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      1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
      2  *
      3  * LibTomCrypt is a library that provides various cryptographic
      4  * algorithms in a highly modular and flexible manner.
      5  *
      6  * The library is free for all purposes without any express
      7  * guarantee it works.
      8  *
      9  * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com
     10  */
     11 #include "tomcrypt.h"
     12 
     13 /**
     14   @file der_length_object_identifier.c
     15   ASN.1 DER, get length of Object Identifier, Tom St Denis
     16 */
     17 
     18 #ifdef LTC_DER
     19 
     20 unsigned long der_object_identifier_bits(unsigned long x)
     21 {
     22    unsigned long c;
     23    x &= 0xFFFFFFFF;
     24    c  = 0;
     25    while (x) {
     26      ++c;
     27      x >>= 1;
     28    }
     29    return c;
     30 }
     31 
     32 
     33 /**
     34   Gets length of DER encoding of Object Identifier
     35   @param nwords   The number of OID words
     36   @param words    The actual OID words to get the size of
     37   @param outlen   [out] The length of the DER encoding for the given string
     38   @return CRYPT_OK if successful
     39 */
     40 int der_length_object_identifier(unsigned long *words, unsigned long nwords, unsigned long *outlen)
     41 {
     42    unsigned long y, z, t, wordbuf;
     43 
     44    LTC_ARGCHK(words  != NULL);
     45    LTC_ARGCHK(outlen != NULL);
     46 
     47 
     48    /* must be >= 2 words */
     49    if (nwords < 2) {
     50       return CRYPT_INVALID_ARG;
     51    }
     52 
     53    /* word1 = 0,1,2,3 and word2 0..39 */
     54    if (words[0] > 3 || (words[0] < 2 && words[1] > 39)) {
     55       return CRYPT_INVALID_ARG;
     56    }
     57 
     58    /* leading word is the first two */
     59    z = 0;
     60    wordbuf = words[0] * 40 + words[1];
     61    for (y = 1; y < nwords; y++) {
     62        t = der_object_identifier_bits(wordbuf);
     63        z += t/7 + ((t%7) ? 1 : 0) + (wordbuf == 0 ? 1 : 0);
     64        if (y < nwords - 1) {
     65           /* grab next word */
     66           wordbuf = words[y+1];
     67        }
     68    }
     69 
     70    /* now depending on the length our length encoding changes */
     71    if (z < 128) {
     72       z += 2;
     73    } else if (z < 256) {
     74       z += 3;
     75    } else if (z < 65536UL) {
     76       z += 4;
     77    } else {
     78       return CRYPT_INVALID_ARG;
     79    }
     80 
     81    *outlen = z;
     82    return CRYPT_OK;
     83 }
     84 
     85 #endif
     86 
     87 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/object_identifier/der_length_object_identifier.c,v $ */
     88 /* $Revision: 1.4 $ */
     89 /* $Date: 2006/04/16 20:17:42 $ */
     90