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protocol-reverse

Analyze captured network traffic and binary messages to recover custom protocol structures. The skill organizes message types, fields, and connection states, then produces reproducible decoding steps with supporting evidence for authorized investigations.

OriginalShow the original description

Use for authorized reverse engineering of custom binary protocols, Protobuf/gRPC, WebSocket frames, and PCAP-driven protocol recovery.

See how to install

Good for

  • Recover message fields from captured network traffic
  • Investigate unknown Protobuf message structures
  • Map handshakes, heartbeats, and connection states
  • Document reproducible decoding steps

Files included (2)

  • SKILL.md3.5 KB
  • references/protocol-workflow.md807 B

SKILL.md (original)

Review the instructions the agent will receive before you install.

Protocol Reverse Engineering

ACTION REQUIRED(读完后立刻执行)

  1. NOW: 读取 ../field-journal/precedent-reverse.md — 确认授权与常规操作边界
  2. NOW: 确认任务是否为协议/流量/序列化格式逆向(非纯 Web 参数签名 → 转 js-reverse/)
  3. NOW: 若有目标网络交互 → ../scripts/case-init.ps1 完成 scope;auth 未 granted 禁止对目标 ACT
  4. NEXT: 读取 ../tool-index.md;缺工具 bootstrap(tshark/wireshark 等可能需手动)
  5. ACT: 进入工作流 Phase 1,产出帧布局或消息字典草稿

适用场景

  • 自定义 TCP/UDP 二进制协议
  • Protobuf / gRPC / FlatBuffers / MessagePack
  • WebSocket / MQTT / 私有 RPC
  • PCAP / PCAPNG 还原字段与状态机
  • 客户端-服务端校验、序列号、加密帧头

不走本 skill

情况去哪
仅 HTTP 参数签名 / JS 加密js-reverse/
仅 TLS 证书问题pentest-tools/ 或浏览器代理
固件内协议栈深挖 + 仿真firmware-pentest/ 后再回本 skill

工作流

Phase 1 — 采集与分诊

□ 拿到样本:PCAP / 代理导出 / 客户端日志 / 二进制
□ 标记方向:C→S / S→C;是否有握手、心跳、重连
□ 固定头?魔数?长度字段?TLV?定长?
□ 是否压缩(zlib/gzip/lz4)或加密(AES/ChaCha 帧内)
□ tshark -r cap.pcap -T fields -e frame.number -e ip.src -e tcp.payload

Phase 2 — 帧布局还原

□ 对齐多个同类消息,找不变字节 / 自增序列号
□ 长度字段:大端/小端、含头/不含头
□ 校验:CRC16/32、checksum、HMAC 位置
□ 画出状态机:Connect → Auth → Ready → Request/Response → Close
□ 工具:Wireshark 自定义 dissector 草稿 / ImHex / 010 Editor 模板 / Kaitai Struct

Phase 3 — 序列化与加密

□ Protobuf:.proto 恢复(blackboxprotobuf / pbtk / protoc --decode_raw)
□ gRPC:HTTP/2 headers + protobuf body
□ 加密:找密钥派生(客户端 so/dll/JS)→ 联合 ida-reverse / js-reverse / apk-reverse
□ 重放:仅在授权 scope 内;先无害字段再敏感操作

Phase 4 — 产物

MUST 产出:
- 消息类型表(name / opcode / fields)
- 至少 1 条可复现的解码命令或脚本
- Evidence:原始 hex 摘录 + 解码结果(脱敏)

工具链

工具必需用途自举
tshark / Wireshark强烈建议PCAP 解析手动 / winget
Python3是解码脚本系统
blackboxprotobuf可选未知 protobufpip
ImHex / 010可选结构模板手动
IDA / r2 / Ghidra按需客户端序列化函数见对应 skill

参考

  • references/protocol-workflow.md — 帧布局与 Protobuf 速查
  • 相关:../ida-reverse/ ../js-reverse/ ../firmware-pentest/ ../pentest-tools/

路由上下文

上游: MASTER-ROUTING R21 · routing.md
下游: 需客户端算法 → ida-reverse/js-reverse;需利用重放 → pentest-tools/api-security
同级: malware-analysis(C2 协议)、digital-forensics(流量取证)

任务完成自检

  • 是否还原了消息布局或状态机(而非只贴 hex)?
  • 是否有可复现解码命令?
  • 是否遵守 scope / 脱敏?
  • 是否回写 field-journal / 报告 Checklist?

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