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129 lines
3.5 KiB
C
129 lines
3.5 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*/
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#include "tomcrypt.h"
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/**
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@file der_encode_integer.c
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ASN.1 DER, encode an integer, Tom St Denis
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*/
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#ifdef LTC_DER
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/* Exports a positive bignum as DER format (upto 2^32 bytes in size) */
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/**
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Store a mp_int integer
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@param num The first mp_int to encode
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@param out [out] The destination for the DER encoded integers
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@param outlen [in/out] The max size and resulting size of the DER encoded integers
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@return CRYPT_OK if successful
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*/
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int der_encode_integer(void *num, unsigned char *out, unsigned long *outlen)
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{
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unsigned long tmplen, y;
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int err, leading_zero;
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LTC_ARGCHK(num != NULL);
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LTC_ARGCHK(out != NULL);
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LTC_ARGCHK(outlen != NULL);
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/* find out how big this will be */
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if ((err = der_length_integer(num, &tmplen)) != CRYPT_OK) {
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return err;
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}
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if (*outlen < tmplen) {
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*outlen = tmplen;
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return CRYPT_BUFFER_OVERFLOW;
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}
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if (mp_cmp_d(num, 0) != LTC_MP_LT) {
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/* we only need a leading zero if the msb of the first byte is one */
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if ((mp_count_bits(num) & 7) == 0 || mp_iszero(num) == LTC_MP_YES) {
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leading_zero = 1;
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} else {
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leading_zero = 0;
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}
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/* get length of num in bytes (plus 1 since we force the msbyte to zero) */
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y = mp_unsigned_bin_size(num) + leading_zero;
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} else {
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leading_zero = 0;
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y = mp_count_bits(num);
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y = y + (8 - (y & 7));
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y = y >> 3;
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if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) --y;
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}
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/* now store initial data */
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*out++ = 0x02;
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if (y < 128) {
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/* short form */
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*out++ = (unsigned char)y;
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} else if (y < 256) {
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*out++ = 0x81;
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*out++ = (unsigned char)y;
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} else if (y < 65536UL) {
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*out++ = 0x82;
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*out++ = (unsigned char)((y>>8)&255);
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*out++ = (unsigned char)y;
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} else if (y < 16777216UL) {
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*out++ = 0x83;
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*out++ = (unsigned char)((y>>16)&255);
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*out++ = (unsigned char)((y>>8)&255);
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*out++ = (unsigned char)y;
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} else {
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return CRYPT_INVALID_ARG;
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}
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/* now store msbyte of zero if num is non-zero */
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if (leading_zero) {
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*out++ = 0x00;
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}
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/* if it's not zero store it as big endian */
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if (mp_cmp_d(num, 0) == LTC_MP_GT) {
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/* now store the mpint */
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if ((err = mp_to_unsigned_bin(num, out)) != CRYPT_OK) {
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return err;
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}
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} else if (mp_iszero(num) != LTC_MP_YES) {
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void *tmp;
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/* negative */
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if (mp_init(&tmp) != CRYPT_OK) {
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return CRYPT_MEM;
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}
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/* 2^roundup and subtract */
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y = mp_count_bits(num);
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y = y + (8 - (y & 7));
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if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) y -= 8;
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if (mp_2expt(tmp, y) != CRYPT_OK || mp_add(tmp, num, tmp) != CRYPT_OK) {
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mp_clear(tmp);
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return CRYPT_MEM;
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}
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if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) {
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mp_clear(tmp);
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return err;
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}
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mp_clear(tmp);
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}
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/* we good */
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*outlen = tmplen;
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return CRYPT_OK;
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}
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#endif
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/* ref: HEAD -> master, tag: v1.18.2 */
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/* git commit: 7e7eb695d581782f04b24dc444cbfde86af59853 */
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/* commit time: 2018-07-01 22:49:01 +0200 */
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