1/* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11#include "tomcrypt.h"
12
13/**
14  @file der_length_bit_string.c
15  ASN.1 DER, get length of BIT STRING, Tom St Denis
16*/
17
18#ifdef LTC_DER
19/**
20  Gets length of DER encoding of BIT STRING
21  @param nbits  The number of bits in the string to encode
22  @param outlen [out] The length of the DER encoding for the given string
23  @return CRYPT_OK if successful
24*/
25int der_length_bit_string(unsigned long nbits, unsigned long *outlen)
26{
27   unsigned long nbytes;
28   LTC_ARGCHK(outlen != NULL);
29
30   /* get the number of the bytes */
31   nbytes = (nbits >> 3) + ((nbits & 7) ? 1 : 0) + 1;
32
33   if (nbytes < 128) {
34      /* 03 LL PP DD DD DD ... */
35      *outlen = 2 + nbytes;
36   } else if (nbytes < 256) {
37      /* 03 81 LL PP DD DD DD ... */
38      *outlen = 3 + nbytes;
39   } else if (nbytes < 65536) {
40      /* 03 82 LL LL PP DD DD DD ... */
41      *outlen = 4 + nbytes;
42   } else {
43      return CRYPT_INVALID_ARG;
44   }
45
46   return CRYPT_OK;
47}
48
49#endif
50
51
52/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/bit/der_length_bit_string.c,v $ */
53/* $Revision: 1.2 $ */
54/* $Date: 2006/03/31 14:15:35 $ */
55