by Patterson Programming (5 Submissions)
Category: Internet/HTML
Compatability: Visual Basic 4.0 (32-bit)
Difficulty: Unknown Difficulty
Originally Published: Sun 14th November 1999
Date Added: Mon 8th February 2021
Rating: 
(1 Votes)
StealthMail 2.1 - DESCRIPTION of the LeapFrog2 CIPHER used in the StealthMail 2.1 program. This cipher is designed for VB. (no shifts/no
VBcoders
The LeapFrog2 cipher design is for implementations
that require a cipher which does not use any shifts/rotates.
The user-entered key is expanded into S-boxes using a
non-linear method somewhat similar to the stream cipher RC4.
The diffusion is provided by compound lookups into the S-boxes.
The cipher is implemented with a Feistel-like structure. Three
bytes on the left are mixed through the S-box function and
combined with a target byte on the right using the Xor operator.
This is used for each of the four target bytes on the right.
Using asymmetry in the function, groups of two and three are
selected to provide maximal diffusion. Also, each byte on the
left is added to its opposite on the right. Note that the Xor/Add
combination create a Feistel cipher that is NOT self-inverse with
an odd number of rounds. Also, the cipher uses distinct S-boxes
for each half of the Feistel network, and halves are not
actually swapped.
This is a pseudo-code example showing the LeapFrog2
block-cipher. It uses a 64-bit block and a variable-bit key.
How the LeapFrog2 cipher differs from the LeapFrog cipher:
1) Instead of simple whitening Xors LeapFrog2 uses
pseudo-random round keys like Blowfish, etc.
2) The front to back symmetry is broken up by using
a different ordering in rounds 0-3 and rounds 4-7.
(the hash function MD5 uses something similar)
T1, T2, T3, T4 are signed integers
p1....p8 are signed integers
Subroutine LeapFrogEncrypt
For BlockNumber = 1 To Blocks
* read plaintext block into p1....p8
* LeapFrogRounds are 8
For x = 0 To (LeapFrogRounds / 2) - 1
* create the T variables
T1 = A1(p1 Xor SK(x, 0))
T2 = A2(p2 Xor SK(x, 1))
T3 = A3(p3 Xor SK(x, 2))
T4 = A4(p4 Xor SK(x, 3))
* T variable order "A"
p5 = p5 Xor A1(A1(T2 Xor T3) Xor T4)
p6 = p6 Xor A2(A2(T1 Xor T4) Xor T3)
p7 = p7 Xor A3(A3(T4 Xor T2) Xor T1)
p8 = p8 Xor A4(A4(T3 Xor T1) Xor T2)
p5 = (p5 + T1) And HFF
p6 = (p6 + T2) And HFF
p7 = (p7 + T3) And HFF
p8 = (p8 + T4) And HFF
* do other half without swapping
T1 = A5(p5 Xor SK(x, 4))
T2 = A6(p6 Xor SK(x, 5))
T3 = A7(p7 Xor SK(x, 6))
T4 = A8(p8 Xor SK(x, 7))
p1 = p1 Xor A5(A5(T2 Xor T3) Xor T4)
p2 = p2 Xor A6(A6(T1 Xor T4) Xor T3)
p3 = p3 Xor A7(A7(T4 Xor T2) Xor T1)
p4 = p4 Xor A8(A8(T3 Xor T1) Xor T2)
p1 = (p1 + T1) And HFF
p2 = (p2 + T2) And HFF
p3 = (p3 + T3) And HFF
p4 = (p4 + T4) And HFF
Next
For x = (LeapFrogRounds / 2) To (LeapFrogRounds - 1)
* create the T variables
T1 = A1(p1 Xor SK(x, 0))
T2 = A2(p2 Xor SK(x, 1))
T3 = A3(p3 Xor SK(x, 2))
T4 = A4(p4 Xor SK(x, 3))
* T variable order "B"
p5 = p5 Xor A1(A1(T2 Xor T3) Xor T4)
p6 = p6 Xor A2(A2(T3 Xor T4) Xor T1)
p7 = p7 Xor A3(A3(T4 Xor T1) Xor T2)
p8 = p8 Xor A4(A4(T1 Xor T2) Xor T3)
p5 = (p5 + T1) And HFF
p6 = (p6 + T2) And HFF
p7 = (p7 + T3) And HFF
p8 = (p8 + T4) And HFF
* do other half without swapping
T1 = A5(p5 Xor SK(x, 4))
T2 = A6(p6 Xor SK(x, 5))
T3 = A7(p7 Xor SK(x, 6))
T4 = A8(p8 Xor SK(x, 7))
p1 = p1 Xor A5(A5(T2 Xor T3) Xor T4)
p2 = p2 Xor A6(A6(T3 Xor T4) Xor T1)
p3 = p3 Xor A7(A7(T4 Xor T1) Xor T2)
p4 = p4 Xor A8(A8(T1 Xor T2) Xor T3)
p1 = (p1 + T1) And HFF
p2 = (p2 + T2) And HFF
p3 = (p3 + T3) And HFF
p4 = (p4 + T4) And HFF
Next
* whiten data
p1 = p1 Xor SK(LeapFrogRounds, 0)
p2 = p2 Xor SK(LeapFrogRounds, 1)
p3 = p3 Xor SK(LeapFrogRounds, 2)
p4 = p4 Xor SK(LeapFrogRounds, 3)
p5 = p5 Xor SK(LeapFrogRounds, 4)
p6 = p6 Xor SK(LeapFrogRounds, 5)
p7 = p7 Xor SK(LeapFrogRounds, 6)
p8 = p8 Xor SK(LeapFrogRounds, 7)
* write ciphertext block from p1....p8
Next
End Subroutine LeapFrogEncrypt
Subroutine LeapFrogDecrypt
For BlockNumber = 1 To Blocks
* read ciphertext block into p1....p8
* unwhiten data
p1 = p1 Xor SK(LeapFrogRounds, 0)
p2 = p2 Xor SK(LeapFrogRounds, 1)
p3 = p3 Xor SK(LeapFrogRounds, 2)
p4 = p4 Xor SK(LeapFrogRounds, 3)
p5 = p5 Xor SK(LeapFrogRounds, 4)
p6 = p6 Xor SK(LeapFrogRounds, 5)
p7 = p7 Xor SK(LeapFrogRounds, 6)
p8 = p8 Xor SK(LeapFrogRounds, 7)
For y = 0 To (LeapFrogRounds / 2) - 1
* invert subkeys
x = (LeapFrogRounds - 1) - y
* create the T variables
T1 = A5(p5 Xor SK(x, 4))
T2 = A6(p6 Xor SK(x, 5))
T3 = A7(p7 Xor SK(x, 6))
T4 = A8(p8 Xor SK(x, 7))
* T variable order "B"
p1 = (p1 - T1) And HFF
p2 = (p2 - T2) And HFF
p3 = (p3 - T3) And HFF
p4 = (p4 - T4) And HFF
p1 = p1 Xor A5(A5(T2 Xor T3) Xor T4)
p2 = p2 Xor A6(A6(T3 Xor T4) Xor T1)
p3 = p3 Xor A7(A7(T4 Xor T1) Xor T2)
p4 = p4 Xor A8(A8(T1 Xor T2) Xor T3)
* do other half without swapping
T1 = A1(p1 Xor SK(x, 0))
T2 = A2(p2 Xor SK(x, 1))
T3 = A3(p3 Xor SK(x, 2))
T4 = A4(p4 Xor SK(x, 3))
p5 = (p5 - T1) And HFF
p6 = (p6 - T2) And HFF
p7 = (p7 - T3) And HFF
p8 = (p8 - T4) And HFF
p5 = p5 Xor A1(A1(T2 Xor T3) Xor T4)
p6 = p6 Xor A2(A2(T3 Xor T4) Xor T1)
p7 = p7 Xor A3(A3(T4 Xor T1) Xor T2)
p8 = p8 Xor A4(A4(T1 Xor T2) Xor T3)
Next
For y = (LeapFrogRounds / 2) To (LeapFrogRounds - 1)
* invert subkeys
x = (LeapFrogRounds - 1) - y
* create the T variables
T1 = A5(p5 Xor SK(x, 4))
T2 = A6(p6 Xor SK(x, 5))
T3 = A7(p7 Xor SK(x, 6))
T4 = A8(p8 Xor SK(x, 7))
* T variable order "A"
p1 = (p1 - T1) And HFF
p2 = (p2 - T2) And HFF
p3 = (p3 - T3) And HFF
p4 = (p4 - T4) And HFF
p1 = p1 Xor A5(A5(T2 Xor T3) Xor T4)
p2 = p2 Xor A6(A6(T1 Xor T4) Xor T3)
p3 = p3 Xor A7(A7(T4 Xor T2) Xor T1)
p4 = p4 Xor A8(A8(T3 Xor T1) Xor T2)
* do other half without swapping
T1 = A1(p1 Xor SK(x, 0))
T2 = A2(p2 Xor SK(x, 1))
T3 = A3(p3 Xor SK(x, 2))
T4 = A4(p4 Xor SK(x, 3))
p5 = (p5 - T1) And HFF
p6 = (p6 - T2) And HFF
p7 = (p7 - T3) And HFF
p8 = (p8 - T4) And HFF
p5 = p5 Xor A1(A1(T2 Xor T3) Xor T4)
p6 = p6 Xor A2(A2(T1 Xor T4) Xor T3)
p7 = p7 Xor A3(A3(T4 Xor T2) Xor T1)
p8 = p8 Xor A4(A4(T3 Xor T1) Xor T2)
Next
* write plaintext block from p1....p8
Next
End Subroutine LeapFrogDecrypt
Subroutine LeapFrogExpandKey
* replicate key into array
y = 0
For x = 0 To 255
LongKey(x) = k(y)
y = (y + 1) Mod RealKeyLen
Next
* initialize expanded key arrays
For i = 0 To 255
A1(i) = i, A5(i) = i
A2(i) = i, A6(i) = i
A3(i) = i, A7(i) = i
A4(i) = i, A8(i) = i
Next
j = 0
* randomize array
For i = 0 To 255
j = (j + A1(i) + LongKey(i)) And HFF
Exchange A1(i), A1(j)
Next
For i = 0 To 255
j = (j + A1(i)) And HFF, Exchange A1(i), A1(j)
Next
* randomize the other arrays
For i = 0 To 255
j = (j + A1(A2(i)) + A1(LongKey(i))) And HFF
Exchange A2(i), A2(j)
Next
For i = 0 To 255
j = (j + A2(A3(i)) + A2(LongKey(i))) And HFF
Exchange A3(i), A3(j)
Next
For i = 0 To 255
j = (j + A3(A4(i)) + A3(LongKey(i))) And HFF
Exchange A4(i), A4(j)
Next
For i = 0 To 255
j = (j + A4(A5(i)) + A4(LongKey(i))) And HFF
Exchange A5(i), A5(j)
Next
For i = 0 To 255
j = (j + A5(A6(i)) + A5(LongKey(i))) And HFF
Exchange A6(i), A6(j)
Next
For i = 0 To 255
j = (j + A6(A7(i)) + A6(LongKey(i))) And HFF
Exchange A7(i), A7(j)
Next
For i = 0 To 255
j = (j + A7(A8(i)) + A7(LongKey(i))) And HFF
Exchange A8(i), A8(j)
Next
* store zeros to SK array
* make subkeys from S-boxes
For i = 0 To 63
SK(0, 0) = (SK(0, 0) + A1(i)) And HFF
SK(0, 1) = (SK(0, 1) + A2(i)) And HFF
SK(0, 2) = (SK(0, 2) + A3(i)) And HFF
SK(0, 3) = (SK(0, 3) + A4(i)) And HFF
SK(0, 4) = (SK(0, 4) + A5(i)) And HFF
SK(0, 5) = (SK(0, 5) + A6(i)) And HFF
SK(0, 6) = (SK(0, 6) + A7(i)) And HFF
SK(0, 7) = (SK(0, 7) + A8(i)) And HFF
Next
For i = 0 To LeapFrogRounds - 1
SK(i + 1, 0) = (SK(i, 0) + A1(64 + i)) And HFF
SK(i + 1, 1) = (SK(i, 1) + A2(64 + i)) And HFF
SK(i + 1, 2) = (SK(i, 2) + A3(64 + i)) And HFF
SK(i + 1, 3) = (SK(i, 3) + A4(64 + i)) And HFF
SK(i + 1, 4) = (SK(i, 4) + A5(64 + i)) And HFF
SK(i + 1, 5) = (SK(i, 5) + A6(64 + i)) And HFF
SK(i + 1, 6) = (SK(i, 6) + A7(64 + i)) And HFF
SK(i + 1, 7) = (SK(i, 7) + A8(64 + i)) And HFF
Next
For i = 0 To LeapFrogRounds
SK(i, 0) = A5(SK(i, 0))
SK(i, 1) = A6(SK(i, 1))
SK(i, 2) = A7(SK(i, 2))
SK(i, 3) = A8(SK(i, 3))
Next
For i = 0 To LeapFrogRounds
SK(i, 4) = A1(SK(i, 4))
SK(i, 5) = A2(SK(i, 5))
SK(i, 6) = A3(SK(i, 6))
SK(i, 7) = A4(SK(i, 7))
Next
End Sub LeapFrogExpand
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