PEM Private Key Block Regex for Java

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching pem private key block, 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

// PEM Private Key Block
// ReDoS-safe | RegexVault — Security > Certificates & PKI

import java.util.regex.Pattern;

public class PemPrivateKeyBlockValidator {
    private static final Pattern PATTERN =
        Pattern.compile("-----BEGIN (?:RSA |EC |DSA |OPENSSH )?PRIVATE KEY-----[\\r\\n]+(?:[A-Za-z0-9+/=\\r\\n]{1,80}[\\r\\n]+)*-----END (?:RSA |EC |DSA |OPENSSH )?PRIVATE KEY-----");

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

    // Example
    public static void main(String[] args) {
        System.out.println(validate("-----BEGIN PRIVATE KEY-----
MIIEvAIBADANBgk=
-----END PRIVATE KEY-----")); // 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

CRITICAL detection pattern. Key type headers: 'PRIVATE KEY' (PKCS#8, unencrypted), 'RSA PRIVATE KEY' (PKCS#1, legacy OpenSSL), 'EC PRIVATE KEY' (SEC1), 'OPENSSH PRIVATE KEY' (SSH private keys). Encrypted private keys have 'ENCRYPTED PRIVATE KEY' header.