SubtleCrypto: digest() method

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

The digest() method of the SubtleCrypto interface generates a digest of the given data. A digest is a short fixed-length value derived from some variable-length input. Cryptographic digests should exhibit collision-resistance, meaning that it's hard to come up with two different inputs that have the same digest value.

It takes as its arguments an identifier for the digest algorithm to use and the data to digest. It returns a Promise which will be fulfilled with the digest.

Note that this API does not support streaming input: you must read the entire input into memory before passing it into the digest function.

Syntax

js

digest(algorithm, data)

Parameters

algorithm

This may be a string or an object with a single property name that is a string. The string names the hash function to use. Supported values are:

  • "SHA-1" (but don't use this in cryptographic applications)
  • "SHA-256"
  • "SHA-384"
  • "SHA-512".
data

An ArrayBuffer, a TypedArray or a DataView object containing the data to be digested.

Return value

A Promise that fulfills with an ArrayBuffer containing the digest.

Supported algorithms

Digest algorithms, also known as cryptographic hash functions, transform an arbitrarily large block of data into a fixed-size output, usually much shorter than the input. They have a variety of applications in cryptography.

Algorithm Output length (bits) Block size (bits) Specification
SHA-1 160 512 FIPS 180-4, section 6.1
SHA-256 256 512 FIPS 180-4, section 6.2
SHA-384 384 1024 FIPS 180-4, section 6.5
SHA-512 512 1024 FIPS 180-4, section 6.4

Warning: SHA-1 is now considered vulnerable and should not be used for cryptographic applications.

Note: If you are looking here for how to create a keyed-hash message authentication code (HMAC), you need to use the SubtleCrypto.sign() instead.

Examples

For more examples of using the digest() API, see Non-cryptographic uses of SubtleCrypto.

Basic example

This example encodes a message, then calculates its SHA-256 digest and logs the digest length:

js

const text =
  "An obscure body in the S-K System, your majesty. The inhabitants refer to it as the planet Earth.";

async function digestMessage(message) {
  const encoder = new TextEncoder();
  const data = encoder.encode(message);
  const hash = await crypto.subtle.digest("SHA-256", data);
  return hash;
}

digestMessage(text).then((digestBuffer) =>
  console.log(digestBuffer.byteLength)
);

Converting a digest to a hex string

The digest is returned as an ArrayBuffer, but for comparison and display digests are often represented as hex strings. This example calculates a digest, then converts the ArrayBuffer to a hex string:

js

const text =
  "An obscure body in the S-K System, your majesty. The inhabitants refer to it as the planet Earth.";

async function digestMessage(message) {
  const msgUint8 = new TextEncoder().encode(message); // encode as (utf-8) Uint8Array
  const hashBuffer = await crypto.subtle.digest("SHA-256", msgUint8); // hash the message
  const hashArray = Array.from(new Uint8Array(hashBuffer)); // convert buffer to byte array
  const hashHex = hashArray
    .map((b) => b.toString(16).padStart(2, "0"))
    .join(""); // convert bytes to hex string
  return hashHex;
}

digestMessage(text).then((digestHex) => console.log(digestHex));

Specifications

Specification
Web Cryptography API
# SubtleCrypto-method-digest

Browser compatibility

BCD tables only load in the browser

See also