Stream Cipher Advantages And Disadvantages

Part A.

1. Block Cipher is a method for encrypting the plain text to cipher text by breaking the plain text into blocks having the same size (64 or 128) as usual. It encrypts the group of blocks, block by block instead of bit at a time.

Stream Cipher is a method for encrypting the plain text to cipher text by applying the algorithm to bit level. As stream cipher deals with a very small segment of data, the start encrypting data on the fly, bit at once and sometimes Byte.

2. Advantages of Block cipher:

1. The information of one plaintext is diffused out into different cipher text symbols; hat what we call “High diffusion”.

2. Immunity of Tampering; it is hard insertion of symbols without being detected. Disadvantages

Fast and easy to implement in hardware.

2. Low error propagation: error encrypting any symbol will not affect the other symbols. Disadvantages:

1. Every information of plain text symbol will be contained in one cipher text symbol; it is Low diffusion.

2. Stream ciphers could be vulnerable if used incorrectly, like to use the same key more than once. 3. Stream cipher is suitable when the input stream length is not predictable or the input buffering is limited. 4. The two approaches of Block cipher as below:

• Each block will be encrypted independently than the others

• Each block will dependent on the output of the previous block.

 Electronic Codebook (ECB) is an independent encryption approach, the key used for encryption will be used for all blocks and the encryption of the blocks will be independent from the other blocks. Drawbacks as below:

• If two blocks have the same plaintext; will produce the same ciphertext and as the positions of the cipher text keeps same plaintext then this will cause vulnerability.

• ECB is not workable when the data includes long repetitive stings of 0 and 1, like

MD5 describes mathematical functions that work on the variable string length, and one of its common uses, validating strings or files. It is based on simple ideas and not complicated such like how it looks like; first we split the String or File into blocks and an algorithm will apply to the file or String to create MD5 hash. One of the vulnerabilities is that MD5 is one way function and can’t be reversed. A misunderstanding or mistake that people may fall in is that MD5 is used for encryption; it is not but a cryptographic hash algorithm.