Block ciphers are encryption algorithms that break up the text to be encrypted (plaintext) into blocks of a fixed length and apply the encryption block-by-block.
Block ciphers are generally built using a design strategy known as a Feistel cipher.
How Data Is Encrypted in Fixed-Size Chunks for Maximum Security
Recent block ciphers, such as AES (Rijndael) have been built using a combination of substitution and permutation called a Substitution-Permutation Network (SPN).
Feistel ciphers are based on the Feistel network, which is a structure developed by Horst Feistel.
This structure is based on the idea of combining multiple rounds of repeated operations to achieve desirable cryptographic properties known as confusion and diffusion.
Feistel networks operate by dividing data into two blocks (left and right) and processing these blocks via keyed round functions in iterations to provide sufficient pseudorandom permutation.
Confusion makes the relationship between the encrypted text and plaintext complex.
In practice, A in plaintext is replaced by X in encrypted text.
Why This Matters for Blockchain Technology
In modern cryptographic algorithms, substitution is performed using lookup tables called S-boxes.
The diffusion property spreads the plaintext statistically over the encrypted data.
This ensures that even if a single bit is changed in the input text, it results in changing at least half (on average) of the bits in the ciphertext.
Confusion is required to make finding the encryption key very difficult, even if many encrypted and decrypted data pairs are created using the same key.
Key Points to Remember
- Block ciphers Block ciphers are encryption algorithms that break up the text to be encrypted (plaintext) into blocks of a fixed length and apply the encryption block-by-block.
- Block ciphers are generally built using a design strategy known as a Feistel cipher.
- Recent block ciphers, such as AES (Rijndael) have been built using a combination of substitution and permutation called a Substitution-Permutation Network (SPN).
- Feistel ciphers are based on the Feistel network, which is a structure developed by Horst Feistel.
Going Deeper: Advanced Concepts
In practice, this is achieved by transposition or permutation.
A key advantage of using a Feistel cipher is that encryption and decryption operations are almost identical and only require a reversal of the encryption process to achieve decryption.
DES is a prime example of Feistel-based ciphers: Simplified operation of a block cipher Various modes of operation for block ciphers are Electronic Code Book (ECB), Cipher Block Chaining (CBC), Output Feedback (OFB) mode, and Counter (CTR) mode.
These modes are used to specify the way in which an encryption function is applied to the plaintext.
Conclusion
Block ciphers represents one of the many innovative layers that make blockchain technology so powerful and transformative. As distributed systems continue to evolve, a solid understanding of these core concepts becomes increasingly valuable — not just for developers, but for anyone building, investing in, or working alongside blockchain-powered systems.
Whether you are just starting your blockchain journey or deepening existing expertise, mastering these fundamentals gives you the tools to think clearly about decentralized systems and make smarter decisions in this rapidly evolving space.