SSH 密钥认证深度解析 | AI生成和翻译
SSH 密钥认证 — 深入解析
什么是 SSH 密钥对？
当你运行 ssh-keygen 时，它会创建两个数学上相关的文件：
id_ed25519 → Private Key (SECRET, never leave your machine)
id_ed25519.pub → Public Key (share freely, paste into servers)
对于 Ed25519（现代标准），它们实际包含的内容如下：
Private key (id_ed25519)：
-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtz
c2gtZWQyNTUxOQAAACB4G3kR2f8J... (base64 encoded binary data)
-----END OPENSSH PRIVATE KEY-----
包含：你的 private scalar（一个 256 位秘密数字）+ 你的 public key + 元数据。
Public key (id_ed25519.pub)：
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMTRoCy6Uo67vc1CJSAAnZQCHftNB5kbq9jf8ZsEsa+o lzwjava@gmail.com
三个部分：
| Part | Value | Meaning |
|---|---|---|
ssh-ed25519 |
Key type | Algorithm used |
AAAAC3NzaC... |
Public key | 256-bit public point (base64) |
lzwjava@gmail.com |
Comment | Your label (optional) |
Ed25519 背后的数学原理
基于 Curve25519 椭圆曲线：
Private key = random 256-bit number (k)
Public key = k × G (point multiplication on the curve)
G = base point (fixed, everyone agrees on it)
Given k → easy to compute k×G (one operation)
Given k×G → impossible to find k (would need to solve ECDLP)
这种 one-way trapdoor 是你为什么可以自由共享公钥的原因。
认证握手（逐步解析）
当你的 Mac 连接到 Gitea 时：
Client (Mac) Server (Gitea Container)
| |
|--- TCP connection to :2222 ----------->|
|<-- "Hello, I'm an SSH server" ---------|
|--- "Hello, I'm an SSH client" -------->|
| |
| [ Key Exchange - Diffie-Hellman ]|
| |
|--- eph_pub_key_A ------------------> |
|<-- eph_pub_key_B ------------------- |
| |
| Both compute: shared_secret = A×B |
| Session encryption key derived |
| |
| [ User Authentication ] |
| |
|--- "I am 'git', prove my key" ------->|
| |
| Server checks ~/.ssh/authorized_keys|
| Finds matching public key |
| |
|<-- challenge = random data + signature |
| signed with server's HOST key |
| |
|--- signature(challenge, priv_key) --->|
| |
| Server verifies signature using |
| the public key from authorized_keys |
| |
| sig == expected? → ✅ AUTHENTICATED |
| |
|--- "shell access granted" ----------->|
签名步骤（你的修复起作用的地方）
这是关键时刻：
1. Server generates random bytes: R = [0x4a, 0x1f, 0x8c, ...]
2. Server signs R with its HOST private key (proves it's the real server)
Server sends: (R, server_signature)
3. Client verifies server's signature (anti-MITM check)
4. Client signs R with its USER private key
Client sends: client_signature = Sign(R, private_key)
5. Server verifies:
Verify(client_signature, R, public_key_from_authorized_keys) → true/false
步骤 5 是你之前失败、之后成功的地方：
BEFORE (Mac had different key):
Client signs with: key_B_private
Server checks against: key_A_public (only key in authorized_keys)
Verify(key_B_sig, R, key_A_pub) → ❌ MATH DOESN'T CHECK OUT
AFTER (Mac had same key as server):
Client signs with: key_A_private
Server checks against: key_A_public (same key in authorized_keys)
Verify(key_A_sig, R, key_A_pub) → ✅ PERFECT MATCH
Gitea 中的 authorized_keys 样子
# Inside the Gitea container at /data/git/.ssh/authorized_keys:
# gitea public key
command="/usr/local/bin/gitea --config=/data/gitea/conf/app.ini serv key-1",
no-port-forwarding,
no-X11-forwarding,
no-agent-forwarding,
no-pty,
no-user-rc,
restrict
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMTRoCy6Uo67vc1CJSAAnZQCHftNB5kbq9jf8ZsEsa+o user-1
关键细节：
| Part | Purpose |
|---|---|
command="...gitea serv key-1" |
Forces the connection into Gitea’s handler (not a shell) |
no-port-forwarding etc. |
Security restrictions — you can only use Git, not tunnel |
restrict |
Master switch for all the no-* options |
ssh-ed25519 AAAA... |
The actual public key to match against |
key-1 |
Gitea’s internal key ID |
为什么 SSH 密钥优于密码
Password auth:
Client sends password over encrypted channel
Server hashes it, compares to stored hash
Problem: password can be brute-forced, phished, reused
Key auth:
Client NEVER sends the private key
Client proves it HAS the key by solving a mathematical challenge
Even if someone captures the entire session, they learn nothing about the private key
The private key never leaves your machine (unless you copy it, like you did 😉)
你的具体设置
┌─────────────────────────────────────────────────────┐
│ Gitea Container (192.168.1.36) │
│ ┌─────────────────────────────────────────────┐ │
│ │ /data/git/.ssh/authorized_keys │ │
│ │ ┌─────────────────────────────────────┐ │ │
│ │ │ ssh-ed25519 AAAA...sa+o user-1 │ │ │
│ │ │ ↑ │ │ │
│ │ │ Public key trusted by Gitea │ │ │
│ │ └─────────────────────────────────────┘ │ │
│ └─────────────────────────────────────────────┘ │
│ ▲ ▲ │
│ │ matches │ matches │
│ ┌──────┴──────┐ ┌──────┴──────┐ │
│ │ Server │ │ Mac │ │
│ │ id_ed25519 │ │ id_ed25519 │ (copied) │
│ │ (private) │ │ (private) │ │
│ │ AAAA...sa+o │ │ AAAA...sa+o │ │
│ └─────────────┘ └─────────────┘ │
└─────────────────────────────────────────────────────┘
Both machines have the SAME private key.
Gitea trusts that key.
So both machines can authenticate. ✅
你的修复核心：你让两台机器共享 Gitea 已信任的一个身份。 🦞