iOS Question Error decoding data as string AES Decryption

[Nana Osei Afrifa]

Please am getting this error when decrypting an encrypted string using IV and . "Error decoding data as string."
When I Use Dim result As String= BytesToString(data,0,data.Length,"UTF-8")
<B4IExceptionWrapper: Error Domain=caught_exception Code=0 " Error decoding data as string." UserInfo={NSLocalizedDescription= Error decoding data as string.}>


But When I Use Dim result As String= Bconv.HexFromBytes(data) , then there is no error
Please I want to get the original string but not in hexa format.

 

[Erel]

Moved to B4i forum.

How did you encrypt the string? Maybe you have used a different encoding.

 

[Nana Osei Afrifa]

Here's the encryption code I used.

Sub Encrypt(Msg As String) As String
    Dim op As Int
    Dim Bconv As ByteConverter
    Dim data(0) As Byte
    Dim iv(0) As Byte
    Dim ivtxt As String="@" & Main.RandomString(15,True,True,True,"")
    iv = ivtxt.GetBytes("UTF8")
    data = Bconv.StringToBytes(Msg, "UTF8")
    op = Bit.Or(c.OPTION_ECBMode, c.OPTION_PKCS7Padding)
  
    data = c.Encrypt2(data, key,"AES",iv, op)
  
    Dim newarr(iv.Length + data.Length) As Byte
    Bconv.ArrayCopy(iv,0,newarr,0,iv.Length)
    Bconv.ArrayCopy(data,0,newarr,iv.Length,data.Length)
  
    Dim result As String
    result=su.EncodeBase64(newarr)
    Return result
End Sub

Here's the decryption code

Sub Decrypt(EncMsg As String) As String
    Try
        Dim op As Int
        Dim Bconv As ByteConverter
        Dim fulldata(0) As Byte
        fulldata = su.DecodeBase64(EncMsg)
       
        Dim ln As Int
        ln=fulldata.Length-16
        Dim data(ln) As Byte
        Dim iv(16) As Byte
       
        Bconv.ArrayCopy(fulldata,0,iv,0,16)
        Bconv.ArrayCopy(fulldata,16,data,0,ln)
       
        op = Bit.Or(c.OPTION_ECBMode, c.OPTION_PKCS7Padding)
       
        data = c.Decrypt2(data, key,"AES",iv,op)
        Dim result As String= BytesToString(data,0,data.Length,"UTF-8")' Bconv.HexFromBytes(data)
       
        Return result
    Catch
        Log(LastException)
    End Try
    Return ""
End Sub

 

[Erel]

Tip:
Instead of:

 Dim fulldata(0) As Byte
        fulldata = su.DecodeBase64(EncMsg)

Write:

Dim fulldata() As Byte = su.DecodeBase64(EncMsg)

What is the output of:

Log(Bconv.HexFromBytes(data)) 'right after you convert Msg to an array of bytes
Log(Bconv.HexFromBytes(data)) 'right after you decrypt the data

 

[Nana Osei Afrifa]

Here's the

Data before decryption
862ED1E12C173E3921B1F7EE63EE20B470B02ABF75CD80A404CA739049269D7157EA4526D33888C4972AFCE165E669757141B073561E83D240E519D1465483FA7E0EBECD34863D39D113AFCFC2791622FE6C14FAA86E4E536A2800506DDB79AD
Data after decryption
3E12B1AD869FB49D7DC1E0ACAAA5551D484590570D08F6EDA2302086E4338AE211A184F0ACC8F3B99C0C07C43106C5C60540EDF87198D22CCA7F22A245F9C9D82C022482F79D90A2EBCA067604A020026F75AF10E299ED3653D4FAAEB4546A2C

The encrypted data from server is encryped using cipher option PKCS5Padding, but there's no PKCS5Padding option on the cipher library of b4i. How do i specify the cipher option like I did in android.

'Android version of the cipher
Dim c As Cipher
c.Initialize("AES/CBC/PKCS5Padding")
c.InitialisationVector = iv

.

 

[Erel]

You shouldn't set ECBMode. The default mode is CBC.

 

[Nana Osei Afrifa]

Please what about the padding because our server is using PKCS5Padding to encrypt but there's no PKCS5Padding in B4i cipher library option.

 

[Erel]

I don't think that this is the cause of this error. You should be able to use PKCS7Padding instead.

 

[Nana Osei Afrifa]

Am still not able to solve this problem. I used UTF-8 encoding between my android application with the web services and everything works perfect.
But always getting error when I use B4I with UTF-8. Please help.

 

[Erel]

Can you upload two small examples, one with B4A and one with B4i, with your encryption code?