certspotter/asn1time.go

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2016-05-04 20:53:48 +02:00
// Copyright (C) 2016 Opsmate, Inc.
//
// 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/.
//
// This software is distributed WITHOUT A WARRANTY OF ANY KIND.
// See the Mozilla Public License for details.
2016-05-04 20:49:07 +02:00
package certspotter
import (
"encoding/asn1"
"errors"
"strconv"
"time"
"unicode"
)
const (
tagUTCTime = 23
tagGeneralizedTime = 24
)
func isDigit(b byte) bool {
return unicode.IsDigit(rune(b))
}
func bytesToInt(bytes []byte) (int, error) {
return strconv.Atoi(string(bytes))
}
func parseUTCTime(bytes []byte) (time.Time, error) {
var err error
var year, month, day int
var hour, min, sec int
var tz *time.Location
// YYMMDDhhmm
if len(bytes) < 10 {
return time.Time{}, errors.New("UTCTime is too short")
}
year, err = bytesToInt(bytes[0:2])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
month, err = bytesToInt(bytes[2:4])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
day, err = bytesToInt(bytes[4:6])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
hour, err = bytesToInt(bytes[6:8])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
min, err = bytesToInt(bytes[8:10])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
bytes = bytes[10:]
// (optional) ss
if len(bytes) >= 2 && isDigit(bytes[0]) {
sec, err = bytesToInt(bytes[0:2])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
bytes = bytes[2:]
}
// timezone (required but allow it to be omitted, since this is a common error)
if len(bytes) >= 1 {
if bytes[0] == 'Z' {
tz = time.UTC
bytes = bytes[1:]
} else if bytes[0] == '+' {
// +hhmm
if len(bytes) < 5 {
return time.Time{}, errors.New("UTCTime positive timezone offset is too short")
}
tzHour, err := bytesToInt(bytes[1:3])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
tzMin, err := bytesToInt(bytes[3:5])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
tz = time.FixedZone("", tzHour*3600+tzMin*60)
bytes = bytes[5:]
} else if bytes[0] == '-' {
// -hhmm
if len(bytes) < 5 {
return time.Time{}, errors.New("UTCTime negative timezone offset is too short")
}
tzHour, err := bytesToInt(bytes[1:3])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
tzMin, err := bytesToInt(bytes[3:5])
if err != nil {
return time.Time{}, errors.New("UTCTime contains invalid integer: " + err.Error())
}
tz = time.FixedZone("", -1*(tzHour*3600+tzMin*60))
bytes = bytes[5:]
}
} else {
tz = time.UTC
}
if len(bytes) > 0 {
return time.Time{}, errors.New("UTCTime has trailing garbage")
}
// https://tools.ietf.org/html/rfc5280#section-4.1.2.5.1
if year >= 50 {
year = 1900 + year
} else {
year = 2000 + year
}
return time.Date(year, time.Month(month), day, hour, min, sec, 0, tz), nil
}
func parseGeneralizedTime(bytes []byte) (time.Time, error) {
var err error
var year, month, day int
var hour, min, sec, ms int
var tz *time.Location
// YYYYMMDDHH
if len(bytes) < 10 {
return time.Time{}, errors.New("GeneralizedTime is too short")
}
year, err = bytesToInt(bytes[0:4])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
month, err = bytesToInt(bytes[4:6])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
day, err = bytesToInt(bytes[6:8])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
hour, err = bytesToInt(bytes[8:10])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
bytes = bytes[10:]
// (optional) MM
if len(bytes) >= 2 && isDigit(bytes[0]) {
min, err = bytesToInt(bytes[0:2])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
bytes = bytes[2:]
// (optional) SS
if len(bytes) >= 2 && isDigit(bytes[0]) {
sec, err = bytesToInt(bytes[0:2])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
bytes = bytes[2:]
// (optional) .fff
if len(bytes) >= 1 && bytes[0] == '.' {
if len(bytes) < 4 {
return time.Time{}, errors.New("GeneralizedTime fractional seconds is too short")
}
ms, err = bytesToInt(bytes[1:4])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
bytes = bytes[4:]
}
}
}
// timezone (Z or +hhmm or -hhmm or nothing)
if len(bytes) >= 1 {
if bytes[0] == 'Z' {
bytes = bytes[1:]
tz = time.UTC
} else if bytes[0] == '+' {
// +hhmm
if len(bytes) < 5 {
return time.Time{}, errors.New("GeneralizedTime positive timezone offset is too short")
}
tzHour, err := bytesToInt(bytes[1:3])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
tzMin, err := bytesToInt(bytes[3:5])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
tz = time.FixedZone("", tzHour*3600+tzMin*60)
bytes = bytes[5:]
} else if bytes[0] == '-' {
// -hhmm
if len(bytes) < 5 {
return time.Time{}, errors.New("GeneralizedTime negative timezone offset is too short")
}
tzHour, err := bytesToInt(bytes[1:3])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
tzMin, err := bytesToInt(bytes[3:5])
if err != nil {
return time.Time{}, errors.New("GeneralizedTime contains invalid integer: " + err.Error())
}
tz = time.FixedZone("", -1*(tzHour*3600+tzMin*60))
bytes = bytes[5:]
}
} else {
tz = time.UTC
}
if len(bytes) > 0 {
return time.Time{}, errors.New("GeneralizedTime has trailing garbage")
}
return time.Date(year, time.Month(month), day, hour, min, sec, ms*1000*1000, tz), nil
}
func decodeASN1Time(value *asn1.RawValue) (time.Time, error) {
if !value.IsCompound && value.Class == 0 {
if value.Tag == tagUTCTime {
return parseUTCTime(value.Bytes)
} else if value.Tag == tagGeneralizedTime {
return parseGeneralizedTime(value.Bytes)
}
}
return time.Time{}, errors.New("Not a time value")
}