x448 - curve448 ECDH

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x448
Overview

x448 - curve448 ECDH

Yawning Angel (yawning at schwanenlied dot me)

See: https://www.rfc-editor.org/rfc/rfc7748.txt

If you're familiar with how to use golang.org/x/crypto/curve25519, you will be right at home with using x448, since the functions are the same. Generate a random secret key, ScalarBaseMult() to get the public key, etc etc etc.

On 64-bit targets the underlying field arithmetic uses output taken from the fiat-crypto project. The 32-bit version and the actual ECDH implementation are based off Michael Hamburg's portable x448 implementation.

Notes:

  • The build-tag system used to determine which version to build is sub-optimal in the extreme (https://github.com/golang/go/issues/33388)

  • Unless your system has a constant-time 32x32=64-bit or 64x64=128-bit multiply (depending on backend), this is unsafe to use. Most modern CPUs provide something adequate, with the notable exception of WASM.

  • As a matter of taste, and because it is prefered when implementing Noise, the optional all-zero check is not done.