the repeating block in plain text produces the same ciphertext, a new technique was required which is Cipher Block Chaining (CBC) Mode. Hence, ECB is considered for encrypting the small messages which have a rare possibility of repeating text. Here also the same key is used to decrypt each block which was used to encrypt each block.Īs the same key used to encrypt each block of plain text there arises an issue that for a repeating plain text block it would generate the same cipher and will ease the cryptanalysis to crack the algorithm. This ciphertext is again divided into blocks, each of 64-bit and each block is decrypted independently one at a time to obtain the corresponding plain text block. When the receiver receives the message i.e. The same key is used to encrypt each block. Each block is encrypted one at a time to produce the cipher block. In electronic codebook mode (ECB) the plain text is divided into the blocks, each of 64-bit. This is considered to be the easiest block cipher mode of operation. These five modes of operation enhance the algorithm so that it can be adapted by a wide range of applications which uses block cipher for encryption. There are five important block cipher modes of operation defined by NIST. It is suggested that the key schedule should confirm the strict avalanche effect and bit independence criterion. The Function F should be designed such that it possesses a bit independence criterion which states that the output bits must change independently if there is any change in the input bit. Well, while designing the function F it should be confirmed that it has a good avalanche property which states that a change in one-bit of input must reflect the change in many bits of output. More the function F is nonlinear, more it would be difficult to crack it. The criterion that strengthens the function F is it non-linearity. The function F of the block cipher must be designed such that it must be impossible for any cryptanalysis to unscramble the substitution. It is considered that even if the function F is relatively weak, the number of rounds would make the algorithm tough to break. It is considered that more is the number of rounds, difficult is for cryptanalysis to break the algorithm. The number of rounds judges the strength of the block cipher algorithm. However, this limitation was resolved by implementing chaining in the block cipher.Ī block cipher is designed by considering its three critical aspects which are listed as below: That’s why operating one block of bits at a time makes it faster as compared to a stream cipher.īut there was a limitation in the block cipher as it would generate the same ciphertext for the repeating text pattern in plain text. Operating bit by bit is a very time-consuming process and as block cipher is a computer-based cryptographic algorithm it needs to be fast. On an all the block cipher operates on a block of bits at a time instead of one bit a time. In DES the decryption algorithm is the same as the encryption one. Key of 56-bit is applied to each block of plain text to produce its corresponding ciphertext of 64-bit.ĭuring decryption also only one block of ciphertext is operated at a time to produce its corresponding block plain text. DES operates on one block of plain text at a time. Data Encryption Standard (DES) is the best example of it.ĭES divides the plain text into the number of blocks, each of 64-bit. While decryption also only one block of ciphertext is operated to produce its corresponding plain text. At a time, block cipher operates only on one block of plain text and applies key on it to produce the corresponding block of ciphertext. Content: Block Cipher in Cryptographyīlock cipher is an encryption method which divides the plain text into blocks of fixed size. We will also consider the design principle of a block cipher and the modes of operation of the block cipher. In this section, we will discuss the definition of block cipher.
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