Android Question Conversion AES Encrypt Function (vb.net) to B4A Error

[laomms]

the vb.net code as below:

Dim sKy As String = "lkirwf897+22#bbtrm8814z5qq=498j5"  '32 chr shared ascii string (32 * 8 = 256 bit)
Dim sIV As String = "741952hheeyy66#cs!9hjv887mxx7@8y"  '32 chr shared ascii string (32 * 8 = 256 bit)
Public Function EncryptRJ256(ByVal prm_key As String, ByVal prm_iv As String, ByVal prm_text_to_encrypt As String)

        Dim sToEncrypt As String = prm_text_to_encrypt

        Dim myRijndael As New RijndaelManaged
        myRijndael.Padding = PaddingMode.Zeros
        myRijndael.Mode = CipherMode.CBC
        myRijndael.KeySize = 256
        myRijndael.BlockSize = 256

        Dim encrypted() As Byte
        Dim toEncrypt() As Byte
        Dim key() As Byte
        Dim IV() As Byte

        key = System.Text.Encoding.UTF8.GetBytes(prm_key)
        IV = System.Text.Encoding.UTF8.GetBytes(prm_iv)

        Dim encryptor As ICryptoTransform = myRijndael.CreateEncryptor(key, IV)

        Dim msEncrypt As New MemoryStream()
        Dim csEncrypt As New CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)

        toEncrypt = System.Text.Encoding.UTF8.GetBytes(sToEncrypt)

        csEncrypt.Write(toEncrypt, 0, toEncrypt.Length)
        csEncrypt.FlushFinalBlock()

        encrypted = msEncrypt.ToArray()

        Return (Convert.ToBase64String(encrypted))

    End Function
    Public Function DecryptRJ256(ByVal prm_key As String, ByVal prm_iv As String, ByVal prm_text_to_decrypt As String)

        Dim sEncryptedString As String = prm_text_to_decrypt

        Dim myRijndael As New RijndaelManaged
        myRijndael.Padding = PaddingMode.Zeros
        myRijndael.Mode = CipherMode.CBC
        myRijndael.KeySize = 256
        myRijndael.BlockSize = 256

        Dim key() As Byte
        Dim IV() As Byte

        key = System.Text.Encoding.UTF8.GetBytes(prm_key)
        IV = System.Text.Encoding.UTF8.GetBytes(prm_iv)

        Dim decryptor As ICryptoTransform = myRijndael.CreateDecryptor(key, IV)

        Dim sEncrypted As Byte() = Convert.FromBase64String(sEncryptedString)

        Dim fromEncrypt() As Byte = New Byte(sEncrypted.Length) {}

        Dim msDecrypt As New MemoryStream(sEncrypted)
        Dim csDecrypt As New CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)

        csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length)

        Return (System.Text.Encoding.UTF8.GetString(fromEncrypt))

    End Function

I search forum found this:

Sub AES_Encrypt(input As String, IV As String, pass As String) As String
    Dim  su As StringUtils
    Dim inputB() As Byte = input.GetBytes("UTF8")
    Dim passB() As Byte = pass.GetBytes("UTF8")
    Dim IVb() As Byte = IV.GetBytes("UTF8")
 
    Dim kg As KeyGenerator
    Dim C As Cipher
 
    kg.Initialize("AES") 'Yes, AES only
    kg.KeyFromBytes(passB)
 
    C.Initialize("AES/CBC/PKCS5Padding")
    C.InitialisationVector = IVb
 
    Dim datas() As Byte = C.Encrypt(inputB, kg.Key, True)
    Return su.EncodeBase64(datas)
End Sub

When I use :

    Dim IV As String ="lkirwf897+22#bbtrm8814z5qq=498j5"  '
    Dim PWC As String = "741952hheeyy66#cs!9hjv887mxx7@8y"
    AES_Encrypt("ABC",IV,PWC)

It occurr error in line ; Dim datas() As Byte = C.Encrypt(inputB, kg.Key, True)
java.security.InvalidAlgorithmParameterException: expected IV length of 16 but was 32

 

[laomms]

how to change IV length to 32.
the only way is modify server's IV length to 16 ?

 

[mangojack]

is this thread of any help ..
https://www.b4x.com/android/forum/threads/solved-vb-net-and-b4a-aes-encryption-problem.101415/

 

[laomms]

B4A is AES128, vb.net is AES256

 

[laomms]

I modify vb.net to AES128, now is new problem, after encrypt string, there are only half string is samed:
B4A:
6YWyvhVsEzjC06wMKEBplbnV8ZdbGGIWsZt/Bt2+9q4=

VB.NET:
6YWyvhVsEzjC06wMKEBplYH+tqrQnKWxcP3UFHta4XM=

 

[agraham]

Different padding modes?

 

[laomms]

vb.net modify block to 16 byte,modify keysize 32byte :

Dim sIV As String = "741952hheeyy66#c"
BlockSize = 128
KeySize=256

same result:
rO7rmJV/x0ZAjd/FbrlBr02Zm+RXml7DyWDyudBrqA0=
rO7rmJV/x0ZAjd/FbrlBr/N7oGhKXvnijh7y3Lox430=
half diffrent

 

[laomms]

Different padding modes?

yes, you are right!!!!
vb.net:
myRijndael.Padding = PaddingMode.Zeros
b4a:
C.Initialize("AES/CBC/PKCS5Padding")


b4a no zeros mode?

 

[Erel]

What is the output of Log(bc.HexFromBytes(...)) for the B4A output?

bc = ByteConverter

 

[agraham]

You should try using PaddingMode.PKCS7 in VB.Net (it's the same as PKCS5). This padding is superior to padding with zeros as it copes with trailing byte values of zero in the encrypted data.