1 files changed, 58 insertions, 0 deletions
diff --git a/vendor/go.mau.fi/whatsmeow/appstate/lthash/lthash.go b/vendor/go.mau.fi/whatsmeow/appstate/lthash/lthash.go
new file mode 100644
index 00000000..8d3045d6
--- /dev/null
+++ b/vendor/go.mau.fi/whatsmeow/appstate/lthash/lthash.go
@@ -0,0 +1,58 @@
+// Copyright (c) 2021 Tulir Asokan
+//
+// 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 lthash implements a summation based hash algorithm that maintains the
+// integrity of a piece of data over a series of mutations. You can add/remove
+// mutations, and it'll return a hash equal to if the same series of mutations
+// was made sequentially.
+package lthash
+
+import (
+	"encoding/binary"
+
+	"go.mau.fi/whatsmeow/util/hkdfutil"
+)
+
+type LTHash struct {
+	HKDFInfo []byte
+	HKDFSize uint8
+}
+
+// WAPatchIntegrity is a LTHash instance initialized with the details used for verifying integrity of WhatsApp app state sync patches.
+var WAPatchIntegrity = LTHash{[]byte("WhatsApp Patch Integrity"), 128}
+
+func (lth LTHash) SubtractThenAdd(base []byte, subtract, add [][]byte) []byte {
+	output := make([]byte, len(base))
+	copy(output, base)
+	lth.SubtractThenAddInPlace(output, subtract, add)
+	return output
+}
+
+func (lth LTHash) SubtractThenAddInPlace(base []byte, subtract, add [][]byte) {
+	lth.multipleOp(base, subtract, true)
+	lth.multipleOp(base, add, false)
+}
+
+func (lth LTHash) multipleOp(base []byte, input [][]byte, subtract bool) {
+	for _, item := range input {
+		performPointwiseWithOverflow(base, hkdfutil.SHA256(item, nil, lth.HKDFInfo, lth.HKDFSize), subtract)
+	}
+}
+
+func performPointwiseWithOverflow(base, input []byte, subtract bool) []byte {
+	for i := 0; i < len(base); i += 2 {
+		x := binary.LittleEndian.Uint16(base[i : i+2])
+		y := binary.LittleEndian.Uint16(input[i : i+2])
+		var result uint16
+		if subtract {
+			result = x - y
+		} else {
+			result = x + y
+		}
+		binary.LittleEndian.PutUint16(base[i:i+2], result)
+	}
+	return base
+}