Java

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. Java

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean success = false;

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Let's say you have a file containing the 32-bytes of a SHA256 hash,
    // and a file that is an RSA signature of those 32 bytes.
    // Here's how you verify using the RSA public key found in a PEM.

    CkPublicKey pubKey = new CkPublicKey();
    success = pubKey.LoadFromFile("rsaPubKey.pem");
    if (success == false) {
        System.out.println(pubKey.lastErrorText());
        return;
        }

    CkRsa rsa = new CkRsa();

    // Get the public key.
    success = rsa.UsePublicKey(pubKey);
    if (success == false) {
        System.out.println(rsa.lastErrorText());
        return;
        }

    // Get the 32-byte SHA256 hash.
    CkBinData bdHash = new CkBinData();
    success = bdHash.LoadFile("myHash.sha256");
    if (success == false) {
        System.out.println("Failed to load SHA256 hash.");
        return;
        }

    // Get the RSA signature to be validated.
    CkBinData bdSig = new CkBinData();
    success = bdSig.LoadFile("mySig.sig");
    if (success == false) {
        System.out.println("Failed to load RSA signature.");
        return;
        }

    // Verify the signature against the SHA256 hash.
    String enc = "base64";
    rsa.put_EncodingMode(enc);
    success = rsa.VerifyHashENC(bdHash.getEncoded(enc),"sha256",bdSig.getEncoded(enc));
    if (success == false) {
        System.out.println(rsa.lastErrorText());
        return;
        }

    System.out.println("Signature validated.");
  }
}