From 95df5d765a3a71a4ff75d598fbba1bceb6fa2e6c Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rosehogenson@posteo.net>
Date: Tue, 23 Sep 2025 22:48:50 -0700
Subject: Don't reuse cipher.AEAD between threads

I'm not sure if it's safe or not, but better to be cautious
---
 roseh.moe.go | 53 ++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 34 insertions(+), 19 deletions(-)

diff --git a/roseh.moe.go b/roseh.moe.go
index f24bc58..99d1bed 100644
--- a/roseh.moe.go
+++ b/roseh.moe.go
@@ -40,7 +40,7 @@ var (
 	privateKey          []byte
 
 	encryptionKeyMu sync.Mutex
-	encryptionKey   cipher.AEAD
+	encryptionKey   []byte
 )
 
 func loadSecrets() error {
@@ -51,7 +51,7 @@ func loadSecrets() error {
 	for _, line := range bytes.Split(bytes.TrimSuffix(secrets, []byte("\n")), []byte("\n")) {
 		if pw, ok := bytes.CutPrefix(line, []byte("notepad-password=")); ok {
 			buf := make([]byte, hex.DecodedLen(len(pw)))
-			if _, err := hex.Decode(notepadPassword, pw); err != nil {
+			if _, err := hex.Decode(buf, pw); err != nil {
 				return err
 			}
 			notepadPasswordSalt, notepadPassword = buf[:pwhash.SaltLen], buf[pwhash.SaltLen:]
@@ -215,7 +215,7 @@ type loginTemplateArgs struct {
 }
 
 func login(w http.ResponseWriter, r *http.Request) {
-	keyBytes, pwHash, err := pwhash.Hash(r.FormValue("password"), notepadPasswordSalt)
+	key, pwHash, err := pwhash.Hash(r.FormValue("password"), notepadPasswordSalt)
 	if err != nil {
 		http.Error(w, fmt.Sprintf("Unable to hash password: %s", err), http.StatusInternalServerError)
 		return
@@ -226,12 +226,6 @@ func login(w http.ResponseWriter, r *http.Request) {
 		}
 		return
 	}
-	block, err := aes.NewCipher(keyBytes)
-	if err != nil {
-		http.Error(w, fmt.Sprintf("Could not create AES key: %s", err), http.StatusInternalServerError)
-		return
-	}
-	key, err := cipher.NewGCMWithRandomNonce(block)
 	encryptionKeyMu.Lock()
 	if encryptionKey == nil {
 		encryptionKey = key
@@ -241,6 +235,26 @@ func login(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, r.FormValue("redirect"), http.StatusSeeOther)
 }
 
+func readNotepad(key []byte) (string, error) {
+	encrypted, err := os.ReadFile(*notepadFile)
+	if err != nil {
+		return "", err
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	aead, err := cipher.NewGCMWithRandomNonce(block)
+	if err != nil {
+		return "", err
+	}
+	decrypted, err := aead.Open(nil, nil, encrypted, nil)
+	if err != nil {
+		return "", err
+	}
+	return string(decrypted), nil
+}
+
 var (
 	//go:embed templates/note.html.template
 	notepadString   string
@@ -269,16 +283,9 @@ func notepad(w http.ResponseWriter, r *http.Request) {
 		}
 		return
 	}
-	var currentContent string
-	if currentContentBytes, err := os.ReadFile(*notepadFile); err != nil {
+	currentContent, err := readNotepad(key)
+	if err != nil {
 		currentContent = fmt.Sprintf("Error reading notepad file: %s", err)
-	} else {
-		decrypted, err := key.Open(nil, nil, currentContentBytes, nil)
-		if err != nil {
-			currentContent = fmt.Sprintf("Could not decrypt notepad contents: %s", err)
-		} else {
-			currentContent = string(decrypted)
-		}
 	}
 	if err := notepadTemplate.Execute(w, notepadTemplateArgs{Content: currentContent, CSRFToken: csrfToken}); err != nil {
 		log.Printf("Warning: notepad: %s", err)
@@ -298,12 +305,20 @@ func saveNote(w http.ResponseWriter, r *http.Request) error {
 	if key == nil {
 		return fmt.Errorf("not logged in")
 	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return err
+	}
+	aead, err := cipher.NewGCMWithRandomNonce(block)
+	if err != nil {
+		return err
+	}
 	f, err := os.CreateTemp(filepath.Dir(*notepadFile), "notepad")
 	if err != nil {
 		return err
 	}
 	defer f.Close()
-	if _, err = f.Write(key.Seal(nil, nil, []byte(r.FormValue("content")), nil)); err != nil {
+	if _, err = f.Write(aead.Seal(nil, nil, []byte(r.FormValue("content")), nil)); err != nil {
 		return err
 	}
 	if err := f.Close(); err != nil {
-- 
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