| /* 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.org |
| */ |
| #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 mp_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(mp_int *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) != 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) == 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)); |
| 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: 1.1 $ */ |
| /* $Date: 2005/05/16 15:08:11 $ */ |