1. write programs to implement the following: 1) one-time pad 2) the RC4 stream cipher 3) construction for a deterministic polynomial-time algorithm G zs a variable output-length pseudorandom generator if the following hold:

1. Let s be a string and .e > 0 be an integer. Then G ( s, 11) outputs a string of length .e.

2. For all s, .e, f' with .e < .e, the string G( s, 1 E) is a prefix of G(s, 1 E') .

3. Define GE (s) def G(s, 1E(Isl)). Then for every polynomial C() it holds that G E is a pseudorandom generator with expansion factor .e. 4) stream-cipher mode of operation for encrypting a single variable-length message