SubtleCrypto: exportKey() method

{{APIRef("Web Crypto API")}} {{SecureContext_header}} {{AvailableInWorkers}}

The exportKey() method of the {{domxref("SubtleCrypto")}} interface exports a key: that is, it takes as input a {{domxref("CryptoKey")}} object and gives you the key in an external, portable format.

To export a key, the key must have {{domxref("CryptoKey.extractable")}} set to true.

Keys can be exported in several formats: see Supported formats in the SubtleCrypto.importKey() page for details.

Keys are not exported in an encrypted format: to encrypt keys when exporting them use the SubtleCrypto.wrapKey() API instead.

Syntax

exportKey(format, key)

Parameters

format
- : A string value describing the data format in which the key should be exported. It can be one of the following:
  - raw: Raw format.
  - pkcs8: PKCS #8 format.
  - spki: SubjectPublicKeyInfo format.
  - jwk: JSON Web Key format.
key
- : The {{domxref("CryptoKey")}} to export.

Return value

A Promise.

If format was jwk, then the promise fulfills with a JSON object containing the key.
Otherwise the promise fulfills with an ArrayBuffer containing the key.

Exceptions

The promise is rejected when one of the following exceptions is encountered:

InvalidAccessError {{domxref("DOMException")}}
- : Raised when trying to export a non-extractable key.
NotSupported {{domxref("DOMException")}}
- : Raised when trying to export in an unknown format.
{{jsxref("TypeError")}}
- : Raised when trying to use an invalid format.

Examples

[!NOTE] You can try the working examples out on GitHub.

Raw export

This example exports an AES key as an ArrayBuffer containing the bytes for the key. See the complete code on GitHub.

/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
  const exported = await window.crypto.subtle.exportKey("raw", key);
  const exportedKeyBuffer = new Uint8Array(exported);

  const exportKeyOutput = document.querySelector(".exported-key");
  exportKeyOutput.textContent = `[${exportedKeyBuffer}]`;
}

/*
Generate an encrypt/decrypt secret key,
then set up an event listener on the "Export" button.
*/
window.crypto.subtle
  .generateKey(
    {
      name: "AES-GCM",
      length: 256,
    },
    true,
    ["encrypt", "decrypt"],
  )
  .then((key) => {
    const exportButton = document.querySelector(".raw");
    exportButton.addEventListener("click", () => {
      exportCryptoKey(key);
    });
  });

PKCS #8 export

This example exports an RSA private signing key as a PKCS #8 object. The exported key is then PEM-encoded. See the complete code on GitHub.

/*
Convert an ArrayBuffer into a string
from https://developer.chrome.com/blog/how-to-convert-arraybuffer-to-and-from-string/
*/
function ab2str(buf) {
  return String.fromCharCode.apply(null, new Uint8Array(buf));
}

/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
  const exported = await window.crypto.subtle.exportKey("pkcs8", key);
  const exportedAsString = ab2str(exported);
  const exportedAsBase64 = window.btoa(exportedAsString);
  const pemExported = `-----BEGIN PRIVATE KEY-----\n${exportedAsBase64}\n-----END PRIVATE KEY-----`;

  const exportKeyOutput = document.querySelector(".exported-key");
  exportKeyOutput.textContent = pemExported;
}

/*
Generate a sign/verify key pair,
then set up an event listener on the "Export" button.
*/
window.crypto.subtle
  .generateKey(
    {
      name: "RSA-PSS",
      // Consider using a 4096-bit key for systems that require long-term security
      modulusLength: 2048,
      publicExponent: new Uint8Array([1, 0, 1]),
      hash: "SHA-256",
    },
    true,
    ["sign", "verify"],
  )
  .then((keyPair) => {
    const exportButton = document.querySelector(".pkcs8");
    exportButton.addEventListener("click", () => {
      exportCryptoKey(keyPair.privateKey);
    });
  });

SubjectPublicKeyInfo export

This example exports an RSA public encryption key as a PEM-encoded SubjectPublicKeyInfo object. See the complete code on GitHub.

/*
Convert an ArrayBuffer into a string
from https://developer.chrome.com/blog/how-to-convert-arraybuffer-to-and-from-string/
*/
function ab2str(buf) {
  return String.fromCharCode.apply(null, new Uint8Array(buf));
}

/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
  const exported = await window.crypto.subtle.exportKey("spki", key);
  const exportedAsString = ab2str(exported);
  const exportedAsBase64 = window.btoa(exportedAsString);
  const pemExported = `-----BEGIN PUBLIC KEY-----\n${exportedAsBase64}\n-----END PUBLIC KEY-----`;

  const exportKeyOutput = document.querySelector(".exported-key");
  exportKeyOutput.textContent = pemExported;
}

/*
Generate an encrypt/decrypt key pair,
then set up an event listener on the "Export" button.
*/
window.crypto.subtle
  .generateKey(
    {
      name: "RSA-OAEP",
      // Consider using a 4096-bit key for systems that require long-term security
      modulusLength: 2048,
      publicExponent: new Uint8Array([1, 0, 1]),
      hash: "SHA-256",
    },
    true,
    ["encrypt", "decrypt"],
  )
  .then((keyPair) => {
    const exportButton = document.querySelector(".spki");
    exportButton.addEventListener("click", () => {
      exportCryptoKey(keyPair.publicKey);
    });
  });

JSON Web Key export

This example exports an ECDSA private signing key as a JSON Web Key object. See the complete code on GitHub.

/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
  const exported = await window.crypto.subtle.exportKey("jwk", key);
  const exportKeyOutput = document.querySelector(".exported-key");
  exportKeyOutput.textContent = JSON.stringify(exported, null, " ");
}

/*
Generate a sign/verify key pair,
then set up an event listener on the "Export" button.
*/
window.crypto.subtle
  .generateKey(
    {
      name: "ECDSA",
      namedCurve: "P-384",
    },
    true,
    ["sign", "verify"],
  )
  .then((keyPair) => {
    const exportButton = document.querySelector(".jwk");
    exportButton.addEventListener("click", () => {
      exportCryptoKey(keyPair.privateKey);
    });
  });

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

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