1
CIPHER Circuit
Specification
Specification:
The CIPHER circuit is specified below using its:
1. Pseudocode
2. Table of input/output ports
3. Timing requirements.
1. Pseudocode:
A = I3; B = I2; C = I1; D=I0
B = B + S[0]
D = D + S[1]
for i = 1 to r do
{
T = (B*(2B + 1)) <<< k
U = (D*(2D + 1)) <<< k
A = ((A ⊕ T) <<< U) + S[2i]
C = ((C ⊕ U) <<< T) + S[2i + 1]
(A, B, C, D) = (B, C, D, A)
}
A = A + S[2r + 2]
C = C + S[2r + 3]
O = (A, B, C, D)
Notation:
w: word size, e.g., w=8 (constant)
k: log2(w) (constant)
A, B, C, D, U, T: w-bit variables
I3, I2, I1, I0: Four w-bit words of the input I
r: number of rounds (constant)
O: output of the size of 4w bits
S[j] : 2r+4 round keys stored in two RAMs. Each key is a w-bit word. The first RAM stores
values of S[j=2i], i.e., only round keys with even indices. The second memory stores values of
S[j=2i+1], i.e., only round keys with odd indices.
Operations:
⊕ : XOR
+ : addition modulo 2w
– : subtraction modulo 2w
* : multiplication modulo 2w
X <<< Y : rotation of X to the left by the number of positions given in Y
X >>> Y : rotation of X to the right by the number of positions given in Y
(A, B, C, D) : Concatenation of A, B, C, and D.
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