With the ECB mode, if there is an error in a block of the transmitted ciphertext, only the corresponding plaintext block is affected. However, in the CBC mode, this error propagates. For example, an error in the transmitted C1 (see Figure 20.6 ) obviously corrupts P1 and P21. a. Are any blocks beyond P2 affected? b. Suppose there is a bit error in the source version of P1 Through how many ciphertext blocks is this error propagated? What is the effect at the receiver?

Figure 20.6 illustrates the RC4 logic. (a) Initial state of S and T T S (b) Initial permutation of S Figure 20.6 RC4 (c) Stream generation