Botan: src/pubkey/pubkey_enums.cpp Source File

00001 /*
00002 * KeyUsage
00003 * (C) 1999-2007 Jack Lloyd
00004 *
00005 * Distributed under the terms of the Botan license
00006 */
00007 
00008 #include <botan/pubkey_enums.h>
00009 #include <botan/ber_dec.h>
00010 
00011 namespace Botan {
00012 
00013 namespace BER {
00014 
00015 /*
00016 * Decode a BER encoded KeyUsage
00017 */
00018 void decode(BER_Decoder& source, Key_Constraints& key_usage)
00019    {
00020    BER_Object obj = source.get_next_object();
00021 
00022    if(obj.type_tag != BIT_STRING || obj.class_tag != UNIVERSAL)
00023       throw BER_Bad_Tag("Bad tag for usage constraint",
00024                         obj.type_tag, obj.class_tag);
00025    if(obj.value.size() != 2 && obj.value.size() != 3)
00026       throw BER_Decoding_Error("Bad size for BITSTRING in usage constraint");
00027    if(obj.value[0] >= 8)
00028       throw BER_Decoding_Error("Invalid unused bits in usage constraint");
00029 
00030    const byte mask = (0xFF << obj.value[0]);
00031    obj.value[obj.value.size()-1] &= mask;
00032 
00033    u16bit usage = 0;
00034    for(u32bit j = 1; j != obj.value.size(); ++j)
00035       usage = (obj.value[j] << 8) | usage;
00036 
00037    key_usage = Key_Constraints(usage);
00038    }
00039 
00040 }
00041 
00042 }