76 lines
2.5 KiB
Plaintext
76 lines
2.5 KiB
Plaintext
@c acl_streamciphers.texi
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@section Stream ciphers
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A stream cipher normally generates a deterministic, random looking stream of
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bits, known as key stream. For encryption purpose this key stream is XORed with
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the data stream. So decryption is exactly the same as encryption. The
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data-stream is XORed with the key stream giving the plaintext. So both sides
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need exactly the same stream cipher in the same state.
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@subsection List of available stream ciphers
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The following stream ciphers are currently implemented:
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@itemize @bullet
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@item ARCFOUR (RC4 compatibel)
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@item Trivium
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@item Grain
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@item MUGI
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@item Mickey-128 (v2)
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@end itemize
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@subsection High frequent parameters
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@table @asis
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@item output-size
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8 bit, 1 bit
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@item keysize
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64 bit, 80 bit, 128 bit
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@item IVsize
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64 bit
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@end table
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@subsection Parts of a stream cipher
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@itemize @bullet
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@item generation algorithm
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@item initialization algorithm
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@item state
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@end itemize
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As we can see all stream ciphers seem to utilize an internal state which
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determines the output. This state is initialized by the initialization
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algorithm with a key and an IV (initialization vector). It is very important
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for security that _never_ the same key with the same IV is used again. The
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IV is not required to be kept secret.
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@subsection API of stream ciphers
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The API is not always consistent due to the fact that we tried to optimize the
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code for size (flash, heap and stack) and speed (runtime of the different
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components).
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Generally the API of the implemented stream ciphers consists of:
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@table @code
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@item *_init
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function, which implements the initialization
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@item *_gen
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function, which implements the streamcipher algorithm and generates a
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keystream output
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@item *_ctx_t
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context type, which contains internal state information
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@end table
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@subsubsection @code{*_init} function
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The *_init function generally takes a pointer to the key as first parameter.
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For ciphers where the keysize is not fixed the second parameter gives the
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keysize (in bits regularly) followed by a pointer to the IV and a length
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parameter for not fixed IV sizes (both are omitted if the algorithm does not
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specify IV handling, in this case a part of the key should be used as IV).
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The last parameter points to the context variable to fill.
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@subsubsection @code{*_gen} function
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The *_gen function updates the internal state to which a pointer is given as
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parameter and returns a fixed length part of the keystream as return value.
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@subsection Stream cipher abstraction layer (SCAL)
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