SubtleCrypto.digest()

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.

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 or ArrayBufferView containing the data to be digested.

digest

Promise that fulfills with an ArrayBuffer containing the digest.

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.

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

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));

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:

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));

• Non-cryptographic uses of SubtleCrypto
• Chromium secure origins specification
• FIPS 180-4 specifies the SHA family of digest algorithms.