What is a characteristic of SHA-256?

SHA-256 stands for Secure Hash Algorithm 256-bit and is a member of the SHA-2 family of cryptographic hash functions. One of its defining characteristics is that it produces a fixed-size output, specifically a 256-bit hash value. This means that no matter the size of the input data, whether it be a single byte or an entire file, the hash produced will always be 256 bits in length.

This fixed output size is crucial for applications in digital signatures, password hashing, and data integrity verification, as it ensures consistency and helps maintain security across different platforms and systems. The design of SHA-256 ensures that even the slightest change in input will result in a completely different hash output, enhancing security against collision attacks.

In contrast, the other options describe characteristics that are not applicable to SHA-256. For example, it does not use variable length keys, as it is not an encryption algorithm; rather, it is a hashing function. Additionally, SHA-256 is not an encryption algorithm at all, let alone a symmetric one, and it is not specifically designed for data compression, but rather for producing a unique digest of the data.