[Resource Topic] 2005/155: Py (Roo): A Fast and Secure Stream Cipher using Rolling Arrays

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Py (Roo): A Fast and Secure Stream Cipher using Rolling Arrays

Authors: Eli Biham, Jennifer Seberry


Py (pronounced Roo, a shorthand for Kangaroo) is a new stream
cipher designed especially for the Ecrypt stream cipher contest.
It is based on a new kind of primitive, which we call
Rolling Arrays.
It also uses various other ideas from many types of ciphers, including
variable rotations and permutations.
In some sense, this design is a kind of a new type of rotor machine,
which is specially designed with operations that are very efficient in
The allowed stream size is 2^{64} bytes in each stream (or 2^{40}
in the smaller version Py6).
The security claims of the cipher are that no key recovery attacks can
be performed with complexity smaller than that of exhaustive search,
and distinguishing attacks are also impractical with a similar complexity.
The speed of the cipher is impressively fast, as it is more than 2.5
times faster than RC4 on a Pentium III (with less than 2.9 cycles/byte
when implemented with the API of NESSIE and tested with the NESSIE

ePrint: https://eprint.iacr.org/2005/155

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