What is Block Cipher? Block Cipher Operation Modes

Block Cipher is an encryption method in which data is divided into blocks of fixed size. Nowadays, information security is extremely important and Block Cipher plays an essential role in ensuring data security. So what is Block Cipher? Let's find out with  TipsMake  through the article below.

What is Block Cipher?

Block Cipher is a data encryption method in which data is divided into fixed-size blocks, usually 64 or 128 bits. Each block of data is encrypted independently or linked together with other blocks depending on the mode of operation used. Block Cipher uses a symmetric encryption algorithm, meaning that the same key is used for both encryption and decryption.

What is Block Cipher? Block Cipher Operation Modes Picture 1

What is Block Cipher?

The history of Block Cipher development dates back to the 1970s when DES was introduced as an official encryption standard for the US government. Since then, much research has been done to improve the security and performance of encryption algorithms.

How does Block Cipher work?

Steps in Block Cipher encryption process:

1. Data block division: Input data will be divided into equal blocks.
2. Applying an encryption function: Each block of data is subjected to an encryption function using a secret key. This function performs complex mathematical operations to transform the original block of data into an unreadable form.
3. Generate encrypted data blocks: After applying the encryption function to all the blocks, the final result will be a chain of encrypted data blocks.

The decoding process includes:

1. Blocking the encrypted data: Similar to the first step in the encryption process.
2. Applying the decryption function: Each encrypted block of data will be subjected to a decryption function, using the same secret key.
3. Restore original data: After applying the decryption function to all blocks, the original data will be recovered.

Block Cipher Modes of Operation

Block Cipher modes of operation are the different methods in which data is encrypted and decrypted. Below are some of the most common modes of Block Cipher.

Electronic Codebook (ECB) Mode

Electronic Codebook (ECB) mode is one of the simplest and most understandable modes in Block Cipher. In this mode, each block of data is encrypted independently. When a block of data is encrypted, it uses the same secret key to generate a block of encrypted data. Therefore, if the same block of data is encrypted multiple times, the encryption result will always be the same.

Cipher Block Chaining (CBC) Mode

Unlike ECB mode, Cipher Block Chaining (CBC) encrypts blocks of data in a chained manner. The first block of data is encrypted with the secret key. However, subsequent blocks of data are encrypted by combining the previous block of data with the key.

What is Block Cipher? Block Cipher Operation Modes Picture 2

Cipher Block Chaining (CBC) Mode

CBC mode offers many security benefits over ECB. However, it also has some disadvantages. Chaining encryption can slow down processing, especially when encrypting large amounts of data. 

Ciphertext Feedback (CFB) mode

Ciphertext Feedback (CFB) mode allows data to be encrypted in a way that does not require waiting for the encryption of an entire block to be completed first. The input data is encrypted byte by byte instead of block by block. This is a unique feature of CFB, allowing it to function like a stream cipher. When encrypting a byte, the previous block of data is used to generate a new value, which encrypts the current byte.

Output Feedback Mode (OFB)

Output Feedback (OFB) mode is similar to CFB but has some significant differences.

In OFB mode, an initialization value (IV) is used to generate a stream of encrypted data. This stream is used to encrypt each input block. Unlike CFB, OFB does not use previously encrypted data blocks to generate new values, but instead uses a fixed initialization value.

Counter Mode (CTR)

Counter Mode (CTR) is commonly used in Block Cipher. It converts the encryption process into a parallelizable process. Each block of data is encrypted by combining it with an incrementing counter value. This counter value is encrypted together with the secret key to create an encrypted data stream. This stream is then combined with the input data block to produce the encrypted data block.

One of the big advantages of CTR is the ability to encode blocks of data in parallel, allowing for increased processing speed and performance.

Authenticated encryption with additional data modes

Authenticated Encryption is an important concept in data security, allowing verification of the integrity of encrypted data. There are various methods to implement authenticated encryption, which include combining Block Cipher modes of operation with authentication algorithms. 

Galois/Counter Mode (GCM): Is an operating mode that combines CTR encryption with authentication via Galois operations. GCM allows for simultaneous encryption and authentication of data, providing high performance and good security.

Cipher Block Chaining Message Authentication Code (CBC-MAC): Combines CBC to provide integrity to encrypted data. This method is quite simple but does not support simultaneous encryption.

Conclude

Block Cipher is one of the important data encryption methods, thanks to the ability to divide data into blocks and encrypt them independently, Block Cipher not only brings high performance but also contributes to improving information security.

Block Cipher modes of operation, from ECB, CBC to CTR, each have their own advantages and disadvantages and are suitable for specific applications. Choosing the appropriate mode depends not only on the security requirements but also on the processing power and speed required by the application.

Jessica Tanner

Update 01 April 2025