feat: implement internal PKI utilities for CA and certificate management

internal/pki/ca.go

@@ -0,0 +1,166 @@
+package pki
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"fmt"
+	"math/big"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+const (
+	// Default key size for RSA keys
+	DefaultRSAKeySize = 2048
+	// Default CA certificate validity period
+	DefaultCAValidityDays = 3650 // ~10 years
+	// Default certificate validity period
+	DefaultCertValidityDays = 365 // 1 year
+	// Default PKI directory
+	DefaultPKIDir = "/var/lib/kat/pki"
+)
+
+// GenerateCA creates a new Certificate Authority key pair and certificate.
+// It saves the private key and certificate to the specified paths.
+func GenerateCA(pkiDir string, keyPath, certPath string) error {
+	// Create PKI directory if it doesn't exist
+	if err := os.MkdirAll(pkiDir, 0700); err != nil {
+		return fmt.Errorf("failed to create PKI directory: %w", err)
+	}
+
+	// Generate RSA key
+	key, err := rsa.GenerateKey(rand.Reader, DefaultRSAKeySize)
+	if err != nil {
+		return fmt.Errorf("failed to generate CA key: %w", err)
+	}
+
+	// Create self-signed certificate
+	serialNumber, err := generateSerialNumber()
+	if err != nil {
+		return fmt.Errorf("failed to generate serial number: %w", err)
+	}
+
+	// Certificate template
+	notBefore := time.Now()
+	notAfter := notBefore.Add(time.Duration(DefaultCAValidityDays) * 24 * time.Hour)
+
+	template := x509.Certificate{
+		SerialNumber: serialNumber,
+		Subject: pkix.Name{
+			CommonName:   "KAT Root CA",
+			Organization: []string{"KAT System"},
+		},
+		NotBefore:             notBefore,
+		NotAfter:              notAfter,
+		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
+		BasicConstraintsValid: true,
+		IsCA:                  true,
+		MaxPathLen:            1, // Only allow one level of intermediate certs
+	}
+
+	// Create certificate
+	derBytes, err := x509.CreateCertificate(
+		rand.Reader,
+		&template,
+		&template, // Self-signed
+		&key.PublicKey,
+		key,
+	)
+	if err != nil {
+		return fmt.Errorf("failed to create CA certificate: %w", err)
+	}
+
+	// Save private key
+	keyOut, err := os.OpenFile(keyPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return fmt.Errorf("failed to open CA key file for writing: %w", err)
+	}
+	defer keyOut.Close()
+
+	err = pem.Encode(keyOut, &pem.Block{
+		Type:  "RSA PRIVATE KEY",
+		Bytes: x509.MarshalPKCS1PrivateKey(key),
+	})
+	if err != nil {
+		return fmt.Errorf("failed to write CA key to file: %w", err)
+	}
+
+	// Save certificate
+	certOut, err := os.OpenFile(certPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to open CA certificate file for writing: %w", err)
+	}
+	defer certOut.Close()
+
+	err = pem.Encode(certOut, &pem.Block{
+		Type:  "CERTIFICATE",
+		Bytes: derBytes,
+	})
+	if err != nil {
+		return fmt.Errorf("failed to write CA certificate to file: %w", err)
+	}
+
+	return nil
+}
+
+// GetPKIPathFromClusterConfig determines the PKI directory from the cluster configuration.
+// If backupPath is provided, it uses the parent directory of backupPath.
+// Otherwise, it uses the default PKI directory.
+func GetPKIPathFromClusterConfig(backupPath string) string {
+	if backupPath == "" {
+		return DefaultPKIDir
+	}
+	
+	// Use the parent directory of backupPath
+	return filepath.Dir(backupPath) + "/pki"
+}
+
+// generateSerialNumber creates a random serial number for certificates
+func generateSerialNumber() (*big.Int, error) {
+	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128) // 128 bits
+	return rand.Int(rand.Reader, serialNumberLimit)
+}
+
+// LoadCACertificate loads a CA certificate from a file
+func LoadCACertificate(certPath string) (*x509.Certificate, error) {
+	certPEM, err := os.ReadFile(certPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read CA certificate file: %w", err)
+	}
+
+	block, _ := pem.Decode(certPEM)
+	if block == nil || block.Type != "CERTIFICATE" {
+		return nil, fmt.Errorf("failed to decode PEM block containing certificate")
+	}
+
+	cert, err := x509.ParseCertificate(block.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse CA certificate: %w", err)
+	}
+
+	return cert, nil
+}
+
+// LoadCAPrivateKey loads a CA private key from a file
+func LoadCAPrivateKey(keyPath string) (*rsa.PrivateKey, error) {
+	keyPEM, err := os.ReadFile(keyPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read CA key file: %w", err)
+	}
+
+	block, _ := pem.Decode(keyPEM)
+	if block == nil || block.Type != "RSA PRIVATE KEY" {
+		return nil, fmt.Errorf("failed to decode PEM block containing private key")
+	}
+
+	key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse CA private key: %w", err)
+	}
+
+	return key, nil
+}