certspotter/asn1.go

79 lines
2.4 KiB
Go

// 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.
package certspotter
import (
"bytes"
"encoding/asn1"
"encoding/binary"
"errors"
"unicode/utf8"
)
func stringFromByteSlice(chars []byte) string {
runes := make([]rune, len(chars))
for i, ch := range chars {
runes[i] = rune(ch)
}
return string(runes)
}
func stringFromUint16Slice(chars []uint16) string {
runes := make([]rune, len(chars))
for i, ch := range chars {
runes[i] = rune(ch)
}
return string(runes)
}
func stringFromUint32Slice(chars []uint32) string {
runes := make([]rune, len(chars))
for i, ch := range chars {
runes[i] = rune(ch)
}
return string(runes)
}
func decodeASN1String(value *asn1.RawValue) (string, error) {
if !value.IsCompound && value.Class == 0 {
if value.Tag == 12 {
// UTF8String
if !utf8.Valid(value.Bytes) {
return "", errors.New("Malformed UTF8String")
}
return string(value.Bytes), nil
} else if value.Tag == 19 || value.Tag == 22 || value.Tag == 20 || value.Tag == 26 {
// * PrintableString - subset of ASCII
// * IA5String - ASCII
// * TeletexString - 8 bit charset; not quite ISO-8859-1, but often treated as such
// * VisibleString - subset of ASCII
// Don't enforce character set rules. Allow any 8 bit character, since
// CAs routinely mess this up
return stringFromByteSlice(value.Bytes), nil
} else if value.Tag == 30 {
// BMPString - Unicode, encoded in big-endian format using two octets
runes := make([]uint16, len(value.Bytes)/2)
if err := binary.Read(bytes.NewReader(value.Bytes), binary.BigEndian, runes); err != nil {
return "", errors.New("Malformed BMPString: " + err.Error())
}
return stringFromUint16Slice(runes), nil
} else if value.Tag == 28 {
// UniversalString - Unicode, encoded in big-endian format using four octets
runes := make([]uint32, len(value.Bytes)/4)
if err := binary.Read(bytes.NewReader(value.Bytes), binary.BigEndian, runes); err != nil {
return "", errors.New("Malformed UniversalString: " + err.Error())
}
return stringFromUint32Slice(runes), nil
}
}
return "", errors.New("Not a string")
}