# hash(data:) Computes a SHA-256 digest of arbitrary bytes. ``` static func hash(data: Data) -> SHA256.SHA256Digest ``` ## Parameters `data` The bytes to hash. May be empty; SHA-256 of the empty string is the well-defined value `e3b0c442...b855` per FIPS 180-4 §A.1. ## Return Value A [`SHA256.SHA256Digest`](/documentation/OpenSSL/SHA256/SHA256Digest) of exactly 32 bytes. Obtain the lowercase hex form via [`hexString`](/documentation/OpenSSL/SHA256/SHA256Digest/hexString). ## Discussion Produces a fixed 32-byte / 256-bit digest per [FIPS PUB 180-4](https://csrc.nist.gov/publications/detail/fips/180/4/final) by wrapping the legacy C routines [`SHA256_Init`](https://docs.openssl.org/3.6/man3/SHA256_Init/), `SHA256_Update`, and `SHA256_Final`. Typical uses: integrity checks over arbitrary payloads, HMAC-SHA256 key derivation, and content-addressed identifiers (JWT payload fingerprints, Nostr NIP-01 event IDs, Git-style blob hashes). Every call allocates a fresh `SHA256_CTX` on the stack, so the function is safe to call concurrently from multiple tasks without synchronization. Output is stable across platforms and builds. > Note: The `SHA256_*` C family is deprecated in OpenSSL 3.0 in > favor of the `EVP_MD` high-level interface. This wrapper keeps > the legacy path for simplicity and may migrate to `EVP_MD` in > a future release — no public API change is expected.