package field

import "crypto/internal/fips140/edwards25519/field"

Package field implements fast arithmetic modulo 2^255-19.

Index

Types

type Element

type Element struct {
	// contains filtered or unexported fields
}

Element represents an element of the field GF(2^255-19). Note that this is not a cryptographically secure group, and should only be used to interact with edwards25519.Point coordinates.

This type works similarly to math/big.Int, and all arguments and receivers are allowed to alias.

The zero value is a valid zero element.

func (*Element) Absolute
func (v *Element) Absolute(u *Element) *Element

Absolute sets v to |u|, and returns v.

func (*Element) Add
func (v *Element) Add(a, b *Element) *Element

Add sets v = a + b, and returns v.

func (*Element) Bytes
func (v *Element) Bytes() []byte

Bytes returns the canonical 32-byte little-endian encoding of v.

func (*Element) Equal
func (v *Element) Equal(u *Element) int

Equal returns 1 if v and u are equal, and 0 otherwise.

func (*Element) Invert
func (v *Element) Invert(z *Element) *Element

Invert sets v = 1/z mod p, and returns v.

If z == 0, Invert returns v = 0.

func (*Element) IsNegative
func (v *Element) IsNegative() int

IsNegative returns 1 if v is negative, and 0 otherwise.

func (*Element) Mult32
func (v *Element) Mult32(x *Element, y uint32) *Element

Mult32 sets v = x * y, and returns v.

func (*Element) Multiply
func (v *Element) Multiply(x, y *Element) *Element

Multiply sets v = x * y, and returns v.

func (*Element) Negate
func (v *Element) Negate(a *Element) *Element

Negate sets v = -a, and returns v.

func (*Element) One
func (v *Element) One() *Element

One sets v = 1, and returns v.

func (*Element) Pow22523
func (v *Element) Pow22523(x *Element) *Element

Pow22523 set v = x^((p-5)/8), and returns v. (p-5)/8 is 2^252-3.

func (*Element) Select
func (v *Element) Select(a, b *Element, cond int) *Element

Select sets v to a if cond == 1, and to b if cond == 0.

func (*Element) Set
func (v *Element) Set(a *Element) *Element

Set sets v = a, and returns v.

func (*Element) SetBytes
func (v *Element) SetBytes(x []byte) (*Element, error)

SetBytes sets v to x, where x is a 32-byte little-endian encoding. If x is not of the right length, SetBytes returns nil and an error, and the receiver is unchanged.

Consistent with RFC 7748, the most significant bit (the high bit of the last byte) is ignored, and non-canonical values (2^255-19 through 2^255-1) are accepted. Note that this is laxer than specified by RFC 8032, but consistent with most Ed25519 implementations.

func (*Element) SqrtRatio
func (r *Element) SqrtRatio(u, v *Element) (R *Element, wasSquare int)

SqrtRatio sets r to the non-negative square root of the ratio of u and v.

If u/v is square, SqrtRatio returns r and 1. If u/v is not square, SqrtRatio sets r according to Section 4.3 of draft-irtf-cfrg-ristretto255-decaf448-00, and returns r and 0.

func (*Element) Square
func (v *Element) Square(x *Element) *Element

Square sets v = x * x, and returns v.

func (*Element) Subtract
func (v *Element) Subtract(a, b *Element) *Element

Subtract sets v = a - b, and returns v.

func (*Element) Swap
func (v *Element) Swap(u *Element, cond int)

Swap swaps v and u if cond == 1 or leaves them unchanged if cond == 0, and returns v.

func (*Element) Zero
func (v *Element) Zero() *Element

Zero sets v = 0, and returns v.