new helpers for drive decryption (#73)

* new helpers for drive decryption

* modular helper functions and reciprocals

* removed duplicates helper functions

* added mobile wrapper

* unit tests for new helpers

Co-authored-by: wussler <aron@wussler.it>

helper/helper.go

@@ -168,49 +168,18 @@ func DecryptVerifyAttachment(
 	passphrase, keyPacket, dataPacket []byte,
 	armoredSignature string,
 ) (plainData []byte, err error) {
-	var publicKeyObj, privateKeyObj, unlockedKeyObj *crypto.Key
-	var publicKeyRing, privateKeyRing *crypto.KeyRing
-	var detachedSignature *crypto.PGPSignature
-	var message *crypto.PlainMessage
-
-	var packets = crypto.NewPGPSplitMessage(keyPacket, dataPacket)
-
-	if publicKeyObj, err = crypto.NewKeyFromArmored(publicKey); err != nil {
-		return nil, err
-	}
-	if publicKeyObj.IsPrivate() {
-		publicKeyObj, err = publicKeyObj.ToPublic()
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	if publicKeyRing, err = crypto.NewKeyRing(publicKeyObj); err != nil {
+	// We decrypt the attachment
+	message, err := decryptAttachment(privateKey, passphrase, keyPacket, dataPacket)
+	if err != nil {
 		return nil, err
 	}
 
-	if privateKeyObj, err = crypto.NewKeyFromArmored(privateKey); err != nil {
+	// We verify the signature
+	var check bool
+	if check, err = verifyDetachedArmored(publicKey, message, armoredSignature); err != nil {
 		return nil, err
 	}
-
-	if unlockedKeyObj, err = privateKeyObj.Unlock(passphrase); err != nil {
-		return nil, err
-	}
-	defer unlockedKeyObj.ClearPrivateParams()
-
-	if privateKeyRing, err = crypto.NewKeyRing(unlockedKeyObj); err != nil {
-		return nil, err
-	}
-
-	if detachedSignature, err = crypto.NewPGPSignatureFromArmored(armoredSignature); err != nil {
-		return nil, err
-	}
-
-	if message, err = privateKeyRing.DecryptAttachment(packets); err != nil {
-		return nil, err
-	}
-
-	if publicKeyRing.VerifyDetached(message, detachedSignature, crypto.GetUnixTime()) != nil {
+	if !check {
 		return nil, errors.New("gopenpgp: unable to verify attachment")
 	}
 
@@ -235,6 +204,58 @@ func DecryptBinaryMessageArmored(privateKey string, passphrase []byte, ciphertex
 	return message.GetBinary(), nil
 }
 
+// EncryptSignArmoredDetached takes a public key for encryption,
+// a private key and its passphrase for signature, and the plaintext data
+// Returns an armored ciphertext and a detached armored signature.
+func EncryptSignArmoredDetached(
+	publicKey, privateKey string,
+	passphrase, plainData []byte,
+) (ciphertext, signature string, err error) {
+	var message *crypto.PlainMessage = crypto.NewPlainMessage(plainData)
+
+	// We encrypt the message
+	if ciphertext, err = encryptMessageArmored(publicKey, message); err != nil {
+		return "", "", err
+	}
+
+	// We sign the message
+	if signature, err = signDetachedArmored(privateKey, passphrase, message); err != nil {
+		return "", "", err
+	}
+
+	return ciphertext, signature, nil
+}
+
+// DecryptVerifyArmoredDetached decrypts an armored pgp message
+// and verify a detached armored signature
+// given a publicKey, and a privateKey with its passphrase.
+// Returns the plain data or an error on
+// signature verification failure.
+func DecryptVerifyArmoredDetached(
+	publicKey, privateKey string,
+	passphrase []byte,
+	ciphertext string,
+	armoredSignature string,
+) (plainData []byte, err error) {
+	var message *crypto.PlainMessage
+
+	// We decrypt the message
+	if message, err = decryptMessageArmored(privateKey, passphrase, ciphertext); err != nil {
+		return nil, err
+	}
+
+	// We verify the signature
+	var check bool
+	if check, err = verifyDetachedArmored(publicKey, message, armoredSignature); err != nil {
+		return nil, err
+	}
+	if !check {
+		return nil, errors.New("gopenpgp: unable to verify message")
+	}
+
+	return message.GetBinary(), nil
+}
+
 func encryptMessageArmored(key string, message *crypto.PlainMessage) (string, error) {
 	publicKey, err := crypto.NewKeyFromArmored(key)
 	if publicKey.IsPrivate() {
@@ -304,3 +325,96 @@ func decryptMessageArmored(privateKey string, passphrase []byte, ciphertext stri
 
 	return message, nil
 }
+
+func signDetachedArmored(privateKey string, passphrase []byte, message *crypto.PlainMessage) (signature string, err error) {
+	privateKeyObj, err := crypto.NewKeyFromArmored(privateKey)
+
+	if err != nil {
+		return "", err
+	}
+
+	privateKeyUnlocked, err := privateKeyObj.Unlock(passphrase)
+
+	if err != nil {
+		return "", err
+	}
+
+	defer privateKeyUnlocked.ClearPrivateParams()
+
+	privateKeyRing, err := crypto.NewKeyRing(privateKeyUnlocked)
+
+	if err != nil {
+		return "", err
+	}
+
+	detachedSignature, err := privateKeyRing.SignDetached(message)
+
+	if err != nil {
+		return "", err
+	}
+
+	armoredSignature, err := detachedSignature.GetArmored()
+
+	if err != nil {
+		return "", err
+	}
+
+	return armoredSignature, nil
+}
+
+func verifyDetachedArmored(publicKey string, message *crypto.PlainMessage, armoredSignature string) (check bool, err error) {
+	var publicKeyObj *crypto.Key
+	var publicKeyRing *crypto.KeyRing
+	var detachedSignature *crypto.PGPSignature
+	// We prepare the public key for signature verification
+	if publicKeyObj, err = crypto.NewKeyFromArmored(publicKey); err != nil {
+		return false, err
+	}
+	if publicKeyObj.IsPrivate() {
+		publicKeyObj, err = publicKeyObj.ToPublic()
+		if err != nil {
+			return false, err
+		}
+	}
+	if publicKeyRing, err = crypto.NewKeyRing(publicKeyObj); err != nil {
+		return false, err
+	}
+
+	// We verify the signature
+	if detachedSignature, err = crypto.NewPGPSignatureFromArmored(armoredSignature); err != nil {
+		return false, err
+	}
+	if publicKeyRing.VerifyDetached(message, detachedSignature, crypto.GetUnixTime()) != nil {
+		return false, nil
+	}
+	return true, nil
+}
+
+func decryptAttachment(
+	privateKey string,
+	passphrase, keyPacket, dataPacket []byte,
+) (message *crypto.PlainMessage, err error) {
+	var privateKeyObj, unlockedKeyObj *crypto.Key
+	var privateKeyRing *crypto.KeyRing
+
+	packets := crypto.NewPGPSplitMessage(keyPacket, dataPacket)
+
+	// prepare the private key for decryption
+	if privateKeyObj, err = crypto.NewKeyFromArmored(privateKey); err != nil {
+		return nil, err
+	}
+	if unlockedKeyObj, err = privateKeyObj.Unlock(passphrase); err != nil {
+		return nil, err
+	}
+	defer unlockedKeyObj.ClearPrivateParams()
+
+	if privateKeyRing, err = crypto.NewKeyRing(unlockedKeyObj); err != nil {
+		return nil, err
+	}
+
+	if message, err = privateKeyRing.DecryptAttachment(packets); err != nil {
+		return nil, err
+	}
+
+	return message, nil
+}

helper/helper_test.go

@@ -1,6 +1,7 @@
 package helper
 
 import (
+	"bytes"
 	"testing"
 
 	"github.com/ProtonMail/gopenpgp/v2/crypto"
@@ -154,3 +155,64 @@ func TestArmoredBinaryMessageEncryption(t *testing.T) {
 
 	assert.Exactly(t, plainData, decrypted)
 }
+
+func TestEncryptSignArmoredDetached(t *testing.T) {
+	plainData := []byte("Secret message")
+	privateKeyString := readTestFile("keyring_privateKey", false)
+	privateKey, err := crypto.NewKeyFromArmored(privateKeyString)
+	if err != nil {
+		t.Fatal("Error reading the test private key: ", err)
+	}
+	publicKeyString, err := privateKey.GetArmoredPublicKey()
+	if err != nil {
+		t.Fatal("Error reading the test public key: ", err)
+	}
+	armoredCiphertext, armoredSignature, err := EncryptSignArmoredDetached(
+		publicKeyString,
+		privateKeyString,
+		testMailboxPassword, // Password defined in base_test
+		plainData,
+	)
+	if err != nil {
+		t.Fatal("Expected no error while encrypting and signing, got:", err)
+	}
+
+	decrypted, err := DecryptVerifyArmoredDetached(
+		publicKeyString,
+		privateKeyString,
+		testMailboxPassword,
+		armoredCiphertext,
+		armoredSignature,
+	)
+
+	if err != nil {
+		t.Fatal("Expected no error while decrypting and verifying, got:", err)
+	}
+
+	if !bytes.Equal(decrypted, plainData) {
+		t.Error("Decrypted is not equal to the plaintext")
+	}
+
+	_, modifiedSignature, err := EncryptSignArmoredDetached(
+		publicKeyString,
+		privateKeyString,
+		testMailboxPassword, // Password defined in base_test
+		[]byte("Different message"),
+	)
+
+	if err != nil {
+		t.Fatal("Expected no error while encrypting and signing, got:", err)
+	}
+
+	_, err = DecryptVerifyArmoredDetached(
+		publicKeyString,
+		privateKeyString,
+		testMailboxPassword,
+		armoredCiphertext,
+		modifiedSignature,
+	)
+
+	if err == nil {
+		t.Fatal("Expected an error while decrypting and verifying with a wrong signature")
+	}
+}

helper/mobile.go

@@ -79,3 +79,20 @@ func GetJsonSHA256Fingerprints(publicKey string) ([]byte, error) {
 
 	return json.Marshal(key.GetSHA256Fingerprints())
 }
+
+type EncryptSignArmoredDetachedMobileResult struct {
+	Ciphertext, Signature string
+}
+
+//EncryptSignArmoredDetachedMobile wraps the EncryptSignArmoredDetached method
+//to have only one return argument for mobile.
+func EncryptSignArmoredDetachedMobile(
+	publicKey, privateKey string,
+	passphrase, plainData []byte,
+) (wrappedTuple *EncryptSignArmoredDetachedMobileResult, err error) {
+	ciphertext, signature, err := EncryptSignArmoredDetached(publicKey, privateKey, passphrase, plainData)
+	if err != nil {
+		return nil, err
+	}
+	return &EncryptSignArmoredDetachedMobileResult{ciphertext, signature}, nil
+}