Support multiple age recipients

README.md

@@ -230,7 +230,7 @@ Ideally you should have the drive fully encrypted, but that might not always be
 
 Alternatively, androidqf allows to encrypt each acquisition with a provided [age](https://age-encryption.org) public key. Preferably, this public key belongs to a keypair for which the end-user does not possess, or at least carry, the private key. In this way, the end-user would not be able to decrypt the acquired data even under duress.
 
-androidqf streams each acquisition into a zip archive. If you place a file called `key.txt` in the current working directory, androidqf will encrypt the zip stream with age and write `<UUID>.zip.age`; otherwise, it writes an unencrypted `<UUID>.zip`. androidqf also checks for `key.txt` in the same folder as the executable; if both files exist, the current working directory takes precedence.
+androidqf streams each acquisition into a zip archive. If you place a file called `key.txt` in the current working directory, androidqf will encrypt the zip stream with age and write `<UUID>.zip.age`; otherwise, it writes an unencrypted `<UUID>.zip`. Put one age recipient per line in `key.txt`; each recipient can decrypt the resulting acquisition. Empty lines and lines beginning with `#` are ignored. androidqf also checks for `key.txt` in the same folder as the executable; if both files exist, the current working directory takes precedence.
 
 Encrypted acquisitions do not create a plaintext acquisition archive. Device
 files that must be validated before they are added to an encrypted archive are

acquisition/streaming_zip.go

@@ -55,7 +55,8 @@ func (hw *hashingWriter) Write(p []byte) (int, error) {
 }
 
 // NewStreamingZipWriter creates a streaming zip writer in outputDir. If key.txt
-// exists, the zip stream is age-encrypted and written as .zip.age.
+// exists, the zip stream is age-encrypted for every recipient in the file and
+// written as .zip.age.
 func NewStreamingZipWriter(uuid, outputDir string) (*StreamingZipWriter, error) {
 	if outputDir == "" {
 		cwd, err := os.Getwd()
@@ -95,24 +96,29 @@ func NewStreamingZipWriter(uuid, outputDir string) (*StreamingZipWriter, error)
 	var encWriter io.WriteCloser
 	var zipSink io.Writer = file
 	if ok {
-		log.Info("Found age public key, streaming to encrypted zip archive.")
+		log.Info("Found age recipient file, streaming to encrypted zip archive.")
 
-		publicKey, err := os.ReadFile(keyFilePath)
+		keyFile, err := os.Open(keyFilePath)
 		if err != nil {
 			file.Close()
 			os.Remove(outputPath)
-			return nil, fmt.Errorf("failed to read public key: %v", err)
+			return nil, fmt.Errorf("failed to open age recipient file: %v", err)
 		}
-		publicKeyStr := strings.TrimSpace(string(publicKey))
 
-		recipient, err := age.ParseX25519Recipient(publicKeyStr)
+		recipients, err := age.ParseRecipients(keyFile)
+		closeErr := keyFile.Close()
 		if err != nil {
 			file.Close()
 			os.Remove(outputPath)
-			return nil, fmt.Errorf("failed to parse public key %q: %v", publicKeyStr, err)
+			return nil, fmt.Errorf("failed to parse age recipient file: %v", err)
+		}
+		if closeErr != nil {
+			file.Close()
+			os.Remove(outputPath)
+			return nil, fmt.Errorf("failed to close age recipient file: %v", closeErr)
 		}
 
-		encWriter, err = age.Encrypt(file, recipient)
+		encWriter, err = age.Encrypt(file, recipients...)
 		if err != nil {
 			file.Close()
 			os.Remove(outputPath)

acquisition/streaming_zip_test.go

@@ -138,6 +138,74 @@ func TestNewStreamingZipWriterUsesCurrentWorkingDirectory(t *testing.T) {
 	}
 }
 
+func TestNewStreamingZipWriterEncryptsForEveryRecipient(t *testing.T) {
+	cwd := t.TempDir()
+	t.Chdir(cwd)
+
+	var identities []*age.X25519Identity
+	var recipientFile strings.Builder
+	recipientFile.WriteString("# Acquisition recipients\n\n")
+	for range 2 {
+		identity, err := age.GenerateX25519Identity()
+		if err != nil {
+			t.Fatalf("GenerateX25519Identity() error = %v", err)
+		}
+		identities = append(identities, identity)
+		recipientFile.WriteString(identity.Recipient().String())
+		recipientFile.WriteByte('\n')
+	}
+	if err := os.WriteFile(
+		filepath.Join(cwd, keyFileName),
+		[]byte(recipientFile.String()),
+		0o600,
+	); err != nil {
+		t.Fatalf("WriteFile(key.txt) error = %v", err)
+	}
+
+	ezw, err := NewStreamingZipWriter("test-acquisition", cwd)
+	if err != nil {
+		t.Fatalf("NewStreamingZipWriter() error = %v", err)
+	}
+	if err := ezw.CreateFileFromString("evidence.txt", "collected evidence"); err != nil {
+		t.Fatalf("CreateFileFromString() error = %v", err)
+	}
+	if err := ezw.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+
+	encrypted, err := os.ReadFile(ezw.GetOutputPath())
+	if err != nil {
+		t.Fatalf("ReadFile(encrypted archive) error = %v", err)
+	}
+	for i, identity := range identities {
+		decrypted, err := age.Decrypt(bytes.NewReader(encrypted), identity)
+		if err != nil {
+			t.Fatalf("age.Decrypt() for recipient %d error = %v", i+1, err)
+		}
+		archive, err := io.ReadAll(decrypted)
+		if err != nil {
+			t.Fatalf("ReadAll(decrypted archive) for recipient %d error = %v", i+1, err)
+		}
+
+		reader, err := zip.NewReader(bytes.NewReader(archive), int64(len(archive)))
+		if err != nil {
+			t.Fatalf("zip.NewReader() for recipient %d error = %v", i+1, err)
+		}
+		entry, err := reader.File[0].Open()
+		if err != nil {
+			t.Fatalf("Open(evidence.txt) for recipient %d error = %v", i+1, err)
+		}
+		content, err := io.ReadAll(entry)
+		entry.Close()
+		if err != nil {
+			t.Fatalf("ReadAll(evidence.txt) for recipient %d error = %v", i+1, err)
+		}
+		if string(content) != "collected evidence" {
+			t.Fatalf("evidence.txt for recipient %d = %q", i+1, content)
+		}
+	}
+}
+
 func TestValidateZipEntryName(t *testing.T) {
 	tests := []struct {
 		name    string

docs/acquisition-archives.md

@@ -13,10 +13,12 @@ acquisition UUID:
 | Configuration | Output |
 |---|---|
 | No `key.txt` found | `<UUID>.zip` |
-| Valid age recipient in `key.txt` | `<UUID>.zip.age` |
+| One or more valid age recipients in `key.txt` | `<UUID>.zip.age` |
 
 androidqf looks for `key.txt` in the current working directory and then beside
-the executable. A key in the current working directory takes precedence.
+the executable. A key in the current working directory takes precedence. The
+file accepts one age recipient per line; empty lines and lines beginning with
+`#` are ignored. Every listed recipient can decrypt the resulting acquisition.
 
 The archive contains the collected module outputs documented in the main
 [README](../README.md#how-to-use), plus these acquisition-level entries:
@@ -50,8 +52,8 @@ finalized.
 
 ## Encrypted acquisitions
 
-When `key.txt` is present, the ZIP stream is passed directly through age into
-`<UUID>.zip.age`:
+When a valid `key.txt` is present, the ZIP stream is encrypted to every
+recipient in the file and passed directly through age into `<UUID>.zip.age`:
 
 ```text
 device data -> ZIP writer -> age encryption -> <UUID>.zip.age