Slightly more endianness documentation

[gogost.git] / gost3410 / private.go

diff --git a/gost3410/private.go b/gost3410/private.go
index 645881bfd5c1944814637e5387899932a095a542..983d8d2849399c80a5617e8a5917180f9b96eb75 100644 (file)
--- a/gost3410/private.go
+++ b/gost3410/private.go
@@ -1,5 +1,5 @@
 // GoGOST -- Pure Go GOST cryptographic functions library
-// Copyright (C) 2015-2020 Sergey Matveev <stargrave@stargrave.org>
+// Copyright (C) 2015-2023 Sergey Matveev <stargrave@stargrave.org>
 //
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
@@ -24,16 +24,17 @@ import (
 )
 
 type PrivateKey struct {
-       C    *Curve
-       Mode Mode
-       Key  *big.Int
+       C   *Curve
+       Key *big.Int
 }
 
-func NewPrivateKey(curve *Curve, mode Mode, raw []byte) (*PrivateKey, error) {
-       if len(raw) != int(mode) {
-               return nil, fmt.Errorf("gogost/gost3410: len(key) != %d", mode)
+// Unmarshal little-endian private key. "raw" must be c.PointSize() length.
+func NewPrivateKey(c *Curve, raw []byte) (*PrivateKey, error) {
+       pointSize := c.PointSize()
+       if len(raw) != pointSize {
+               return nil, fmt.Errorf("gogost/gost3410: len(key)=%d != %d", len(raw), pointSize)
        }
-       key := make([]byte, int(mode))
+       key := make([]byte, pointSize)
        for i := 0; i < len(key); i++ {
                key[i] = raw[len(raw)-i-1]
        }
@@ -41,19 +42,20 @@ func NewPrivateKey(curve *Curve, mode Mode, raw []byte) (*PrivateKey, error) {
        if k.Cmp(zero) == 0 {
                return nil, errors.New("gogost/gost3410: zero private key")
        }
-       return &PrivateKey{curve, mode, k}, nil
+       return &PrivateKey{c, k.Mod(k, c.Q)}, nil
 }
 
-func GenPrivateKey(curve *Curve, mode Mode, rand io.Reader) (*PrivateKey, error) {
-       raw := make([]byte, int(mode))
+func GenPrivateKey(c *Curve, rand io.Reader) (*PrivateKey, error) {
+       raw := make([]byte, c.PointSize())
        if _, err := io.ReadFull(rand, raw); err != nil {
-               return nil, err
+               return nil, fmt.Errorf("gogost/gost3410.GenPrivateKey: %w", err)
        }
-       return NewPrivateKey(curve, mode, raw)
+       return NewPrivateKey(c, raw)
 }
 
-func (prv *PrivateKey) Raw() []byte {
-       raw := pad(prv.Key.Bytes(), int(prv.Mode))
+// Marshal little-endian private key. raw will be prv.C.PointSize() length.
+func (prv *PrivateKey) Raw() (raw []byte) {
+       raw = pad(prv.Key.Bytes(), prv.C.PointSize())
        reverse(raw)
        return raw
 }
@@ -61,9 +63,9 @@ func (prv *PrivateKey) Raw() []byte {
 func (prv *PrivateKey) PublicKey() (*PublicKey, error) {
        x, y, err := prv.C.Exp(prv.Key, prv.C.X, prv.C.Y)
        if err != nil {
-               return nil, err
+               return nil, fmt.Errorf("gogost/gost3410.PrivateKey.PublicKey: %w", err)
        }
-       return &PublicKey{prv.C, prv.Mode, x, y}, nil
+       return &PublicKey{prv.C, x, y}, nil
 }
 
 func (prv *PrivateKey) SignDigest(digest []byte, rand io.Reader) ([]byte, error) {
@@ -72,7 +74,7 @@ func (prv *PrivateKey) SignDigest(digest []byte, rand io.Reader) ([]byte, error)
        if e.Cmp(zero) == 0 {
                e = big.NewInt(1)
        }
-       kRaw := make([]byte, int(prv.Mode))
+       kRaw := make([]byte, prv.C.PointSize())
        var err error
        var k *big.Int
        var r *big.Int
@@ -80,7 +82,7 @@ func (prv *PrivateKey) SignDigest(digest []byte, rand io.Reader) ([]byte, error)
        s := big.NewInt(0)
 Retry:
        if _, err = io.ReadFull(rand, kRaw); err != nil {
-               return nil, err
+               return nil, fmt.Errorf("gogost/gost3410.PrivateKey.SignDigest: %w", err)
        }
        k = bytes2big(kRaw)
        k.Mod(k, prv.C.Q)
@@ -89,7 +91,7 @@ Retry:
        }
        r, _, err = prv.C.Exp(k, prv.C.X, prv.C.Y)
        if err != nil {
-               return nil, err
+               return nil, fmt.Errorf("gogost/gost3410.PrivateKey.SignDigest: %w", err)
        }
        r.Mod(r, prv.C.Q)
        if r.Cmp(zero) == 0 {
@@ -102,12 +104,14 @@ Retry:
        if s.Cmp(zero) == 0 {
                goto Retry
        }
+       pointSize := prv.C.PointSize()
        return append(
-               pad(s.Bytes(), int(prv.Mode)),
-               pad(r.Bytes(), int(prv.Mode))...,
+               pad(s.Bytes(), pointSize),
+               pad(r.Bytes(), pointSize)...,
        ), nil
 }
 
+// Sign the digest. opts argument is unused.
 func (prv *PrivateKey) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
        return prv.SignDigest(digest, rand)
 }