A blockcipher normally can be considered as a pseudorandom permutation, i.e. E : {0,1}128 {0,1}128, when encrypting a picture m, say with n = 105 blocks (each with 128 bits, total about 1.5 megabytes), and we use an ECB mode, i.e., c1 = E(k,m1),...,cn = E(k,mn). It is very common that the picture has many identical blocks, e.g., m1 = m2 = ...,= mk, explain why ECB mode will reveal this pattern; and why other modes such as counter mode will not? A counter mode encryption generates ciphertext as c1 = E(k,1) m1,c2 = E(k,2) m2,...,cn = E(k,n) mn and here 1,2,3,...,n are all treated as a 128-bit binary string, assuming n 2128 1.