Triple DES − It is a variant scheme based on repeated DES applications.
It is now considered as a ‘broken’ block cipher, due primarily to its small key size. Most popular and prominent block ciphers are listed below.ĭigital Encryption Standard (DES) − The popular block cipher of the 1990s. There is a vast number of block ciphers schemes that are in use. Also, padding may render the system insecure at times, if the padding is done with same bits always. Too much padding makes the system inefficient. The process of adding bits to the last block is referred to as padding.
In our example, the remaining 22 bits need to have additional 42 redundant bits added to provide a complete block. The last block of bits needs to be padded up with redundant information so that the length of the final block equal to block size of the scheme.
#Block cipher 64 bits
For example, a 150-bit plaintext provides two blocks of 64 bits each with third block of balance 22 bits. The length of plaintexts is mostly not a multiple of the block size. Multiples of 8 bit − A preferred block size is a multiple of 8 as it is easy for implementation as most computer processor handle data in multiple of 8 bits.īlock ciphers process blocks of fixed sizes (say 64 bits). Such plaintexts will need to be padded before being encrypted. A larger block size makes attack harder as the dictionary needs to be larger.ĭo not have very large block size − With very large block size, the cipher becomes inefficient to operate. If the attacker discovers the plain text blocks corresponding to some previously sent ciphertext blocks, then the attacker can launch a type of ‘dictionary attack’ by building up a dictionary of plaintext/ciphertext pairs sent using that encryption key. Then the possible plaintext bits combinations are then 2 m. Though any size of block is acceptable, following aspects are borne in mind while selecting a size of a block.Īvoid very small block size − Say a block size is m bits. The strength of cipher depends up on the key length. The choice of block size does not directly affect to the strength of encryption scheme. The size of block is fixed in the given scheme. The basic scheme of a block cipher is depicted as follows −Ī block cipher takes a block of plaintext bits and generates a block of ciphertext bits, generally of same size.
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