Add APIs to get the creation time of verified detached signatures

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Added
+- Function to verify a detached signature and get its creation time: 
+```go
+func (keyRing *KeyRing) GetVerifiedSignatureTimestamp(message *PlainMessage, signature *PGPSignature, verifyTime int64) (int64, error)
+```
+
 ## [2.3.1] 2021-12-15
 ### Fixed
 - Fix the verification of PGP/MIME message signatures:

crypto/keyring_message.go

@@ -118,6 +118,44 @@ func (keyRing *KeyRing) VerifyDetachedEncrypted(message *PlainMessage, encrypted
 	return keyRing.VerifyDetached(message, signature, verifyTime)
 }
 
+// GetVerifiedSignatureTimestamp verifies a PlainMessage with a detached PGPSignature
+// returns the creation time of the signature if it succeeds
+// and returns a SignatureVerificationError if fails.
+func (keyRing *KeyRing) GetVerifiedSignatureTimestamp(message *PlainMessage, signature *PGPSignature, verifyTime int64) (int64, error) {
+	packets := packet.NewReader(bytes.NewReader(signature.Data))
+	var err error
+	var p packet.Packet
+	for {
+		p, err = packets.Next()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			continue
+		}
+		sigPacket, ok := p.(*packet.Signature)
+		if !ok {
+			continue
+		}
+		var outBuf bytes.Buffer
+		err = sigPacket.Serialize(&outBuf)
+		if err != nil {
+			continue
+		}
+		err = verifySignature(
+			keyRing.entities,
+			message.NewReader(),
+			outBuf.Bytes(),
+			verifyTime,
+		)
+		if err != nil {
+			continue
+		}
+		return sigPacket.CreationTime.Unix(), nil
+	}
+	return 0, errors.Wrap(err, "gopenpgp: can't verify any signature packets")
+}
+
 // ------ INTERNAL FUNCTIONS -------
 
 // Core for encryption+signature (non-streaming) functions.

crypto/message.go

@@ -423,23 +423,23 @@ func (msg *PGPMessage) SeparateKeyAndData(estimatedLength, garbageCollector int)
 }
 
 // GetBinary returns the unarmored binary content of the signature as a []byte.
-func (msg *PGPSignature) GetBinary() []byte {
-	return msg.Data
+func (sig *PGPSignature) GetBinary() []byte {
+	return sig.Data
 }
 
 // GetArmored returns the armored signature as a string.
-func (msg *PGPSignature) GetArmored() (string, error) {
-	return armor.ArmorWithType(msg.Data, constants.PGPSignatureHeader)
+func (sig *PGPSignature) GetArmored() (string, error) {
+	return armor.ArmorWithType(sig.Data, constants.PGPSignatureHeader)
 }
 
 // GetSignatureKeyIDs Returns the key IDs of the keys to which the (readable) signature packets are encrypted to.
-func (msg *PGPSignature) GetSignatureKeyIDs() ([]uint64, bool) {
-	return getSignatureKeyIDs(msg.Data)
+func (sig *PGPSignature) GetSignatureKeyIDs() ([]uint64, bool) {
+	return getSignatureKeyIDs(sig.Data)
 }
 
 // GetHexSignatureKeyIDs Returns the key IDs of the keys to which the session key is encrypted.
-func (msg *PGPSignature) GetHexSignatureKeyIDs() ([]string, bool) {
-	return getHexKeyIDs(msg.GetSignatureKeyIDs())
+func (sig *PGPSignature) GetHexSignatureKeyIDs() ([]string, bool) {
+	return getHexKeyIDs(sig.GetSignatureKeyIDs())
 }
 
 // GetBinary returns the unarmored signed data as a []byte.

crypto/signature_test.go

@@ -1,10 +1,14 @@
 package crypto
 
 import (
+	"bytes"
 	"errors"
+	"io"
+	"io/ioutil"
 	"regexp"
 	"testing"
 
+	"github.com/ProtonMail/go-crypto/openpgp/packet"
 	"github.com/ProtonMail/gopenpgp/v2/constants"
 	"github.com/stretchr/testify/assert"
 )
@@ -73,3 +77,120 @@ func TestVerifyBinDetachedSig(t *testing.T) {
 		t.Fatal("Cannot verify binary signature:", verificationError)
 	}
 }
+
+func Test_KeyRing_GetVerifiedSignatureTimestampSuccess(t *testing.T) {
+	message := NewPlainMessageFromString("Hello world!")
+	var time int64 = 1600000000
+	pgp.latestServerTime = time
+	defer func() {
+		pgp.latestServerTime = testTime
+	}()
+	signature, err := keyRingTestPrivate.SignDetached(message)
+	if err != nil {
+		t.Errorf("Got an error while generating the signature: %v", err)
+	}
+	actualTime, err := keyRingTestPublic.GetVerifiedSignatureTimestamp(message, signature, 0)
+	if err != nil {
+		t.Errorf("Got an error while parsing the signature creation time: %v", err)
+	}
+	if time != actualTime {
+		t.Errorf("Expected creation time to be %d, got %d", time, actualTime)
+	}
+}
+
+func Test_KeyRing_GetVerifiedSignatureWithTwoKeysTimestampSuccess(t *testing.T) {
+	publicKey1Armored, err := ioutil.ReadFile("testdata/signature/publicKey1")
+	if err != nil {
+		t.Errorf("Couldn't read the public key file: %v", err)
+	}
+	publicKey1 := parseKey(t, string(publicKey1Armored))
+	publicKey2Armored, err := ioutil.ReadFile("testdata/signature/publicKey2")
+	if err != nil {
+		t.Errorf("Couldn't read the public key file: %v", err)
+	}
+	publicKey2 := parseKey(t, string(publicKey2Armored))
+	message := NewPlainMessageFromString("hello world")
+	signatureArmored, err := ioutil.ReadFile("testdata/signature/detachedSigSignedTwice")
+	if err != nil {
+		t.Errorf("Couldn't read the signature file: %v", err)
+	}
+	signature, err := NewPGPSignatureFromArmored(string(signatureArmored))
+	if err != nil {
+		t.Errorf("Got an error while parsing the signature: %v", err)
+	}
+	time1 := getTimestampOfIssuer(signature, publicKey1.GetKeyID())
+	time2 := getTimestampOfIssuer(signature, publicKey2.GetKeyID())
+	keyRing, err := NewKeyRing(publicKey1)
+	if err != nil {
+		t.Errorf("Got an error while building the key ring: %v", err)
+	}
+	err = keyRing.AddKey(publicKey2)
+	if err != nil {
+		t.Errorf("Got an error while adding key 2 to the key ring: %v", err)
+	}
+	actualTime, err := keyRing.GetVerifiedSignatureTimestamp(message, signature, 0)
+	if err != nil {
+		t.Errorf("Got an error while parsing the signature creation time: %v", err)
+	}
+	if time1 != actualTime {
+		t.Errorf("Expected creation time to be %d, got %d", time1, actualTime)
+	}
+	if time2 == actualTime {
+		t.Errorf("Expected creation time to be different from %d", time2)
+	}
+}
+
+func parseKey(t *testing.T, keyArmored string) *Key {
+	key, err := NewKeyFromArmored(keyArmored)
+	if err != nil {
+		t.Errorf("Couldn't parse key: %v", err)
+		return nil
+	}
+	return key
+}
+
+func getTimestampOfIssuer(signature *PGPSignature, keyID uint64) int64 {
+	packets := packet.NewReader(bytes.NewReader(signature.Data))
+	var err error
+	var p packet.Packet
+	for {
+		p, err = packets.Next()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			continue
+		}
+		sigPacket, ok := p.(*packet.Signature)
+		if !ok {
+			continue
+		}
+		var outBuf bytes.Buffer
+		err = sigPacket.Serialize(&outBuf)
+		if err != nil {
+			continue
+		}
+		if *sigPacket.IssuerKeyId == keyID {
+			return sigPacket.CreationTime.Unix()
+		}
+	}
+	return -1
+}
+
+func Test_KeyRing_GetVerifiedSignatureTimestampError(t *testing.T) {
+	message := NewPlainMessageFromString("Hello world!")
+	var time int64 = 1600000000
+	pgp.latestServerTime = time
+	defer func() {
+		pgp.latestServerTime = testTime
+	}()
+	signature, err := keyRingTestPrivate.SignDetached(message)
+	if err != nil {
+		t.Errorf("Got an error while generating the signature: %v", err)
+	}
+	message_corrupted := NewPlainMessageFromString("Ciao world!")
+	_, err = keyRingTestPublic.GetVerifiedSignatureTimestamp(message_corrupted, signature, 0)
+	if err == nil {
+		t.Errorf("Expected an error while parsing the creation time of a wrong signature, got nil")
+	}
+}

crypto/testdata/signature/detachedSigSignedTwice

@@ -0,0 +1,10 @@
+-----BEGIN PGP SIGNATURE-----
+
+wnUEARYKAAYFAmCCo8gAIQkQyQtnL+EYbekWIQTopSabUSqDUEv/FMHJC2cv
+4Rht6VeGAP4mUJl+WYN9nLE57YByTh95OmcZmwfgz5Z4R570YqTVngD/VBym
+icc7YREcxij1gC6SSAe8kgKW6oVOWzxJ8HkOSQrCdQQBFgoABgUCYIK9vQAh
+CRCGHCX3YYW5NRYhBErDPc6OYkUaNQCLhoYcJfdhhbk1W1QBAPhrkAjimO22
+jh1V2A8pRCOs53Ig/AMAFbN37BaAIEVKAP0SVMTL6zTxYJcxWNPog7Bv5lM4
+Px4G+hZ2Kia//qlgBg==
+=0aeU
+-----END PGP SIGNATURE-----

crypto/testdata/signature/publicKey1

@@ -0,0 +1,13 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=ZWrn
+-----END PGP PUBLIC KEY BLOCK-----

crypto/testdata/signature/publicKey2

@@ -0,0 +1,13 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=IEm4
+-----END PGP PUBLIC KEY BLOCK-----