Move complex crypto logic into a helper package

1 files changed, 36 insertions, 110 deletions

diff --git a/roseh.moe.go b/roseh.moe.go
index 3c5e7a9..6624706 100644
--- a/roseh.moe.go
+++ b/roseh.moe.go
@@ -2,12 +2,7 @@ package main
 
 import (
 	"bytes"
-	"crypto/aes"
-	"crypto/cipher"
-	"crypto/hkdf"
-	"crypto/hmac"
 	"crypto/rand"
-	"crypto/sha256"
 	"crypto/subtle"
 	"embed"
 	"encoding/base64"
@@ -25,7 +20,7 @@ import (
 	"sync"
 	"time"
 
-	"gitlab.com/rhogenson/roseh.moe/internal/pwhash"
+	"gitlab.com/rhogenson/roseh.moe/internal/cryptoutil"
 )
 
 var (
@@ -37,12 +32,11 @@ var (
 )
 
 var (
-	notepadPassword     []byte
-	notepadPasswordSalt []byte
-	privateKey          []byte
+	notepadPassword cryptoutil.PasswordHash
+	secretKey       cryptoutil.HMACKey
 
 	encryptionKeyMu sync.Mutex
-	encryptionKey   []byte
+	encryptionKey   cryptoutil.EncryptionKey
 )
 
 func loadSecrets() error {
@@ -52,20 +46,19 @@ 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(buf, pw); err != nil {
-				return err
+			if hex.DecodedLen(len(pw)) != cryptoutil.PasswordHashSize {
+				return fmt.Errorf("invalid PBKDF2-SHA256 hash")
 			}
-			if len(buf) < pwhash.SaltLen {
-				return fmt.Errorf("bad password hash")
+			notepadPassword = make(cryptoutil.PasswordHash, hex.DecodedLen(len(pw)))
+			if _, err := hex.Decode(notepadPassword, pw); err != nil {
+				return err
 			}
-			notepadPasswordSalt, notepadPassword = buf[:pwhash.SaltLen], buf[pwhash.SaltLen:]
 		} else if key, ok := bytes.CutPrefix(line, []byte("secret-key=")); ok {
-			if hex.DecodedLen(len(key)) != sha256.Size {
+			if hex.DecodedLen(len(key)) != cryptoutil.HMACKeySize {
 				return fmt.Errorf("invalid HMAC-SHA256 key")
 			}
-			privateKey = make([]byte, hex.DecodedLen(len(key)))
-			if _, err := hex.Decode(privateKey, key); err != nil {
+			secretKey = make(cryptoutil.HMACKey, hex.DecodedLen(len(key)))
+			if _, err := hex.Decode(secretKey, key); err != nil {
 				return err
 			}
 		}
@@ -73,78 +66,6 @@ func loadSecrets() error {
 	return nil
 }
 
-func sign(msg []byte) []byte {
-	mac := hmac.New(sha256.New, privateKey)
-	mac.Write(msg)
-	return mac.Sum(msg)
-}
-
-func verify(msg []byte) ([]byte, bool) {
-	if len(msg) < sha256.Size {
-		return nil, false
-	}
-	msg, sig := msg[:len(msg)-sha256.Size], msg[len(msg)-sha256.Size:]
-	mac := hmac.New(sha256.New, privateKey)
-	mac.Write(msg)
-	return msg, hmac.Equal(sig, mac.Sum(nil))
-}
-
-var errNoKey = errors.New("not logged in")
-
-const (
-	aesKeyLen = 32
-	nonceLen  = aes.BlockSize
-	certLen   = sha256.Size
-)
-
-func encrypt(msg string) ([]byte, error) {
-	encryptionKeyMu.Lock()
-	key := encryptionKey
-	encryptionKeyMu.Unlock()
-	if key == nil {
-		return nil, errNoKey
-	}
-	block, err := aes.NewCipher(key[:aesKeyLen])
-	if err != nil {
-		return nil, err
-	}
-	buf := make([]byte, nonceLen+len(msg)+certLen)
-	nonce := buf[:nonceLen]
-	rand.Read(nonce)
-	cipher.NewCTR(block, nonce).XORKeyStream(buf[nonceLen:], []byte(msg))
-	cipherText := buf[:nonceLen+len(msg)]
-	mac := hmac.New(sha256.New, key[aesKeyLen:])
-	mac.Write(cipherText)
-	return mac.Sum(cipherText), nil
-}
-
-func decrypt(msg []byte) (string, error) {
-	encryptionKeyMu.Lock()
-	key := encryptionKey
-	encryptionKeyMu.Unlock()
-	if key == nil {
-		return "", errNoKey
-	}
-	if len(msg) < certLen+nonceLen {
-		return "", fmt.Errorf("message too short")
-	}
-	msg, messageMAC := msg[:len(msg)-certLen], msg[len(msg)-certLen:]
-	mac := hmac.New(sha256.New, key[aesKeyLen:])
-	mac.Write(msg)
-	expectedMAC := mac.Sum(nil)
-	if !hmac.Equal(messageMAC, expectedMAC) {
-		return "", fmt.Errorf("bad signature")
-	}
-	block, err := aes.NewCipher(key[:aesKeyLen])
-	if err != nil {
-		return "", err
-	}
-	nonce, msg := msg[:nonceLen], msg[nonceLen:]
-	buf := make([]byte, len(msg))
-	cipher.NewCTR(block, nonce).XORKeyStream(buf, msg)
-	return string(buf), nil
-}
-
 var (
 	//go:embed templates/404.html.template
 	notFoundString   string
@@ -219,7 +140,7 @@ func attachCookie(w http.ResponseWriter) error {
 	}
 	http.SetCookie(w, &http.Cookie{
 		Name:        "auth",
-		Value:       base64.RawStdEncoding.EncodeToString(sign(nowBytes)),
+		Value:       base64.RawStdEncoding.EncodeToString(secretKey.Sign(nowBytes)),
 		Path:        "/notepad",
 		Expires:     time.Now().Add(cookieExpiration),
 		Secure:      true,
@@ -241,7 +162,7 @@ func cookieAuth(w http.ResponseWriter, r *http.Request) (string, bool) {
 	if err != nil {
 		return "", false
 	}
-	msg, ok := verify(authCookie)
+	msg, ok := secretKey.Verify(authCookie)
 	if !ok {
 		return "", false
 	}
@@ -284,12 +205,8 @@ type loginTemplateArgs struct {
 }
 
 func login(w http.ResponseWriter, r *http.Request) {
-	rawKey, pwHash, err := pwhash.Hash(r.FormValue("password"), notepadPasswordSalt)
+	rawKey, err := cryptoutil.CheckPassword(r.FormValue("password"), notepadPassword)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("Unable to hash password: %s", err), http.StatusInternalServerError)
-		return
-	}
-	if subtle.ConstantTimeCompare(pwHash[:], notepadPassword) == 0 {
 		if err := loginTemplate.Execute(w, loginTemplateArgs{Error: true}); err != nil {
 			log.Printf("Warning: login: %s", err)
 		}
@@ -299,7 +216,7 @@ func login(w http.ResponseWriter, r *http.Request) {
 	currentKey := encryptionKey
 	encryptionKeyMu.Unlock()
 	if currentKey == nil {
-		key, err := hkdf.Expand(sha256.New, rawKey, "encrypt", aesKeyLen+certLen)
+		key, err := rawKey.EncryptionKey()
 		if err != nil {
 			http.Error(w, fmt.Sprintf("failed to derive encryption key: %s", err), http.StatusInternalServerError)
 			return
@@ -314,16 +231,16 @@ func login(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, "/notepad", http.StatusSeeOther)
 }
 
-func readNotepad() (string, error) {
+func readNotepad(key cryptoutil.EncryptionKey) (string, error) {
 	encrypted, err := os.ReadFile(*notepadFile)
 	if err != nil {
 		return "", err
 	}
-	decrypted, err := decrypt(encrypted)
+	decrypted, err := key.Decrypt(encrypted)
 	if err != nil {
 		return "", err
 	}
-	return decrypted, nil
+	return string(decrypted), nil
 }
 
 var (
@@ -345,14 +262,17 @@ func notepad(w http.ResponseWriter, r *http.Request) {
 		}
 		return
 	}
-	currentContent, err := readNotepad()
-	if err != nil {
-		if err == errNoKey {
-			if err := loginTemplate.Execute(w, loginTemplateArgs{}); err != nil {
-				log.Printf("Warning: login: %s", err)
-			}
-			return
+	encryptionKeyMu.Lock()
+	key := encryptionKey
+	encryptionKeyMu.Unlock()
+	if key == nil {
+		if err := loginTemplate.Execute(w, loginTemplateArgs{}); err != nil {
+			log.Printf("Warning: login: %s", err)
 		}
+		return
+	}
+	currentContent, err := readNotepad(key)
+	if err != nil {
 		currentContent = fmt.Sprintf("Error reading notepad file: %s", err)
 	}
 	if err := notepadTemplate.Execute(w, notepadTemplateArgs{Content: currentContent, CSRFToken: csrfToken}); err != nil {
@@ -367,7 +287,13 @@ func saveNote(w http.ResponseWriter, r *http.Request) error {
 	if _, ok := cookieAuth(w, r); !ok {
 		return fmt.Errorf("not logged in")
 	}
-	encrypted, err := encrypt(r.FormValue("content"))
+	encryptionKeyMu.Lock()
+	key := encryptionKey
+	encryptionKeyMu.Unlock()
+	if key == nil {
+		return errors.New("not logged in")
+	}
+	encrypted, err := key.Encrypt([]byte(r.FormValue("content")))
 	if err != nil {
 		return err
 	}