Version 5.0 The LEDA User Manual

10.4 Example for a Stream-Cipher ( CBCCoder )
1. Definition
A stream-cipher is a coder that encrypts and decrypts data streams. In this section
we discuss the interface of such a coder by an example: CBCCoder< BlkCipher >. Every
stream-cipher in LEDA uses a block-cipher BlkCipher which is specified as a template
parameter. (More information about stream-ciphers and block-ciphers can be found
in Section 10.3.) The following stream-ciphers are available: ECBCoder, CBCCoder,
CFBCoder and OFBCoder. All of them, except for OFBCoder, support fast seek operations
(see Section 9.22). The available block-ciphers are: Blowfish, Twofish and Rijndael.
#include < LEDA/coding/stream ciphers.h >
2. Creation
CBCCoder< BlkCipher > 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.
CBCCoder< BlkCipher > 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.encode( ) encodes the source stream and writes the output to
the target stream.
void C.decode( ) decodes the source stream and writes the output to
the target stream.
uint32
C.calculate length of encoded data(uint32 input length)
calculates the length (in bytes) of the output when
encoding some input of the given length with the current
settings. (This function is helpful for encoding
memory chunks (see below).)