Recreating nodejs aes-256-cbc cipher

[milomg]

Thanks for the awesome library!

I'm currently working on replicating the following code

import crypto from 'crypto'

const cipher = crypto.createCipheriv('aes-256-cbc', derivedKey, derivedIv)
const encrypted = Buffer.concat([cipher.update(text), cipher.final()])
return encrypted.toString('base64')

I've converted it into the following, but when I attempt to decode this, I get ERR_OSSL_EVP_WRONG_FINAL_BLOCK_LENGTH. I believe this is because I haven't implemented PKCS7 correctly.

import { cbc } from '@noble/ciphers/aes'
import { encode as tob64 } from 'uint8-to-base64'

const cipher = cbc(derivedKey, derivedIv, { disablePadding: true })

const str = new TextEncoder().encode(text)
const padding = 16 - (str.length % 16)
const paddedArray = new Uint8Array(str.length + padding)
paddedArray.set(str)
paddedArray.fill(padding, str.length)

return tob64(cipher.encrypt(paddedArray))

Looking at the source code, this seems pretty similar to the PKCS5, so I also tried the following, but that didn't work either.

import { cbc } from '@noble/ciphers/aes'
import { encode as tob64 } from 'uint8-to-base64'

const cipher = cbc(derivedKey, derivedIv, { disablePadding: false })

const str = new TextEncoder().encode(text)

return tob64(cipher.encrypt(str))

Do you have any advice?

[milomg]

Turns out the issue was with tob64, I should've written a custom function

function uint8ArrayToBase64(arr, options) {
  const lookup =
    'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
  let result = ''

  let i = 0
  for (; i + 2 < arr.length; i += 3) {
    const triplet = (arr[i] << 16) + (arr[i + 1] << 8) + arr[i + 2]
    result +=
      lookup[(triplet >> 18) & 63] +
      lookup[(triplet >> 12) & 63] +
      lookup[(triplet >> 6) & 63] +
      lookup[triplet & 63]
  }
  if (i + 2 === arr.length) {
    const triplet = (arr[i] << 16) + (arr[i + 1] << 8)
    result +=
      lookup[(triplet >> 18) & 63] +
      lookup[(triplet >> 12) & 63] +
      lookup[(triplet >> 6) & 63] +
      '='
  } else if (i + 1 === arr.length) {
    const triplet = arr[i] << 16
    result += lookup[(triplet >> 18) & 63] + lookup[(triplet >> 12) & 63] + '=='
  }
  return result
}