Question 2

Which from the following is describe Output Feedback mode OFB, where is P_j and P_j-1 are plaintext and previous plaintext, and C_j and C_j-1 ciphertext and previous cipher text, K is a key and E encryption function

	a	Cj = E(K, [Cj-1 XOR Pj])
	b	Cj = E(K, Pj)
	c	Cj = Pj_ E(K, [Cj-1 XOR Pj-1])
	d	None of above

Public key encryption, assume that the A encrypts a Text uses private key and send to B, which one from the following described the process of encryption

	a	Even if B knows who sent the text it cannot be decrypted
	b	It cannot be decrypted at all as no one knows Private key of A
	c	A should send his public key with text
	d	B knows its from A and it could decrypt using A public key

How many bits are in a block of the SHA algorithm?

	a	128
	b	2048
	c	512
	d	56