X509 serial number using java

Question

I need to get some data from X509 certificate.

If I open a certificate file in windows, its showing its serial number in this format.

ex. 39 65 70 eb d8 9f 28 20 4e c2 a0 6b 98 48 31 0d 

The same data I am trying to obtain using java. After get it loaded, I use

x509.getSerialNumber();
and result is : 76292708057987193002565060032465481997

So what is the difference between both of these ? I want the result as upper one.

Answer 1

Windows shows the hexadecimal representation of the serial number, whereas Java returns a BigInteger result from X509Certificate.getSerialNumber().

To display the BigInteger as a hexadecimal value, just call toString(16).

BigInteger bi = new BigInteger("76292708057987193002565060032465481997");
System.out.println(bi.toString(16));

Will output:

396570ebd89f28204ec2a06b9848310d

Answer 2

The first one is hexadecimal value of the certificate. The other one is decimal.

Now it depends on how you convert the initial certificate bytearray for printing it out.

Lets say this is your certificate:

byte[] cert = { (byte) 0xFD, (byte) 0xB1, (byte) 0xDD, ..., (byte) 0x00 };
BigInteger certVal = new BigInteger(cert);  
System.out.println("And result is  (hex): " + certVal.toString(16));