SubtleCrypto.exportKey() - Web APIs 编辑

Secure context

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

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

To export a key, the key must have 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

const result = crypto.subtle.exportKey(format, key);

Parameters

• format is 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 is the CryptoKey to export.

Return value

• result is 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

Raised when trying to export a non-extractable key.

NotSupported

Raised when trying to export in an unknown format.

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://developers.google.com/web/updates/2012/06/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://developers.google.com/web/updates/2012/06/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 import

This code 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

Browser compatibility

BCD tables only load in the browser

See also

• SubtleCrypto.importKey()
• SubtleCrypto.wrapKey()
• PKCS #8 format.
• SubjectPublicKeyInfo format.
• JSON Web Key format.