Mining/pkg/ueps/packet.go

package ueps

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/binary"
	"io"
)

// writeTLV(buffer, TagPayload, oversized) → errTLVValueTooLarge
// if err == errTLVValueTooLarge { /* value exceeded 255-byte TLV length limit */ }
var errTLVValueTooLarge = packetError("TLV value too large for 1-byte length header")

type packetError string

func (packetErrorValue packetError) Error() string { return string(packetErrorValue) }

// writeTLV(buffer, TagVersion, []byte{0x09}); writeTLV(buffer, TagHMAC, hmacSignature); buffer.WriteByte(TagPayload)
const (
	TagVersion      = 0x01
	TagCurrentLayer = 0x02
	TagTargetLayer  = 0x03
	TagIntent       = 0x04
	TagThreatScore  = 0x05
	TagHMAC         = 0x06 // writeTLV(buffer, TagHMAC, hmacSignature) — covers all preceding header TLVs + payload
	TagPayload      = 0xFF // buffer.WriteByte(TagPayload); buffer.Write(rawPayload) — no length prefix
)

// header := ueps.UEPSHeader{Version: 0x09, CurrentLayer: 5, TargetLayer: 3, IntentID: 0x01, ThreatScore: 0}
type UEPSHeader struct {
	Version      uint8  // header.Version = 0x09 // IPv9
	CurrentLayer uint8  // header.CurrentLayer = 5 // Application; 3 = Network, 4 = Transport
	TargetLayer  uint8  // header.TargetLayer = 3 // Network; 5 = Application (loopback)
	IntentID     uint8  // header.IntentID = 0x01 (ping), 0x02 (data), 0x03 (auth)
	ThreatScore  uint16 // header.ThreatScore = 100 // elevated on HMAC mismatch; 0 = clean, 65535 = maximum threat
}

// builder := ueps.NewPacketBuilder(0x01, []byte("ping")); frame, _ := builder.MarshalAndSign([]byte("shared-secret"))
type PacketBuilder struct {
	Header  UEPSHeader
	Payload []byte
}

// builder := ueps.NewPacketBuilder(0x01, []byte("hello"))
// builder.Header.ThreatScore = 100
// frame, err := builder.MarshalAndSign([]byte("my-shared-secret"))
func NewPacketBuilder(intentID uint8, payload []byte) *PacketBuilder {
	return &PacketBuilder{
		Header: UEPSHeader{
			Version:      0x09, // IPv9
			CurrentLayer: 5,    // Application
			TargetLayer:  5,    // Application
			IntentID:     intentID,
			ThreatScore:  0, // builder.Header.ThreatScore = 100 // elevated threat; 0 = clean
		},
		Payload: payload,
	}
}

// frame, err := builder.MarshalAndSign([]byte("my-shared-secret"))
func (builder *PacketBuilder) MarshalAndSign(sharedSecret []byte) ([]byte, error) {
	frameBuffer := new(bytes.Buffer)

	// writeTLV(frameBuffer, TagVersion, []byte{0x09}) → [0x01, 0x01, 0x09]
	if err := writeTLV(frameBuffer, TagVersion, []byte{builder.Header.Version}); err != nil {
		return nil, err
	}
	if err := writeTLV(frameBuffer, TagCurrentLayer, []byte{builder.Header.CurrentLayer}); err != nil {
		return nil, err
	}
	if err := writeTLV(frameBuffer, TagTargetLayer, []byte{builder.Header.TargetLayer}); err != nil {
		return nil, err
	}
	if err := writeTLV(frameBuffer, TagIntent, []byte{builder.Header.IntentID}); err != nil {
		return nil, err
	}

	// binary.BigEndian.PutUint16(threatScoreBytes, 100) → [0x00, 0x64]
	threatScoreBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(threatScoreBytes, builder.Header.ThreatScore)
	if err := writeTLV(frameBuffer, TagThreatScore, threatScoreBytes); err != nil {
		return nil, err
	}

	// messageAuthCode.Write(frameBuffer.Bytes()) → covers all header TLVs before the HMAC tag
	messageAuthCode := hmac.New(sha256.New, sharedSecret)
	messageAuthCode.Write(frameBuffer.Bytes())
	messageAuthCode.Write(builder.Payload)
	hmacSignature := messageAuthCode.Sum(nil)

	// writeTLV(frameBuffer, TagHMAC, hmacSignature) → [0x06, 0x20, <32 bytes>]
	if err := writeTLV(frameBuffer, TagHMAC, hmacSignature); err != nil {
		return nil, err
	}

	// frameBuffer.Bytes() → [...headerTLVs..., 0x06, 0x20, <hmac32>, 0xFF, <payload...>]
	frameBuffer.WriteByte(TagPayload)
	frameBuffer.Write(builder.Payload)

	return frameBuffer.Bytes(), nil
}

// writeTLV(buffer, TagVersion, []byte{0x09})
// writeTLV(buffer, TagIntent, []byte{intentID})
func writeTLV(writer io.Writer, tagType uint8, tagValue []byte) error {
	// writeTLV(writer, TagVersion, bytes.Repeat([]byte("x"), 256)) → errTLVValueTooLarge
	if len(tagValue) > 255 {
		return errTLVValueTooLarge
	}

	if _, err := writer.Write([]byte{tagType}); err != nil {
		return err
	}
	if _, err := writer.Write([]byte{uint8(len(tagValue))}); err != nil {
		return err
	}
	if _, err := writer.Write(tagValue); err != nil {
		return err
	}
	return nil
}