Java Programmatically read informations from a Key

问题:

I'm tryin to build a certificate/key management tool, but i don't understand how to obtain md5 fingerprint of a certificate/key.

For example if i use keytool command on a keystore i obtain the

Keystore type: JKS
Keystore provider: SUN

Your keystore contains 1 entry

Alias name: myname
Creation date: 21-Aug-2011
Entry type: PrivateKeyEntry
Certificate chain length: 1
Certificate[1]:
Owner: CN=bla bla, L=bla, ST=bla
Issuer: CN=bla bla, L=bla, ST=bla
Serial number: 123w3qa
Valid from: Sun Aug 21 00:12:31 CEST 2011 until: Mon Jul 28 00:12:31 CEST 2110
Certificate fingerprints:
         MD5:  1A:DE:60:21:DE:B1:BF:C3:D1:AD:11:F1:21:22:D7:9E
         SHA1: 72:3A:D9:2E:1A:DE:60:21:DE:B1:BF:C3:D1:AD:11:F1:21:22:D7:9E
         Signature algorithm name: SHA256withRSA
         Version: 3

Extensions:

#1: ObjectId: 2.5.29.14 Criticality=false
SubjectKeyIdentifier [
KeyIdentifier [
0000: AA EA FA FE 34 DA 6E C6   FC 8B 6C DE S9 21 S9 S4  ......^...l.I!.D
0010: S3 33 29 SD                                        .S..
]
]

*******************************************
*******************************************

Now i want to obtain via java the following informations: 1. MD5 fingerprint 2. KeyIdentifier

I obtained some informations using X500Certificate object and X500Principal(for example date from and to, owner, issuer, alias name), but i didn't found where i can obtain other informations. Can someone help me?

回答1:

If you check the source code for keytool you can see the following:

 2830       getCertFingerPrint("MD5", cert),

which calls:

 3167       /**
 3168        * Gets the requested finger print of the certificate.
 3169        */
 3170       private String getCertFingerPrint(String mdAlg, Certificate cert)
 3171           throws Exception
 3172       {
 3173           byte[] encCertInfo = cert.getEncoded();
 3174           MessageDigest md = MessageDigest.getInstance(mdAlg);
 3175           byte[] digest = md.digest(encCertInfo);
 3176           return toHexString(digest);
 3177       }

回答2:

You can try the following code -

  // Load the JDK's cacerts keystore file
            String filename = System.getProperty("java.home") + "/lib/security/cacerts".replace('/', File.separatorChar);

            FileInputStream is = new FileInputStream(filename);
            KeyStore keystore = KeyStore.getInstance(KeyStore.getDefaultType());
            String password = "changeit";
            keystore.load(is, password.toCharArray());

            // This class retrieves the most-trusted CAs from the keystore
            PKIXParameters params = new PKIXParameters(keystore);

            // Get the set of trust anchors, which contain the most-trusted CA certificates
            Iterator it = params.getTrustAnchors().iterator();
            while( it.hasNext() ) {
                TrustAnchor ta = (TrustAnchor)it.next();
                // Get certificate
                X509Certificate cert = ta.getTrustedCert();
                System.out.println(cert);
            }

回答3:

I went through keytool source code and came up with this (expanded version of DNA's answer):

String filename = "path to your keystore";
String keyPassword = "your key password";
String keyAlias = "your key alias";

FileInputStream is = new FileInputStream(filename);

KeyStore keystore = KeyStore.getInstance(KeyStore.getDefaultType());

keystore.load(is, keyPassword.toCharArray());

/* Gets the requested finger print of the certificate. */
X509Certificate cert = keystore.getCertificate(keyAlias);
byte[] encCertInfo = cert.getEncoded();
MessageDigest md = MessageDigest.getInstance("MD5");
byte[] digest = md.digest(encCertInfo);

/* Converts a byte array to hex string */
StringBuffer buf = new StringBuffer();
int len = digest.length;
for (int i = 0; i < len; i++) {
    /* Converts a byte to hex digit and writes to the supplied buffer */
    char[] hexChars = [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' ];
    int high = ((digest[i] & 0xf0) >> 4);
    int low = (digest[i] & 0x0f);
    buf.append(hexChars[high]);
    buf.append(hexChars[low]);

    if (i < len-1) {
        buf.append(":");
    }
}

String your_md5_fingerprint = buf.toString();

I tested it on Android, works like a charm.