Support encrypted database keys on Windows

#48

safestorage/decrypt.go

@@ -35,6 +35,10 @@ const (
 	linuxPrefixV10  = "v10"
 	linuxPrefixV11  = "v11"
 	linuxIterations = 1
+
+	windowsPrefix    = "v10"
+	windowsKeySize   = 32 // AES-256
+	windowsNonceSize = 12
 )
 
 func DecryptWithPassword(ciphertext, password []byte) ([]byte, error) {
@@ -43,6 +47,8 @@ func DecryptWithPassword(ciphertext, password []byte) ([]byte, error) {
 		return decryptWithMacosPassword(ciphertext, password)
 	case "linux", "openbsd":
 		return decryptWithLinuxPassword(ciphertext, password)
+	case "windows":
+		return decryptWithWindowsPassword(ciphertext, password)
 	default:
 		return nil, errors.New("not yet supported")
 	}
@@ -67,6 +73,39 @@ func decryptWithLinuxPassword(ciphertext, password []byte) ([]byte, error) {
 	return decryptWithPassword(ciphertext, password, linuxIterations)
 }
 
+func decryptWithWindowsPassword(ciphertext, password []byte) ([]byte, error) {
+	if !bytes.HasPrefix(ciphertext, []byte(windowsPrefix)) {
+		return nil, errors.New("unsupported ciphertext format")
+	}
+	ciphertext = bytes.TrimPrefix(ciphertext, []byte(windowsPrefix))
+
+	if len(ciphertext) < windowsNonceSize {
+		return nil, errors.New("invalid ciphertext length")
+	}
+	nonce := ciphertext[:windowsNonceSize]
+	ciphertext = ciphertext[windowsNonceSize:]
+
+	if len(password) != windowsKeySize {
+		return nil, errors.New("invalid password length")
+	}
+
+	c, err := aes.NewCipher(password)
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCMWithNonceSize(c, windowsNonceSize)
+	if err != nil {
+		return nil, err
+	}
+
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return plaintext, nil
+}
+
 func decryptWithPassword(ciphertext, password []byte, iters int) ([]byte, error) {
 	if len(ciphertext)%aes.BlockSize != 0 {
 		return nil, errors.New("invalid ciphertext length")

safestorage/decrypt_other.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2024 Tim van der Molen <tim@kariliq.nl>
+//
+// Permission to use, copy, modify, and distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+//go:build !windows
+
+package safestorage
+
+import "errors"
+
+func Decrypt(ciphertext []byte) ([]byte, error) {
+	return nil, errors.New("not yet supported")
+}
+
+func DecryptWithLocalState(ciphertext []byte, localStateFile string) ([]byte, error) {
+	return nil, errors.New("not supported")
+}

safestorage/decrypt_windows.go

@@ -0,0 +1,89 @@
+// Copyright (c) 2024 Tim van der Molen <tim@kariliq.nl>
+//
+// Permission to use, copy, modify, and distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+package safestorage
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"os"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+const dpapiKeyPrefix = "DPAPI"
+
+func Decrypt(ciphertext []byte) ([]byte, error) {
+	return nil, fmt.Errorf("not supported")
+}
+
+func DecryptWithLocalState(ciphertext []byte, localStateFile string) ([]byte, error) {
+	key, err := encryptionKey(localStateFile)
+	if err != nil {
+		return nil, err
+	}
+	return decryptWithWindowsPassword(ciphertext, key)
+}
+
+func encryptionKey(localStateFile string) ([]byte, error) {
+	data, err := os.ReadFile(localStateFile)
+	if err != nil {
+		return nil, err
+	}
+
+	var localState struct {
+		OSCrypt struct {
+			EncryptedKey *string `json:"encrypted_key"`
+		} `json:"os_crypt"`
+	}
+	if err := json.Unmarshal(data, &localState); err != nil {
+		return nil, fmt.Errorf("cannot parse %s: %w", localStateFile, err)
+	}
+
+	if localState.OSCrypt.EncryptedKey == nil {
+		return nil, fmt.Errorf("encryption key not found")
+	}
+
+	key, err := base64.StdEncoding.DecodeString(*localState.OSCrypt.EncryptedKey)
+	if err != nil {
+		return nil, fmt.Errorf("cannot decode encryption key: %w", err)
+	}
+
+	if !bytes.HasPrefix(key, []byte(dpapiKeyPrefix)) {
+		return nil, fmt.Errorf("invalid encryption key format")
+	}
+	key = bytes.TrimPrefix(key, []byte(dpapiKeyPrefix))
+
+	return decryptWithDPAPI(key)
+}
+
+func decryptWithDPAPI(ciphertext []byte) ([]byte, error) {
+	in := windows.DataBlob{
+		Data: &ciphertext[0],
+		Size: uint32(len(ciphertext)),
+	}
+	var out windows.DataBlob
+	if err := windows.CryptUnprotectData(&in, nil, nil, 0, nil, 0, &out); err != nil {
+		return nil, err
+	}
+
+	plaintext := make([]byte, out.Size)
+	copy(plaintext, unsafe.Slice(out.Data, out.Size))
+	windows.LocalFree(windows.Handle(unsafe.Pointer(out.Data)))
+
+	return plaintext, nil
+}

signal/const.go

@@ -17,9 +17,10 @@ package signal
 import "os"
 
 const (
-	DatabaseFile  = "sql" + string(os.PathSeparator) + "db.sqlite"
-	ConfigFile    = "config.json"
-	AttachmentDir = "attachments.noindex"
+	DatabaseFile   = "sql" + string(os.PathSeparator) + "db.sqlite"
+	ConfigFile     = "config.json"
+	LocalStateFile = "Local State"
+	AttachmentDir  = "attachments.noindex"
 
 	// Content type of the long-text attachment of a long message
 	LongTextType = "text/x-signal-plain"

signal/open.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"runtime"
 
 	"github.com/tbvdm/sigtop/safestorage"
 	"github.com/tbvdm/sigtop/sqlcipher"
@@ -129,7 +130,12 @@ func databaseKey(dir string, password []byte) ([]byte, error) {
 	if password != nil {
 		dbKey, err = safestorage.DecryptWithPassword(key, password)
 	} else {
-		err = fmt.Errorf("not yet supported")
+		if runtime.GOOS == "windows" {
+			localStateFile := filepath.Join(dir, LocalStateFile)
+			dbKey, err = safestorage.DecryptWithLocalState(key, localStateFile)
+		} else {
+			dbKey, err = safestorage.Decrypt(key)
+		}
 	}
 	if err != nil {
 		return nil, fmt.Errorf("cannot decrypt database key: %w", err)