feat(protbot): add headless MHF protocol bot as cmd/protbot

Copy MHBridge into the Erupe module as cmd/protbot/ so it can be
built, tested, and maintained alongside the server. The bot
implements the full sign → entrance → channel login flow and
supports lobby entry, chat, session setup, and quest enumeration.

The conn/ package keeps its own Blowfish crypto primitives to avoid
importing erupe-ce/config (which requires a config file at init).

cmd/protbot/conn/crypt_conn.go

@@ -0,0 +1,115 @@
+package conn
+
+import (
+	"encoding/hex"
+	"errors"
+	"erupe-ce/network/crypto"
+	"fmt"
+	"io"
+	"net"
+)
+
+// CryptConn is an MHF encrypted two-way connection.
+// Adapted from Erupe's network/crypt_conn.go with config dependency removed.
+// Hardcoded to ZZ mode (supports Pf0-based extended data size).
+type CryptConn struct {
+	conn                        net.Conn
+	readKeyRot                  uint32
+	sendKeyRot                  uint32
+	sentPackets                 int32
+	prevRecvPacketCombinedCheck uint16
+	prevSendPacketCombinedCheck uint16
+}
+
+// NewCryptConn creates a new CryptConn with proper default values.
+func NewCryptConn(conn net.Conn) *CryptConn {
+	return &CryptConn{
+		conn:       conn,
+		readKeyRot: 995117,
+		sendKeyRot: 995117,
+	}
+}
+
+// ReadPacket reads a packet from the connection and returns the decrypted data.
+func (cc *CryptConn) ReadPacket() ([]byte, error) {
+	headerData := make([]byte, CryptPacketHeaderLength)
+	_, err := io.ReadFull(cc.conn, headerData)
+	if err != nil {
+		return nil, err
+	}
+
+	cph, err := NewCryptPacketHeader(headerData)
+	if err != nil {
+		return nil, err
+	}
+
+	// ZZ mode: extended data size using Pf0 field.
+	encryptedPacketBody := make([]byte, uint32(cph.DataSize)+(uint32(cph.Pf0-0x03)*0x1000))
+	_, err = io.ReadFull(cc.conn, encryptedPacketBody)
+	if err != nil {
+		return nil, err
+	}
+
+	if cph.KeyRotDelta != 0 {
+		cc.readKeyRot = uint32(cph.KeyRotDelta) * (cc.readKeyRot + 1)
+	}
+
+	out, combinedCheck, check0, check1, check2 := crypto.Crypto(encryptedPacketBody, cc.readKeyRot, false, nil)
+	if cph.Check0 != check0 || cph.Check1 != check1 || cph.Check2 != check2 {
+		fmt.Printf("got c0 %X, c1 %X, c2 %X\n", check0, check1, check2)
+		fmt.Printf("want c0 %X, c1 %X, c2 %X\n", cph.Check0, cph.Check1, cph.Check2)
+		fmt.Printf("headerData:\n%s\n", hex.Dump(headerData))
+		fmt.Printf("encryptedPacketBody:\n%s\n", hex.Dump(encryptedPacketBody))
+
+		// Attempt bruteforce recovery.
+		fmt.Println("Crypto out of sync? Attempting bruteforce")
+		for key := byte(0); key < 255; key++ {
+			out, combinedCheck, check0, check1, check2 = crypto.Crypto(encryptedPacketBody, 0, false, &key)
+			if cph.Check0 == check0 && cph.Check1 == check1 && cph.Check2 == check2 {
+				fmt.Printf("Bruteforce successful, override key: 0x%X\n", key)
+				cc.prevRecvPacketCombinedCheck = combinedCheck
+				return out, nil
+			}
+		}
+
+		return nil, errors.New("decrypted data checksum doesn't match header")
+	}
+
+	cc.prevRecvPacketCombinedCheck = combinedCheck
+	return out, nil
+}
+
+// SendPacket encrypts and sends a packet.
+func (cc *CryptConn) SendPacket(data []byte) error {
+	keyRotDelta := byte(3)
+
+	if keyRotDelta != 0 {
+		cc.sendKeyRot = uint32(keyRotDelta) * (cc.sendKeyRot + 1)
+	}
+
+	encData, combinedCheck, check0, check1, check2 := crypto.Crypto(data, cc.sendKeyRot, true, nil)
+
+	header := &CryptPacketHeader{}
+	header.Pf0 = byte(((uint(len(encData)) >> 12) & 0xF3) | 3)
+	header.KeyRotDelta = keyRotDelta
+	header.PacketNum = uint16(cc.sentPackets)
+	header.DataSize = uint16(len(encData))
+	header.PrevPacketCombinedCheck = cc.prevSendPacketCombinedCheck
+	header.Check0 = check0
+	header.Check1 = check1
+	header.Check2 = check2
+
+	headerBytes, err := header.Encode()
+	if err != nil {
+		return err
+	}
+
+	_, err = cc.conn.Write(append(headerBytes, encData...))
+	if err != nil {
+		return err
+	}
+	cc.sentPackets++
+	cc.prevSendPacketCombinedCheck = combinedCheck
+
+	return nil
+}