Using RSA to encrypt a message in JS and decrypt in Python - rsa

Question

I want to encrypt a message using RSA with a provided PEM public key in Javascript, using SubtleCrypto window.crypto.subtle and then decode it with Python (PyCryptodome) in the back-end. However, I get a ValueError: Incorrect decryption.. I'm not sure if the data is being correctly handled though. Here is my code:
JavaScript:
var publicKey;
var pemPublicKey = `public.pem key with stripped header and footer and newlines (just the base64 data)`;
function base64ToArrayBuffer(b64) {
var byteString = window.atob(b64);
var byteArray = new Uint8Array(byteString.length);
for (var i = 0; i < byteString.length; i++) { byteArray[i] = byteString.charCodeAt(i); }
return byteArray;
}
function arrayBufferToBase64(buffer) {
var binary = '';
var bytes = new Uint8Array(buffer);
var len = bytes.byteLength;
for (var i = 0; i < len; i++) { binary += String.fromCharCode(bytes[i]); }
return window.btoa(binary);
}
window.crypto.subtle.importKey(
"spki",
base64ToArrayBuffer(pemPublicKey),
{ name: "RSA-OAEP", hash: { name: "SHA-256" } },
false,
["encrypt"])
.then(function (key) {
publicKey = key
})
console.log(publicKey)
var enc = new TextEncoder()
var encmessage = enc.encode("test14")
var encryptedData;
window.crypto.subtle.encrypt({
name: "RSA-OAEP"
}, publicKey, encmessage).then(function (encrypted) { encryptedData = encrypted })
var encodedData = arrayBufferToBase64(encryptedData);
console.log(encodedData)
What the code above does is convert the public PEM key, generate a CryptoKey object out of it (using crypto.subtle.importKey) and then encrypts a simple message "test14".
Python backend:
import base64
from Cryptodome.PublicKey import RSA
from Cryptodome.Cipher import AES, PKCS1_OAEP
with open('private.pem', 'r') as f: keypair = RSA.import_key(f.read())
decryptor = PKCS1_OAEP.new(keypair)
decrypted = decryptor.decrypt(base64.b64decode(encrypted)) # encrypted is the data that is returned by JavaScript code
print(decrypted)

Answer 1

Directly from the documentation of Crypto.Cipher.PKCS1_OAEP.new(key, hashAlgo=None, mgfunc=None, label='', randfunc=None):
...
hashAlgo (hash object) - The hash function to use. This can be a module under Crypto.Hash or an existing hash object created from any of such modules. If not specified, Crypto.Hash.SHA1 is used.
...