Android: How to get SHA1/MD5 fingerprint programmatically?

Question

I'm trying to implement a way to communicate with my backend-server and be sure that my backend only answers, if it's my application which is calling.

So my idea is, that i just send the SHA1/MD5 fingerprint with the HTTPS POST request and verify it on the backend server. If the fingerprint matches, the server will answer.

So my first question is: How do I get these programmatically at runtime? Is it even possible?

The second question is: Can it be that easy? Or do i really have to set up an OAuth-Server (or use the google-api)?...The thing is, that I think that OAuth is a bit overkill for my use case and I don't want to handle the expiration/refresh-token stuff.

Answer 1

I have complemented the solution, proposed by Zulqumain Jutt, to be able to get the the result in the common form, like:

KeyHelper: MD5 56:ff:2f:1f:55:fa:79:3b:2c:ba:c9:7d:e3:b1:d2:af

public class KeyHelper {

    /**
     * @param key string like: SHA1, SHA256, MD5.
     */
    @SuppressLint("PackageManagerGetSignatures") // test purpose
    static void get(Context context, String key) {
        try {
            final PackageInfo info = context.getPackageManager()
                    .getPackageInfo(BuildConfig.APPLICATION_ID, PackageManager.GET_SIGNATURES);

            for (Signature signature : info.signatures) {
                final MessageDigest md = MessageDigest.getInstance(key);
                md.update(signature.toByteArray());

                final byte[] digest = md.digest();
                final StringBuilder toRet = new StringBuilder();
                for (int i = 0; i < digest.length; i++) {
                    if (i != 0) toRet.append(":");
                    int b = digest[i] & 0xff;
                    String hex = Integer.toHexString(b);
                    if (hex.length() == 1) toRet.append("0");
                    toRet.append(hex);
                }

                Log.e(KeyHelper.class.getSimpleName(), key + " " + toRet.toString());
            }
        } catch (PackageManager.NameNotFoundException e1) {
            Log.e("name not found", e1.toString());
        } catch (NoSuchAlgorithmException e) {
            Log.e("no such an algorithm", e.toString());
        } catch (Exception e) {
            Log.e("exception", e.toString());
        }
    }
}

Answer 2

You can generate one something like in below example:

private void getKeyHash(String hashStretagy) {
        PackageInfo info;
        try {
            info = getPackageManager().getPackageInfo(BuildConfig.APPLICATION_ID, PackageManager.GET_SIGNATURES);
            for (Signature signature : info.signatures) {
                MessageDigest md;
                md = MessageDigest.getInstance(hashStretagy);
                md.update(signature.toByteArray());
                String something = new String(Base64.encode(md.digest(), 0));
                Log.e("KeyHash  -->>>>>>>>>>>>" , something);

               // Notification.registerGCM(this);
            }
        } catch (PackageManager.NameNotFoundException e1) {
            Log.e("name not found" , e1.toString());
        } catch (NoSuchAlgorithmException e) {
            Log.e("no such an algorithm" , e.toString());
        } catch (Exception e) {
            Log.e("exception" , e.toString());
        }
    }

use Like This:

getKeyHash("SHA");
getKeyHash("MD5");

First Answer: You can use above method it's secure and unique i use it all the time.

Second Answer: You can Use Auth keys but that entirely depends on you , what are you comfortable with

Answer 3

Kotlin Version of Artur's Example key string: "SHA1" or "SHA256" or "MD5".

fun getSig(context: Context, key: String) {
            try {
                val info = context.packageManager.getPackageInfo(
                    BuildConfig.APPLICATION_ID,
                    PackageManager.GET_SIGNATURES
                )
                for (signature in info.signatures) {
                    val md = MessageDigest.getInstance(key)
                    md.update(signature.toByteArray())
                    val digest = md.digest()
                    val toRet = StringBuilder()
                    for (i in digest.indices) {
                        if (i != 0) toRet.append(":")
                        val b = digest[i].toInt() and 0xff
                        val hex = Integer.toHexString(b)
                        if (hex.length == 1) toRet.append("0")
                        toRet.append(hex)
                    }
                    val s = toRet.toString()
                    Log.e("sig", s)
                    
                }
            } catch (e1: PackageManager.NameNotFoundException) {
                Log.e("name not found", e1.toString())
            } catch (e: NoSuchAlgorithmException) {
                Log.e("no such an algorithm", e.toString())
            } catch (e: Exception) {
                Log.e("exception", e.toString())
            }
}

Answer 4

What you're trying to do is impossible. Anything you send to the server as an id can be copied by another application. That's why you have user's with passwords that aren't in the application- the password from an outside source is the only way to be sure the request is valid. And that only proves the user is valid, not that its from your application.