Pega hash para o cadastro de app no facebook.

UtilsPackages.java

package br.com.consultoriadigital.insights.core;

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.Signature;
import android.util.Base64;
import android.util.Log;

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

/**
 * Created by Thiago on 05/06/2016.
 */
public class UtilsPackages {

    public static String getSignature(Context context) {
        PackageInfo info;
        String hash = null;

        try {
            info = context.getPackageManager().getPackageInfo(
                    context.getPackageName(), PackageManager.GET_SIGNATURES);
            for (Signature signature : info.signatures) {
                MessageDigest md;

                md = MessageDigest.getInstance("SHA1");
                md.update(signature.toByteArray());

                hash = new String(Base64.encode(md.digest(), 0));

                Log.e("hash key", hash);
            }
        } catch (PackageManager.NameNotFoundException e) {
            Log.e("name not found", e.toString());
        } catch (NoSuchAlgorithmException e) {
            Log.e("no such an algorithm", e.toString());
        } catch (Exception e) {
            Log.e("exception", e.toString());
        }

        return hash;
    }
}