/* 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_encode_integer.c  ASN.1 DER, encode an integer, Tom St Denis*/#ifdef LTC_DER/* Exports a positive bignum as DER format (upto 2^32 bytes in size) *//**  Store a mp_int integer  @param num      The first mp_int to encode  @param out      [out] The destination for the DER encoded integers  @param outlen   [in/out] The max size and resulting size of the DER encoded integers  @return CRYPT_OK if successful*/int der_encode_integer(mp_int *num, unsigned char *out, unsigned long *outlen){     unsigned long tmplen, y;   int           err, leading_zero;   LTC_ARGCHK(num    != NULL);   LTC_ARGCHK(out    != NULL);   LTC_ARGCHK(outlen != NULL);   /* find out how big this will be */   if ((err = der_length_integer(num, &tmplen)) != CRYPT_OK) {      return err;   }   if (*outlen < tmplen) {      return CRYPT_BUFFER_OVERFLOW;   }   if (mp_cmp_d(num, 0) != MP_LT) {      /* 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;      }      /* get length of num in bytes (plus 1 since we force the msbyte to zero) */      y = mp_unsigned_bin_size(num) + leading_zero;   } else {      leading_zero = 0;      y            = mp_count_bits(num);      y            = y + (8 - (y & 7));      y            = y >> 3;   }   /* now store initial data */   *out++ = 0x02;   if (y < 128) {      /* short form */      *out++ = (unsigned char)y;   } else if (y < 256) {      *out++ = 0x81;      *out++ = y;   } else if (y < 65536UL) {      *out++ = 0x82;      *out++ = (y>>8)&255;      *out++ = y;   } else if (y < 16777216UL) {      *out++ = 0x83;      *out++ = (y>>16)&255;      *out++ = (y>>8)&255;      *out++ = y;   } else {      return CRYPT_INVALID_ARG;   }   /* now store msbyte of zero if num is non-zero */   if (leading_zero) {      *out++ = 0x00;   }   /* if it's not zero store it as big endian */   if (mp_cmp_d(num, 0) == MP_GT) {      /* now store the mpint */      if ((err = mp_to_unsigned_bin(num, out)) != MP_OKAY) {          return mpi_to_ltc_error(err);      }   } else if (mp_iszero(num) != MP_YES) {      mp_int tmp;      /* negative */      if (mp_init(&tmp) != MP_OKAY) {         return CRYPT_MEM;      }      /* 2^roundup and subtract */      y = mp_count_bits(num);      y = y + (8 - (y & 7));      if (mp_2expt(&tmp, y) != MP_OKAY || mp_add(&tmp, num, &tmp) != MP_OKAY) {         mp_clear(&tmp);         return CRYPT_MEM;      }      if ((err = mp_to_unsigned_bin(&tmp, out)) != MP_OKAY) {         mp_clear(&tmp);         return mpi_to_ltc_error(err);      }      mp_clear(&tmp);   }   /* we good */   *outlen = tmplen;    return CRYPT_OK;}#endif/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_encode_integer.c,v $ *//* $Revision: 1.1 $ *//* $Date: 2005/05/16 15:08:11 $ */