From caf9fc91ed18cd844dee210e69788dc96d24a166 Mon Sep 17 00:00:00 2001
From: Andrew Gutekanst <andrew.gutekanst@gmail.com>
Date: Wed, 1 Jan 2020 06:42:36 +0900
Subject: [PATCH] Port entrance server crypto to Go

---
 entranceserver/crypto.go      | 57 +++++++++++++++++++++++++++
 entranceserver/crypto_test.go | 73 +++++++++++++++++++++++++++++++++++
 2 files changed, 130 insertions(+)
 create mode 100644 entranceserver/crypto.go
 create mode 100644 entranceserver/crypto_test.go

diff --git a/entranceserver/crypto.go b/entranceserver/crypto.go
new file mode 100644
index 000000000..7fec6b7c5
--- /dev/null
+++ b/entranceserver/crypto.go
@@ -0,0 +1,57 @@
+package entranceserver
+
+import (
+	"encoding/binary"
+)
+
+var (
+	_bin8Key     = []byte{0x01, 0x23, 0x34, 0x45, 0x56, 0xAB, 0xCD, 0xEF}
+	_sum32Table0 = []byte{0x7A, 0xAA, 0x97, 0x53, 0x66, 0x12, 0xDE, 0xDE, 0x35}
+	_sum32Table1 = []byte{0x35, 0x7A, 0xAA, 0x97, 0x53, 0x66, 0x12}
+)
+
+// CalcSum32 calculates the custom MHF "sum32" checksum of the given data.
+func CalcSum32(data []byte) uint32 {
+	tableIdx0 := byte(len(data) & 0xFF)
+	tableIdx1 := byte(data[len(data)>>1])
+
+	out := make([]byte, 4)
+	for i := 0; i < len(data); i++ {
+		tableIdx0++
+		tableIdx1++
+
+		tmp := byte((_sum32Table0[tableIdx1%9] ^ _sum32Table1[tableIdx0%7]) ^ data[i])
+		out[i&3] = (out[i&3] + tmp) & 0xFF
+
+	}
+
+	return binary.BigEndian.Uint32(out)
+}
+
+// EncryptBin8 encrypts the given data using MHF's "binary8" encryption.
+func EncryptBin8(data []byte, key byte) []byte {
+	curKey := uint32(((54323 * uint(key)) + 1) & 0xFFFFFFFF)
+
+	var output []byte
+	for i := 0; i < len(data); i++ {
+		tmp := (_bin8Key[i&7] ^ byte((curKey>>13)&0xFF))
+		output = append(output, data[i]^tmp)
+		curKey = uint32(((54323 * uint(curKey)) + 1) & 0xFFFFFFFF)
+	}
+
+	return output
+}
+
+// DecryptBin8 decrypts the given MHF "binary8" data.
+func DecryptBin8(data []byte, key byte) []byte {
+	curKey := uint32(((54323 * uint(key)) + 1) & 0xFFFFFFFF)
+
+	var output []byte
+	for i := 0; i < len(data); i++ {
+		tmp := (data[i] ^ byte((curKey>>13)&0xFF))
+		output = append(output, tmp^_bin8Key[i&7])
+		curKey = uint32(((54323 * uint(curKey)) + 1) & 0xFFFFFFFF)
+	}
+
+	return output
+}
diff --git a/entranceserver/crypto_test.go b/entranceserver/crypto_test.go
new file mode 100644
index 000000000..c89baf231
--- /dev/null
+++ b/entranceserver/crypto_test.go
@@ -0,0 +1,73 @@
+package entranceserver
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"testing"
+)
+
+var tests = []struct {
+	data          []byte
+	sum           uint32
+	encryptedData []byte
+	encryptionKey byte
+}{
+	{
+		[]byte{0x4C, 0x6F, 0x72, 0x65, 0x6D, 0x20},
+		0xAE6CA2C,
+		[]byte{0x7E, 0x4C, 0x1D, 0x16, 0x9D, 0x46},
+		0x55,
+	},
+	{
+		[]byte{0x69, 0x70, 0x73, 0x75, 0x6D, 0x20, 0x64, 0x6F, 0x6C, 0x6F, 0x72, 0x20, 0x73, 0x69, 0x74, 0x20, 0x61, 0x6D, 0x65, 0x74, 0x2C, 0x20},
+		0xCE5F1E96,
+		[]byte{0x41, 0x65, 0xFF, 0x74, 0x64, 0x45, 0xB8, 0xB1, 0x18, 0xB0, 0x94, 0xA3, 0xF8, 0xD, 0xBF, 0x3C, 0xC8, 0x24, 0xE2, 0xEC, 0x3B, 0xCE},
+		0x7A,
+	},
+	{
+		[]byte{0x63, 0x6F, 0x6E, 0x73, 0x65, 0x63, 0x74, 0x65, 0x74, 0x75, 0x72, 0x20, 0x61, 0x64, 0x69, 0x70, 0x69, 0x73, 0x63, 0x69, 0x6E, 0x67, 0x20, 0x65, 0x6C, 0x69, 0x74, 0x2C, 0x20},
+		0xF3EECEBB,
+		[]byte{0xE, 0xBB, 0x19, 0xA5, 0xB9, 0x34, 0xFE, 0x51, 0x0, 0x61, 0x2D, 0x38, 0xB2, 0x98, 0xC2, 0xE0, 0x17, 0xDE, 0x6E, 0xE3, 0x6C, 0x1E, 0x19, 0xB6, 0x8C, 0x57, 0x32, 0x32, 0xD8},
+		0xF8,
+	},
+}
+
+func TestSum32(t *testing.T) {
+	for k, test := range tests {
+		testname := fmt.Sprintf("sum32_test_%d", k)
+		t.Run(testname, func(t *testing.T) {
+			gotSum := CalcSum32(test.data)
+
+			if gotSum != test.sum {
+				t.Errorf("got sum32 0x%X, want 0x%X", gotSum, test.sum)
+			}
+		})
+	}
+}
+
+func TestEncryptBin8(t *testing.T) {
+	for k, test := range tests {
+		testname := fmt.Sprintf("encrypt_bin8_test_%d", k)
+		t.Run(testname, func(t *testing.T) {
+			gotEncData := EncryptBin8(test.data, test.encryptionKey)
+
+			if !bytes.Equal(gotEncData, test.encryptedData) {
+				t.Errorf("got\n\t%s\nwant\n\t%s", hex.Dump(gotEncData), hex.Dump(test.encryptedData))
+			}
+		})
+	}
+}
+
+func TestDecryptBin8(t *testing.T) {
+	for k, test := range tests {
+		testname := fmt.Sprintf("decrypt_bin8_test_%d", k)
+		t.Run(testname, func(t *testing.T) {
+			gotDecData := DecryptBin8(test.encryptedData, test.encryptionKey)
+
+			if !bytes.Equal(gotDecData, test.data) {
+				t.Errorf("got\n\t%s\nwant\n\t%s", hex.Dump(gotDecData), hex.Dump(test.data))
+			}
+		})
+	}
+}