Argon2 Hash (Argon2i, Argon2d, Argon2id) Regex for Java

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching argon2 hash (argon2i, argon2d, argon2id), ported and verified for Java. 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 Java project — whether you're validating in a Spring Boot controller, a Jakarta EE service, or a standalone utility class.

Java Implementation

// Argon2 Hash (Argon2i, Argon2d, Argon2id)
// ReDoS-safe | RegexVault — Security > Password Formats

import java.util.regex.Pattern;

public class Argon2HashArgon2iArgon2dArgon2idValidator {
    private static final Pattern PATTERN =
        Pattern.compile("^\\$(argon2(?:i|d|id))\\$v=19\\$m=([0-9]+),t=([0-9]+),p=([0-9]+)(?:,keyid=[A-Za-z0-9+/]{0,11}(?:=*))?(?:,data=[A-Za-z0-9+/]{0,43}(?:=*))?\\$([A-Za-z0-9+/]{11,64}(?:={0,2}))\\$([A-Za-z0-9+/]{16,86}(?:={0,2}))$");

    public static boolean validate(String input) {
        return PATTERN.matcher(input).matches();
    }

    // Example
    public static void main(String[] args) {
        System.out.println(validate("$argon2id$v=19$m=65536,t=2,p=1$c29tZXNhbHQ$RdescudvJCsgt3ub+b+dWRWJTmaaJObG")); // true
    }
}

Test Cases

When to use this pattern

This pattern is drawn from the Security > Password Formats category and carries a ReDoS-safe certification. That matters for Java developers because critical in Java applications since the JVM regex engine uses backtracking and is susceptible to ReDoS without careful pattern design. 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

Argon2id is the recommended variant (memory-hard + side-channel resistant). Parameters: m=memory in KiB, t=time iterations, p=parallelism. OWASP recommends argon2id with m=19456 (19 MiB), t=2, p=1 as minimum. v=19 is the current version.