Node.js: migrating from `createCipher` to `createCipheriv`

March 14, 2020

If you still use the createCipher and createDecipher methods of the crypto module, you’re likely getting the following deprecation warnings when running your code:

(node:477082) [DEP0106] DeprecationWarning: crypto.createCipher is deprecated.
(node:468005) [DEP0106] DeprecationWarning: crypto.createDecipher is deprecated.

This is because this method didn’t allow for passing an initialization vector (IV), and instead derived the IV from the key using the OpenSSL EVP_BytesToKey derivation function, using a null salt meaning that the IV would be deterministic for a given key which is an issue for ciphers with counter mode like CTR, GCM and CCM.

Your code might have looked like:

const cipher = crypto.createCipher('aes256', key)

If you want to make this code backwards compatible, you need to call OpenSSL’s EVP_BytesToKey function yourself, typically through this module which makes it available in JS userland.

However the reason this function is deprecated in the first place is because you shouldn’t use it, and instead use a random unpredictable IV, which requires you to change your code to something like this:

const iv = crypto.randomBytes(16)
const cipher = crypto.createCipher('aes256', key, iv)

Here, for AES-256 in CBC mode (aes256 being aliased to AES-256-CBC by OpenSSL), the IV size is expected to be the same as the block size, which is always 16 bytes.

In order to decrypt the message, you will need the IV as well. Typically you’d store the IV together with the message, as the important part is for the IV to not be predictable ahead of time.

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