Block Cipher vs Stream Cipher – Know the Difference

A Comparison of Cryptographic Algorithms: Block Cipher vs Stream Cipher

Block ciphers and stream ciphers are the two main encryption processes in cryptography. While both ciphers serve the same purpose of data security, they vary in many important ways, making them appropriate for various uses. In this article, we will look at the differences between Block ciphers and Stream ciphers and how both secure communications.

Block Cipher

It is an encryption method that encrypts a fixed group of bits, or “block,” at a time. The block size of a cipher can differ, but typical block sizes are 64 bits, 128 bits, or 256 bits, and it employs a secret key for encrypting the data, and the same key can decrypt the data as well. The encryption procedure of this method includes several iterations of a mathematical operation known as a substitution-permutation network.

• The Data Encryption Standard (DES), TripleDES, and the Advanced Encryption Standard (AES) are popular block cipher algorithm variants. (AES).
• The stream cipher employs a shared key and runs on its input one bit at a time, which is the counterpart of a block cipher.
• Alternatives to the block cipher method include public-key encryption and asymmetric cryptography.

Block Cipher: Methods of Operation

• Electronic Code Book (ECB) Mode
• Cipher Feedback (CFB) Mode
• Output Feedback (OFB) Mode
• Cipher Block Chaining (CBC) Mode
• Counter (CTR) Mode

Procedural rules for a generic block cipher govern these modes, which interestingly yield different properties that enhance the security of the underlying block cipher.

Examples of Block cipher

Here are some examples of block ciphers, including their features:

• Advanced Encryption Standard (AES)
• Blowfish
• Twofish
• Serpent
• Triple DES (3DES)

Advanced Encryption Standard (AES)

AES is one of the world’s most used block ciphers for data security. It has a block size of 128 bits and key lengths of 128 bits, 192 bits, or 256 bits. The algorithm is potent in hardware and software and extensively used in high-security apps such as finance, healthcare, and government.

Blowfish

Blowfish is a symmetric block cipher that works on 64-bit blocks and can handle key values up to 448 bits. Its creation aimed to replace the outdated DES algorithm, and it has gained recognition for its ease of use, speed, and efficiency. While it may not be as widely employed as AES, it continues to find application in specific scenarios for confidential data communication.

Twofis

Twofis is a symmetric block cipher that works on 128-bit blocks and allows up to 256 bits of key sizes. It competed in the AES competition and received praise for its high security and versatility. It finds applications in diverse encryption-reliant applications, such as VoIP, virtual private networks, and online banking.

Serpent

The Serpent is a symmetric block cipher created as a contender for the AES competition. It uses a 128-bit block and can handle key values up to 256 bits. It is well-known for its excellent security and resilience to various kinds of malicious activities. Although it is not as extensively used as a few other block ciphers, it is still used for certain secure communication applications.

Triple DES (3DES)

Triple DES is an updated version of the DES algorithm that employs three DES keys to provide more effective and stronger encryption. It works on 64-bit blocks and has key lengths of up to 168 bits. While AES is faster and more efficient than 3DES, older applications that necessitate secure transmission continue to utilize 3DES.

Learn more about Difference Encryption Algorithms.

Stream Cipher

It is an encryption method that encodes data in streams of bits or one bit at a time. Consequently, this technique of encryption works bit by bit, using keystreams to create ciphertext for plain text communications of arbitrary lengths. The cipher connects a key of 128 or 256 bits and a nonce digit of 64-128 bits to produce the keystream – a pseudorandom number XORs with the plaintext to generate the ciphertext.

Since an error in the translation of one bit rarely impacts the complete plaintext block, stream cipher encryption methods are less likely to propagate system-wide mistakes; and also linear and constant, which makes it simpler and faster to implement.

• Generating pseudorandom cipher digits involves using digital shift registers and multiple random seed values.
• For this sort of encryption to be safe, the pseudorandom cipher numbers should be random (unpredictable), and the key must never be used more than once.
• State cipher is another name for a stream cipher. The term “state cipher” refers to the reality that the cipher’s present state determines the encryption of each number.

Categories of Stream Ciphers

• Synchronous Stream Ciphers
• Self-Synchronizing/Asynchronous Stream Ciphers

Example of Stream Ciphers

Renowned encryption methods that employ stream ciphers include:

• RC4
• Salsa20
• SEAL (Software-optimized Encryption Algorithm)
• ChaCha20

RC4

An encryption technique employs a variable key size of 40 to 2048 bits. It is widely used in wireless transmission methods such as TLS (Transport Layer Security), SSL (Secure Sockets Layer), and the IEEE 802.11 WLAN standard. The keystream is generated by RC4 and combined with the plaintext to generate the ciphertext. The prevalent encryption methods come in various essences, which include  RC4A, SPRITZ, and RC4A+

Salsa20

Contemporary applications, such as Linux IPSec, cryptography, and Tor, heavily rely on its widespread usage. It generates a keystream from a 256-bit key and a 64-bit nonce, which then combines with the plaintext to create ciphertext. Salsa20 is well-known for its high speed and reliability.

SEAL (Software-optimized Encryption Algorithm)

SEAL is an additive binary stream cipher designed for computers with 32-bit CPUs and adequate memory. The encryption standard depends on a pseudorandom family with a length-increasing function and a 160-bit key to convert a 32-bit string into a variable-length string. Scream, PANAMA, HC-256, Rabbit, and Grain are a few other examples of stream ciphers.

ChaCha20

It is widely used in emerging applications. Daniel J. Bernstein created it, which is now included in the most recent versions of TLS and SSH. It generates a keystream that is used to encode data using a 256-bit key, a 96-bit nonce, and a 32-bit counter. ChaCha20 is quicker and more secure compared to Salsa20 and has gained recognition.

Key Differences between Block Cipher vs Stream Cipher

Criteria	Block Cipher	Stream Cipher
Process	Divides the data into blocks and encrypts each one individually.	Encrypts data bit by bit or byte by byte.
Speed	Slower than stream ciphers in encrypting large amounts of data	Faster than block ciphers in encrypting large amounts of data.
Decryption	Reverse encryption or decryption is more difficult in block cipher than in stream cipher because more bits are combined to be encrypted in this situation.	XOR is used in a stream cipher for encryption that can be rapidly transformed back to plain text.
Principle	It employs both the “confusion” and “diffusion” standards for the conversion required for encryption	It uses “confusion” alone for the conversion
Security	Due to the challenges involved in encrypting and decrypting each block, generally, block ciphers are more secure than stream ciphers.	Because of the potential of key-stream reuse or attack on the initialization vector, they are usually considered less secure than block ciphers.
Algorithm modes used	ECB (Electronic Code Book) CBC (Cipher Block Chaining)	CFB (Cipher Feedback) OFB (Output Feedback)
Key management	Since each block’s key must be initialized and managed individually, key management becomes more complicated.	Less complicated key management is required because a single key can be used to encrypt and decrypt the complete communication.
Implementation	The most widely used algorithm is the Feistel Cipher.	The primary application of Stream Cipher is Vernam Cipher.
Applicability	Usually used to encrypt a large amount of data or communications.	Used for encrypting and securing real-time communications or small communications
The number of bits used.	64 bits or greater	8 Bits
Examples	DES, AES, Blowfish	RC4, Salsa20, ChaCha20

Know What is SSL Cipher Suite and how it works?

Final Words

Finally, Block Cipher and Stream Cipher are two distinct encryption methods. Block ciphers are appropriate for applications that handle data blocks, such as file transmission, e-mail, and databases, and are majorly used to encrypt large amounts of data. On the other hand, stream ciphers are more suitable for applications that require the encryption/decryption of a stream of data, like browser/Web communication, and are used to encrypt small amounts of data. The application determines the appropriate encryption technique, the quantity of data, and the degree of security needed.