2 GoVPN -- simple secure free software virtual private network daemon
3 Copyright (C) 2014-2016 Sergey Matveev <stargrave@stargrave.org>
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
19 // All-Or-Nothing-Transform, based on OAEP.
21 // This package implements OAEP (Optimal Asymmetric Encryption Padding)
22 // (http://cseweb.ucsd.edu/~mihir/papers/oaep.html)
23 // used there as All-Or-Nothing-Transformation
24 // (http://theory.lcs.mit.edu/~cis/pubs/rivest/fusion.ps).
25 // We do not fix OAEP parts lengths, instead we add hash-based
26 // checksum like in SAEP+
27 // (http://crypto.stanford.edu/~dabo/abstracts/saep.html).
29 // AONT takes 128-bit random r, data M to be encoded and produce the
33 // P1 = HKDF(BLAKE2b, r) XOR (M || BLAKE2b(r || M)) ||
34 // P2 = BLAKE2b(P1) XOR r
41 "github.com/dchest/blake2b"
42 "golang.org/x/crypto/hkdf"
50 // Encode the data, produce AONT package. Data size will be larger than
51 // the original one for 48 bytes.
52 func Encode(r *[RSize]byte, in []byte) ([]byte, error) {
53 out := make([]byte, len(in)+HSize+RSize)
54 hr := hkdf.New(blake2b.New512, r[:], nil, nil)
55 if _, err := hr.Read(out[:len(in)+HSize]); err != nil {
59 for i = 0; i < len(in); i++ {
65 for _, b := range h.Sum(nil) {
71 for _, b := range h.Sum(nil)[:RSize] {
72 out[i] = b ^ r[i-len(in)-HSize]
78 // Decode the data from AONT package. Data size will be smaller than the
79 // original one for 48 bytes.
80 func Decode(in []byte) ([]byte, error) {
81 if len(in) < HSize+RSize {
82 return nil, errors.New("Too small input buffer")
85 h.Write(in[:len(in)-RSize])
86 out := make([]byte, len(in)-RSize)
87 for i, b := range h.Sum(nil)[:RSize] {
88 out[i] = b ^ in[len(in)-RSize+i]
92 hr := hkdf.New(blake2b.New512, out[:RSize], nil, nil)
93 if _, err := hr.Read(out); err != nil {
96 for i := 0; i < len(out); i++ {
99 h.Write(out[:len(out)-HSize])
100 if subtle.ConstantTimeCompare(h.Sum(nil), out[len(out)-HSize:]) != 1 {
101 return nil, errors.New("Invalid checksum")
103 return out[:len(out)-HSize], nil