verificationhelper/qrcode: add (en|de)coder

Signed-off-by: Sumner Evans <sumner@beeper.com>

crypto/verificationhelper/qrcode.go

@@ -0,0 +1,98 @@
+// Copyright (c) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package verificationhelper
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+
+	"go.mau.fi/util/random"
+
+	"maunium.net/go/mautrix/id"
+)
+
+var (
+	ErrInvalidQRCodeHeader  = errors.New("invalid QR code header")
+	ErrUnknownQRCodeVersion = errors.New("invalid QR code version")
+	ErrInvalidQRCodeMode    = errors.New("invalid QR code mode")
+)
+
+type QRCodeMode byte
+
+const (
+	QRCodeModeCrossSigning                    QRCodeMode = 0x00
+	QRCodeModeSelfVerifyingMasterKeyTrusted   QRCodeMode = 0x01
+	QRCodeModeSelfVerifyingMasterKeyUntrusted QRCodeMode = 0x02
+)
+
+type QRCode struct {
+	Mode          QRCodeMode
+	TransactionID id.VerificationTransactionID
+	Key1, Key2    [32]byte
+	SharedSecret  []byte
+}
+
+func NewQRCode(mode QRCodeMode, txnID id.VerificationTransactionID, key1, key2 [32]byte) *QRCode {
+	return &QRCode{
+		Mode:          mode,
+		TransactionID: txnID,
+		Key1:          key1,
+		Key2:          key2,
+		SharedSecret:  random.Bytes(16),
+	}
+}
+
+// NewQRCodeFromBytes parses the bytes from a QR code scan as defined in
+// [Section 11.12.2.4.1] of the Spec.
+//
+// [Section 11.12.2.4.1]: https://spec.matrix.org/v1.9/client-server-api/#qr-code-format
+func NewQRCodeFromBytes(data []byte) (*QRCode, error) {
+	if !bytes.HasPrefix(data, []byte("MATRIX")) {
+		return nil, ErrInvalidQRCodeHeader
+	}
+	if data[6] != 0x02 {
+		return nil, ErrUnknownQRCodeVersion
+	}
+	if data[7] != 0x00 && data[7] != 0x01 && data[7] != 0x02 {
+		return nil, ErrInvalidQRCodeMode
+	}
+	transactionIDLength := binary.BigEndian.Uint16(data[8:10])
+	transactionID := data[10 : 10+transactionIDLength]
+
+	var key1, key2 [32]byte
+	copy(key1[:], data[10+transactionIDLength:10+transactionIDLength+32])
+	copy(key2[:], data[10+transactionIDLength+32:10+transactionIDLength+64])
+
+	return &QRCode{
+		Mode:          QRCodeMode(data[7]),
+		TransactionID: id.VerificationTransactionID(transactionID),
+		Key1:          key1,
+		Key2:          key2,
+		SharedSecret:  data[10+transactionIDLength+64:],
+	}, nil
+}
+
+// Bytes returns the bytes that need to be encoded in the QR code as defined in
+// [Section 11.12.2.4.1] of the Spec.
+//
+// [Section 11.12.2.4.1]: https://spec.matrix.org/v1.9/client-server-api/#qr-code-format
+func (q *QRCode) Bytes() []byte {
+	var buf bytes.Buffer
+	buf.WriteString("MATRIX")   // Header
+	buf.WriteByte(0x02)         // Version
+	buf.WriteByte(byte(q.Mode)) // Mode
+
+	// Transaction ID length + Transaction ID
+	buf.Write(binary.BigEndian.AppendUint16(nil, uint16(len(q.TransactionID.String()))))
+	buf.WriteString(q.TransactionID.String())
+
+	buf.Write(q.Key1[:])      // Key 1
+	buf.Write(q.Key2[:])      // Key 2
+	buf.Write(q.SharedSecret) // Shared secret
+	return buf.Bytes()
+}

crypto/verificationhelper/qrcode_test.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package verificationhelper_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"maunium.net/go/mautrix/crypto/verificationhelper"
+)
+
+func TestQRCode_Roundtrip(t *testing.T) {
+	var key1, key2 [32]byte
+	copy(key1[:], bytes.Repeat([]byte{0x01}, 32))
+	copy(key2[:], bytes.Repeat([]byte{0x02}, 32))
+	qrCode := verificationhelper.NewQRCode(verificationhelper.QRCodeModeCrossSigning, "test", key1, key2)
+
+	encoded := qrCode.Bytes()
+	decoded, err := verificationhelper.NewQRCodeFromBytes(encoded)
+	require.NoError(t, err)
+
+	assert.Equal(t, verificationhelper.QRCodeModeCrossSigning, decoded.Mode)
+	assert.EqualValues(t, "test", decoded.TransactionID)
+	assert.Equal(t, key1, decoded.Key1)
+	assert.Equal(t, key2, decoded.Key2)
+}
+
+func TestQRCodeDecode(t *testing.T) {
+	qrcodeData := []byte{
+		0x4d, 0x41, 0x54, 0x52, 0x49, 0x58, 0x02, 0x01, 0x00, 0x20, 0x47, 0x6e, 0x41, 0x65, 0x43, 0x76,
+		0x74, 0x57, 0x6a, 0x7a, 0x4d, 0x4f, 0x56, 0x57, 0x51, 0x54, 0x6b, 0x74, 0x33, 0x35, 0x59, 0x52,
+		0x55, 0x72, 0x75, 0x6a, 0x6d, 0x52, 0x50, 0x63, 0x38, 0x61, 0x18, 0x32, 0x7c, 0xc3, 0x8c, 0xc2,
+		0xa6, 0xc2, 0xb5, 0xc2, 0xa7, 0x50, 0x57, 0x67, 0x19, 0x5e, 0xc3, 0xaf, 0xc2, 0xa0, 0xc2, 0x98,
+		0xc2, 0x9d, 0x36, 0xc3, 0xad, 0x7a, 0x10, 0x2e, 0x18, 0x3e, 0x4e, 0xc3, 0x84, 0xc3, 0x81, 0x45,
+		0x0c, 0xc2, 0xae, 0x19, 0x78, 0xc2, 0x99, 0x06, 0xc2, 0x92, 0xc2, 0x94, 0xc2, 0x8e, 0xc2, 0xb7,
+		0x59, 0xc2, 0x96, 0xc2, 0xad, 0xc3, 0xbd, 0x70, 0x6a, 0x11, 0xc2, 0xba, 0xc2, 0xa9, 0x29, 0xc3,
+		0x8f, 0x0d, 0xc2, 0xb8, 0xc2, 0x88, 0x67, 0x5b, 0xc3, 0xb3, 0x01, 0xc2, 0xb0, 0x63, 0x2e, 0xc2,
+		0xa5, 0xc3, 0xb3, 0x60, 0xc3, 0x82, 0x04, 0xc3, 0xa3, 0x72, 0x7d, 0x7c, 0x1d, 0xc2, 0xb6, 0xc2,
+		0xba, 0xc2, 0x81, 0x1e, 0xc2, 0x99, 0xc2, 0xb8, 0x7f, 0x0a,
+	}
+	decoded, err := verificationhelper.NewQRCodeFromBytes(qrcodeData)
+	require.NoError(t, err)
+	assert.Equal(t, verificationhelper.QRCodeModeSelfVerifyingMasterKeyTrusted, decoded.Mode)
+	assert.EqualValues(t, "GnAeCvtWjzMOVWQTkt35YRUrujmRPc8a", decoded.TransactionID)
+	assert.Equal(t,
+		[32]byte{0x18, 0x32, 0x7c, 0xc3, 0x8c, 0xc2, 0xa6, 0xc2, 0xb5, 0xc2, 0xa7, 0x50, 0x57, 0x67, 0x19, 0x5e, 0xc3, 0xaf, 0xc2, 0xa0, 0xc2, 0x98, 0xc2, 0x9d, 0x36, 0xc3, 0xad, 0x7a, 0x10, 0x2e, 0x18, 0x3e},
+		decoded.Key1)
+	assert.Equal(t,
+		[32]byte{0x4e, 0xc3, 0x84, 0xc3, 0x81, 0x45, 0xc, 0xc2, 0xae, 0x19, 0x78, 0xc2, 0x99, 0x6, 0xc2, 0x92, 0xc2, 0x94, 0xc2, 0x8e, 0xc2, 0xb7, 0x59, 0xc2, 0x96, 0xc2, 0xad, 0xc3, 0xbd, 0x70, 0x6a, 0x11},
+		decoded.Key2)
+}