A little utility to calculate an md5 sum of an APK's signature in a form that matches the client code

getsig/getsig.java

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+import java.io.IOException;
+import java.io.InputStream;
+import java.math.BigInteger;
+import java.security.Signature;
+import java.security.cert.*;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Enumeration;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+
+public class getsig {
+ 
+    public static void main(String[] args) {
+
+        if (args.length != 1) {
+            System.out.println("Specify the APK file to get the signature from!");
+            System.exit(1);
+        }
+ 
+        String apkPath = args[0];
+ 
+        try {
+
+            JarFile apk = new JarFile(apkPath);
+            java.security.cert.Certificate[] certs = null;
+ 
+            Enumeration entries = apk.entries();
+            while (entries.hasMoreElements()) {
+                JarEntry je = (JarEntry) entries.nextElement();
+                if (!je.isDirectory() && !je.getName().startsWith("META-INF/")) {
+                    // Just need to read the stream (discarding the data) to get
+                    // it to process the certificate...
+                    byte[] b = new byte[4096];
+                    InputStream is = apk.getInputStream(je);
+                    while (is.read(b, 0, b.length) != -1);
+                    is.close();
+                    certs = je.getCertificates();
+                    if(certs != null)
+                        break;
+                }
+            }
+            apk.close();
+
+            if (certs == null) {
+                System.out.println("Not signed");
+                System.exit(1);
+            }
+            if (certs.length != 1) {
+                System.out.println("One signature expected");
+                System.exit(1);
+            }
+
+            // Get the signature in the same form that is returned by
+            // android.content.pm.Signature.toCharsString() (but in the
+            // form of a byte array so we can pass it to the MD5 function)...
+            byte[] sig = certs[0].getEncoded();
+            byte[] csig = new byte[sig.length * 2];
+            for (int j=0; j<sig.length; j++) {
+                byte v = sig[j];
+                int d = (v>>4)&0xf;
+                csig[j*2] = (byte)(d >= 10 ? ('a' + d - 10) : ('0' + d));
+                d = v&0xf;
+                csig[j*2+1] = (byte)(d >= 10 ? ('a' + d - 10) : ('0' + d));
+            }
+
+            // Get the MD5 sum of that...
+            MessageDigest md;
+            md = MessageDigest.getInstance("MD5");
+            byte[] md5sum = new byte[32];
+            md.update(csig);
+            md5sum = md.digest();
+            BigInteger bigInt = new BigInteger(1, md5sum);
+            String md5hash = bigInt.toString(16);
+            while (md5hash.length() < 32)
+                md5hash = "0" + md5hash;
+            System.out.println("Result:" + md5hash);
+            System.exit(0);
+
+        } catch (Exception e) {
+            System.out.println("Exception:" + e);
+            System.exit(1);
+        }
+    }
+
+}
+
+

getsig/make.sh

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+#!/bin/sh
+javac getsig.java

getsig/run.sh

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+#!/bin/sh
+java getsig $1 $2 $3