Block Cipher 

A block cipher encrypts bits, the smallest unit of computational information, in blocks. In contrast, other types of encryption methods tend to encrypt bits one by one. Block ciphers are frequently used to encrypt large amounts of data into data blocks. 

While they are effectively used in isolation, block ciphers are also commonly utilized as smaller components within other larger cryptographic protocols, making them an extremely valuable tool in the world of encryption. 

What is a block cipher? 

Modern block ciphers are based on the design of an iterated product cipher. With the use of a fixed key, a block cipher encrypts groups of data in order to maintain maximum confidentiality and security. 

Each block typically consists of 128 bits. Block ciphers then encrypt this data, transforming it from plaintext to ciphertext. A series of different mode operations may also be implemented to further protect the encrypted data. 

Furthermore, a block cipher makes use of two different algorithms – one for encryption and another for decryption. Through the use of a secret key, block ciphers can transform 128-bit blocks from plaintext to ciphertext and back again. 

How does a block cipher work? 

Block ciphers allow plaintext to be transformed into ciphertext via an encryption process using a special key. While most block ciphers are made up of 128-bit blocks, this isn’t necessarily the case, and the size of the blocks, and subsequently the keys, may vary. The keys are a predetermined length – 128 bits, 192 bits or 256 bits long – and most often, the relative strength of the cipher can be determined with this detail. 

The size of the blocks influences the ease at which hackers may be able to decrypt the ciphertext. If they are too small, attackers may solve the encryption relatively quickly as there is less data to sift through and decode. However, if blocks are too large, they are not able to operate as efficiently as possible. Thus, most block ciphers consist of 128 bits, or other similar sizes that are also divisible by eight. 

Since it is unlikely that the total data will be perfectly divisible by 128 bits, or however large the blocks are, a method called padding is used to ensure that the last block is always complete. This is done by adding redundant information to the block to make each block equal in size. 

Different types of block ciphers 

While there is a plethora of different types of block ciphers, only some of them are known publicly. They vary in functionality and popularity, as some of them were developed more recently than others. The most commonly known and used types of block ciphers are listed below: 

  • Digital Encryption Standard (DES) 
  • Triple Digital Encryption Standard (TDES) 
  • Advanced Encryption Standard (AES) 
  • IDEA 
  • Twofish 
  • Serpent 

Today, DES and AES are known as two of the most used and influential block ciphers. 

The advantages and disadvantages of block ciphers 

Just like most methods of encryption, block ciphers have both advantages and disadvantages to their use. 

Advantages of using block ciphers 

  • While they may be tampered with, they generally go undetected and boast strong resistance. 

Disadvantages of using block ciphers 

  • The encryption speed isn’t as fast as other methods may be. This is because encryption occurs within entire blocks and multiple bits at a time. 
  • Small mistakes in even just one symbol may jeopardize the entire block, allowing for errors to spread quickly. 

Protect your business with Sangfor 

Sangfor offers a wide range of IT infrastructure solutions in the areas of cloud computing and network security. If you want to rest assured that your business networks, online presence, and confidential data is as secure as possible through tools like block ciphers, get in touch with a member of our team today. 


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