by Patterson Programming (5 Submissions)
Category: Encryption
Compatability: Visual Basic 5.0
Difficulty: Unknown Difficulty
Originally Published: Thu 21st September 2000
Date Added: Mon 8th February 2021
Rating: 
(1 Votes)
Code example in VB, of the TEA block cipher. (For VB5/6 compiler only) Includes an ECB example. 2nd Error REALLY fixed. Conforms to inventor's
API Declarations
'I've had trouble posting this cipher right! The
'inventor didn't publish test vectors.
'If you want to verify that you have my correct
'post, please email me. But this post IS correct!
VBcoders
'* NOTICE: This post corrects for shifting
'* of negative integers in VB. This version
'* conforms to the inventor's C reference code.
'* Please ignore my other TEA posts.
'* VB5/6 port - You MUST compile this to work.
'* Turn OFF integer overflow checks in the compile options!
'* TEA - Tiny Encryption Algorithm
'* A Feistel cipher. David Wheeler & Roger Needham
'* Easy for learning and it's in the public domain.
'* 64-bit block, ECB mode
'* build into a class module if desired
Option Explicit
Const Rounds = 32
Const Delta = &H9E3779B9
'* VB style shifts
Const shl4 = 16
Const shr5 = 32
'* copy the 16 key-bytes into this array
Dim k(15) As Byte
'* the 128-bit key (as 4 32-bit integers)
Dim Tk(3) As Long
'* data you want to encrypt/decrypt
Dim CryptBuffer() As Byte
Dim BufferPointer&, i&
'* scratch variables
Dim b1 As Byte, b2 As Byte, b3 As Byte, b4 As Byte
Dim w1&, w2&, w3&, w4&
Sub TEST()
For i& = 0 To 15: k(i&) = i&: Next
TEA_Key
ReDim CryptBuffer(7) As Byte
For i& = 0 To 7
CryptBuffer(i&) = i&
Next
BufferPointer& = 0
TEA_Encrypt (1)
BufferPointer& = 0
TEA_Decrypt (1)
End Sub
'* encryption function
Sub TEA_Encrypt(Blocks&)
'* left and right half of Feistel block
Dim Xl As Long, Xr As Long, Sl As Long, Sr As Long
Dim sum As Long, x As Integer
For i& = 0 To Blocks& - 1
'* Copy the plaintext bytes into 32-bit words
w1& = CryptBuffer(BufferPointer& + 3)
w2& = CryptBuffer(BufferPointer& + 2)
w3& = CryptBuffer(BufferPointer& + 1)
w4& = CryptBuffer(BufferPointer&)
w2& = (w2& * &H100)
w3& = (w3& * &H10000)
w4& = (w4& * &H1000000)
Xl = w1& Or w2& Or w3& Or w4&
w1& = CryptBuffer(BufferPointer& + 7)
w2& = CryptBuffer(BufferPointer& + 6)
w3& = CryptBuffer(BufferPointer& + 5)
w4& = CryptBuffer(BufferPointer& + 4)
w2& = (w2& * &H100)
w3& = (w3& * &H10000)
w4& = (w4& * &H1000000)
Xr = w1& Or w2& Or w3& Or w4&
sum = 0
For x = 1 To Rounds
sum = (sum + Delta)
' correct for shr5 negative integers
Sr = Xr And &HFFFFFFE0
Sr = (Sr \ shr5) And &H7FFFFFF
Xl = Xl + (((Xr * shl4) + Tk(0)) Xor (Xr + _
sum) Xor (Sr + Tk(1)))
Sl = Xl And &HFFFFFFE0
Sl = (Sl \ shr5) And &H7FFFFFF
Xr = Xr + (((Xl * shl4) + Tk(2)) Xor (Xl + _
sum) Xor (Sl + Tk(3)))
Next
b1 = (Xl And &HFF)
b2 = (Xl And &HFF00) \ 256
b3 = (Xl And &HFF0000) \ 65536
b4 = (Xl And &HFF000000) \ 16777216
CryptBuffer(BufferPointer&) = b4
CryptBuffer(BufferPointer& + 1) = b3
CryptBuffer(BufferPointer& + 2) = b2
CryptBuffer(BufferPointer& + 3) = b1
b1 = (Xr And &HFF)
b2 = (Xr And &HFF00) \ 256
b3 = (Xr And &HFF0000) \ 65536
b4 = (Xr And &HFF000000) \ 16777216
CryptBuffer(BufferPointer& + 4) = b4
CryptBuffer(BufferPointer& + 5) = b3
CryptBuffer(BufferPointer& + 6) = b2
CryptBuffer(BufferPointer& + 7) = b1
'* 64-bit block
BufferPointer& = BufferPointer& + 8
Next
End Sub
'* decryption function
Sub TEA_Decrypt(Blocks&)
'* left and right half of Feistel block
Dim Xl As Long, Xr As Long, Sl As Long, Sr As Long
Dim sum As Long, x As Integer
For i& = 0 To Blocks& - 1
w1& = CryptBuffer(BufferPointer& + 3)
w2& = CryptBuffer(BufferPointer& + 2)
w3& = CryptBuffer(BufferPointer& + 1)
w4& = CryptBuffer(BufferPointer&)
w2& = (w2& * &H100)
w3& = (w3& * &H10000)
w4& = (w4& * &H1000000)
Xl = w1& Or w2& Or w3& Or w4&
w1& = CryptBuffer(BufferPointer& + 7)
w2& = CryptBuffer(BufferPointer& + 6)
w3& = CryptBuffer(BufferPointer& + 5)
w4& = CryptBuffer(BufferPointer& + 4)
w2& = (w2& * &H100)
w3& = (w3& * &H10000)
w4& = (w4& * &H1000000)
Xr = w1& Or w2& Or w3& Or w4&
'Note: {Delta * 32 != &H6526b0d9}
sum = (Delta * Rounds)
For x = 1 To Rounds
' correct for shr5 negative integers
Sl = Xl And &HFFFFFFE0
Sl = (Sl \ shr5) And &H7FFFFFF
Xr = Xr - (((Xl * shl4) + Tk(2)) Xor (Xl + _
sum) Xor (Sl + Tk(3)))
Sr = Xr And &HFFFFFFE0
Sr = (Sr \ shr5) And &H7FFFFFF
Xl = Xl - (((Xr * shl4) + Tk(0)) Xor (Xr + _
sum) Xor (Sr + Tk(1)))
sum = (sum - Delta)
Next
b1 = (Xl And &HFF)
b2 = (Xl And &HFF00) \ 256
b3 = (Xl And &HFF0000) \ 65536
b4 = (Xl And &HFF000000) \ 16777216
CryptBuffer(BufferPointer&) = b4
CryptBuffer(BufferPointer& + 1) = b3
CryptBuffer(BufferPointer& + 2) = b2
CryptBuffer(BufferPointer& + 3) = b1
b1 = (Xr And &HFF)
b2 = (Xr And &HFF00) \ 256
b3 = (Xr And &HFF0000) \ 65536
b4 = (Xr And &HFF000000) \ 16777216
CryptBuffer(BufferPointer& + 4) = b4
CryptBuffer(BufferPointer& + 5) = b3
CryptBuffer(BufferPointer& + 6) = b2
CryptBuffer(BufferPointer& + 7) = b1
BufferPointer& = BufferPointer& + 8
Next
End Sub
Sub TEA_Key()
'* copy 128-bits of key
w1& = k(3)
w2& = k(2): w2& = (w2& * &H100)
w3& = k(1): w3& = (w3& * &H10000)
w4& = k(0): w4& = (w4& * &H1000000)
Tk(0) = w1& Or w2& Or w3& Or w4&
w1& = k(7)
w2& = k(6): w2& = (w2& * &H100)
w3& = k(5): w3& = (w3& * &H10000)
w4& = k(4): w4& = (w4& * &H1000000)
Tk(1) = w1& Or w2& Or w3& Or w4&
w1& = k(11)
w2& = k(10): w2& = (w2& * &H100)
w3& = k(9): w3& = (w3& * &H10000)
w4& = k(8): w4& = (w4& * &H1000000)
Tk(2) = w1& Or w2& Or w3& Or w4&
w1& = k(15)
w2& = k(14): w2& = (w2& * &H100)
w3& = k(13): w3& = (w3& * &H10000)
w4& = k(12): w4& = (w4& * &H1000000)
Tk(3) = w1& Or w2& Or w3& Or w4&
End Sub
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