Android Question AES 128 Encrypt problem

[Lello1964]

Hi again,

i have to encrypt with AES 128 using this :

String to encrypt hex = 01000000A707192BFF4CFFEFCCAA67C8
password hex = 000000000000000D0123456701234567

result cripted hex must be same lenght of String hex 32

 

[Erel]

What is the question or problem?

AES 128 related threads: https://www.b4x.com/android/forum/pages/results/?query=aes+128

Use ByteConverter to convert the hex strings to bytes.

 

[Lello1964]

Hello Erel,

i have tryed more solution, but encrypted result is't 32 byte, but more

example :

Sub Globals
   'These global variables will be redeclared each time the activity is created.
   'These variables can only be accessed from this module.
   Dim bc As ByteConverter   
   Dim sr As SecureRandom
End Sub

Sub Activity_Create(FirstTime As Boolean)
   Dim cmd As String=HexToString("01000000A707192BFF4CFFEFCCAA67C8")
   Dim pwd As String=HexToString("00000000000000040123456701234567")
   Dim su As StringUtils
   Dim c As Cipher
   Dim k As KeyGenerator
   Dim cipherText As String = ""
   Dim keyBytes() As Byte = MakeKeyBytes(128, pwd)
   Dim dataBytes() As Byte = cmd.GetBytes("UTF8")

   k.Initialize("AES")
   k.KeyFromBytes(keyBytes)

   'Autogenerate nonce and insert into IV
   Dim nonce(8) As Byte
   sr.GetRandomBytes(nonce)
   Dim IV(16) As Byte
   bc.ArrayCopy(nonce, 0, IV, 0, 8)

   If dataBytes.Length > 15 Then
       c.Initialize("AES/CTR/NoPadding")
   Else
       c.Initialize("AES/CFB8/NoPadding")
   End If
   c.InitialisationVector = IV
   Dim encryptedBytes() As Byte = c.Encrypt(dataBytes, k.Key, True)

   'Create result byte array, consisting of nonce and encrypted data
   Dim cipherTextBytes(encryptedBytes.Length + 8) As Byte
   bc.ArrayCopy(nonce, 0, cipherTextBytes, 0, 8)
   bc.ArrayCopy(encryptedBytes, 0, cipherTextBytes, 8, encryptedBytes.Length)
   cipherText= bc.HexFromBytes(cipherTextBytes)

End Sub

Sub Activity_Resume

End Sub

Sub Activity_Pause (UserClosed As Boolean)

End Sub

Private Sub MakeKeyBytes(keySize As Int, password As String) As Byte()
   'If the password is keySize / 8 bytes or greater in length, just truncate password to proper byte size
   'If password is less than keySize /8 bytes in length, create a SHA1 digest of the password
   ' (20 bytes), and concatenate the digest and truncate to proper byte size.

   Dim bc As ByteConverter
   Dim keyBytes(keySize / 8) As Byte
   Dim passwordBytes() As Byte = password.GetBytes("UTF8")

   If passwordBytes.Length >= keyBytes.Length Then
       bc.ArrayCopy(passwordBytes, 0, keyBytes, 0, keyBytes.Length)
   Else
       Dim md As MessageDigest
       Dim hash() As Byte = md.GetMessageDigest(passwordBytes, "SHA1")
       Dim offset As Int = 0
       Do While offset < keyBytes.Length
           If offset + hash.Length < keyBytes.Length Then
               bc.ArrayCopy(hash, 0, keyBytes, offset, hash.Length)
           Else
               bc.ArrayCopy(hash, 0, keyBytes, offset, keyBytes.Length - offset)
           End If
           offset = offset + hash.Length
       Loop
   End If

   Return keyBytes
End Sub

Sub HexToString(HexToStr As String) As String
   Dim bc As ByteConverter
   Dim b() As Byte = bc.HexToBytes(HexToStr)
   Return BytesToString(b, 0, b.Length, "UTF8")
End Sub

result : F8872A1B27A4A352D5CB0F151B48B053C2204BC1F3863DB2BC7A7F3F73F053FBA218

if i try using web Aes :
http://extranet.cryptomathic.com/aescalc/index
result is : 751457CE4F77F436F14AA00CE5BE8716
32 bytes

I don't know where is problem

 

[Erel]

Try it with: AES/CBC/PKCS5Padding

 

[Lello1964]

result 133101FC0B38309BC51503308396F95BB0C87AE2CD24908AE102840747CAF8365D691883C9D67142
more than 32 bytes

 

[Erel]

Why do you assume that the encryption output will be with a specific size? This is not a hash function.

You can use MessageDigest with MD5 to create 16 bytes (32 hex chars) hashes.