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 = tlvError("TLV value too large for 1-byte length header")

// var errMyError = tlvError("my error message")
type tlvError string

func (e tlvError) Error() string { return string(e) }

// TLV Types
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  // 0x09 = IPv9
	CurrentLayer uint8  // OSI layer of the sender (5 = Application)
	TargetLayer  uint8  // OSI layer of the destination
	IntentID     uint8  // header.IntentID = 0x01 (ping), 0x02 (data), 0x03 (auth)
	ThreatScore  uint16 // 0–65535; elevated by integrity violations
}

// builder := ueps.NewPacketBuilder(intentID, payload); frame, _ := builder.MarshalAndSign(secret)
type PacketBuilder struct {
	Header  UEPSHeader
	Payload []byte
}

// builder := ueps.NewPacketBuilder(0x01, []byte("hello"))
// builder.Header.ThreatScore = 100
// frame, err := builder.MarshalAndSign(sharedSecret)
func NewPacketBuilder(intentID uint8, payload []byte) *PacketBuilder {
	return &PacketBuilder{
		Header: UEPSHeader{
			Version:      0x09, // IPv9
			CurrentLayer: 5,    // Application
			TargetLayer:  5,    // Application
			IntentID:     intentID,
			ThreatScore:  0, // Assumed innocent until proven guilty
		},
		Payload: payload,
	}
}

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

	// 1. Write Standard Header Tags (0x01 - 0x05)
	// We write these first because they are part of what we sign.
	if err := writeTLV(buffer, TagVersion, []byte{builder.Header.Version}); err != nil {
		return nil, err
	}
	if err := writeTLV(buffer, TagCurrentLayer, []byte{builder.Header.CurrentLayer}); err != nil {
		return nil, err
	}
	if err := writeTLV(buffer, TagTargetLayer, []byte{builder.Header.TargetLayer}); err != nil {
		return nil, err
	}
	if err := writeTLV(buffer, TagIntent, []byte{builder.Header.IntentID}); err != nil {
		return nil, err
	}

	// Threat Score is uint16, needs binary packing
	threatScoreBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(threatScoreBytes, builder.Header.ThreatScore)
	if err := writeTLV(buffer, TagThreatScore, threatScoreBytes); err != nil {
		return nil, err
	}

	// 2. Calculate HMAC
	// The signature covers: Existing Header TLVs + The Payload
	// It does NOT cover the HMAC TLV tag itself (obviously)
	messageAuthCode := hmac.New(sha256.New, sharedSecret)
	messageAuthCode.Write(buffer.Bytes())  // The headers so far
	messageAuthCode.Write(builder.Payload) // The data
	signature := messageAuthCode.Sum(nil)

	// 3. Write HMAC TLV (0x06)
	// Length is 32 bytes for SHA256
	if err := writeTLV(buffer, TagHMAC, signature); err != nil {
		return nil, err
	}

	// 4. Write Payload TLV (0xFF) — tag byte only; payload appended length-prefixless.
	// buffer.Bytes() → [...headerTLVs..., 0x06, 0x20, <hmac32>, 0xFF, <payload...>]
	buffer.WriteByte(TagPayload)
	buffer.Write(builder.Payload)

	return buffer.Bytes(), nil
}

// writeTLV(buffer, TagVersion, []byte{0x09})
// writeTLV(buffer, TagIntent, []byte{intentID})
func writeTLV(writer io.Writer, tag uint8, value []byte) error {
	// Check strict length constraint (1 byte length = max 255 bytes)
	if len(value) > 255 {
		return errTLVValueTooLarge
	}

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