The decrypt() method of the SubtleCrypto interface decrypts some encrypted data. It takes as arguments a key to decrypt with, some optional extra parameters, and the data to decrypt (also known as "ciphertext"). It returns a Promise which will be fulfilled with the decrypted data (also known as "plaintext").

algorithm

An object specifying the algorithm to be used, and any extra parameters as required. The values given for the extra parameters must match those passed into the corresponding encrypt() call.

• To use RSA-OAEP, pass an RsaOaepParams object.
• To use AES-CTR, pass an AesCtrParams object.
• To use AES-CBC, pass an AesCbcParams object.
• To use AES-GCM, pass an AesGcmParams object.

key

A CryptoKey containing the key to be used for decryption. If using RSA-OAEP, this is the privateKey property of the CryptoKeyPair object.

data

An ArrayBuffer, a TypedArray, or a DataView containing the data to be decrypted (also known as ciphertext).

A Promise that fulfills with an ArrayBuffer containing the plaintext.

The promise is rejected when the following exceptions are encountered:

InvalidAccessError DOMException

Raised when the requested operation is not valid for the provided key (e.g. invalid encryption algorithm, or invalid key for the specified encryption algorithm*)*.

OperationError DOMException

Raised when the operation failed for an operation-specific reason (e.g. algorithm parameters of invalid sizes, or there was an error decrypting the ciphertext).

The decrypt() method supports the same algorithms as the encrypt() method.

This code decrypts ciphertext using RSA-OAEP. See the complete code on GitHub.

function decryptMessage(privateKey, ciphertext) {
  return window.crypto.subtle.decrypt(
    { name: "RSA-OAEP" },
    privateKey,
    ciphertext,
  );
}

This code decrypts ciphertext using AES in CTR mode. Note that counter must match the value that was used for encryption. See the complete code on GitHub.

function decryptMessage(key, ciphertext) {
  return window.crypto.subtle.decrypt(
    { name: "AES-CTR", counter, length: 64 },
    key,
    ciphertext,
  );
}

This code decrypts ciphertext using AES in CBC mode. Note that iv must match the value that was used for encryption. See the complete code on GitHub.

function decryptMessage(key, ciphertext) {
  // The iv value is the same as that used for encryption
  return window.crypto.subtle.decrypt({ name: "AES-CBC", iv }, key, ciphertext);
}

This code decrypts ciphertext using AES in GCM mode. Note that iv must match the value that was used for encryption. See the complete code on GitHub.

function decryptMessage(key, ciphertext) {
  // The iv value is the same as that used for encryption
  return window.crypto.subtle.decrypt({ name: "AES-GCM", iv }, key, ciphertext);
}

• SubtleCrypto.encrypt().
• RFC 3447 specifies RSAOAEP.
• NIST SP800-38A specifies CTR mode.
• NIST SP800-38A specifies CBC mode.
• NIST SP800-38D specifies GCM mode.
• FIPS 198-1 specifies HMAC.