Begin improved OCSP stapling by persisting staple to disk

caddytls/certificates.go

@@ -10,7 +10,6 @@ import (
 	"sync"
 	"time"
 
-	"github.com/xenolf/lego/acme"
 	"golang.org/x/crypto/ocsp"
 )
 
@@ -183,19 +182,13 @@ func makeCertificate(certPEMBlock, keyPEMBlock []byte) (Certificate, error) {
 		}
 	}
 	cert.NotAfter = leaf.NotAfter
+	cert.Certificate = tlsCert
 
-	// Staple OCSP
-	ocspBytes, ocspResp, err := acme.GetOCSPForCert(certPEMBlock)
+	err = stapleOCSP(&cert, certPEMBlock)
 	if err != nil {
-		// An error here is not a problem because a certificate may simply
-		// not contain a link to an OCSP server. But we should log it anyway.
-		log.Printf("[WARNING] No OCSP stapling for %v: %v", cert.Names, err)
-	} else if ocspResp.Status == ocsp.Good {
-		tlsCert.OCSPStaple = ocspBytes
-		cert.OCSP = ocspResp
+		log.Printf("[WARNING] Stapling OCSP: %v", err)
 	}
 
-	cert.Certificate = tlsCert
 	return cert, nil
 }
 

caddytls/crypto.go

@@ -13,11 +13,19 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
+	"hash/fnv"
 	"io"
+	"io/ioutil"
+	"log"
 	"math/big"
 	"net"
+	"os"
+	"path/filepath"
 	"time"
 
+	"golang.org/x/crypto/ocsp"
+
+	"github.com/mholt/caddy"
 	"github.com/xenolf/lego/acme"
 )
 
@@ -59,7 +67,7 @@ func savePrivateKey(key crypto.PrivateKey) ([]byte, error) {
 // stapleOCSP staples OCSP information to cert for hostname name.
 // If you have it handy, you should pass in the PEM-encoded certificate
 // bundle; otherwise the DER-encoded cert will have to be PEM-encoded.
-// If you don't have the PEM blocks handy, just pass in nil.
+// If you don't have the PEM blocks already, just pass in nil.
 //
 // Errors here are not necessarily fatal, it could just be that the
 // certificate doesn't have an issuer URL.
@@ -73,13 +81,66 @@ func stapleOCSP(cert *Certificate, pemBundle []byte) error {
 		pemBundle = bundle.Bytes()
 	}
 
-	ocspBytes, ocspResp, err := acme.GetOCSPForCert(pemBundle)
-	if err != nil {
-		return err
+	var ocspBytes []byte
+	var ocspResp *ocsp.Response
+	var ocspErr error
+	var gotNewOCSP bool
+
+	// First try to load OCSP staple from storage and see if
+	// we can still use it.
+	// TODO: Use Storage interface instead of disk directly
+	ocspFolder := filepath.Join(caddy.AssetsPath(), "ocsp")
+	ocspFileName := cert.Names[0] + "-" + fastHash(pemBundle)
+	ocspCachePath := filepath.Join(ocspFolder, ocspFileName)
+	cachedOCSP, err := ioutil.ReadFile(ocspCachePath)
+	if err == nil {
+		resp, err := ocsp.ParseResponse(cachedOCSP, nil)
+		if err == nil {
+			if freshOCSP(resp) {
+				// staple is still fresh; use it
+				ocspBytes = cachedOCSP
+				ocspResp = resp
+			}
+		} else {
+			// invalid contents; delete the file
+			err := os.Remove(ocspCachePath)
+			if err != nil {
+				log.Printf("[WARNING] Unable to delete invalid OCSP staple file: %v", err)
+			}
+		}
 	}
 
-	cert.Certificate.OCSPStaple = ocspBytes
-	cert.OCSP = ocspResp
+	// If we couldn't get a fresh staple by reading the cache,
+	// then we need to request it from the OCSP responder
+	if ocspResp == nil || len(ocspBytes) == 0 {
+		ocspBytes, ocspResp, ocspErr = acme.GetOCSPForCert(pemBundle)
+		if ocspErr != nil {
+			// An error here is not a problem because a certificate may simply
+			// not contain a link to an OCSP server. But we should log it anyway.
+			// There's nothing else we can do to get OCSP for this certificate,
+			// so we can return here with the error.
+			return fmt.Errorf("no OCSP stapling for %v: %v", cert.Names, ocspErr)
+		}
+		gotNewOCSP = true
+	}
+
+	// By now, we should have a response. If good, staple it to
+	// the certificate. If the OCSP response was not loaded from
+	// storage, we persist it for next time.
+	if ocspResp.Status == ocsp.Good {
+		cert.Certificate.OCSPStaple = ocspBytes
+		cert.OCSP = ocspResp
+		if gotNewOCSP {
+			err := os.MkdirAll(filepath.Join(caddy.AssetsPath(), "ocsp"), 0700)
+			if err != nil {
+				return fmt.Errorf("unable to make OCSP staple path for %v: %v", cert.Names, err)
+			}
+			err = ioutil.WriteFile(ocspCachePath, ocspBytes, 0644)
+			if err != nil {
+				return fmt.Errorf("unable to write OCSP staple file for %v: %v", cert.Names, err)
+			}
+		}
+	}
 
 	return nil
 }
@@ -235,6 +296,15 @@ func standaloneTLSTicketKeyRotation(c *tls.Config, ticker *time.Ticker, exitChan
 	}
 }
 
+// fastHash hashes input using a hashing algorithm that
+// is fast, and returns the hash as a hex-encoded string.
+// Do not use this for cryptographic purposes.
+func fastHash(input []byte) string {
+	h := fnv.New32a()
+	h.Write([]byte(input))
+	return fmt.Sprintf("%x", h.Sum32())
+}
+
 const (
 	// NumTickets is how many tickets to hold and consider
 	// to decrypt TLS sessions.

caddytls/maintain.go

@@ -17,11 +17,11 @@ const (
 	// RenewInterval is how often to check certificates for renewal.
 	RenewInterval = 12 * time.Hour
 
-	// OCSPInterval is how often to check if OCSP stapling needs updating.
-	OCSPInterval = 1 * time.Hour
-
 	// RenewDurationBefore is how long before expiration to renew certificates.
 	RenewDurationBefore = (24 * time.Hour) * 30
+
+	// OCSPInterval is how often to check if OCSP stapling needs updating.
+	OCSPInterval = 1 * time.Hour
 )
 
 // maintainAssets is a permanently-blocking function
@@ -154,6 +154,10 @@ func RenewManagedCertificates(allowPrompts bool) (err error) {
 
 // UpdateOCSPStaples updates the OCSP stapling in all
 // eligible, cached certificates.
+//
+// OCSP maintenance strives to abide the relevant points on
+// Ryan Sleevi's recommendations for good OCSP support:
+// https://gist.github.com/sleevi/5efe9ef98961ecfb4da8
 func UpdateOCSPStaples() {
 	// Create a temporary place to store updates
 	// until we release the potentially long-lived
@@ -187,12 +191,9 @@ func UpdateOCSPStaples() {
 
 		var lastNextUpdate time.Time
 		if cert.OCSP != nil {
-			// start checking OCSP staple about halfway through validity period for good measure
 			lastNextUpdate = cert.OCSP.NextUpdate
-			refreshTime := cert.OCSP.ThisUpdate.Add(lastNextUpdate.Sub(cert.OCSP.ThisUpdate) / 2)
-
-			// since OCSP is already stapled, we need only check if we're in that "refresh window"
-			if time.Now().Before(refreshTime) {
+			if freshOCSP(cert.OCSP) {
+				// no need to update staple if ours is still fresh
 				continue
 			}
 		}
@@ -201,7 +202,7 @@ func UpdateOCSPStaples() {
 		if err != nil {
 			if cert.OCSP != nil {
 				// if there was no staple before, that's fine; otherwise we should log the error
-				log.Printf("[ERROR] Checking OCSP for %v: %v", cert.Names, err)
+				log.Printf("[ERROR] Checking OCSP: %v", err)
 			}
 			continue
 		}
@@ -229,3 +230,9 @@ func UpdateOCSPStaples() {
 	}
 	certCacheMu.Unlock()
 }
+
+func freshOCSP(resp *ocsp.Response) bool {
+	// start checking OCSP staple about halfway through validity period for good measure
+	refreshTime := resp.ThisUpdate.Add(resp.NextUpdate.Sub(resp.ThisUpdate) / 2)
+	return time.Now().Before(refreshTime)
+}