janmanx / encrypttextapp

EncryptText App for Android

A simple application to encrypt text. Can be used in combination with many other applications, to increase security and privacy.

Usage

The application can be opened just as any other application. However, to avoid the tedious application switching, the encryption can happen in-place, in any application.

First, select the text you want to encrypt:

Enter the password at the top ( *optional, but recommended* ), and hit **ENCRYPT**:

The encrypted message will appear at the bottom. Click **REPLACE** to close the application and replace the original text:

Installation

encrypttextapp's Issues

Incompatible with popular Android devices

The app supports min SDK 23, which is incompatible with some of the popular Android devices currently in use such as Galaxy J2, J1 Ace, Grand Prime, and Oppo A37f. These Android devices support min SDK 22.

Decrypt Text on Linux or Windows

Hello Jan,

I am using your great App https://f-droid.org/de/packages/dk.meznik.jan.encrypttext since a while.
It would be very helpful, if you can give me a hint how to encrypt/decrypt the text from the App
on a PC with Linux or Windows (I send very often Text between my Smartphone and a PC)
I found a Web page https://encode-decode.com/aes256-encrypt-online/
where it is possible to encrypt/decrypt AES256 Text but it does not work.

Or is it maybe compatible with https://www.aescrypt.com/download/ ?

Best Regards
Thor

Unable to decipher text

Expected behavior

I expected the app. to decrypt the encrypted text, since the text was encrypted from the app.

Actual behavior

When I input a text I want to encrypt in the Password textbox, after clicking on the ENCRYPT, it successfully encrypted but when I want to decrypt it didn't Decrypt the Encrypted text

How to reproduce

• Open the App
• Input text you want to encrypt in the Password textbox
• Click Encrypt to encrypt the text. you have successfully encrypted your text
• Copy the Encrypted text
• paste it in the Password textbox or the Textbox under Password
• Click DECRYPT

---

• App version: Encrypt Text v1.0
• Operating system: Android 6.0, Marshmallow
• Device: Tecno C9 Pro

Recording Of The Bug

Possible Vulnerabilities

I saw this in f-droid and felt like checking your crypto code.

I'm not familiar with the Java crypto libraries, but from what I can tell, it has a number of crypto issues:

• it appears you are using SHA256 for key derivation. This is very fast to compute (and brute force) and unsuitable for deriving an AES key from. Consider using, say, PBKDF2 instead.
• You are using CBC, however it appears you are not using a Message Authentication Code to verify the integrity of the message. This means your code is, at least theoretically, vulnerable to a padding oracle, and message modification. You can verify the integrity of the ciphertext with e.g. a sha256 HMAC to prevent this.
• it appears you are using a hardcoded IV. This is un-ideal in general, but with some modes, like CBC, it is potentially catastrophical, in this case if the same message is encrypted with multiple keys.

F-Droid update

Unfortunately, F-Droid still only has v1.0 – which is most likely due to the fact that versionCode and versionName in your build.gradle have never been updated and still say "1.0, 1" even at tag 1.2.

Could you please fix that at tag 1.2, so that gets built by F-Droid?

        versionCode 3
        versionName "1.2"

would be fine there. Thanks!

Tag releases

Can you please tag your releases (see here), it would be helpful for the F-Droid release. You could also attach the binaries to your releases (see here).

That's pretty easy and very helpful for those of us who aren't using Google services.

App Crashing

I have a Motorola Moto e5 Play running Android 8.0.0. It used to work fine but now it's crashing every time I open it. Tried uninstalling and reinstalling to no avail. It's one of my favorite apps too. Have it on all my phones. Please find a patch. Thanks.