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https://github.com/clearml/dropbear
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0c10d50a69
--HG-- branch : libtomcrypt-orig extra : convert_revision : 7122128aa22564d1a53eebfac79c0393c4d0c011
55 lines
1.1 KiB
C
55 lines
1.1 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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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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#include "mycrypt.h"
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/* Gets length of DER encoding of num */
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int der_length_integer(mp_int *num, unsigned long *outlen)
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{
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unsigned long z, len;
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int leading_zero;
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_ARGCHK(num != NULL);
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_ARGCHK(outlen != NULL);
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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) == 7 || mp_iszero(num) == 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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/* size for bignum */
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z = len = leading_zero + mp_unsigned_bin_size(num);
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/* we need a 0x02 */
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++len;
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/* now we need a length */
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if (z < 128) {
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/* short form */
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++len;
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} else {
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/* long form (relies on z != 0) */
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++len;
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while (z) {
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++len;
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z >>= 8;
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}
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}
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*outlen = len;
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return CRYPT_OK;
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}
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