X.509 Certificate Serial Number Regex for Java

What this pattern does

This page provides a well-structured, multi-part regular expression for matching x.509 certificate serial number, 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

// X.509 Certificate Serial Number
// ReDoS-safe | RegexVault — Security > Certificates & PKI

import java.util.regex.Pattern;

public class X509CertificateSerialNumberValidator {
    private static final Pattern PATTERN =
        Pattern.compile("^[0-9a-f]{2}(?::[0-9a-f]{2}){7,19}$");

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

    // Example
    public static void main(String[] args) {
        System.out.println(validate("01:23:45:67:89:ab:cd:ef:01:23:45:67:89:ab:cd:ef")); // 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 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

X.509 serial numbers are 1-20 byte (8-160 bit) integers, typically displayed in colon-separated hex pairs. CA/Browser Forum requires serial numbers be at least 64 bits and generated with at least 64 bits of entropy. Used for certificate revocation lookups (CRL, OCSP).