How to retrieve/compute an X509 certificate's

Question

I have a java client that is calling a web service operation which takes a certificate "thumbprint" as a parameter. I believe the thumbprint is some kind of SHA1 hash, in hexadecimal string format, of the cert's public key, but I'm not sure.

The .NET framework seems to include a simple way to get this value (X509Certificate2.Thumbprint property). Viewing a .cer file's properties in Windows also displays the thumbprint, which looks like:

a6 9c fd b0 58 0d a4 ee ae 9a 47 75 24 c3 0b 9f 5d b6 1c 77

My question is therefore: Does anybody know how to retrieve or compute this thumbprint string within Java, if I have an instance of a java.security.cert.X509Certificate?

Answer 1

One-liner using Google's Guava

String sha256AsHex = Hashing.sha256().hashBytes(x509Certificate.getEncoded()).toString();

Answer 2

Using Apache Commons Codec you can do:

DigestUtils.sha1Hex(cert.getEncoded())

Answer 3

You can generate the thumbprint by using the openssl command, so example if you have the pem format of the certificate in a file (file.txt)

then:

cat file.txt | openssl x509 -sha1 -fingerprint - this would generate the same thumbprint

Answer 4

Short example without using any libraries.

object MessageDigestUtil {

    private val hexCode = "0123456789ABCDEF".toCharArray()

    fun sha1(input: ByteArray): ByteArray {
        return digest(input,"SHA-1")
    }

    @Throws(NoSuchAlgorithmException::class)
    fun getFingerprint(publicKey: PublicKey): String? {
        return printHexBinary(sha1(publicKey.encoded))
    }

    private fun printHexBinary(data: ByteArray): String {
        val r = StringBuilder(data.size * 2)
        for (b in data) {
            r.append(hexCode[b.toInt() shr 4 and 0xF])
            r.append(hexCode[(b and 0xF).toInt()])
        }
        return r.toString()
    }

    @Throws(NoSuchAlgorithmException::class)
    private fun digest(input: ByteArray, algorithm: String): ByteArray {
        val digest = MessageDigest.getInstance(algorithm)
        digest.update(input)
        return digest.digest()
    }
}

Answer 5

The SHA-1 hash of the DER encoding of the certificate is what .NET is getting with X509Certificate2.Thumbprint.

As noted on the remarks on MSDN:

The thumbprint is dynamically generated using the SHA1 algorithm and does not physically exist in the certificate. Since the thumbprint is a unique value for the certificate, it is commonly used to find a particular certificate in a certificate store.

Java's standard library doesn't provide the thumbprint directly, but you can get it like this:

DatatypeConverter.printHexBinary(
        MessageDigest.getInstance("SHA-1").digest(
                cert.getEncoded())).toLowerCase();

Here's a full worked example using a conveniently accessible PEM file:

1. Create stackoverflow.crt.pem:

   -----BEGIN CERTIFICATE-----
   MIIHHjCCBgagAwIBAgIQDhG71w1UtxDQxvVAtrUspDANBgkqhkiG9w0BAQsFADBw
   MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3
   d3cuZGlnaWNlcnQuY29tMS8wLQYDVQQDEyZEaWdpQ2VydCBTSEEyIEhpZ2ggQXNz
   dXJhbmNlIFNlcnZlciBDQTAeFw0xNjA1MjEwMDAwMDBaFw0xOTA4MTQxMjAwMDBa
   MGoxCzAJBgNVBAYTAlVTMQswCQYDVQQIEwJOWTERMA8GA1UEBxMITmV3IFlvcmsx
   HTAbBgNVBAoTFFN0YWNrIEV4Y2hhbmdlLCBJbmMuMRwwGgYDVQQDDBMqLnN0YWNr
   ZXhjaGFuZ2UuY29tMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAr0YD
   zscT5i6T2FaRsTGNCiLB8OtPXu8N9iAyuaROh/nS0kRRsN8wUMk1TmgZhPuYM6oF
   S377V8W2LqhLBMrPXi7lnhvKt2DFWCyw38RrDbEsM5dzVGErmhux3F0QqcTI92zj
   VW61DmE7NSQLiR4yonVpTpdAaO4jSPJxn8d+4p1sIlU2JGSk8LZSWFqaROc7KtXt
   lWP4HahNRZtdwvL5dIEGGNWx+7B+XVAfY1ygc/UisldkA+a3D2+3WAtXgFZRZZ/1
   CWFjKWJNMAI6ZBAtlbgSNgRYxdcdleIhPLCzkzWysfltfiBmsmgz6VCoFR4KgJo8
   Gd3MeTWojBthM10SLwIDAQABo4IDuDCCA7QwHwYDVR0jBBgwFoAUUWj/kK8CB3U8
   zNllZGKiErhZcjswHQYDVR0OBBYEFFrBQmPCYhOznZSEqjIeF8tto4Z7MIIB6AYD
   VR0RBIIB3zCCAduCEyouc3RhY2tleGNoYW5nZS5jb22CEXN0YWNrb3ZlcmZsb3cu
   Y29tghMqLnN0YWNrb3ZlcmZsb3cuY29tgg1zdGFja2F1dGguY29tggtzc3RhdGlj
   Lm5ldIINKi5zc3RhdGljLm5ldIIPc2VydmVyZmF1bHQuY29tghEqLnNlcnZlcmZh
   dWx0LmNvbYINc3VwZXJ1c2VyLmNvbYIPKi5zdXBlcnVzZXIuY29tgg1zdGFja2Fw
   cHMuY29tghRvcGVuaWQuc3RhY2thdXRoLmNvbYIRc3RhY2tleGNoYW5nZS5jb22C
   GCoubWV0YS5zdGFja2V4Y2hhbmdlLmNvbYIWbWV0YS5zdGFja2V4Y2hhbmdlLmNv
   bYIQbWF0aG92ZXJmbG93Lm5ldIISKi5tYXRob3ZlcmZsb3cubmV0gg1hc2t1YnVu
   dHUuY29tgg8qLmFza3VidW50dS5jb22CEXN0YWNrc25pcHBldHMubmV0ghIqLmJs
   b2dvdmVyZmxvdy5jb22CEGJsb2dvdmVyZmxvdy5jb22CGCoubWV0YS5zdGFja292
   ZXJmbG93LmNvbYIVKi5zdGFja292ZXJmbG93LmVtYWlsghNzdGFja292ZXJmbG93
   LmVtYWlsMA4GA1UdDwEB/wQEAwIFoDAdBgNVHSUEFjAUBggrBgEFBQcDAQYIKwYB
   BQUHAwIwdQYDVR0fBG4wbDA0oDKgMIYuaHR0cDovL2NybDMuZGlnaWNlcnQuY29t
   L3NoYTItaGEtc2VydmVyLWc1LmNybDA0oDKgMIYuaHR0cDovL2NybDQuZGlnaWNl
   cnQuY29tL3NoYTItaGEtc2VydmVyLWc1LmNybDBMBgNVHSAERTBDMDcGCWCGSAGG
   /WwBATAqMCgGCCsGAQUFBwIBFhxodHRwczovL3d3dy5kaWdpY2VydC5jb20vQ1BT
   MAgGBmeBDAECAjCBgwYIKwYBBQUHAQEEdzB1MCQGCCsGAQUFBzABhhhodHRwOi8v
   b2NzcC5kaWdpY2VydC5jb20wTQYIKwYBBQUHMAKGQWh0dHA6Ly9jYWNlcnRzLmRp
   Z2ljZXJ0LmNvbS9EaWdpQ2VydFNIQTJIaWdoQXNzdXJhbmNlU2VydmVyQ0EuY3J0
   MAwGA1UdEwEB/wQCMAAwDQYJKoZIhvcNAQELBQADggEBAAzJAMGSdKoX1frdqNlN
   iXu8Gcbsm/DxWMXpcTXlZn8s+/qQQoc+/3o0CK3C8/j9n5DmsYa88P6Ntt5ysDs+
   b0ynXFva4CAEyKaoPM4SIpOjwfWBRSUOqAIkQO2/LhKBwT/EnpaIHIKGnI0UdXLQ
   oDfkMDg6mgJsEBsKdKF5EfEX7iU3NO5xVJPJE8/R0btLAdYwxB9S6fSpCXGe2HqQ
   D101O/7/4MWNdFSbfdDSFcn5oEm+idimrqiNrF5knmuJy4qPBkL7thNuGK6rvYCF
   ZJM03ZEZhkQmn2jG/7LgjfwZmvfcITeADCpylf88bL+lf+vxe6cCl9CyqWgBDpsI
   xpE=
   -----END CERTIFICATE-----
   

2. Create X509.java:

   import javax.xml.bind.DatatypeConverter;
   import java.io.FileInputStream;
   import java.io.FileNotFoundException;
   import java.security.MessageDigest;
   import java.security.NoSuchAlgorithmException;
   import java.security.cert.CertificateEncodingException;
   import java.security.cert.CertificateException;
   import java.security.cert.CertificateFactory;
   import java.security.cert.X509Certificate;
   
   public final class X509 {
       public static void main(String[] args)
               throws FileNotFoundException, CertificateException, NoSuchAlgorithmException {
           FileInputStream is = new FileInputStream(args[0]);
           CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
           X509Certificate cert = (X509Certificate) certificateFactory.generateCertificate(is);
           String thumbprint = getThumbprint(cert);
           System.out.println(thumbprint);
       }
   
       private static String getThumbprint(X509Certificate cert)
               throws NoSuchAlgorithmException, CertificateEncodingException {
           MessageDigest md = MessageDigest.getInstance("SHA-1");
           byte[] der = cert.getEncoded();
           md.update(der);
           byte[] digest = md.digest();
           String digestHex = DatatypeConverter.printHexBinary(digest);
           return digestHex.toLowerCase();
       }
   }
   

3. Compile the program with Java 8:

   javac X509.java
   

   Or Java 9 - due to modular JDK/JPMS - DataTypeConverter is not in java.base, but java.xml.bind, so you need to explicitly depend on it during your build:

   javac --add-modules java.xml.bind X509.java
   

   Otherwise, on Java 9, you get this when you try to build it:

   X509.java:3: error: package javax.xml.bind is not visible
           import javax.xml.bind.DatatypeConverter;
           ^
           (package javax.xml.bind is declared in module java.xml.bind, which is not in the module graph)
           1 error
   

4. Run it with Java 8:

   java X509 stackoverflow.crt.pem
   

   In Java 9 - due to modular JDK/JPMS - DataTypeConverter is not in java.base, but java.xml.bind, so you need to explicitly depend on it when running your program:

   java --add-modules java.xml.bind X509 stackoverflow.crt.pem
   

   Otherwise, on Java 9, you get this when you try to run it:

   Exception in thread "main" java.lang.NoClassDefFoundError: javax/xml/bind/DatatypeConverter
       at X509.getThumbPrint(X509.java:29)
       at X509.main(X509.java:19)
       Caused by: java.lang.ClassNotFoundException: javax.xml.bind.DatatypeConverter
       at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
       at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
       at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496)
       ... 2 more
   

5. Get the expected output:

   47adb03649a2eb18f63ffa29790818349a99cab7
   

Answer 6

Here's a simpler way:

using System.Security.Cryptography.X509Certificates;    

X509Certificate2 xcert = new X509Certificate2("C:\some_cert.cerpub");
string certSubject = xcert.Subject;
string certThumbprint =  xcert.Thumbprint;