How many plaintexts and ciphertexts are necessary

Assignment Help Basic Computer Science

Reference no: EM131329326

We consider known-plaintext attacks on block ciphers by means of an exhaustive key search where the key is k bits long. The block length counts n bits with n > k.

1. How many plaintexts and ciphertexts are needed to successfully break a block cipher running in ECB mode? How many steps are done in the worst case?

2. Assume that the initialization vector IV for running the considered block cipher in CBC mode is known. How many plaintexts and ciphertexts are now needed to break the cipher by performing an exhaustive key search? How many steps need now maximally be done? Briefly describe the attack.

3. How many plaintexts and ciphertexts are necessary, if you do not know the IV?

4. Is breaking a block cipher in CBC mode by means of an exhaustive key search considerably more difficult than breaking an ECB mode block cipher?

Reference no: EM131329326

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