Version 5.0 The LEDA User Manual

10.6 Automatic Decoder supporting Cryptography (
CryptAutoDecoder )
1. Definition
The class CryptAutoDecoder is an extension of AutoDecoder. It can be used for decoding
encrypted streams (in particular if the coder used for encoding is unknown). In order
to decrypt a stream a key must be provided by the user because the key is – of course
– not stored in the encrypted stream. There are three possibilities to specify a key: as
a CryptKey, as a key stream or as a key file. Sometimes it may be necessary to provide
several keys to CryptAutoDecoder. E.g., if you use CoderPipe2< OMACCoder,
OFBCoder > to encode a stream two keys are needed for decoding. Therefore,
CryptAutoDecoder maintains a list of keys for decoding.
#include < LEDA/coding/crypt auto decoder.h >
2. Creation
CryptAutoDecoder C(streambuf ∗ src stream = 0, streambuf ∗ tgt stream = 0,
bool own streams = false);
creates an instance C which uses the given source and target
streams. If own streams is set, then C is responsible for the destruction
of the streams, otherwise the pointers src stream and tgt stream
must be valid during the life-time of C.
CryptAutoDecoder
C(const char ∗ src file name, const char ∗ tgt file name);
creates an instance C which uses file-streams for input and output.
3. Operations
Standard Operations
void C.decode( ) decodes the source stream and writes the output to
the target stream.
uint32
streambuf ∗
C.decode memory chunk(const char ∗ in buf , uint32 in len,
char ∗ out buf , uint32 out len)
decodes the memory chunk starting at in buf with
size in len into the buffer starting at out buf with
size out len. The function returns actual length
of the encoded chunk which may be smaller than
out len. If the output buffer is too small for the
decoded data the failure flag will be set (see below).
C.get src stream( ) returns the current source stream.