eccsnacks

This package contains a simple reference implementation of Curve25519 and Curve448 (goldilocks) as specified in RFC7748.

Caution: this implementation is inadvisable for use if timing invariance matters. Future versions of this package may implement a C backend.

eccsnacks is a play on the word ecchacks, a cool site by djb and Tanja Lange.

Installation

pip install eccsnacks

Usage

These examples demonstrate the Diffie-Hellman operation for each curve.

Curve25519:

from os import urandom
from eccsnacks.curve25519 import scalarmult, scalarmult_base

# Private keys in Curve25519 can be any 32-byte string.
a = urandom(32)
a_pub = scalarmult_base(a)

b = urandom(32)
b_pub = scalarmult_base(b)

# perform Diffie-Hellman computation for alice and bob
k_ab = scalarmult(a, b_pub)
k_ba = scalarmult(b, a_pub)

# keys should be the same
assert k_ab == k_ba

Curve448:

from os import urandom
from eccsnacks.curve448 import scalarmult, scalarmult_base

# Private keys in Curve448 can be any 32-byte string.
a = urandom(56)
a_pub = scalarmult_base(a)

b = urandom(56)
b_pub = scalarmult_base(b)

# perform Diffie-Hellman computation for alice and bob
k_ab = scalarmult(a, b_pub)
k_ba = scalarmult(b, a_pub)

# keys should be the same
assert k_ab == k_ba

Todo

• Fast timing invariant implementation of both curves in C.
• More curves.

Alternatives

• curve25519-donna
• python-pure25519
• pynacl
• pysodium
• ... and more can be found on pypi

Acknowledgements

• Matthew Dempsky for slownacl which initially served as a baseline when implementing Curve25519.

• djb for Curve25519

• Mike Hamburg for Curve448