Android Question Rijndael encryption with custom PassPhrase

Stephen A Wolfe · Mar 20, 2018

I prefer to use Rijndael encryption, but my VB code for my projects does not work in B4A, although I have seen people use similar examples in threads here. For security reasons, I need to allow each user to set their own PassPhrase in order to prevent wide-scale attacks or reading encrypted data using the same app on a different user's device.

I'm completely new to B4A, but if I can implement this with two subs (Encrypt & Decrypt), that would be great.

Thanks in advance.

DonManfred · Mar 20, 2018

https://www.b4x.com/android/forum/threads/base64-and-encryption-library.6839/#content

agraham said:
Tested symmetric algorithms are DES, Triple DES and AES (Rijndael).

So i guess it should work using the Encryption and ByteConverter libraries.

Stephen A Wolfe · Mar 20, 2018

DonManfred said:
https://www.b4x.com/android/forum/threads/base64-and-encryption-library.6839/#content

So i guess it should work using the Encryption and ByteConverter libraries.

Like I said, I'm new to B4A, so don't really know why I'm having issues.

I put this code in my project and almost everything is red underlined:

B4X:

Sub EncryptText(text As String, password As String) As Byte()
    Dim c As B4XCipher
    Return c.Encrypt(text.GetBytes("utf8"), password)
End Sub

Sub DecryptText(EncryptedData() As Byte, password As String) As String
    Dim c As B4XCipher
    Dim b() As Byte = c.Decrypt(EncryptedData, password)
    Return BytesToString(b, 0, b.Length, "utf8")
End Sub

Dim EncryptedData() As Byte = EncryptText("confidential", "123456")
Log(DecryptText(EncryptedData, "123456"))

Then I have this:

B4X:

ReadString = EncryptText(ReadString)

And that's an error also.

Erel · Mar 20, 2018

B4XEncryption expects the data to be formatted in a very specific way. If you need to decrypt data coming from other non-B4X platforms then you should use the Encryption library instead.

Stephen A Wolfe · Mar 20, 2018

Erel said:
B4XEncryption expects the data to be formatted in a very specific way. If you need to decrypt data coming from other non-B4X platforms then you should use the Encryption library instead.

All I'm trying to do is securely encrypt a string using my example. The unencrypted string is in ReadString.

Erel · Mar 20, 2018

I understand. Your mistake is that you treat raw bytes as a string. It will not work.

Use StringUtils.EncodeBase64 to convert the raw bytes to a base64 string.

Stephen A Wolfe · Mar 20, 2018

Erel said:
I understand. Your mistake is that you treat raw bytes as a string. It will not work.

Use StringUtils.EncodeBase64 to convert the raw bytes to a base64 string.

I'm glad you understand. I don't. What is the code I need to use?

Erel · Mar 20, 2018

Stephen A Wolfe said:
What is the code I need to use?

It depends. Why do you convert the bytes to string?

Using StringUtils.EncodeBase64 is very simple: https://www.b4x.com/android/forum/pages/results/?query=StringUtils.EncodeBase64

I recommend you to start with the video tutorials: https://www.b4x.com/etp.html
This specific issue is discussed in one of the videos (probably about strings though I'm not sure).

Stephen A Wolfe · Mar 20, 2018

Erel said:
It depends. Why do you convert the bytes to string?

Using StringUtils.EncodeBase64 is very simple: https://www.b4x.com/android/forum/pages/results/?query=StringUtils.EncodeBase64

I recommend you to start with the video tutorials: https://www.b4x.com/etp.html
This specific issue is discussed in one of the videos (probably about strings though I'm not sure).

I'm not converting bytes to a string. I need to encrypt a string. For example, ReadString = "Test" After I encrypt it, ReadString should be something like "2lrmu7JPVaQ2DC/jjo9C8A=="

Erel · Mar 20, 2018

This is indeed a base64 encoded string. I think that all the information you need is available in this thread and it is quite simple. Give it a try...

All you need is to replace BytesToString...

Stephen A Wolfe · Mar 20, 2018

Erel said:
It depends. Why do you convert the bytes to string?

Using StringUtils.EncodeBase64 is very simple: https://www.b4x.com/android/forum/pages/results/?query=StringUtils.EncodeBase64

I recommend you to start with the video tutorials: https://www.b4x.com/etp.html
This specific issue is discussed in one of the videos (probably about strings though I'm not sure).

So, this is secure?

B4X:

Dim su As StringUtils
Dim encoded As String
encoded = su.EncodeBase64(data) 'data is a bytes array

I put this in my project and get an error for su. How do I add the library reference?

Erel · Mar 20, 2018

Yes it is secure.

Stephen A Wolfe said:
How do I add the library reference?

Everything you need is available in B4X guide: https://www.b4x.com/b4a.html#documentation
Or in the video tutorials.

Stephen A Wolfe · Mar 20, 2018

Erel said:
Yes it is secure.

Everything you need is available in B4X guide: https://www.b4x.com/b4a.html#documentation
Or in the video tutorials.

Thanks. I figured out how to add the library reference. I'm down to one final issue.

B4X:

    ReadString = su.EncodeBase64(Data) 'data is a bytes array

Gives the error Undeclared variable 'Data' is used before it was assigned any value.

lemonisdead · Mar 20, 2018

Stephen A Wolfe said:
variable 'Data' is used before it was assigned any value.

"Data" is the name of the String you want to be Base64 encoded. So in your case the string you wan't to be encrypted, I guess. Just replace the name "Data" with the name of your own variable

Stephen A Wolfe · Mar 20, 2018

lemonisdead said:
"Data" is the name of the String you want to be Base64 encoded. So in your case the string you wan't to be encrypted, I guess. Just replace the name "Data" with the name of your own variable

I tried that using ReadString = su.EncodeBase64(ReadString)

But it gives an error. Also, this method isn't even remotely secure. I do know that much. I'm not planning to write banking software, but the encryption does need to be a lot more secure than Base64 encoding.

Stephen A Wolfe · Mar 20, 2018

lemonisdead said:
"Data" is the name of the String you want to be Base64 encoded. So in your case the string you wan't to be encrypted, I guess. Just replace the name "Data" with the name of your own variable

Here's what I've come up with:

B4X:

Sub EncryptText(text As String, password As String) As Byte()
    Dim c As B4XCipher
    Return c.Encrypt(text.GetBytes("utf8"), password)
End Sub

And:

B4X:

    ReadString = "Testing"
    EncryptText(ReadString, "MyPassword")
    File.WriteString(File.DirRootExternal, "MyProduct/Settings.txt", ReadString)

But ReadString in this code does not get encrypted. What am I missing here? I tried ReadString = EncryptText(ReadString, "MyPassword") but that doesn't work.

DonManfred · Mar 21, 2018

EncryptText is a method which return a string- But you are NOT using the result....

Stephen A Wolfe said:
I tried ReadString = EncryptText(ReadString, "MyPassword") but that doesn't work

it should work. Do you get any error?

Erel · Mar 21, 2018

B4X:

Sub Activity_Create(FirstTime As Boolean)
   Dim EncryptedData As String = EncryptText("confidential", "123456")
   Log("Encrypted: " & EncryptedData)
   Dim Decrypted As String = DecryptText(EncryptedData, "123456")
   Log("Decrypted: " & Decrypted)
End Sub

Sub EncryptText(text As String, password As String) As String
   Dim c As B4XCipher
   Dim su As StringUtils
   Return su.EncodeBase64(c.Encrypt(text.GetBytes("utf8"), password))
End Sub

Sub DecryptText(EncryptedData As String, password As String) As String
   Dim c As B4XCipher
   Dim su As StringUtils
   Dim b() As Byte = c.Decrypt(su.DecodeBase64(EncryptedData), password)
   Return BytesToString(b, 0, b.Length, "utf8")
End Sub

Stephen A Wolfe · Mar 21, 2018

DonManfred said:
EncryptText is a method which return a string- But you are NOT using the result....

it should work. Do you get any error?

I'm indeed getting an error. ReadString = DecryptText(ReadString, "MyPassword")
is underlined red and says this super vague message "Type=String, Rank=0 --> Type=Byte, Rank1

I have been able to get this working mostly. I'm able to read in the encrypted string into an Object variable, but I can't seem to figure out how to read in the string lines into a string array.

Erel said:

B4X:

Sub Activity_Create(FirstTime As Boolean)
   Dim EncryptedData As String = EncryptText("confidential", "123456")
   Log("Encrypted: " & EncryptedData)
   Dim Decrypted As String = DecryptText(EncryptedData, "123456")
   Log("Decrypted: " & Decrypted)
End Sub

Sub EncryptText(text As String, password As String) As String
   Dim c As B4XCipher
   Dim su As StringUtils
   Return su.EncodeBase64(c.Encrypt(text.GetBytes("utf8"), password))
End Sub

Sub DecryptText(EncryptedData As String, password As String) As String
   Dim c As B4XCipher
   Dim su As StringUtils
   Dim b() As Byte = c.Decrypt(su.DecodeBase64(EncryptedData), password)
   Return BytesToString(b, 0, b.Length, "utf8")
End Sub

Here's what I've come up with so far. I only get an error when I run it though. I have tried so many things but need help to figure out what I'm doing wrong. The encryption part is working great and I can decrypt the encrypted string, but reading the encrypting string and trying to put the string lines into a string array is giving me issues. Here is my code:

B4X:

       Dim ReadString As String
    Dim EncryptedString As Object
    Dim MyPhone As PhoneId

B4X:

    EncryptedString = File.ReadString(File.DirRootExternal, "MyFolder/MyFile.txt")
    ReadString = DecryptText(EncryptedString, MyPhone.GetDeviceId)
    FileLoc = Regex.Split(CRLF, ReadString)
    Msgbox(FileLoc(1), "The line of decoded array I need")

I'm getting an error "String cannot be cast to Byte". It seems like this should work. The error occurs for the decrypt line. I am saving the file using the reverse method (
File.WriteString(File.DirRootExternal, "MyFolder/MyFile.txt", EncryptedString)

Erel · Mar 22, 2018

Please start a new thread for this. Make sure to include all the relevant information.

Android Question Rijndael encryption with custom PassPhrase

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