SSH Public Key Regex

Developer

Regular expression

/^ssh-(?:rsa|ed25519)\s+[A-Za-z0-9+/=]+(?:\s+.*)?$/

Pattern breakdown

Part	Meaning
`Anchor or context`	Use anchors when you need whole-string validation.
`Main token`	The core token sequence describes the accepted text shape.
`Character class`	Character classes limit which characters are valid.
`Quantifier`	Quantifiers control how many characters or groups are accepted.
`Flags`	Use language-specific flags such as i, m, or u only when needed.

Should match

ssh-ed25519 AAAAC3Nza user
ssh-ed25519AAAAC3Nzauser

Should not match

PRIVATE KEY
not matching sample
ssh-ed25519 AAAAC3Nza user invalid
PRIVATE KEYssh-ed25519 AAAAC3Nza user

Test cases

Input	Expected	Why it matters
`ssh-ed25519 AAAAC3Nza user`	Match	Representative valid input for this pattern.
`ssh-ed25519AAAAC3Nzauser`	Match	Representative valid input for this pattern.
`PRIVATE KEY`	No match	Common invalid or boundary input.
`(empty string)`	No match	Common invalid or boundary input.
`not matching sample`	No match	Common invalid or boundary input.
`ssh-ed25519 AAAAC3Nza user invalid`	No match	Common invalid or boundary input.
`PRIVATE KEYssh-ed25519 AAAAC3Nza user`	No match	Common invalid or boundary input.

JavaScript

const re = /^ssh-(?:rsa|ed25519)\s+[A-Za-z0-9+/=]+(?:\s+.*)?$/;
re.test(input);

Python

import re
bool(re.search(r"^ssh-(?:rsa|ed25519)\s+[A-Za-z0-9+/=]+(?:\s+.*)?$", text))

PHP

$ok = preg_match('/^ssh-(?:rsa|ed25519)\s+[A-Za-z0-9+\/=]+(?:\s+.*)?$/', $value) === 1;

Java

Pattern pattern = Pattern.compile("^ssh-(?:rsa|ed25519)\\s+[A-Za-z0-9+/=]+(?:\\s+.*)?$");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`^ssh-(?:rsa|ed25519)\s+[A-Za-z0-9+/=]+(?:\s+.*)?$`)
ok := re.MatchString(value)

Notes and production use

SSH Public Key regex is useful as a practical starting point. Test it against your real input, avoid using it as the only security control, and prefer a parser when the format has complex grammar.

Performance tip: avoid running complex regular expressions repeatedly on very large untrusted strings without limits. Prefer anchored validation patterns, cap input length before matching, and use a parser when the target format has nested grammar.

SSH Public Key