Skip to content

p384: document assumed reductions #670

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
bwesterb merged 1 commit into from
Jul 31, 2026
+13 −0
Merged

p384: document assumed reductions #670

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
13 changes: 13 additions & 0 deletions ecc/p384/arith.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,11 +11,15 @@ import (

const sizeFp = 48

// fp384 is an element of the base field, stored as a little-endian byte array.
// Only guaranteed to be reduced below 2^384.
type fp384 [sizeFp]byte

func (e fp384) BigInt() *big.Int { return conv.BytesLe2BigInt(e[:]) }
func (e fp384) String() string { return conv.BytesLe2Hex(e[:]) }

// SetBigInt stores b into e, reducing it modulo p as necessary. Any b is
// accepted, including negative and out-of-range values.
func (e *fp384) SetBigInt(b *big.Int) {
if b.BitLen() > 384 || b.Sign() < 0 {
b = new(big.Int).Mod(b, p.BigInt())
Expand Down Expand Up @@ -105,15 +109,24 @@ func fp384Inv(z, x *fp384) {
//go:noescape
func fp384Cmov(x, y *fp384, b int)

// fp384Neg requires a reduced a, as it computes p-a.
//
//go:noescape
func fp384Neg(c, a *fp384)

// fp384Add requires at least one of a and b to be reduced, and c may itself be
// non-reduced, as only a single p is conditionally subtracted.
//
//go:noescape
func fp384Add(c, a, b *fp384)

// fp384Sub requires a reduced b.
//
//go:noescape
func fp384Sub(c, a, b *fp384)

// fp384Mul accepts non-reduced operands and always returns a reduced c.
//
//go:noescape
func fp384Mul(c, a, b *fp384)

Expand Down
Loading