564 research outputs found
On the Hardness of Gray Code Problems for Combinatorial Objects
Can a list of binary strings be ordered so that consecutive strings differ in
a single bit? Can a list of permutations be ordered so that consecutive
permutations differ by a swap? Can a list of non-crossing set partitions be
ordered so that consecutive partitions differ by refinement? These are examples
of Gray coding problems: Can a list of combinatorial objects (of a particular
type and size) be ordered so that consecutive objects differ by a flip (of a
particular type)? For example, 000, 001, 010, 100 is a no instance of the first
question, while 1234, 1324, 1243 is a yes instance of the second question due
to the order 1243, 1234, 1324. We prove that a variety of Gray coding problems
are NP-complete using a new tool we call a Gray code reduction.Comment: 15 pages, 5 figures, WALCOM 202
PassGAN: A Deep Learning Approach for Password Guessing
State-of-the-art password guessing tools, such as HashCat and John the
Ripper, enable users to check billions of passwords per second against password
hashes. In addition to performing straightforward dictionary attacks, these
tools can expand password dictionaries using password generation rules, such as
concatenation of words (e.g., "password123456") and leet speak (e.g.,
"password" becomes "p4s5w0rd"). Although these rules work well in practice,
expanding them to model further passwords is a laborious task that requires
specialized expertise. To address this issue, in this paper we introduce
PassGAN, a novel approach that replaces human-generated password rules with
theory-grounded machine learning algorithms. Instead of relying on manual
password analysis, PassGAN uses a Generative Adversarial Network (GAN) to
autonomously learn the distribution of real passwords from actual password
leaks, and to generate high-quality password guesses. Our experiments show that
this approach is very promising. When we evaluated PassGAN on two large
password datasets, we were able to surpass rule-based and state-of-the-art
machine learning password guessing tools. However, in contrast with the other
tools, PassGAN achieved this result without any a-priori knowledge on passwords
or common password structures. Additionally, when we combined the output of
PassGAN with the output of HashCat, we were able to match 51%-73% more
passwords than with HashCat alone. This is remarkable, because it shows that
PassGAN can autonomously extract a considerable number of password properties
that current state-of-the art rules do not encode.Comment: This is an extended version of the paper which appeared in NeurIPS
2018 Workshop on Security in Machine Learning (SecML'18), see
https://github.com/secml2018/secml2018.github.io/raw/master/PASSGAN_SECML2018.pd
Subset-lex: did we miss an order?
We generalize a well-known algorithm for the generation of all subsets of a
set in lexicographic order with respect to the sets as lists of elements
(subset-lex order). We obtain algorithms for various combinatorial objects such
as the subsets of a multiset, compositions and partitions represented as lists
of parts, and for certain restricted growth strings. The algorithms are often
loopless and require at most one extra variable for the computation of the next
object. The performance of the algorithms is very competitive even when not
loopless. A Gray code corresponding to the subset-lex order and a Gray code for
compositions that was found during this work are described.Comment: Two obvious errors corrected (indicated by "Correction:" in the LaTeX
source
Two Reflected Gray Code based orders on some restricted growth sequences
We consider two order relations: that induced by the m-ary reflected Gray
code and a suffix partitioned variation of it. We show that both of them when
applied to some sets of restricted growth sequences still yield Gray codes.
These sets of sequences are: subexcedant or ascent sequences, restricted growth
functions, and staircase words. In each case we give efficient exhaustive
generating algorithms and compare the obtained results
Demystifying our Grandparent's De Bruijn Sequences with Concatenation Trees
Some of the most interesting de Bruijn sequences can be constructed in
seemingly unrelated ways. In particular, the "Granddaddy" and "Grandmama" can
be understood by joining necklace cycles into a tree using simple parent rules,
or by concatenating smaller strings (e.g., Lyndon words) in lexicographic
orders. These constructions are elegant, but their equivalences seem to come
out of thin air, and the community has had limited success in finding others of
the same ilk. We aim to demystify the connection between cycle-joining trees
and concatenation schemes by introducing "concatenation trees". These
structures combine binary trees and ordered trees, and traversals yield
concatenation schemes for their sequences.
In this work, we focus on the four simplest cycle-joining trees using the
pure cycling register (PCR): "Granddaddy" (PCR1), "Grandmama" (PCR2), "Granny"
(PCR3), and "Grandpa" (PCR4). In particular, we formally prove a previously
observed correspondence for PCR3 and we unravel the mystery behind PCR4. More
broadly, this work lays the foundation for translating cycle-joining trees to
known concatenation constructions for a variety of underlying feedback
functions including the complementing cycling register (CCR), pure summing
register (PSR), complementing summing register (CSR), and pure run-length
register (PRR)
On universal partial words
A universal word for a finite alphabet and some integer is a
word over such that every word in appears exactly once as a subword
(cyclically or linearly). It is well-known and easy to prove that universal
words exist for any and . In this work we initiate the systematic study
of universal partial words. These are words that in addition to the letters
from may contain an arbitrary number of occurrences of a special `joker'
symbol , which can be substituted by any symbol from . For
example, is a linear partial word for the binary alphabet
and for (e.g., the first three letters of yield the
subwords and ). We present results on the existence and
non-existence of linear and cyclic universal partial words in different
situations (depending on the number of s and their positions),
including various explicit constructions. We also provide numerous examples of
universal partial words that we found with the help of a computer
A survey and method for analysing SoHo router firmware currency
Network routers are a core component of contemporary SoHo networks. The firmware within these devices provides routing, control and monitoring functionality coupled with mechanisms to ensure a secure and reliable network. End-users are typically reliant on manufacturers to provide timely firmware updates to mitigate known vulnerabilities. An investigation was undertaken to identify the underlying software components used in the firmware of currently available, SoHo network devices used in Australia. Firmware from 37 devices was deconstructed to identify potential security issues; in each instance, the firmware images were found to include vulnerabilities, obsolete software and out-of-date operating system components. 95% of the deconstructed firmware was based on Linux. The Linux kernels identified were typically discontinued and are no longer actively maintained. This paper demonstrates a method for undertaking the analysis and summaries the outcomes of the research
A Data Science Course for Undergraduates: Thinking with Data
Data science is an emerging interdisciplinary field that combines elements of
mathematics, statistics, computer science, and knowledge in a particular
application domain for the purpose of extracting meaningful information from
the increasingly sophisticated array of data available in many settings. These
data tend to be non-traditional, in the sense that they are often live, large,
complex, and/or messy. A first course in statistics at the undergraduate level
typically introduces students with a variety of techniques to analyze small,
neat, and clean data sets. However, whether they pursue more formal training in
statistics or not, many of these students will end up working with data that is
considerably more complex, and will need facility with statistical computing
techniques. More importantly, these students require a framework for thinking
structurally about data. We describe an undergraduate course in a liberal arts
environment that provides students with the tools necessary to apply data
science. The course emphasizes modern, practical, and useful skills that cover
the full data analysis spectrum, from asking an interesting question to
acquiring, managing, manipulating, processing, querying, analyzing, and
visualizing data, as well communicating findings in written, graphical, and
oral forms.Comment: 21 pages total including supplementary material
- …