Mercurial > dropbear
view libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c @ 913:6e2aa862e167
The arguments are for configure, not make!
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Fri, 07 Mar 2014 20:52:57 +0800 |
parents | 0cbe8f6dbf9e |
children | f849a5ca2efc |
line wrap: on
line source
/* 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, [email protected], http://libtomcrypt.com */ #include "tomcrypt.h" /** @file der_length_integer.c ASN.1 DER, get length of encoding, Tom St Denis */ #ifdef LTC_DER /** Gets length of DER encoding of num @param num The int to get the size of @param outlen [out] The length of the DER encoding for the given integer @return CRYPT_OK if successful */ int der_length_integer(void *num, unsigned long *outlen) { unsigned long z, len; int leading_zero; LTC_ARGCHK(num != NULL); LTC_ARGCHK(outlen != NULL); if (mp_cmp_d(num, 0) != LTC_MP_LT) { /* positive */ /* we only need a leading zero if the msb of the first byte is one */ if ((mp_count_bits(num) & 7) == 0 || mp_iszero(num) == LTC_MP_YES) { leading_zero = 1; } else { leading_zero = 0; } /* size for bignum */ z = len = leading_zero + mp_unsigned_bin_size(num); } else { /* it's negative */ /* find power of 2 that is a multiple of eight and greater than count bits */ leading_zero = 0; z = mp_count_bits(num); z = z + (8 - (z & 7)); if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) --z; len = z = z >> 3; } /* now we need a length */ if (z < 128) { /* short form */ ++len; } else { /* long form (relies on z != 0), assumes length bytes < 128 */ ++len; while (z) { ++len; z >>= 8; } } /* we need a 0x02 to indicate it's INTEGER */ ++len; /* return length */ *outlen = len; return CRYPT_OK; } #endif /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c,v $ */ /* $Revision: 1.4 $ */ /* $Date: 2006/04/22 01:22:55 $ */