The licensing library allows you to use Android market licensing service to verify that the user is allowed to access your application.
Your applications sends a request to the local market application. The market application contacts the market server and returns the result. The result is cached based on the market rules.
It is recommended to go over Google's documentation related to the licensing method: Application Licensing | Android Developers
Configuring the licensing library is simple. You should first have a publisher account in the market.
The license key is available in Google Play developer console under Development tools - Services & APIs.
The licensing library and service will not prevent a dedicated hacker from hacking your application. It will however make it more difficult.
The first step is to initialize a LicenseChecker object:
The result of the licensing check is cached locally. The cache is encrypted with AES algorithm. In order to avoid users from tampering with the cache and copying the cache to different devices, the device id is used together with the package name as the password.
Note that the same user will be able to download your application to other devices running with the same user account.
PhoneId (from the Phone library) requires the READ_STATE permission. The protection will still work if you pass an arbitrary string. It will be weaker however.
The Salt parameter should be an array of bytes with some random values (the values should be the same on each run).
Edit: It is recommended to use the alternative id method as described here: http://www.b4x.com/forum/basic4andr...oid-device-unique-id-alternative-phoneid.html
The next step is to call lc.CheckAccess. This in turn calls the market application or the local cache and checks whether the user is allowed to access the program.
One of the following events will be raised when the result arrives: Allow, DontAllow or Error (ErrorCode As String).
It is up to you to handle the event subs as required.
LicenseChecker.SetVariableAndValue
A simple way to hack an application is to "jump over" the checking code. For example a hacker might remove the call to CheckAccess and instead call your Allow event sub.
In order to make it a bit more complicated you can call LicenseChecker.SetVariableAndValue.
For example:
The above code will set the value of a process global string value in the main activity named test1 to "some secret value" if the check was successful. You should not use or test the value of test1 in the Allow event sub as it will be too obvious. Instead you should use it later in your program.
You can be creative and pass the name of the variable or the value by using BytesToString or some other way.
As this variable is accessed in a dynamic way it will fail when the code is obfuscated. Therefore you need to include an underscore in the variable name to prevent it from being obfuscated. For example: test_1.
Note that SetVariableAndValue method will fail when running in rapid debug mode as the variable is part of the "debugger engine".
A more complete example:
The library is available here: http://www.b4x.com/forum/additional-libraries-official-updates/11430-licensing-library.html
Your applications sends a request to the local market application. The market application contacts the market server and returns the result. The result is cached based on the market rules.
It is recommended to go over Google's documentation related to the licensing method: Application Licensing | Android Developers
Configuring the licensing library is simple. You should first have a publisher account in the market.
The license key is available in Google Play developer console under Development tools - Services & APIs.
The licensing library and service will not prevent a dedicated hacker from hacking your application. It will however make it more difficult.
The first step is to initialize a LicenseChecker object:
B4X:
Sub Activity_Create(FirstTime As Boolean)
Dim lc As LicenseChecker
Dim p As PhoneId
lc.Initialize("lc", p.GetDeviceId, publicKey, "kljdflkf".GetBytes("UTF8"))
lc.SetVariableAndValue("test_1", "some secret value")
lc.CheckAccess
End SubNote that the same user will be able to download your application to other devices running with the same user account.
PhoneId (from the Phone library) requires the READ_STATE permission. The protection will still work if you pass an arbitrary string. It will be weaker however.
The Salt parameter should be an array of bytes with some random values (the values should be the same on each run).
Edit: It is recommended to use the alternative id method as described here: http://www.b4x.com/forum/basic4andr...oid-device-unique-id-alternative-phoneid.html
The next step is to call lc.CheckAccess. This in turn calls the market application or the local cache and checks whether the user is allowed to access the program.
One of the following events will be raised when the result arrives: Allow, DontAllow or Error (ErrorCode As String).
It is up to you to handle the event subs as required.
LicenseChecker.SetVariableAndValue
A simple way to hack an application is to "jump over" the checking code. For example a hacker might remove the call to CheckAccess and instead call your Allow event sub.
In order to make it a bit more complicated you can call LicenseChecker.SetVariableAndValue.
For example:
B4X:
lc.SetVariableAndValue("test_1", "some secret value")You can be creative and pass the name of the variable or the value by using BytesToString or some other way.
As this variable is accessed in a dynamic way it will fail when the code is obfuscated. Therefore you need to include an underscore in the variable name to prevent it from being obfuscated. For example: test_1.
Note that SetVariableAndValue method will fail when running in rapid debug mode as the variable is part of the "debugger engine".
A more complete example:
B4X:
Sub Process_Globals
Dim publicKey As String
publicKey = "MIIBIjANBgkqhAADSFEFEFkiG9w0BfW/cGhTbtIs6QIDAQAB..."
Dim test_1 As String
End Sub
Sub Globals
End Sub
Sub Activity_Create(FirstTime As Boolean)
Dim lc As LicenseChecker
Dim p As PhoneId
lc.Initialize("lc", p.GetDeviceId, publicKey, "kljdflkf".GetBytes("UTF8"))
lc.SetVariableAndValue("test1", "some secret value")
lc.CheckAccess
End Sub
Sub lc_Allow
Log("Allow")
End Sub
Sub lc_DontAllow
Log("DontAllow")
ToastMessageShow("Closing application.", True)
Activity.Finish
End Sub
Sub lc_Error (ErrorCode As String)
Log("error: " & ErrorCode)
ToastMessageShow("Closing application.", True)
Activity.Finish
End Sub
Sub Activity_Pause(UserClosed As Boolean)
End Sub
Sub Activity_Resume
End SubThe library is available here: http://www.b4x.com/forum/additional-libraries-official-updates/11430-licensing-library.html
Last edited: