1// Copyright 2015 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package pkcs12
6
7import (
8	"errors"
9	"unicode/utf16"
10)
11
12// bmpString returns s encoded in UCS-2 with a zero terminator.
13func bmpString(s string) ([]byte, error) {
14	// References:
15	// https://tools.ietf.org/html/rfc7292#appendix-B.1
16	// https://en.wikipedia.org/wiki/Plane_(Unicode)#Basic_Multilingual_Plane
17	//  - non-BMP characters are encoded in UTF 16 by using a surrogate pair of 16-bit codes
18	//	  EncodeRune returns 0xfffd if the rune does not need special encoding
19	//  - the above RFC provides the info that BMPStrings are NULL terminated.
20
21	ret := make([]byte, 0, 2*len(s)+2)
22
23	for _, r := range s {
24		if t, _ := utf16.EncodeRune(r); t != 0xfffd {
25			return nil, errors.New("pkcs12: string contains characters that cannot be encoded in UCS-2")
26		}
27		ret = append(ret, byte(r/256), byte(r%256))
28	}
29
30	return append(ret, 0, 0), nil
31}
32
33func decodeBMPString(bmpString []byte) (string, error) {
34	if len(bmpString)%2 != 0 {
35		return "", errors.New("pkcs12: odd-length BMP string")
36	}
37
38	// strip terminator if present
39	if l := len(bmpString); l >= 2 && bmpString[l-1] == 0 && bmpString[l-2] == 0 {
40		bmpString = bmpString[:l-2]
41	}
42
43	s := make([]uint16, 0, len(bmpString)/2)
44	for len(bmpString) > 0 {
45		s = append(s, uint16(bmpString[0])<<8+uint16(bmpString[1]))
46		bmpString = bmpString[2:]
47	}
48
49	return string(utf16.Decode(s)), nil
50}
51