What is meant by a 'block cipher' in cryptography?

In cryptography, a block cipher specifically refers to a symmetric encryption algorithm that processes fixed-size blocks of data. This means that regardless of the size of the original data, the cipher divides it into uniform chunks or blocks, typically 64, 128, or 256 bits depending on the specific algorithm used. Each block is encrypted independently using the same cryptographic key, which is a hallmark of symmetric encryption. This approach allows block ciphers to efficiently manage data and provides a consistent security mechanism across all the blocks.

The concept of encrypting fixed-size blocks helps ensure that the entire data set can be handled securely and methodically, making block ciphers suitable for various applications, including file encryption and secure communications. This fixed-size characteristic differentiates block ciphers from other types of encryption methods, such as stream ciphers, which process continuous streams of data rather than distinct blocks. Therefore, the definition aligns perfectly with the characteristics of symmetric encryption and the operational methodology involved in block ciphers.