Web Crypto

Background

The Web Crypto API provides a set of low-level functions for common cryptographic tasks. The Workers Runtime implements the full surface of this API, but with some differences in the supported algorithms compared to those implemented in most browsers.

Performing cryptographic operations using the Web Crypto API is significantly faster than performing them purely in JavaScript. If you want to perform CPU-intensive cryptographic operations, you should consider using the Web Crypto API.

The Web Crypto API is implemented through the SubtleCrypto interface, accessible via the global crypto.subtle binding. A simple example of calculating a digest (also known as a hash) is:

const myText = new TextEncoder().encode('Hello world!');

const myDigest = await crypto.subtle.digest(  {    name: 'SHA-256',  },  myText // The data you want to hash as an ArrayBuffer
);
console.log(new Uint8Array(myDigest));

Some common uses include:

Signing requests

Methods

crypto.getRandomValues(bufferArrayBufferView) ArrayBufferView
- Fills the passed ArrayBufferView with cryptographically sound random values and returns the buffer.
  Parameters:
  - bufferArrayBufferView
    - Must be an Int8Array | Uint8Array | Uint8ClampedArray | Int16Array | Uint16Array | Int32Array | Uint32Array | BigInt64Array | BigUint64Array.
crypto.randomUUID() string
- Generates a new random (version 4) UUID as defined in RFC 4122.

SubtleCrypto Methods

These methods are all accessed via crypto.subtle, which is also documented in detail on MDN.

encrypt(algorithm, key, data) Promise<ArrayBuffer>
- Returns a Promise that fulfills with the encrypted data corresponding to the clear text, algorithm, and key given as parameters.
  Parameters:
  - algorithmobject
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - keyCryptoKey
  - dataBufferSource
decrypt(algorithm, key, data) Promise<ArrayBuffer>
- Returns a Promise that fulfills with the clear data corresponding to the ciphertext, algorithm, and key given as parameters.
  Parameters:
  - algorithmobject
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - keyCryptoKey
  - dataBufferSource
sign(algorithm, key, data) Promise<ArrayBuffer>
- Returns a Promise that fulfills with the signature corresponding to the text, algorithm, and key given as parameters.
  Parameters:
  - algorithmstring | object
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - keyCryptoKey
  - dataArrayBuffer
verify(algorithm, key, signature, data) Promise<boolean>
- Returns a Promise that fulfills with a Boolean value indicating if the signature given as a parameter matches the text, algorithm, and key that are also given as parameters.
  Parameters:
  - algorithmstring | object
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - keyCryptoKey
  - signatureArrayBuffer
  - dataArrayBuffer
digest(algorithm, data) Promise<ArrayBuffer>
- Returns a Promise that fulfills with a digest generated from the algorithm and text given as parameters.
  Parameters:
  - algorithmstring | object
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - dataArrayBuffer
generateKey(algorithm, extractable, keyUsages) Promise<CryptoKey> | Promise<CryptoKeyPair>
- Returns a Promise that fulfills with a newly-generated CryptoKey, for symmetrical algorithms, or a CryptoKeyPair, containing two newly generated keys, for asymmetrical algorithms. For example, to generate a new AES-GCM key:

let keyPair = await crypto.subtle.generateKey(  {    name: 'AES-GCM',    length: '256',  },  true,  ['encrypt', 'decrypt']
);

Parameters:

algorithmobject
- Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
extractablebool
keyUsagesArray
- An Array of strings indicating the possible usages of the new key.
deriveKey(algorithm, baseKey, derivedKeyAlgorithm, extractable, keyUsages) Promise<CryptoKey>
- Returns a Promise that fulfills with a newly generated CryptoKey derived from the base key and specific algorithm given as parameters.
  Parameters:
  - algorithmobject
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - baseKeyCryptoKey
  - derivedKeyAlgorithmobject
    - Defines the algorithm the derived key will be used for in an algorithm-specific format.
  - extractablebool
  - keyUsagesArray
    - An Array of strings indicating the possible usages of the new key
deriveBits(algorithm, baseKey, length) Promise<ArrayBuffer>
- Returns a Promise that fulfills with a newly generated buffer of pseudo-random bits derived from the base key and specific algorithm given as parameters. It returns a Promise which will be fulfilled with an ArrayBuffer containing the derived bits. This method is very similar to deriveKey(), except that deriveKey() returns a CryptoKey object rather than an ArrayBuffer. Essentially, deriveKey() is composed of deriveBits() followed by importKey().
  Parameters:
  - algorithmobject
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - baseKeyCryptoKey
  - lengthint
    - Length of the bit string to derive.
importKey(format, keyData, algorithm, extractable, keyUsages) Promise<CryptoKey>
- Transform a key from some external, portable format into a CryptoKey for use with the Web Crypto API.
  Parameters:
  - formatstring
    - Describes the format of the key to be imported.
  - keyDataArrayBuffer
  - algorithmobject
    - Describes the algorithm to be used, including any required parameters, in an algorithm-specific format.
  - extractablebool
  - keyUsagesArray
    - An Array of strings indicating the possible usages of the new key
exportKey(formatstring, keyCryptoKey) Promise<ArrayBuffer>
- Transform a CryptoKey into a portable format, if the CryptoKey is extractable.
  Parameters:
  - formatstring
    - Describes the format in which the key will be exported.
  - keyCryptoKey
wrapKey(format, key, wrappingKey, wrapAlgo) Promise<ArrayBuffer>
- Transform a CryptoKey into a portable format, and then encrypt it with another key. This renders the CryptoKey suitable for storage or transmission in untrusted environments.
  Parameters:
  - formatstring
    - Describes the format in which the key will be exported before being encrypted.
  - keyCryptoKey
  - wrappingKeyCryptoKey
  - wrapAlgoobject
    - Describes the algorithm to be used to encrypt the exported key, including any required parameters, in an algorithm-specific format.
unwrapKey(format, key, unwrappingKey, unwrapAlgo, unwrappedKeyAlgo, extractable, keyUsages) Promise<CryptoKey>
- Transform a key that was wrapped by wrapKey() back into a CryptoKey.
  Parameters:
  - formatstring
    - Described the data format of the key to be unwrapped.
  - keyCryptoKey
  - unwrappingKeyCryptoKey
  - unwrapAlgoobject
    - Describes the algorithm that was used to encrypt the wrapped key, in an algorithm-specific format.
  - unwrappedKeyAlgoobject
    - Describes the key to be unwrapped, in an algorithm-specific format.
  - extractablebool
  - keyUsagesArray
    - An Array of strings indicating the possible usages of the new key

Supported algorithms

Workers implements all operation of the WebCrypto standard, as shown in the following table. The Workers team continuously adds support for more algorithms — share your use case with the community.

A checkmark (✓) indicates that this feature is believed to be fully supported according to the spec.
An x (✘) indicates that this feature is part of the specification but not implemented.
If a feature only implements the operation partially, details are listed.

Algorithm	sign() verify()	encrypt() decrypt()	digest()	deriveBits() deriveKey()	generateKey()	wrapKey() unwrapKey()	exportKey()	importKey()
RSASSA PKCS1 v1.5	✓				✓		✓	✓
RSA PSS	✓				✓		✓	✓
RSA OAEP		✓			✓	✓	✓	✓
ECDSA	✓				✓		✓	✓
ECDH				✓	✓		✓	✓
NODE ED25519¹	✓				✓		✓	✓
AES CTR		✓			✓	✓	✓	✓
AES CBC		✓			✓	✓	✓	✓
AES GCM		✓			✓	✓	✓	✓
AES KW					✓	✓	✓	✓
HMAC	✓				✓		✓	✓
SHA 1			✓
SHA 256			✓
SHA 384			✓
SHA 512			✓
MD5²			✓
HKDF				✓				✓
PBKDF2				✓				✓

Footnotes:

Non-standard EdDSA is supported for the Ed25519 curve. Since this algorithm is non-standard, a few things to keep in mind while using it:
- Use NODE-ED25519 as the algorithm and namedCurve parameters.
- Unlike NodeJS, Cloudflare will not support raw import of private keys.
- The algorithm implementation may change over time. While Cloudflare cannot guarantee it at this time, Cloudflare will strive to maintain backward compatibility and compatibility with NodeJS’s behavior. Any notable compatibility notes will be communicated in release notes and via this developer document.
MD5 is not part of the WebCrypto standard but is supported in Cloudflare Workers for interacting with legacy systems that require MD5. MD5 is considered a weak algorithm — do not rely upon MD5 for security.

Web Crypto

​​ Background

​​ Methods

​​ SubtleCrypto Methods

​​ Supported algorithms

​​ Related resources

Background

Methods

SubtleCrypto Methods

Supported algorithms

Related resources