129 lines
2.4 KiB
Go
129 lines
2.4 KiB
Go
// Copyright 2014 ISRG. All rights reserved
|
|
// This Source Code Form is subject to the terms of the Mozilla Public
|
|
// License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
|
|
package core
|
|
|
|
import (
|
|
"crypto/aes"
|
|
"crypto/cipher"
|
|
"crypto/rand"
|
|
"math/big"
|
|
)
|
|
|
|
const MaxUsed = 65536
|
|
|
|
type NonceService struct {
|
|
latest int64
|
|
earliest int64
|
|
used map[int64]bool
|
|
gcm cipher.AEAD
|
|
maxUsed int
|
|
}
|
|
|
|
func NewNonceService() NonceService {
|
|
// XXX ignoring possible error due to entropy starvation
|
|
key := make([]byte, 16)
|
|
rand.Read(key)
|
|
|
|
// It is safe to ignore these errors because they only happen
|
|
// on key size and block size mismatches.
|
|
c, _ := aes.NewCipher(key)
|
|
gcm, _ := cipher.NewGCM(c)
|
|
|
|
return NonceService{
|
|
earliest: 0,
|
|
latest: 0,
|
|
used: make(map[int64]bool, MaxUsed),
|
|
gcm: gcm,
|
|
maxUsed: MaxUsed,
|
|
}
|
|
}
|
|
|
|
func (ns NonceService) encrypt(counter int64) string {
|
|
// Generate a nonce with upper 4 bytes zero
|
|
// XXX ignoring possible error due to entropy starvation
|
|
nonce := make([]byte, 12)
|
|
for i := 0; i < 4; i += 1 {
|
|
nonce[i] = 0
|
|
}
|
|
rand.Read(nonce[4:])
|
|
|
|
// Encode counter to plaintext
|
|
pt := make([]byte, 8)
|
|
ctr := big.NewInt(counter)
|
|
pad := 8 - len(ctr.Bytes())
|
|
copy(pt[pad:], ctr.Bytes())
|
|
|
|
// Encrypt
|
|
ret := make([]byte, 32)
|
|
ct := ns.gcm.Seal(nil, nonce, pt, nil)
|
|
copy(ret, nonce[4:])
|
|
copy(ret[8:], ct)
|
|
return B64enc(ret)
|
|
}
|
|
|
|
func (ns NonceService) decrypt(nonce string) (int64, error) {
|
|
decoded, err := B64dec(nonce)
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
|
|
n := make([]byte, 12)
|
|
for i := 0; i < 4; i += 1 {
|
|
n[i] = 0
|
|
}
|
|
copy(n[4:], decoded[:8])
|
|
|
|
pt, err := ns.gcm.Open(nil, n, decoded[8:], nil)
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
|
|
ctr := big.NewInt(0)
|
|
ctr.SetBytes(pt)
|
|
return ctr.Int64(), nil
|
|
}
|
|
|
|
func (ns *NonceService) Nonce() string {
|
|
ns.latest += 1
|
|
return ns.encrypt(ns.latest)
|
|
}
|
|
|
|
func (ns *NonceService) minUsed() int64 {
|
|
min := ns.latest
|
|
for t := range ns.used {
|
|
if t < min {
|
|
min = t
|
|
}
|
|
}
|
|
return min
|
|
}
|
|
|
|
func (ns *NonceService) Valid(nonce string) bool {
|
|
c, err := ns.decrypt(nonce)
|
|
if err != nil {
|
|
return false
|
|
}
|
|
|
|
if c > ns.latest {
|
|
return false
|
|
}
|
|
|
|
if c <= ns.earliest {
|
|
return false
|
|
}
|
|
|
|
if ns.used[c] {
|
|
return false
|
|
}
|
|
|
|
ns.used[c] = true
|
|
if len(ns.used) > ns.maxUsed {
|
|
ns.earliest = ns.minUsed()
|
|
delete(ns.used, ns.earliest)
|
|
}
|
|
|
|
return true
|
|
}
|