@c acl_streamciphers.texi
@section Stream ciphers
 A stream cipher normally generates a deterministic, random looking stream of 
 bits, known as key stream. For encryption purpose this key stream is XORed with
 the data stream. So decryption is exactly the same as encryption. The 
 data-stream is XORed with the key stream giving the plaintext. So both sides 
 need exactly the same stream cipher in the same state.

@subsection List of available stream ciphers
 The following stream ciphers are currently implemented:
@itemize @bullet 
  @item ARCFOUR (RC4 compatibel)
  @item Trivium
  @item Grain
  @item MUGI
  @item Mickey-128 (v2)
@end itemize 

@subsection High frequent parameters
@table @asis
  @item output-size
  8 bit, 1 bit
  @item keysize
  64 bit, 80 bit, 128 bit
  @item IVsize
  64 bit
@end table

@subsection Parts of a stream cipher
@itemize @bullet
  @item generation algorithm
  @item initialization algorithm
  @item state
@end itemize

 As we can see all stream ciphers seem to utilize an internal state which
 determines the output. This state is initialized by the initialization 
 algorithm with a key and an IV (initialization vector). It is very important
 for security that _never_ the same key with the same IV is used again. The
 IV is not required to be kept secret.

@subsection API of stream ciphers
 The API is not always consistent due to the fact that we tried to optimize the
 code for size (flash, heap and stack) and speed (runtime of the different 
 components).

 Generally the API of the implemented stream ciphers consists of:
 @table @code 
 @item *_init 
 function, which implements the initialization

 @item *_gen  
 function, which implements the streamcipher algorithm and generates a 
 keystream output

 @item *_ctx_t
 context type, which contains internal state information

 @end table

@subsubsection @code{*_init} function
 The *_init function generally takes a pointer to the key as first parameter.
 For ciphers where the keysize is not fixed the second parameter gives the 
 keysize (in bits regularly) followed by a pointer to the IV and a length 
 parameter for not fixed IV sizes (both are omitted if the algorithm does not 
 specify IV handling, in this case a part of the key should be used as IV).
 The last parameter points to the context variable to fill.

@subsubsection @code{*_gen} function
 The *_gen function updates the internal state to which a pointer is given as
 parameter and returns a fixed length part of the keystream as return value.


@subsection Stream cipher abstraction layer (SCAL)