From c90f36e3dd179d2de96f4f5fe38d8dc9a9de6dfe Mon Sep 17 00:00:00 2001 From: Emile Date: Fri, 25 Oct 2024 15:55:50 +0200 Subject: vendor --- vendor/filippo.io/edwards25519/field/fe_extra.go | 50 ++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 vendor/filippo.io/edwards25519/field/fe_extra.go (limited to 'vendor/filippo.io/edwards25519/field/fe_extra.go') diff --git a/vendor/filippo.io/edwards25519/field/fe_extra.go b/vendor/filippo.io/edwards25519/field/fe_extra.go new file mode 100644 index 0000000..1ef503b --- /dev/null +++ b/vendor/filippo.io/edwards25519/field/fe_extra.go @@ -0,0 +1,50 @@ +// Copyright (c) 2021 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package field + +import "errors" + +// This file contains additional functionality that is not included in the +// upstream crypto/ed25519/edwards25519/field package. + +// SetWideBytes sets v to x, where x is a 64-byte little-endian encoding, which +// is reduced modulo the field order. If x is not of the right length, +// SetWideBytes returns nil and an error, and the receiver is unchanged. +// +// SetWideBytes is not necessary to select a uniformly distributed value, and is +// only provided for compatibility: SetBytes can be used instead as the chance +// of bias is less than 2⁻²⁵⁰. +func (v *Element) SetWideBytes(x []byte) (*Element, error) { + if len(x) != 64 { + return nil, errors.New("edwards25519: invalid SetWideBytes input size") + } + + // Split the 64 bytes into two elements, and extract the most significant + // bit of each, which is ignored by SetBytes. + lo, _ := new(Element).SetBytes(x[:32]) + loMSB := uint64(x[31] >> 7) + hi, _ := new(Element).SetBytes(x[32:]) + hiMSB := uint64(x[63] >> 7) + + // The output we want is + // + // v = lo + loMSB * 2²⁵⁵ + hi * 2²⁵⁶ + hiMSB * 2⁵¹¹ + // + // which applying the reduction identity comes out to + // + // v = lo + loMSB * 19 + hi * 2 * 19 + hiMSB * 2 * 19² + // + // l0 will be the sum of a 52 bits value (lo.l0), plus a 5 bits value + // (loMSB * 19), a 6 bits value (hi.l0 * 2 * 19), and a 10 bits value + // (hiMSB * 2 * 19²), so it fits in a uint64. + + v.l0 = lo.l0 + loMSB*19 + hi.l0*2*19 + hiMSB*2*19*19 + v.l1 = lo.l1 + hi.l1*2*19 + v.l2 = lo.l2 + hi.l2*2*19 + v.l3 = lo.l3 + hi.l3*2*19 + v.l4 = lo.l4 + hi.l4*2*19 + + return v.carryPropagate(), nil +} -- cgit 1.4.1