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https://github.com/icpz/snell-server-reversed
Reverse engineering of surge snell
https://github.com/icpz/snell-server-reversed
Last synced: 22 days ago
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Reverse engineering of surge snell
- Host: GitHub
- URL: https://github.com/icpz/snell-server-reversed
- Owner: icpz
- Created: 2019-02-27T12:55:46.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2022-01-06T17:11:39.000Z (over 2 years ago)
- Last Synced: 2024-02-18T21:36:44.249Z (4 months ago)
- Language: C++
- Homepage: https://github.com/surge-networks/snell
- Size: 20.5 KB
- Stars: 126
- Watchers: 10
- Forks: 23
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Lists
- awesome-stars - icpz/snell-server-reversed - `★129` Reverse engineering of surge snell (C++)
- awesome-stars - icpz/snell-server-reversed - Reverse engineering of surge snell (C++)
README
# Snell Server
对 snell 协议版本 v3.0 RC 的逆向，旧版本详见 [v2](README.v2.md)， [v1](README.v1.md)
开源实现可参考 [open-snell](https://github.com/icpz/open-snell) 和 [clash](https://github.com/Dreamacro/clash)
# Overview
## Encryption Schema
Schema 同 shadowsocks aead 模式，分组密码选用了 chacha20-poly1305-ietf，详见 [Aead Schema](http://shadowsocks.org/en/spec/AEAD-Ciphers.html)
会话密钥生成方式为
```
crypto_pwhash(__out key, 32, psk, psk_len, salt, 3ULL, 0x2000ULL, crypto_pwhash_ALG_ARGON2ID13);
```
参数意义详见 [libsodium documentation](https://libsodium.gitbook.io/doc/password_hashing/the_argon2i_function#key-derivation)
## The Snell Protocol for UDP Session
** Snell v3.0 TCP 连接协议与 v1 相同，详见 [v1](README.v1.md) **
后文主要表述 v3.0 新增的 UDP 转发模式
### Definitions
```
[udp-req-hdr] := [0x01][0x06][1-byte client_id length][variable-length client_id]
[udp-pkt] := [remote-addr][2-byte port][application data...]
[udp-resp] := [ip-addr][2-byte port][application data...]
[remote-addr] := [domain-addr] | [0x00][ip-addr]
[domain-addr] := [1-byte length][variable-length domain]
[ip-addr] := [ip4-addr] | [ip6-addr]
[ip4-addr] := [0x04][4-byte ipv4]
[ip6-addr] := [0x06][16-byte ipv6]
```
其中
```
client_id length: length of client_id
client_id: arbitrary string including empty string
remote-addr: new target address format, either [domain-addr] or [ip*-addr]
domain-addr: first byte is the length of domain (must NOT be zero)
ip4-addr: ipv4 is in network order binary data
ip6-addr: ipv6 is in network order binary data
port: network order port
```
### C to S
```
[udp-req-hdr][0x01][udp-pkt][0x01][udp-pkt][0x01][udp-pkt]...
```
### S to C
```
[1-byte command][content 0][content 1]....
```
其中
```
command:
0x00: READY
0x02: ERROR
```
当 command=0x00 时，表明服务端可以进行 UDP 转发，此时 content 具有如下模式
```
[udp-resp][udp-resp]....
```
当 command=0x02 时，content 具有如下模式
```
[1-byte error code][1-byte error msg length][variable-length error message]
```
### Example Stream
```
C->S : [udp-req-hdr] [0x01][udp-pkt] [0x01][udp-pkt] [0x01][udp-pkt] [0x01][udp-pkt] ...
S->C : [0x00] [udp-resp] [udp-resp] [udp-resp] ...
```
注意，表示 `S->C` 方向中 `[udp-resp]` 中的目标地址仅支持 `[ip4-addr][port]` 或 `[ip6-addr][port]` 格式，内容为原始 target 的地址。
每个 udp packet 长度可由一次 chunk decrypt 的长度计算
## Obfuscating Algorithm
同 [v1](README.v1.md)
# Contact
欢迎大家交流讨论，如果有问题欢迎在 issue 区提出，或 Email [[email protected]](mailto:[email protected])。