Java

Verfies an RSA Signature

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Verifies an RSA signature against the original data. 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;

    //  The following data was signed by the following example:
    //  RSA Sign using a Private Key on a USB Token or Smartcard
    CkBinData bd = new CkBinData();
    int i;
    for (i = 0; i <= 100; i++) {
        bd.AppendEncoded("000102030405060708090A0B0C0D0E0F","hex");
        }

    //  Load the signature
    CkBinData bdSig = new CkBinData();
    success = bdSig.LoadFile("rsaSignatures/test1.sig");
    if (success == false) {
        System.out.println("Failed to load the RSA signature");
        return;
        }

    //  Get the public key to be used for signature verification.
    CkPublicKey pubKey = new CkPublicKey();
    success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem");
    if (success == false) {
        System.out.println(pubKey.lastErrorText());
        return;
        }

    CkRsa rsa = new CkRsa();
    success = rsa.UsePublicKey(pubKey);
    if (success == false) {
        System.out.println(rsa.lastErrorText());
        return;
        }

    //  Verify the hash of the data against the signature.
    //  We pass in the original data.  Internally, the hash is generated
    //  and used to validate the signature.
    //  Validating the RSA signature means two things:  
    //  (1) the original data is exactly what was signed, and 
    //  (2) it was signed by the owner of the RSA private key.
    success = rsa.VerifyBd(bd,"sha256",bdSig);

    if (success == false) {
        System.out.println(rsa.lastErrorText());
        System.out.println("Signature invalid.");
        }
    else {
        System.out.println("Signature valid.");
        }
  }
}