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 < 10 Then
    Debug.Print Chr(48 + H);
Else
    Debug.Print Chr(87 + H);
End If
H = Int(X Mod 16)
If H < 10 Then
    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