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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_encode_bit_string.c
     15   ASN.1 DER, encode a BIT STRING, Tom St Denis
     16 */
     17 
     18 
     19 #ifdef LTC_DER
     20 
     21 /**
     22   Store a BIT STRING
     23   @param in       The array of bits to store (one per char)
     24   @param inlen    The number of bits tostore
     25   @param out      [out] The destination for the DER encoded BIT STRING
     26   @param outlen   [in/out] The max size and resulting size of the DER BIT STRING
     27   @return CRYPT_OK if successful
     28 */
     29 int der_encode_bit_string(const unsigned char *in, unsigned long inlen,
     30                                 unsigned char *out, unsigned long *outlen)
     31 {
     32    unsigned long len, x, y;
     33    unsigned char buf;
     34    int           err;
     35 
     36    LTC_ARGCHK(in     != NULL);
     37    LTC_ARGCHK(out    != NULL);
     38    LTC_ARGCHK(outlen != NULL);
     39 
     40    /* avoid overflows */
     41    if ((err = der_length_bit_string(inlen, &len)) != CRYPT_OK) {
     42       return err;
     43    }
     44 
     45    if (len > *outlen) {
     46       *outlen = len;
     47       return CRYPT_BUFFER_OVERFLOW;
     48    }
     49 
     50    /* store header (include bit padding count in length) */
     51    x = 0;
     52    y = (inlen >> 3) + ((inlen&7) ? 1 : 0) + 1;
     53 
     54    out[x++] = 0x03;
     55    if (y < 128) {
     56       out[x++] = (unsigned char)y;
     57    } else if (y < 256) {
     58       out[x++] = 0x81;
     59       out[x++] = (unsigned char)y;
     60    } else if (y < 65536) {
     61       out[x++] = 0x82;
     62       out[x++] = (unsigned char)((y>>8)&255);
     63       out[x++] = (unsigned char)(y&255);
     64    }
     65 
     66    /* store number of zero padding bits */
     67    out[x++] = (unsigned char)((8 - inlen) & 7);
     68 
     69    /* store the bits in big endian format */
     70    for (y = buf = 0; y < inlen; y++) {
     71        buf |= (in[y] ? 1 : 0) << (7 - (y & 7));
     72        if ((y & 7) == 7) {
     73           out[x++] = buf;
     74           buf      = 0;
     75        }
     76    }
     77    /* store last byte */
     78    if (inlen & 7) {
     79       out[x++] = buf;
     80    }
     81    *outlen = x;
     82    return CRYPT_OK;
     83 }
     84 
     85 #endif
     86 
     87 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/bit/der_encode_bit_string.c,v $ */
     88 /* $Revision: 1.4 $ */
     89 /* $Date: 2006/12/04 21:34:03 $ */
     90