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protocol-reverse

Authorized reverse engineering of custom binary protocols, Protobuf/gRPC schemas, WebSocket frames, and PCAP-driven protocol recovery.

Published by sickn33 ↗sickn33/agentic-awesome-skills

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protocol-reverse

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Use protocol-reverse to recover the unencrypted protocol represented by [authorized PCAP/PCAPNG or exported traffic] for [permitted analysis scope]. Mark traffic directions, infer evidence-supported framing, message types, fields, and state transitions across varied captures, then provide a message table, a reproducible local decoding command or script, and redacted hex-to-decoded evidence. Confirm tshark and Python are available; do not interact with a live target, replay traffic, or extract keys.

Required inputs

[authorized PCAP/PCAPNG or exported traffic]
[permitted analysis scope]

User-approved starter prompt based on a pinned source version; check current skill requirements before running. Task evidence ↗

SKILL.md

name: protocol-reversedescription: "Authorized reverse engineering of custom binary protocols, Protobuf/gRPC schemas, WebSocket frames, and PCAP-driven protocol recovery."risk: safesource: "https://github.com/zhaoxuya520/reverse-skill"source_repo: "zhaoxuya520/reverse-skill"source_type: communitydate_added: "2026-08-25"license: "MIT"license_source: "https://github.com/zhaoxuya520/reverse-skill/blob/main/LICENSE"

Protocol Reverse Engineering

When to Use

Documenting an undocumented wire protocol from captures.
Decoding structured traffic during an authorized analysis.

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 protobuf	pip
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？

Limitations

Encrypted or session-keyed protocols need key material first.
Stateful protocols may require long, varied capture sessions.

Adapted from zhaoxuya520/reverse-skill (MIT).