Decrypt a file encrypted in Python using only OpenSSL

Question

I have a file encrypted in Python and pycryptodome like this:

from Crypto.PublicKey import RSA
from Crypto.Random import get_random_bytes
from Crypto.Cipher import AES, PKCS1_OAEP

key = RSA.generate(2048)
secret_key = key.exportKey(passphrase='letmein', pkcs=8, protection='scryptAndAES128-CBC')
public_key = key.publickey().exportKey()

rsa_key = RSA.importKey(public_key)
session_key = get_random_bytes(16)
cipher_rsa = PKCS1_OAEP.new(rsa_key)
cipher_aes = AES.new(session_key, AES.MODE_EAX)
ciphertext, tag = cipher_aes.encrypt_and_digest(data)

dst.write(cipher_rsa.encrypt(session_key))
dst.write(cipher_aes.nonce)
dst.write(tag)
dst.write(ciphertext)

And I am able to decode it like this:

rsa_key = RSA.importKey(secret_key, 'letmein')

enc_session_key, nonce, tag, ciphertext = [
    src.read(x) for x in (rsa_key.size_in_bytes(), 16, 16, -1)
]

cipher_rsa = PKCS1_OAEP.new(rsa_key)
session_key = cipher_rsa.decrypt(enc_session_key)
cipher_aes = AES.new(session_key, AES.MODE_EAX, nonce)

decoded = cipher_aes.decrypt_and_verify(ciphertext, tag)

Is there a way to decrypt the file using command line with openssl? Or how should I modify the code so that it would be possible?

Maarten Bodewes · Accepted Answer · 2018-05-20 00:40:07Z

1

You could base 64 encode the separate components and then splitting them using a separator. Command line is mainly text based, so it would be easier to program that in e.g. Bash.

EAX mode is not directly supported so trying CBC mode would make it easier. OpenSSL command line doesn't seem to support any AEAD cipher for now so you would lose the authenticity it may have offered.

Finally, the combination of OAEP and a cipher doesn't seem supported, so you may have to handle the binary result and convert it to a symmetric cipher, e.g. in hexadecimals.

answered May 20, 2018 at 0:40

Maarten Bodewes

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