cmd/age-keyserver: add transparency log of stored keys

Author: FiloSottile

cmd/age-keylookup/main.go

@@ -7,7 +7,12 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"strings"
 	"time"
+
+	"filippo.io/torchwood"
+	"golang.org/x/mod/sumdb/note"
+	"golang.org/x/mod/sumdb/tlog"
 )
 
 func main() {
@@ -22,6 +27,7 @@ func main() {
 		fmt.Fprintf(os.Stderr, "\n")
 		fmt.Fprintf(os.Stderr, "Environment:\n")
 		fmt.Fprintf(os.Stderr, "  AGE_KEYSERVER_URL     Default keyserver URL\n")
+		fmt.Fprintf(os.Stderr, "  AGE_KEYSERVER_PUBKEY  Default keyserver transparency log vkey\n")
 		os.Exit(2)
 	}
 
@@ -33,7 +39,17 @@ func main() {
 		server = "https://keyserver.geomys.org"
 	}
 
-	pubkey, err := lookupKey(server, email)
+	vkey := os.Getenv("AGE_KEYSERVER_PUBKEY")
+	if vkey == "" {
+		vkey = "keyserver.geomys.org+be45b77c+Ae58So8awYbwaF+V98htpY0xXlRcjhNuL5Ucrq9en2yp"
+	}
+	v, err := note.NewVerifier(vkey)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error: invalid keyserver public key: %v\n", err)
+		os.Exit(1)
+	}
+
+	pubkey, err := lookupKey(server, v, email)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
 		os.Exit(1)
@@ -42,7 +58,10 @@ func main() {
 	fmt.Println(pubkey)
 }
 
-func lookupKey(serverURL, email string) (string, error) {
+func lookupKey(serverURL string, v note.Verifier, email string) (string, error) {
+	// Normalize email
+	email = strings.TrimSpace(strings.ToLower(email))
+
 	// Build the lookup URL
 	lookupURL := serverURL + "/api/lookup?email=" + url.QueryEscape(email)
 
@@ -72,6 +91,7 @@ func lookupKey(serverURL, email string) (string, error) {
 	var result struct {
 		Email  string `json:"email"`
 		Pubkey string `json:"pubkey"`
+		Proof  string `json:"proof"`
 	}
 
 	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
@@ -85,5 +105,13 @@ func lookupKey(serverURL, email string) (string, error) {
 		return "", fmt.Errorf("empty public key returned")
 	}
 
+	// Verify spicy signature
+	entry := fmt.Appendf(nil, "%s\n%s\n", result.Email, result.Pubkey)
+	if err := torchwood.VerifyProof(v.Name(), func(b []byte) (*note.Note, error) {
+		return note.Open(b, note.VerifierList(v))
+	}, tlog.RecordHash(entry), []byte(result.Proof)); err != nil {
+		return "", fmt.Errorf("failed to verify key proof: %w", err)
+	}
+
 	return result.Pubkey, nil
 }