decrypt()

The decrypt() method of the SubtleCrypto interface decrypts some encrypted data.

It takes as its 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").

The ciphertext is typically produced by the corresponding encrypt() method.

Syntax

decrypt(algorithm, key, data);

Parameters

• 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 AES-CBC, pass an AesCbcParams object.
• key
  • : A CryptoKey containing the key to be used for decryption. Its usages must include "decrypt".
• data
  • : An ArrayBuffer, a TypedArray or a DataView object containing the data to be decrypted.

Return value

A Promise that fulfills with an ArrayBuffer containing the plaintext.

Exceptions

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

• InvalidAccessError
  • : Raised when the key is not a key for the requested decryption algorithm, or when its usages do not include "decrypt".
• NotSupportedError
  • : Raised when trying to use an algorithm that is either unknown or isn't supported for decryption.
• OperationError
  • : Raised when the operation failed for an operation-specific reason, for example because the iv is not 16 bytes long, the ciphertext is empty or not a multiple of 16 bytes, or the padding is invalid (which usually means the wrong key or IV was used).

Supported algorithms

Only AES-CBC is currently supported. AES-CTR, AES-GCM, AES-KW and RSA-OAEP are not yet supported and reject with a NotSupportedError.

AES-CBC

See encrypt() for a description of the algorithm and of the AesCbcParams object. The ciphertext must be a non-empty multiple of 16 bytes, and the PKCS#7 padding is removed from the decrypted data.

Examples

// key and iv are the values used in the encrypt() example
const plaintext = await crypto.subtle.decrypt(
  { name: 'AES-CBC', iv },
  key,
  ciphertext,
);
console.log(new TextDecoder().decode(plaintext)); // "hello world"