Generating Elliptic Curve Private Key in Python with the cryptography library

Question

I am attempting to generate a public/private elliptic curve key pair in python using hazmat in cryptography. Below is the current code that I have. When I run, it is generating the error 'NoneType' object has no attribute 'generate_elliptic_curve_private_key'

ecurve = asymmetric.ec.EllipticCurve
ecurve.name = 'secp256r1'
ecurve.key_size = 128
ec_backend = cryptography.hazmat.backends.interfaces.EllipticCurveBackend.generate_elliptic_curve_private_key(cryptography.hazmat.backends.interfaces.EllipticCurveBackend, ecurve)
key = asymmetric.ec.generate_private_key(curve=ecurve, backend=ec_backend)

Here is the documentation https://cryptography.io/en/latest/hazmat/primitives/asymmetric/ec/#

EllipticCurveBackend ... The term "backend" here shouts "do not use" back at me. Even if it runs, it probably crashes on the first rewrite of the EC functionality. — Maarten Bodewes
– Maarten Bodewes, Commented Dec 9, 2019 at 13:25

Alex Gaynor · Accepted Answer · 2019-12-10 05:55:24Z

16

I don't see where generate_elliptic_curve_private_key method is available.

Here is an example of generating a SECP256R1 and serializing the public key into PEM format:

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec

private_key = ec.generate_private_key(ec.SECP256R1(), default_backend())
public_key = private_key.public_key()
# serializing into PEM
rsa_pem = public_key.public_bytes(encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo)

printing the key

In [14]: print(rsa_pem.decode())
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEilwhueTwySfEbXd9y/inZVsYVG6z
/UJyVbN+cYgtIFd0vLdaP27cME8RGE/enMEcX7/jkb13j2DPnXt2R6teZw==
-----END PUBLIC KEY-----

edited Dec 10, 2019 at 5:55

Alex Gaynor

15.1k10 gold badges66 silver badges113 bronze badges

answered Dec 9, 2019 at 6:15

salparadise

5,8751 gold badge28 silver badges32 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Tim Welles Over a year ago

This does answer the question, however, I was trying to set the size of the key in the original code. Is there any way to do this inside the above?

Paul Kehrer Over a year ago

Key sizes are strictly tied to the curve parameters (e.g. a named curve like secp256r1). If you want a larger key size you need to use a different curve. secp256r1 has private keys that are 256-bit because the secret scalar (the private key) is a value less than the curve's order (which is 256-bit). The example provided here is the correct API for key generation (and public point serialization) on a given curve.

Tim Welles Over a year ago

That makes sense. Thank you!

Collectives™ on Stack Overflow

Generating Elliptic Curve Private Key in Python with the cryptography library

1 Answer 1

printing the key

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

printing the key

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related