A Cipher refers to a code that encrypts a message. Block ciphers and Stream ciphers are two symmetric encryption algorithms widely used in modern cryptography. Block ciphers and Stream ciphers have some differences, but they also have some similarities.
We will explore these differences and similarities and discuss the appropriate use cases for each. By the end of this blog post, you will get familiar with the concepts in detail. So keep reading the blog till the end to learn about Block cipher and Stream cipher.
What is a Block Cipher?
A Block cipher is a type of cipher in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. Simply put, a Block cipher is a symmetric encryption algorithm that encrypts a fixed-sized block of plaintext at a time rather than encrypting one bit at a time as in a Stream cipher.
It operates when a series of mathematical transformations, or “rounds,” gets applied to the plaintext to produce the ciphertext. The length of the block of plaintext encrypted by a Block cipher gets determined by the encryption algorithm and is often 64 or 128 bits long.
Where are the Block Ciphers used?
Block ciphers are widely used in modern cryptography and are the basis for many popular encryption algorithms, such as AES and Blowfish.
What are the modes of operation of Block Cipher?
The modes of operation of a Block cipher are the different methods that combine the plaintext blocks with the encryption key to encrypt the plaintext and produce the ciphertext. The modes of operation of Block cipher are:
Electronic Codebook (ECB) Mode
In ECB, each plaintext block gets encrypted independently using the same key. It means that if the same plaintext block appears multiple times in the message, it will produce the same ciphertext block each time, making the encrypted message vulnerable to attacks.
Cipher Block Chaining (CBC) Mode:
In CBC, each plaintext block is first XORed with the previous ciphertext block before being encrypted. It makes the encrypted message more secure because even if the same plaintext block appears multiple times, it will produce a different ciphertext block each time.
Cipher Feedback (CFB) Mode
In CFB, the previous ciphertext block is encrypted and later XORed with the plaintext block to produce the current ciphertext block. This mode is similar to the CBC mode, but the encryption and XOR operations get performed in a different order.
Output Feedback (OFB) Mode
In OFB, the previous ciphertext block is encrypted and used as a keystream to encrypt the current plaintext block. This mode is similar to the CFB mode, but the encryption and XOR operations get performed in a different order.
Counter (CTR) Mode
In CTR, a counter generates an XORed keystream with the plaintext block to produce the ciphertext block. This mode is similar to OFB mode and uses a counter instead of encrypting the previous ciphertext block to generate the keystream.
What is a Stream Cipher?
A Stream cipher is a type of cipher that encrypts plaintext a bit or byte at a time and is typically much faster than a Block cipher. A Stream cipher refers to a symmetric encryption algorithm that encrypts data by combining it with a stream of pseudorandom bits, known as a keystream.
Unlike a Block cipher, which encrypts a fixed-sized block of plaintext at a time, a Stream cipher encrypts one bit or byte at a time, making it much faster than a Block cipher.
Where are the Stream Ciphers used?
Stream ciphers get used in applications where high-speed encryption is required, such as in wireless communication or real-time data transmission. Some examples of Stream ciphers are RC4 and Salsa20.
What are the types of Stream Cipher?
There are two kinds of Stream ciphers, namely-
1. Synchronous Stream Ciphers
In a Synchronous Stream Cipher, the keystream generates independently of the plaintext and ciphertext. It means the same key encrypts multiple messages. The keystream gets bred using a pseudorandom number generator (PRNG), which initializes using a key and an initialization vector (IV).
Example– RC4 and Salsa20
2. Self-Synchronizing Stream Ciphers
In a Self-synchronizing Stream Cipher, the keystream is generated based on the plaintext and ciphertext, which means that the keystream is “synchronized” to the message. It makes the cipher more resilient to attacks because any errors or deviations in the keystream will get corrected as the encryption proceeds.
Example– MUGI and Trivium
What are the other variations of Stream Ciphers?
Duplexing Stream Ciphers
In a Duplexing Stream Cipher, the keystream gets generated using both the plaintext and the ciphertext, which provides enhanced security than Self-synchronizing Ciphers.
Cryptographically Strong Pseudorandom Number Generators (CSPRNGs)
CSPRNGs secure and resist attacks. They are typically used in Synchronous Stream Ciphers to generate the key stream.
LFSR-based Stream Ciphers
These ciphers use a linear feedback shift register (LFSR) to generate the keystream. LFSRs are a type of PRNG that is simple to implement and widely used in Stream ciphers.
What is the difference between Block Cipher and Stream Cipher?
Block ciphers and Stream ciphers get differentiated on the following basis-
A Block cipher encrypts a fixed-sized block of plaintext at a time, while a Stream cipher encrypts one bit or byte at a time.
A Block cipher operates on the plaintext in rounds, while a Stream cipher operates on the plaintext bit by bit or byte by byte.
In a Block cipher, the same plaintext block will always produce the same ciphertext block, while in a Stream cipher, the same plaintext produces a different ciphertext each time.
Block ciphers typically use a fixed key size, while Stream ciphers can use variable-length keys.
Block ciphers are slower than Stream ciphers, because they operate on larger blocks of data.
- Block ciphers are more secure than Stream ciphers, because they are less susceptible to attacks.
- Block ciphers have a well-defined security level, while the security of Stream ciphers can vary depending on their implementation.
Block ciphers are typically used for long-distance communication or encrypt sensitive data, while Stream ciphers transmit real-time data or wireless communication.
Block ciphers use different modes of operation, while Stream ciphers use keystream generators.
Block ciphers are more resistant to cryptanalysis, while Stream ciphers are more susceptible to attacks.
What are the similarities between Block Cipher and Stream Cipher?
- Both are types of symmetric encryption algorithms.
- Both use a secret key for encryption and decryption.
- Both got designed to be efficient and fast.
- Both can get implemented in hardware or software.
- Both get widely used in modern cryptography.
- Both are subject to cryptographic attacks.
- Both can break if the key is known or easily guessed.
- Both can get used in diverse applications, including secure communication, data encryption and authentication, etc.
Which is better- Block Cipher or Stream Cipher?
It is not accurate to say that one type of cipher is “better” than the other because the definition of an appropriate cipher depends on the requirements. Block ciphers are better suited for applications that require strong security, such as encrypting sensitive data or transmitting messages over long distances. Stream ciphers are better suited for applications demanding high-speed encryption, such as real-time data transmission or wireless communication.
What courses can help in learning Block cipher and Stream cipher?
Block cipher and Stream cipher are both required for encryption. Both implemented together can provide the perfect encryption. Therefore, the specifications and differences make both stand out in cybersecurity. Also, since you are familiar with Block cipher and Stream cipher, you can enroll in the courses to outshine IT.
Any suggestions and comments regarding the topic are welcome. Happy Learning!