Android Question string to Byte Array

[Rusty]

I am having a problem converting strings with "extended" characters to an Encryptable byte array.

...
Sub Globals
    Dim conv As ByteConverter
End Sub

Sub Activity_Create(FirstTime As Boolean)
    conv.LittleEndian = True    
    Dim PaddedString As String = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnoá      "  
    Log("padddestring " & PaddedString.Length & "   >" & PaddedString & "<")
    Dim data() As Byte = conv.StringToBytes(PaddedString, "UTF8") 
Log("Data Len before " & data.Length)
    If data.Length mod 8 <> 0 Then
        Dim tmpdata(PaddedString.Length) As Byte
Log("data len " & data.Length)  
        conv.ArrayCopy(data,0,tmpdata,0,PaddedString.Length-1)
        data = tmpdata
    End If
    Log("Data after: " & data.Length)
End Sub
...

Installing file.
** Activity (main) Pause, UserClosed = false **
PackageAdded: package:b4a.example
** Service (starter) Create **
** Service (starter) Start **
** Service (widgetservice) Start **
** Activity (main) Create, isFirst = true **
padddestring 48 >abcdefghijklmnopqrstuvwxyzabcdefghijklmnoá <
Data Len before 49
data len 49
Data after: 48

In order to encrypt data it must be multiples of 8 bytes (I believe).
When I convert a string of standard ascii characters of 48 bytes to a byte array, it returns a 48 byte array.
When I convert a string of ascii characters with, for example "á" embedded within, it returns a 49 byte array. Each additional "á" (extended character) results in one additional byte added to the array, which in return causes the byte array to fail encryption (because it is not a 8 byte multiple in size).
What is the rule on these "extended characters" when the byte converter converts them to bytes?
and how can I insure the byte array is a multiple of 8 bytes in size?
Thanks,
Rusty

 

[Erel]

You don't need to do anything special. The data will be padded by the encryption library.

 

[KMatle]

What method do you use to en-/decrypt the data?

 

[Rusty]

Dim C As Cipher

...code from above

data = C.Encrypt(data, kg.Key, True)

When I run the code, I get the following error:

javax.crypto.IllegalBlockSizeException: error:0607F08A:digital envelope routines:EVP_EncryptFinal_ex:data not multiple of block length
at com.android.org.conscrypt.NativeCrypto.EVP_CipherFinal_ex(Native Method)
at com.android.org.conscrypt.OpenSSLCipher.doFinalInternal(OpenSSLCipher.java:420)
at com.android.org.conscrypt.OpenSSLCipher.engineDoFinal(OpenSSLCipher.java:456)
at javax.crypto.Cipher.doFinal(Cipher.java:1204)
at anywheresoftware.b4a.agraham.encryption.CipherWrapper.doFinal(CipherWrapper.java:140)
at anywheresoftware.b4a.agraham.encryption.CipherWrapper.Encrypt(CipherWrapper.java:160)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at anywheresoftware.b4a.shell.Shell.runMethod(Shell.java:668)
at anywheresoftware.b4a.shell.Shell.raiseEventImpl(Shell.java:334)
at anywheresoftware.b4a.shell.Shell.raiseEvent(Shell.java:244)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at anywheresoftware.b4a.ShellBA.raiseEvent2(ShellBA.java:132)
at anywheresoftware.b4a.BA.raiseEvent2(BA.java:175)
at anywheresoftware.b4a.BA.raiseEvent(BA.java:171)
at anywheresoftware.b4a.objects.ViewWrapper$1.onClick(ViewWrapper.java:78)
at android.view.View.performClick(View.java:4487)
at android.view.View$PerformClick.run(View.java:18746)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:149)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
at dalvik.system.NativeStart.main(Native Method)
encryption error (Exception) java.lang.Exception: javax.crypto.IllegalBlockSizeException: error:0607F08A:digital envelope routines:EVP_EncryptFinal_ex:data not multiple of block length

Erel, I don't understand how the library pads this automatically. We've had to pad the string to an 8 byte boundary in order for this to work for years.
The question remains, why does the Spanish character increase the size of the byte array?
Thanks, ideas appreciated

 

[James Chamblin]

In UTF-8 encoding, characters are encoded with 1 to 4 bytes. The standard letters, numbers and punctuation are encoded with a single byte. Most special characters, like á are encoded using multiple bytes. So that is why you need an extra byte.

 

[Rusty]

Thanks James
I still don't understand why Erel indicated

You don't need to do anything special. The data will be padded by the encryption library.

Is this clear to you?
Rusty

 

[Erel]

The correct answer is that it depends on the selected algorithm and whether padding is applied automatically or not (for example it will be added with AES/CBC/PKCS5Padding which is the algorithm used by B4XEncryption).

Anyway you can use ByteConverter.ArrayCopy to add the padding by copying the data you get from GetBytes to a larger array.

 

[KMatle]

I still don't understand why Erel indicated

Please post a full code snippet WITH the algorythm you use (En-/and Decryption)