AppUtil

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.Signature;

import androidx.annotation.NonNull;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class AppUtil {
    
    private final static char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
    private static final String SIGNATURE_DIGEST_ALGORITHM = "SHA1";

    public static String getAppCertSignature(@NonNull Context context, @NonNull String packageName) {
        try {
            PackageManager pm = context.getPackageManager();

            PackageInfo packageInfo = pm.getPackageInfo(packageName, PackageManager.GET_SIGNATURES);
            if (packageInfo == null
                    || packageInfo.signatures == null
                    || packageInfo.signatures.length == 0
                    || packageInfo.signatures[0] == null) {
                return null;
            }
            return signatureDigest(packageInfo.signatures[0]);
        } catch (PackageManager.NameNotFoundException e) {
            return null;
        }
    }

    private static String signatureDigest(Signature sig) {
        byte[] signature = sig.toByteArray();
        try {
            MessageDigest md = MessageDigest.getInstance(SIGNATURE_DIGEST_ALGORITHM);
            byte[] digest = md.digest(signature);
            return bytesToHex(digest).toLowerCase();
        } catch (NoSuchAlgorithmException e) {
            return null;
        }
    }

    private static String bytesToHex(final byte[] bytes) {
        if ((bytes == null) || (bytes.length == 0)) {
            return "";
        }

        final char[] hexChars = new char[bytes.length * 2];

        for (int j = 0; j < bytes.length; j++) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = HEX_ARRAY[v >>> 4];
            hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
        }

        return new String(hexChars);
    }
}