config

    signingConfigs {
        deployer {
            keyAlias KEY_ALIAS
            keyPassword KEY_PASSWORD
            storeFile file(STORE_FILE)
            storePassword STORE_PASSWORD
        }
    }

Crypto.java

package tl.domacoski.myapplication;

import android.util.Base64;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

/**
 * Created by thiago.domacoski on 07/02/17.
 */

public class Crypto {

    private static SecretKeySpec secretKey;
    private static byte[] key;

    public static void setKey(String myKey)
    {
        MessageDigest sha = null;
        try {
            key = myKey.getBytes("UTF-8");
            sha = MessageDigest.getInstance("SHA-1");
            key = sha.digest(key);
            key = Arrays.copyOf(key, 16);
            secretKey = new SecretKeySpec(key, "AES");
        }
        catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }

    public static String encrypt(String strToEncrypt, String secret)
    {
        try
        {
            setKey(secret);
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            return Base64.encodeToString(cipher.doFinal(strToEncrypt.getBytes("UTF-8")), Base64.DEFAULT) ;
        }
        catch (Exception e)
        {
            System.out.println("Error while encrypting: " + e.toString());
        }
        return null;
    }

    public static String decrypt(String strToDecrypt, String secret)
    {
        try
        {
            setKey(secret);
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, secretKey);

            return new String(cipher.doFinal(Base64.decode(strToDecrypt, Base64.DEFAULT) ) );
        }
        catch (Exception e)
        {
            System.out.println("Error while decrypting: " + e.toString());
        }
        return null;
    }
}

prog.txt

#-dontpreverify
#-repackageclasses 'com.sulamerica.ceabs.ubimobile'
-repackageclasses 'android'
-allowaccessmodification
-keepattributes *Annotation*,Signature
-optimizationpasses 10

-printmapping build/outputs/mapping/release/proguard-mapping.txt

-keep class * extends android.app.Activity
-keep class * extends com.sulamerica.ceabs.ubimobile.MainActivity
-keep class * extends android.app.Application
-keep class * extends android.app.Service
-keep class * extends android.content.BroadcastReceiver
-keep class * extends android.app.IntentService
-keep class * extends android.content.ContentProvider
-keep class * extends com.ceabs.library.okhttpmodel.JsonModel
-keep class * extends com.sulamerica.ceabs.ubimobile.utils.BaseJson

-keepclassmembers class * implements android.os.Parcelable {
    static ** CREATOR;
}

-keepclassmembers class **.R$* {
    public static <fields>;
}

-keepclassmembers public class * {
    @com.google.gson.annotations.SerializedName *;
}

-keep @com.google.gson.annotations.SerializedName public class *

-keep public class * extends android.view.View {
    public <init>(android.content.Context);
    public <init>(android.content.Context, android.util.AttributeSet);
    public <init>(android.content.Context, android.util.AttributeSet, int);
    public void set*(...);
}

-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet);
}

-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet, int);
}

-keepclassmembers class * extends android.content.Context {
   public void *(android.view.View);
   public void *(android.view.MenuItem);
}

-keepclasseswithmembernames class * extends com.ceabs.library.okhttpmodel.OkHttpModel{
     public <methods> ;
     private <fields> ;
}

-keep class com.sulamerica.ceabs.ubimobile.recognized.UpdateReconized{
    public <methods> ;
    private <fields> ;
    public static <fields> ;
}

-keep class com.sulamerica.ceabs.ubimobile.utils.SharedPreferencesModel{
     public <methods> ;
     private <fields> ;
}