Erupe/network/crypt_conn.go

package network

import (
	"errors"
	"fmt"
	"io"
	"net"

	"github.com/Andoryuuta/Erupe/network/crypto"
)

// CryptConn represents a MHF encrypted two-way connection,
// it automatically handles encryption, decryption, and key rotation via it's methods.
type CryptConn struct {
	conn                        net.Conn
	readKeyRot                  uint32
	sendKeyRot                  uint32
	sentPackets                 int32
	prevSendPacketCombinedCheck uint16
}

// NewCryptConn creates a new CryptConn with proper default values.
func NewCryptConn(conn net.Conn) *CryptConn {
	cc := &CryptConn{
		conn:                        conn,
		readKeyRot:                  995117,
		sendKeyRot:                  995117,
		sentPackets:                 0,
		prevSendPacketCombinedCheck: 0,
	}
	return cc
}

// ReadPacket reads an packet from the connection and returns the decrypted data.
func (cc *CryptConn) ReadPacket() ([]byte, error) {

	// Read the raw 14 byte header.
	headerData := make([]byte, CryptPacketHeaderLength)
	_, err := io.ReadFull(cc.conn, headerData)
	if err != nil {
		return nil, err
	}

	//fmt.Printf("Header: %s\n", hex.Dump(headerData))

	// Parse the data into a usable struct.
	cph, err := NewCryptPacketHeader(headerData)
	if err != nil {
		return nil, err
	}

	// Now read the encrypted packet body after getting its size from the header.
	encryptedPacketBody := make([]byte, cph.DataSize)
	_, err = io.ReadFull(cc.conn, encryptedPacketBody)
	if err != nil {
		return nil, err
	}

	// Update the key rotation before decrypting.
	if cph.KeyRotDelta != 0 {
		cc.readKeyRot = (uint32(cph.KeyRotDelta) * (cc.readKeyRot + 1))
	}

	out, combinedCheck, check0, check1, check2 := crypto.Decrypt(encryptedPacketBody, cc.readKeyRot, 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)
		return nil, errors.New("decrypted data checksum doesn't match header")
	}

	_ = combinedCheck
	/*
		fmt.Printf("cc %X, c0 %X, c1 %X, c2 %X\n", combinedCheck, check0, check1, check2)
		fmt.Printf("cc %X, c0 %X, c1 %X, c2 %X\n", cph.PrevPacketCombinedCheck, cph.Check0, cph.Check1, cph.Check2)
		fmt.Printf("cph: %+v\n", cph)
	*/
	return out, nil
}