SSH Public Key Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching ssh public key, ported and verified for Python. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# SSH Public Key
# ReDoS-safe | RegexVault — Security > Certificates & PKI

import re

ssh_public_key_pattern = re.compile(r'^(ssh-rsa|ssh-ed25519|ssh-ecdsa|ecdsa-sha2-nistp256|ecdsa-sha2-nistp384|ecdsa-sha2-nistp521|sk-ssh-ed25519@openssh\.com|sk-ecdsa-sha2-nistp256@openssh\.com)\s+([A-Za-z0-9+/]{20,800}(?:={0,3}))(?:\s+(.+))?$')

def validate_ssh_public_key(value: str) -> bool:
    return bool(ssh_public_key_pattern.fullmatch(value))

# Example
print(validate_ssh_public_key("ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl user@host"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Security > Certificates & PKI category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Capture groups: 1=key type, 2=base64 key material, 3=comment (optional, usually user@host). Supported types: RSA (deprecated), Ed25519 (preferred), ECDSA (nistp256/384/521), SK (FIDO2 hardware key variants). Prefer Ed25519 for new SSH keys.