serializing with pickle

[hardbyte]

Pickle is very powerful, and therefore very dangerous. I would strongly suggest not serializing anything remotely related to crypto with it.

Here is a quick proof of concept to steal a secret being encrypted by altering the public key before serialization. This using the (slightly tweaked) classes from Paillier.py, full code as a gist:

keypair = KeyPair()
keypair.generate()

class DeviousPhePublicKey(paillier.PaillierPublicKey):

    def encrypt(self, x):
        print("Sending the secret {} to my webserver...".format(x))
        return super().encrypt(x)

pk_devious = DeviousPhePublicKey(keypair.public_key.pk.n)
pk_syft = PublicKey(pk_devious)

# So far nothing scary... now we serialize and send
# our public key to someone else though...

pk_s = pk_syft.serialize()
pk_reconstructed = PublicKey(pickle.loads(pk_s))
cipher_remote = pk_reconstructed.encrypt(42)

Output (assumed to be on a remote machine):

Sending the secret 42 to my webserver...

Instead you could use a standard format such as JWK which will allow interoperability between langauges and be a lot safer.

Also have you seen our paillier keys jwk serialisation docs?

[souravsingh]

@iamtrask I am interested in working on this. How do I start?

[iamtrask]

@souravsingh great choice! This is very important functionality!

1. Look for where "pickle" is being used anywhere in the project (usually in a method called "serialize")
2. at each place, serialize using a better datastructure of your choosing (perhaps a string?)
3. implement the corresponding deserialization function to go with your new serialization function
4. write unit tests for each!!!
5. Party with beer and pizza!!! (mandatory)

@hardbyte care to add any color re:security and performance?

[hardbyte]

I'd recommend reading the spec that defines JSON Web Keys: RFC 7517

[sriranganathan]

If this is still available, I would like to give it a go.