How to obtain public key from a .crt file

Question

Hi
I am new to cryptography Please correct me if my understanding regarding the digital signature is correct and i need help to get the public key.
I have a x.crt file which contains following fields
1) x
2)y
3) Certificate
this certificate contains following fields
certificate version
owner id
name
public key
signature (which is obtained by signing from start of x.crt till public key with private key)
now i need to verify whether the signature for that i need to get the public key & signature from this .crt file. Is it how i need to verify the certificate ?? please help me as I am a newbie in cryptography

Answer 1

Hi all
Thanks for the reply
So to get the public key now i used the following code
byte[] dataPub = new byte[256]; // size of the public key
try {
                    byteArrayInputStream.read(dataPub);
               } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
          BigInteger modulus = new BigInteger(dataPub);
     BigInteger exponent = new BigInteger("65537"); // specified in the document
     RSAPublicKeySpec rpks = new RSAPublicKeySpec(modulus, exponent);
     KeyFactory kf = null;
               try {
                    kf = KeyFactory.getInstance("RSA");
               } catch (NoSuchAlgorithmException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
     try {
                    pk = kf.generatePublic(rpks);
                    System.out.println("Pb Key----------------:"+pk.toString());
               } catch (InvalidKeySpecException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
When I convert the pk.toString I am getting a negative modulus value . Can the modulus value be negative ??
Edited by: 800317 on Oct 8, 2010 5:51 AM