# HashFunction A type that performs cryptographically secure hashing. ``` @preconcurrency protocol HashFunction : Sendable ``` ## Overview The [`HashFunction`](/documentation/CryptoKit/HashFunction) protocol describes an interface for computing a fixed-length digest from an arbitrarily large collection of bytes. Because the digest is small, you can quickly compare the digests to detect a difference in two corresponding data sets. Alternatively, transmit or store data with its digest to detect changes introduced after initially calculating the digest. Use one of the protocol’s adopters, like [`SHA256`](/documentation/CryptoKit/SHA256), [`SHA384`](/documentation/CryptoKit/SHA384), or [`SHA512`](/documentation/CryptoKit/SHA512), to output a digest whose value varies significantly over even small differences in the input data. Checking a digest doesn’t guard against changes made by a malicious user who also changes the digest to match. To handle this, compute a message authentication code (MAC) like [`HMAC`](/documentation/CryptoKit/HMAC) instead. MACs rely on hashing, but incorporate a secret cryptographic key into the digest computation. Only a user that has the key can generate a valid MAC. ## Topics ### Specifying the output type [`Digest`](/documentation/CryptoKit/HashFunction/Digest) [`Digest`](/documentation/CryptoKit/Digest) A type that represents the output of a hash. ### Computing a hash in one call [`hash(data:)`](/documentation/CryptoKit/HashFunction/hash(data:)) Computes the digest of the bytes in the given data instance and returns the computed digest. ### Computing a hash iteratively [`init()`](/documentation/CryptoKit/HashFunction/init()) Creates a hash function. [`update(data:)`](/documentation/CryptoKit/HashFunction/update(data:)) Incrementally updates the hash function with the given data. [`update(bufferPointer:)`](/documentation/CryptoKit/HashFunction/update(bufferPointer:)) Incrementally updates the hash function with the contents of the buffer. [`finalize()`](/documentation/CryptoKit/HashFunction/finalize()) Finalizes the hash function and returns the computed digest. ### Inspecting hash information [`blockByteCount`](/documentation/CryptoKit/HashFunction/blockByteCount) The number of bytes that represents the hash function’s internal state. ## Relationships ### Conforming Types [`SHA3_384`](/documentation/CryptoKit/SHA3_384) [`SHA384`](/documentation/CryptoKit/SHA384) [`SHA3_512`](/documentation/CryptoKit/SHA3_512) [`SHA512`](/documentation/CryptoKit/SHA512) [`MD5`](/documentation/CryptoKit/Insecure/MD5) [`SHA1`](/documentation/CryptoKit/Insecure/SHA1) [`SHA3_256`](/documentation/CryptoKit/SHA3_256) [`SHA256`](/documentation/CryptoKit/SHA256) ### Inherits From [`Sendable`](/documentation/Swift/Sendable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)