How to verify PEM format certificate in Java

Question

I have PEM format file, How can verify the signature in Java, as I followed http://download.oracle.com/javase/tutorial/security/apisign/versig.html but found that Java doesn

Answer 1

You can read a certificate in a PEM file using BouncyCastle's PEMReader. If the content is an X.509 certificate, you should get an instance of X509Certificate and verify it as you want from there.

EDIT: Here is what the code should look like (not tried):

// The key with which you want to verify the cert.
// This is probably a CA certificate's public key.
PublicKey publicKey = ...;

PEMReader reader = new PEMReader(new FileReader("/path/to/file.pem"));
Object pemObject = reader.readObject();
if (pemObject instanceof X509Certificate) {
    X509Certificate cert = (X509Certificate)pemObject;
    cert.checkValidity(); // to check it's valid in time
    cert.verify(publicKey); // verify the sig. using the issuer's public key
}

(Of course, as with any I/O operations, you'll need to close the reader perhaps with try/finally.)

Note that checkValidity and verify don't return anything: instead, they throw exceptions if when they fail.