Re: fingerprint of a x.509 certificate

From:
"emrefan" <dksleung@hotmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
28 Aug 2006 03:00:04 -0700
Message-ID:
<1156759204.574336.106170@p79g2000cwp.googlegroups.com>
emrefan wrote:

Babu Kalakrishnan wrote:

emrefan wrote:

My question is this: how to calculate the fingerprint of an x.509
certificate, programmatically in java, that is. I have already tried
this below but the result didn't look like what I
obtained otherwise (running "openssl x509 -noout -fingerprint -sha1 -in

<the cert file>"), so...

MessageDigest md = MessageDigest.getInstance( "SHA1" );
X509Certificate cert = X509Certificate.getInstance( new
FileInputStream( "somecert.crt" ) );
md.update( cert.getEncoded() );
byte[] fp = md.digest();


In my experience the above method of obtaining the fingerprint works
fine, and does give results that match with openssl outputs. How are
you comparing the two ? Here's a utility routine that I use to dump the
fingerprint in a format that matches the output of openssl. Try using
this to dump the byte array "fp" and see if matches.

public static char[] HEX_CHARS =
{'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
public static String dumpHex(byte[] data)
{
    int n = data.length;
    StringBuffer sb = new StringBuffer(n*3-1);
    for (int i=0; i < n; i++)
    {
        if (i > 0) sb.append(':');
        sb.append(HEX_CHARS[(data[i] >> 4) & 0x0F]);
        sb.append(HEX_CHARS[data[i] & 0x0F]);
    }
    return sb.toString();
}


Thanks for Babu for the answer! Yes indeed I had the correct
fingerprint but was misprinting it. How silly! I was using a
left-pad-string function (lPad()) written by a colleague without close
examination. <blush>

public static String bytesToHexString( byte[] paBytes ) {

      StringBuffer sbRsltStr = new StringBuffer( paBytes.length * 3 );

      for (int aryNdx=0; aryNdx < paBytes.length; aryNdx++) {
          sbRsltStr.append(
             Integer.toHexString( lPad( paBytes[ aryNdx ] & 0xFF, 2,
'0' ) ) );
      }

      return sbRsltStr.toString();
}

I think the way I called lPad() caused this definition of lPad() to be
matched:

     public static String lPad( String str, int length, char padChr )


Oops! Another mistake! It must be this below that I wrote (I corrected
the code and lost the bad version and I reconstructed it wrongly).

public static String bytesToHexString( byte[] paBytes ) {

      StringBuffer sbRsltStr = new StringBuffer( paBytes.length * 3 );

      for (int aryNdx=0; aryNdx < paBytes.length; aryNdx++) {
         sbRsltStr.append(
            lPad( Integer.toHexString( paBytes[ aryNdx ] & 0xFF ),
                    2, '0' ) );
      }

      return sbRsltStr.toString();
   }

Anyway, I will have to restudy this thing carefully. Thanks for the
patience.

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