte{crl_Root_Empty}); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_chain_all_empty.pem", [][]byte{crl_InterCA_Empty, crl_Root_Empty}); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_chain_cert_revoked.pem", [][]byte{crl_Root_Empty, crl_RevokedCert}); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_chain_inter_ca_cert_revoked.pem", [][]byte{crl_revokedInterCA, crl_InterCA_Empty}); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := writeCRLs("testdata/crl_chain_irlvt_cert_revoked.pem", [][]byte{crl_InterCA_Empty, crl_irlvtRevokedCert}); err != nil {
+		log.Fatal(err)
+	}
+
 }