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Raw Message Signatures

Note

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

Signing messages ensures that the message itself has not been tampered with. The application of a signature to a message is something that is is automatically applied when using the public key encryption and is not a required step when sending encrypted messages. This document however is intended to illustrate how to sign plain text messages.

The nacl libs use a separate keypair for signing then is used for public key encryption, it is a high performance key signing algorithm called ed25519, more information on ed25519 can be found here: http://ed25519.cr.yp.to/

The sign messages first generate a signing keypair, this constitutes the signing key which needs to be kept secret, and the verify key which is made available to message recipients.

import libnacl

vk, sk = libnacl.crypto_sign_keypair()

With the signing keypair in hand a message can be signed:

msg = 'And that, my liege, is how we know the Earth to be banana-shaped.'
signed = libnacl.crypto_sign(msg, sk)

The signed message is really just the plain text of the message prepended with the signature. The crypto_sign_open function will read the signed message and return me original message without the signature:

orig = libnacl.crypto_sign_open(signed, vk)

Put all together:

import libnacl

vk, sk = libnacl.crypto_sign_keypair()

msg = 'And that, my liege, is how we know the Earth to be banana-shaped.'
signed = libnacl.crypto_sign(msg, sk)

orig = libnacl.crypto_sign_open(signed, vk)