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 (at) 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 */ 25 int 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
