eac77ef7b4
Collection of operational skills for VaultMesh infrastructure including: - backup-sovereign: Backup and recovery operations - btc-anchor: Bitcoin anchoring - cloudflare-tunnel-manager: Cloudflare tunnel management - container-registry: Container registry operations - disaster-recovery: Disaster recovery procedures - dns-sovereign: DNS management - eth-anchor: Ethereum anchoring - gitea-bootstrap: Gitea setup and configuration - hetzner-bootstrap: Hetzner server provisioning - merkle-forest: Merkle tree operations - node-hardening: Node security hardening - operator-bootstrap: Operator initialization - proof-verifier: Cryptographic proof verification - rfc3161-anchor: RFC3161 timestamping - secrets-vault: Secrets management 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
116 lines
3.5 KiB
Markdown
116 lines
3.5 KiB
Markdown
# SSH Cipher Recommendations
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## Overview
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This document explains the SSH cipher, MAC, and key exchange algorithm choices used in the node-hardening skill's sshd_config template.
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## Current Recommendations (2024)
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### Ciphers (Encryption)
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| Cipher | Recommendation | Notes |
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|--------|----------------|-------|
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| chacha20-poly1305@openssh.com | **Recommended** | Modern, fast, constant-time |
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| aes256-gcm@openssh.com | **Recommended** | Strong, hardware-accelerated |
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| aes128-gcm@openssh.com | **Acceptable** | Fast, hardware-accelerated |
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| aes256-ctr | Acceptable | Legacy compatibility |
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| aes128-ctr | Acceptable | Legacy compatibility |
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| 3des-cbc | **Avoid** | Deprecated, slow |
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| arcfour | **Avoid** | Broken |
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### MACs (Message Authentication)
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| MAC | Recommendation | Notes |
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|-----|----------------|-------|
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| hmac-sha2-512-etm@openssh.com | **Recommended** | Encrypt-then-MAC, strongest |
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| hmac-sha2-256-etm@openssh.com | **Recommended** | Encrypt-then-MAC |
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| umac-128-etm@openssh.com | Acceptable | Fast, Encrypt-then-MAC |
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| hmac-sha2-512 | Acceptable | No ETM |
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| hmac-sha2-256 | Acceptable | No ETM |
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| hmac-sha1 | **Avoid** | Deprecated |
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| hmac-md5 | **Avoid** | Broken |
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### Key Exchange (KEX)
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| KEX Algorithm | Recommendation | Notes |
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|---------------|----------------|-------|
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| curve25519-sha256 | **Recommended** | Modern, safe curve |
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| curve25519-sha256@libssh.org | **Recommended** | Same, legacy name |
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| diffie-hellman-group16-sha512 | Acceptable | 4096-bit DH |
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| diffie-hellman-group18-sha512 | Acceptable | 8192-bit DH |
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| diffie-hellman-group14-sha256 | Acceptable | 2048-bit DH |
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| diffie-hellman-group1-sha1 | **Avoid** | Weak, deprecated |
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| diffie-hellman-group-exchange-sha1 | **Avoid** | SHA1 deprecated |
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### Host Key Algorithms
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| Algorithm | Recommendation | Notes |
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|-----------|----------------|-------|
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| ssh-ed25519 | **Recommended** | Modern, compact |
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| rsa-sha2-512 | **Recommended** | RSA with SHA2 |
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| rsa-sha2-256 | **Recommended** | RSA with SHA2 |
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| ecdsa-sha2-nistp256 | Acceptable | NIST curve concerns |
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| ssh-rsa | **Avoid** | SHA1 deprecated |
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| ssh-dss | **Avoid** | Weak |
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## Template Configuration
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The sshd_config template uses:
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```
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# Strong ciphers only
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Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com
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# Encrypt-then-MAC only
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MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com
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# Modern key exchange
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KexAlgorithms curve25519-sha256,curve25519-sha256@libssh.org
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# Preferred host key algorithms
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HostKeyAlgorithms ssh-ed25519,rsa-sha2-512,rsa-sha2-256
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```
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## Compatibility Notes
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### Minimum Client Versions
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These settings require:
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- OpenSSH 7.3+ (released 2016)
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- PuTTY 0.68+ (released 2017)
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### Legacy Client Support
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If you need to support older clients, add fallback options:
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```
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Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes256-ctr
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MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-256
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KexAlgorithms curve25519-sha256,diffie-hellman-group16-sha512
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```
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## Testing Configuration
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After applying changes, test with:
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```bash
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# Check server offerings
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ssh -Q cipher
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ssh -Q mac
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ssh -Q kex
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# Test connection with verbose output
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ssh -vvv user@server
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# Audit with ssh-audit (recommended)
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pip install ssh-audit
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ssh-audit localhost
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```
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## References
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- [Mozilla SSH Guidelines](https://infosec.mozilla.org/guidelines/openssh)
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- [ssh-audit](https://github.com/jtesta/ssh-audit)
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- [Secure Secure Shell](https://stribika.github.io/2015/01/04/secure-secure-shell.html)
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- [OpenSSH Manual](https://man.openbsd.org/sshd_config)
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