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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
*/
#include "tomcrypt.h"
/**
@file der_length_bit_string.c
ASN.1 DER, get length of BIT STRING, Tom St Denis
*/
#ifdef LTC_DER
/**
Gets length of DER encoding of BIT STRING
@param nbits The number of bits in the string to encode
@param outlen [out] The length of the DER encoding for the given string
@return CRYPT_OK if successful
*/
int der_length_bit_string(unsigned long nbits, unsigned long *outlen)
{
unsigned long nbytes;
LTC_ARGCHK(outlen != NULL);
/* get the number of the bytes */
nbytes = (nbits >> 3) + ((nbits & 7) ? 1 : 0) + 1;
if (nbytes < 128) {
/* 03 LL PP DD DD DD ... */
*outlen = 2 + nbytes;
} else if (nbytes < 256) {
/* 03 81 LL PP DD DD DD ... */
*outlen = 3 + nbytes;
} else if (nbytes < 65536) {
/* 03 82 LL LL PP DD DD DD ... */
*outlen = 4 + nbytes;
} else {
return CRYPT_INVALID_ARG;
}
return CRYPT_OK;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/bit/der_length_bit_string.c,v $ */
/* $Revision: 1.2 $ */
/* $Date: 2006/03/31 14:15:35 $ */
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