Mercurial > dropbear
view libtomcrypt/src/pk/asn1/der/integer/der_encode_integer.c @ 1340:5c9207ceedae
Added tag DROPBEAR_2017.75 for changeset c31276613181
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Thu, 18 May 2017 22:58:14 +0800 |
parents | 0cbe8f6dbf9e |
children | f849a5ca2efc |
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/* 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_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(void *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) { *outlen = tmplen; return CRYPT_BUFFER_OVERFLOW; } if (mp_cmp_d(num, 0) != LTC_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) == LTC_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; if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) --y; } /* now store initial data */ *out++ = 0x02; if (y < 128) { /* short form */ *out++ = (unsigned char)y; } else if (y < 256) { *out++ = 0x81; *out++ = (unsigned char)y; } else if (y < 65536UL) { *out++ = 0x82; *out++ = (unsigned char)((y>>8)&255); *out++ = (unsigned char)y; } else if (y < 16777216UL) { *out++ = 0x83; *out++ = (unsigned char)((y>>16)&255); *out++ = (unsigned char)((y>>8)&255); *out++ = (unsigned char)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) == LTC_MP_GT) { /* now store the mpint */ if ((err = mp_to_unsigned_bin(num, out)) != CRYPT_OK) { return err; } } else if (mp_iszero(num) != LTC_MP_YES) { void *tmp; /* negative */ if (mp_init(&tmp) != CRYPT_OK) { return CRYPT_MEM; } /* 2^roundup and subtract */ y = mp_count_bits(num); y = y + (8 - (y & 7)); if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) y -= 8; if (mp_2expt(tmp, y) != CRYPT_OK || mp_add(tmp, num, tmp) != CRYPT_OK) { mp_clear(tmp); return CRYPT_MEM; } if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) { mp_clear(tmp); return 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: 1.8 $ */ /* $Date: 2006/12/04 21:34:03 $ */