Weak Key for Block Cipher

Question

Give a brief explanation of Weak Key for Block Cipher.

Answer 1

Weak keys are secret keys with the precise value for that the block cipher in question will show convinced regularities in encryption or, in other cases, the poor level of the encryption. For illustration, with DES there are four keys for that encryption is precisely the same as decryption. This means which when one were to encrypt two time with one of such kind of weak keys, then the original plaintext would be recovered. For IDEA there is a class of keys for which cryptanalysis is hugely facilitated and the key can be recovered. But, in both such cases, the number of weak keys is such the small fraction of all possible keys which alter of picking one at random is exceptionally slight. In such cases, they pose no imperative threat to the security of block cipher when employed for encryption.