| /* 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://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 $ */ |