summaryrefslogtreecommitdiffstats
path: root/vendor/filippo.io/edwards25519/field/fe_extra.go
diff options
context:
space:
mode:
authorWim <wim@42.be>2022-08-13 16:14:26 +0200
committerGitHub <noreply@github.com>2022-08-13 16:14:26 +0200
commit6a3fc713978a0c1c9290a4afd08b47886b49b635 (patch)
treeaa62cd85cf5671646c75ee38b3fc140ef7edcea8 /vendor/filippo.io/edwards25519/field/fe_extra.go
parent3c4192ebf6a32e30cdd23a9644c2ceca72a006fa (diff)
downloadmatterbridge-msglm-6a3fc713978a0c1c9290a4afd08b47886b49b635.tar.gz
matterbridge-msglm-6a3fc713978a0c1c9290a4afd08b47886b49b635.tar.bz2
matterbridge-msglm-6a3fc713978a0c1c9290a4afd08b47886b49b635.zip
Update dependencies and go1.18 (#1873)
* Update dependencies and go1.18 * Exclude unnecessary linters and update build to go1.18
Diffstat (limited to 'vendor/filippo.io/edwards25519/field/fe_extra.go')
-rw-r--r--vendor/filippo.io/edwards25519/field/fe_extra.go50
1 files changed, 50 insertions, 0 deletions
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 00000000..699238e9
--- /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/internal/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
+}