Mercurial > dropbear
diff libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c @ 285:1b9e69c058d2
propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 20dccfc09627970a312d77fb41dc2970b62689c3)
to branch 'au.asn.ucc.matt.dropbear' (head fdf4a7a3b97ae5046139915de7e40399cceb2c01)
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 08 Mar 2006 13:23:58 +0000 |
parents | |
children | 0cbe8f6dbf9e |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c Wed Mar 08 13:23:58 2006 +0000 @@ -0,0 +1,97 @@ +/* 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.org + */ +#include "tomcrypt.h" + +/** + @file der_encode_short_integer.c + ASN.1 DER, encode an integer, Tom St Denis +*/ + + +#ifdef LTC_DER + +/* Exports a positive integer as DER format (upto 32-bits in size) */ +/** + Store a mp_int integer + @param num The integer 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_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen) +{ + unsigned long len, x, y, z; + int err; + + LTC_ARGCHK(out != NULL); + LTC_ARGCHK(outlen != NULL); + + /* force to 32 bits */ + num &= 0xFFFFFFFFUL; + + /* find out how big this will be */ + if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) { + return err; + } + + if (*outlen < len) { + return CRYPT_BUFFER_OVERFLOW; + } + + /* get len of output */ + z = 0; + y = num; + while (y) { + ++z; + y >>= 8; + } + + /* handle zero */ + if (z == 0) { + z = 1; + } + + /* see if msb is set */ + z += (num&(1UL<<((z<<3) - 1))) ? 1 : 0; + + /* adjust the number so the msB is non-zero */ + for (x = 0; (z <= 4) && (x < (4 - z)); x++) { + num <<= 8; + } + + /* store header */ + x = 0; + out[x++] = 0x02; + out[x++] = z; + + /* if 31st bit is set output a leading zero and decrement count */ + if (z == 5) { + out[x++] = 0; + --z; + } + + /* store values */ + for (y = 0; y < z; y++) { + out[x++] = (num >> 24) & 0xFF; + num <<= 8; + } + + /* we good */ + *outlen = x; + + return CRYPT_OK; +} + +#endif + +/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c,v $ */ +/* $Revision: 1.3 $ */ +/* $Date: 2005/05/23 01:27:03 $ */