Raw Public Key EncryptionΒΆ

Note

While these routines are perfectly safe, higher level convenience wrappers are under development to make these routines easier.

Public key encryption inside the nacl library has been constructed to ensure that all cryptographic routines are executed correctly and safely.

The public key encryption is executed via the functions which begin with crypto_box and can be easily executed.

First generate a public key and secret key keypair for the two communicating parties, who for tradition’s sake, will be referred to as Alice and Bob:

import libnacl

alice_pk, alice_sk = libnacl.crypto_keypair()
bob_pk, bob_sk = libnacl.crypto_keypair()

Once the keys have been generated a cryptographic box needs to be created. The cryptographic box takes the party’s secret key and the receiving party’s public key. These are used to create a message which is both signed and encrypted.

Before creating the box a nonce is required. The nonce is a 24 character string which should only be used for this message, the nonce should never be reused. This means that the nonce needs to be generated in such a way that the probability of reusing the nonce string with the same keypair is very low. The libnacl wrapper ships with a convenience function which generates a nonce from random bytes:

import libnacl.utils
nonce = libnacl.utils.rand_nonce()

Now, with a nonce a cryptographic box can be created, Alice will send a message:

msg = 'Quiet, quiet.  Quiet!  There are ways of telling whether she is a witch.'
box = libnacl.crypto_box(msg, nonce, bob_pk, alice_sk)

Now with a box in hand it can be decrypted by Bob:

clear_msg = libnacl.crypto_box_open(box, nonce, alice_pk, bob_sk)

The trick here is that the box AND the nonce need to be sent to Bob, so he can decrypt the message. The nonce can be safely sent to Bob in the clear.

To bring it all together:

import libnacl
import libnacl.utils

alice_pk, alice_sk = libnacl.crypto_keypair()
bob_pk, bob_sk = libnacl.crypto_keypair()

nonce = libnacl.utils.rand_nonce()

msg = 'Quiet, quiet.  Quiet!  There are ways of telling whether she is a witch.'
box = libnacl.crypto_box(msg, nonce, bob_pk, alice_sk)

clear_msg = libnacl.crypto_box_open(box, nonce, alice_pk, bob_sk)