Decrypting Windows EC2 password in Python

I would like to launch a Windows EC2 instance and programmatically get the admin password using Python. I know this can be done using the CLI like this, but I would prefer to decrypt locally to avoid sending my private key over the internet.

aws ec2 get-password-data --instance-id i-0d4d8273cadcae0a0 --priv-launch-key .ssh/elliott2.pem

After reading Cryptodome docs, I tried like this:

import boto3
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_OAEP

ec2 = boto3.resource('ec2', 'us-west-2')
i = ec2.Instance('i-028dee2acb533fc59')

encrypted_str = i.password_data()['PasswordData']
with open('mykey.pem') as fp:
  key = RSA.importKey(fp.read())

cipher = PKCS1_OAEP.new(key)
print(cipher.decrypt(enc_str))

This fails with error:

Traceback (most recent call last):
  File "test.py", line 14, in <module>
    print(cipher.decrypt(encrypted_str))
  File "/Users/elliott/Library/Python/3.8/lib/python/site-packages/Crypto/Cipher/PKCS1_OAEP.py", line 167, in decrypt
    raise ValueError("Ciphertext with incorrect length.")
ValueError: Ciphertext with incorrect length.

I think cipherkey must be exactly 256 Bytes. But the password data is longer than this, so I'm not sure what to do.

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