Add certificate storage

storage/storage.go

@@ -0,0 +1,186 @@
+// Package storage handles keeping the files on disk.
+package storage
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/letsencrypt/test-certs-site/config"
+)
+
+type version string
+
+const (
+	next    version = "next"
+	current version = "current"
+)
+
+const (
+	privateKeyFilename  = "private.pem"
+	certificateFilename = "certificate.pem"
+)
+
+const (
+	// dirPerms rwxr-xr-x for created directories. Writable only by user, but global r & x for debugging.
+	dirPerms = 0o755
+
+	// keyPerms rw------- for private keys. No permissions outside of user.
+	keyPerms = 0o600
+
+	// certPerms rw-r--r-- for cert files. Globally readable certs for debugging.
+	certPerms = 0o644
+)
+
+// Storage of files for a domain.
+type Storage struct {
+	// mu prevents simultaneous writing of files, or reading while writing.
+	mu  sync.Mutex
+	dir string
+}
+
+// New storage handle.
+func New(storageDir string) (*Storage, error) {
+	return &Storage{dir: storageDir}, nil
+}
+
+// StoreNextKey generates a new "next" key, writing it to disk.
+func (s *Storage) StoreNextKey(domain string, keyType string) (crypto.Signer, error) {
+	var key crypto.Signer
+	switch keyType {
+	case config.KeyTypeP256:
+		p256Key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+		if err != nil {
+			return nil, err
+		}
+		key = p256Key
+	case config.KeyTypeRSA2048:
+		bits := 2048
+		rsaKey, err := rsa.GenerateKey(rand.Reader, bits)
+		if err != nil {
+			return nil, err
+		}
+		key = rsaKey
+	default:
+		// Should be unreachable due to config validation
+		return nil, fmt.Errorf("unknown key type: %s", keyType)
+	}
+
+	keyBytes, err := x509.MarshalPKCS8PrivateKey(key)
+	if err != nil {
+		return nil, err
+	}
+
+	pemBytes := pem.EncodeToMemory(&pem.Block{
+		Type:  "PRIVATE KEY",
+		Bytes: keyBytes,
+	})
+
+	path := s.pathFor(domain, next, privateKeyFilename)
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	err = os.MkdirAll(filepath.Dir(path), dirPerms)
+	if err != nil {
+		return nil, err
+	}
+
+	err = os.WriteFile(path, pemBytes, keyPerms)
+	if err != nil {
+		return nil, err
+	}
+
+	return key, nil
+}
+
+// StoreNextCert stores the next certificate for the domain.
+// Certificates should be a sequence of DER certificates.
+func (s *Storage) StoreNextCert(domain string, certificates [][]byte) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	certPath := s.pathFor(domain, next, certificateFilename)
+	cert, err := os.OpenFile(certPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, certPerms) //nolint:gosec // Arbitrary file is not a risk here
+	if err != nil {
+		return fmt.Errorf("could not open certificate file: %w", err)
+	}
+	defer cert.Close()
+
+	for _, data := range certificates {
+		err := pem.Encode(cert, &pem.Block{
+			Type:  "CERTIFICATE",
+			Bytes: data,
+		})
+		if err != nil {
+			return fmt.Errorf("could not write certificate: %w", err)
+		}
+	}
+
+	return nil
+}
+
+// TakeNext overwrites the current cert/key with the next cert/key, and returns the new current values.
+func (s *Storage) TakeNext(domain string) (tls.Certificate, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	err := os.MkdirAll(s.pathFor(domain, current, ""), dirPerms)
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	// Read the next values we're about to make current.
+	// Doing this before renaming ensures the key and certificate match.
+	cert, err := s.read(domain, next)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("reading next certificate: %w", err)
+	}
+
+	for _, path := range []string{privateKeyFilename, certificateFilename} {
+		nextPath := s.pathFor(domain, next, path)
+		currPath := s.pathFor(domain, current, path)
+		err := os.Rename(nextPath, currPath)
+		if err != nil {
+			return tls.Certificate{}, err
+		}
+	}
+
+	return cert, nil
+}
+
+// ReadCurrent reads the current cert and key for this domain.
+// Returns an error if the stored value couldn't be read or parsed.
+func (s *Storage) ReadCurrent(domain string) (tls.Certificate, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	return s.read(domain, current)
+}
+
+// ReadNext reads the next cert and key for this domain.
+// Returns an error if the stored value couldn't be read or parsed.
+func (s *Storage) ReadNext(domain string) (tls.Certificate, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	return s.read(domain, next)
+}
+
+// read a cert and key. Common logic for ReadCurrent and ReadNext. Caller should hold mu.
+func (s *Storage) read(domain string, ver version) (tls.Certificate, error) {
+	return tls.LoadX509KeyPair(s.pathFor(domain, ver, certificateFilename), s.pathFor(domain, ver, privateKeyFilename))
+}
+
+func (s *Storage) pathFor(domain string, ver version, file string) string {
+	return filepath.Join(s.dir, domain, string(ver), file)
+}

storage/storage_test.go

@@ -0,0 +1,82 @@
+package storage
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/x509"
+	"testing"
+
+	"github.com/letsencrypt/test-certs-site/config"
+)
+
+// TestStorage goes through the expected storage lifecycle.
+func TestStorage(t *testing.T) {
+	t.Parallel()
+
+	storage, err := New(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	const domain = "interesting.salad"
+
+	// Go through the lifecycle 3 times
+	for i := range 3 {
+		// Alternate key types to test both
+		keyType := config.KeyTypeP256
+		if i%2 == 1 {
+			keyType = config.KeyTypeRSA2048
+		}
+		key, err := storage.StoreNextKey(domain, keyType)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Outside of tests, this would come from a CA:
+		certs := testCert(t, domain, key)
+
+		err = storage.StoreNextCert(domain, certs)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		_, err = storage.ReadNext(domain)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// A real user of the storage package would validate the certs here.
+		// Eg, checking if they're expired or revoked.
+
+		_, err = storage.TakeNext(domain)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		current, err := storage.ReadCurrent(domain)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if current.Leaf.DNSNames[0] != domain {
+			t.Fatalf("Expected %s DNS SAN", domain)
+		}
+	}
+}
+
+// testCert returns a test self-signed cert for the given key.
+func testCert(t *testing.T, domain string, key crypto.Signer) [][]byte {
+	t.Helper()
+
+	// Create a certificate template
+	template := x509.Certificate{
+		DNSNames: []string{domain},
+	}
+
+	certDER, err := x509.CreateCertificate(rand.Reader, &template, &template, key.Public(), key)
+	if err != nil {
+		t.Fatalf("Failed to create certificate: %v", err)
+	}
+
+	return [][]byte{certDER}
+}