When encrypting public key systems operate in a manner analo

When encrypting, public key systems operate in a manner analogous to a block cipher in ECB mode. That is, the plaintext is chopped into blocks and each block is encrypted independently. Why is ECB mode a bad idea when encrypting with a block cipher? Why is a chaining mode, such as CBC, a much better way to use a block cipher? Why is it not necessary to perform any sort of chaining mode when using public key encryption? Could your reasoning in part b be applied to block ciphers? Why or why not?

Solution

a)ecb mode is a bad idea for encrypting with a block cipher because it has a disadvantage The main problem with this tmode is that any of the given resident properties of the plaintext might well show up in the ciphertext.This means it adds to complexity. Moreover, by analyzing the patterns we may be able to deduce properties that we otherwise thought were hidden.

On the other hand cbc mode is better because with this we can manage a partial decryption and easily fill in the blanks, for example if extracting data from an encrypted hard disk. Moreover with this mode if we are missing a few blocks in the sequence then the encryption becomes impossible.

2)It is not necessary to perform any type of chaining with publick key encryption because publick key encryption has 2 keys one private and one publick key and these keys are enough to perform chaining rather than any modes.

3)No the reasoning cannot be applied to block ciphers because it can be applied to every character rather than the entire block.The bigger the block the complicated it becomes.IT takes plave byte by byte not block by block.This is the exact reason for this and moreoever 2 keys may not be enough to secure chaining of the blocks.