Question

Implement the A5/1 algorithm. Suppose that, after a particular step, the values of the register are: X = (x0, x1, …, x18) = (1010101010101010101) Y = (y0, y1, …, y21) = (1100110011001100110011) Z = (z0, z1, …, z22) = (11100001111000011110000) List the next 32 keystream bits and give the contents of X, Y, and Z after these 32 bits have been generated.

Answer 1

Check the explanation

Step-by-step explanation:

After a particular step the registers X, Y and Z values are as it is in the first attached image below.

Now calculate the key stream bit, s using the following formula:

key stream bit , s= x0 XOR y0 XOR z0

s= 1 XOR 1 XOR 1

Hence, the 1st key bit stream ,s= 1

Now, for the next step we have to re calculate the contents of registers X, Y and Z as it is in the second attached image below.

For register X:

t= x5 XOR x2 XOR x1 XOR x0

= 0 XOR 1 XOR 0 XOR 1

t=0

For register Y:

t= y1 XOR y0

=1 XOR 1

t=0

For register Z:

t= z15 XOR z2 XOR z1 XOR z0

=1 XOR 1 XOR 1 XOR 1

t=0

Now, the contents of X, Y and X are as it is in the third attached image below.

Key stream bit, s= x0 XOR y0 XOR z0

S= 0 XOR 1 XOR 1

Hence the 2nd key stream bit, s= 0