diff options
Diffstat (limited to 'libtomcrypt/pk/asn1/der/short_integer/der_encode_short_integer.c')
-rw-r--r-- | libtomcrypt/pk/asn1/der/short_integer/der_encode_short_integer.c | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/libtomcrypt/pk/asn1/der/short_integer/der_encode_short_integer.c b/libtomcrypt/pk/asn1/der/short_integer/der_encode_short_integer.c new file mode 100644 index 0000000..cd9e6d1 --- /dev/null +++ b/libtomcrypt/pk/asn1/der/short_integer/der_encode_short_integer.c @@ -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, tomstdenis@gmail.com, http://libtom.org + */ +#include "tomcrypt.h" + +/** + @file der_encode_short_integer.c + ASN.1 DER, encode an integer, Tom St Denis +*/ + + +#ifdef LTC_DER + +/** + Store a short integer in the range (0,2^32-1) + @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) { + *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++] = (unsigned char)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++] = (unsigned char)((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: 1.8 $ */ +/* $Date: 2006/12/28 01:27:24 $ */ |