Visual Basic for Applications code to illustrate the use of the AES Dynamic Link Library.

Visual Basic for Applications code to illustrate the use of the AES Dynamic Link Library. Very similar code should also work in Visual Basic.

Private Const BlkLenMax = 32 ' maximum block length in bytes

Private Const KeyLenMax = 32 ' maximum block length in bytes

Private Const KeySchLenMax = 128 ' maximum key schedule length in bytes

Private BlkLen As Integer ' actual block length

Private KeyLen As Integer ' actual key length

Private Type AESctx ' Type to hold the AES context data

Ekey(0 To KeySchLenMax - 1) As Long

Nrnd As Long

Ncol As Long

End Type

Private Type KeyBlk ' Type to hold user key data

K(0 To KeyLenMax - 1) As Byte

End Type

Private Type IoBlk ' Type to hold cipher input and output blocks

IO(0 To BlkLenMax - 1) As Byte

End Type

Rem Change "d:\dll_pth" in the following lines to the directory path where the AES DLL is located

Private Declare Function AesBlkLen Lib "d:\dll_path\aes.dll" Alias "_aes_blk_len@8" (ByVal N As Long, C As AESctx) As Integer

Private Declare Function AesEncKey Lib "d:\dll_path\aes.dll" Alias "_aes_enc_key@12" (K As KeyBlk, ByVal N As Long, C As AESctx) As Integer

Private Declare Function AesDecKey Lib "d:\dll_path\aes.dll" Alias "_aes_dec_key@12" (K As KeyBlk, ByVal N As Long, C As AESctx) As Integer

Private Declare Function AesEncBlk Lib "d:\dll_path\aes.dll" Alias "_aes_enc_blk@12" (Ib As IoBlk, Ob As IoBlk, C As AESctx) As Integer

Private Declare Function AesDecBlk Lib "d:\dll_path\aes.dll" Alias "_aes_dec_blk@12" (Ib As IoBlk, Ob As IoBlk, C As AESctx) As Integer

Private Sub Hex(X As Byte) ' Output a byte in hexadecimal format

Dim H As Byte

H = Int(X / 16)

If H <>

Debug.Print Chr(48 + H);

Else

Debug.Print Chr(87 + H);

End If

H = Int(X Mod 16)

If H <>

Debug.Print Chr(48 + H);

Else

Debug.Print Chr(87 + H);

End If

End Sub

Private Sub OutKey(S As String, B As KeyBlk) ' Display a key value

Debug.Print: Debug.Print S;

For i = 0 To KeyLen - 1

Hex B.K(i)

Next i

End Sub

Private Sub OutBlock(S As String, B As IoBlk) ' Display an input/output block

Debug.Print: Debug.Print S;

For i = 0 To BlkLen - 1

Hex B.IO(i)

Next i

End Sub

Rem The following Main routine should output the following in the immediate window:

Rem Key = 00000000000000000000000000000000

Rem Input = 00000000000000000000000000000000

Rem Encrypted Text = 66e94bd4ef8a2c3b884cfa59ca342b2e

Rem Decrypted Text = 00000000000000000000000000000000

Sub Main()

Dim Key As KeyBlk ' These variables are automatically

Dim Ib As IoBlk, Ob As IoBlk, Rb As IoBlk

Dim Cx As AESctx ' initialised to zero values in VBA

Dim RetVal As Integer

BlkLen = 16: KeyLen = 16

Rem RetVal = AesBlkLen(BlkLen, Cx) ' include if the cipher block size is variable

OutKey "Key = ", Key

OutBlock "Input = ", Ib

RetVal = AesEncKey(Key, KeyLen, Cx) ' set an all zero encryption key

RetVal = AesEncBlk(Ib, Ob, Cx) ' encrypt Ib to Ob

OutBlock "Encrypted Text = ", Ob

RetVal = AesDecKey(Key, KeyLen, Cx) ' set an all zero decryption key

RetVal = AesDecBlk(Ob, Rb, Cx) ' decrypt Ob to Rb

OutBlock "Decrypted Text = ", Rb

Debug.Print

End Sub