A restriction of Euclid

Euclid is a well known two-player impartial combinatorial game. A position in Euclid is a pair of positive integers and the players move alternately by subtracting a positive integer multiple of one of the integers from the other integer without making the result negative. The player who makes the last move wins. There is a variation of Euclid due to Grossman in which the game stops when the two entrees are equal. We examine a further variation that we called M-Euclid in which the game stops when one of the entrees is a positive integer multiple of the other. We solve the Sprague-Grundy function for M-Euclid and compare the Sprague-Grundy functions of the three games

Error Free Perfect Secrecy Systems

Shannon's fundamental bound for perfect secrecy says that the entropy of the secret message cannot be larger than the entropy of the secret key initially shared by the sender and the legitimate receiver. Massey gave an information theoretic proof of this result, however this proof does not require independence of the key and ciphertext. By further assuming independence, we obtain a tighter lower bound, namely that the key entropy is not less than the logarithm of the message sample size in any cipher achieving perfect secrecy, even if the source distribution is fixed. The same bound also applies to the entropy of the ciphertext. The bounds still hold if the secret message has been compressed before encryption. This paper also illustrates that the lower bound only gives the minimum size of the pre-shared secret key. When a cipher system is used multiple times, this is no longer a reasonable measure for the portion of key consumed in each round. Instead, this paper proposes and justifies a new measure for key consumption rate. The existence of a fundamental tradeoff between the expected key consumption and the number of channel uses for conveying a ciphertext is shown. Optimal and nearly optimal secure codes are designed.Comment: Submitted to the IEEE Trans. Info. Theor

Modelling, inference and big data in biophysics

Letter to the editorIn recognition of the increasing importance of big data in biophysics, a new session called 'Modelling, inference, big data' is incorporated into the IUPAB/EBSA Congress on 18 July 2017 at Edinburgh, UK

Internet Telephony : optimizing protocols, packet recovery, and packet size

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 104-106).by Grant Ho.M.Eng

Tiresias: Predicting Security Events Through Deep Learning

With the increased complexity of modern computer attacks, there is a need for defenders not only to detect malicious activity as it happens, but also to predict the specific steps that will be taken by an adversary when performing an attack. However this is still an open research problem, and previous research in predicting malicious events only looked at binary outcomes (e.g., whether an attack would happen or not), but not at the specific steps that an attacker would undertake. To fill this gap we present Tiresias, a system that leverages Recurrent Neural Networks (RNNs) to predict future events on a machine, based on previous observations. We test Tiresias on a dataset of 3.4 billion security events collected from a commercial intrusion prevention system, and show that our approach is effective in predicting the next event that will occur on a machine with a precision of up to 0.93. We also show that the models learned by Tiresias are reasonably stable over time, and provide a mechanism that can identify sudden drops in precision and trigger a retraining of the system. Finally, we show that the long-term memory typical of RNNs is key in performing event prediction, rendering simpler methods not up to the task

Forward Pass: On the Security Implications of Email Forwarding Mechanism and Policy

The critical role played by email has led to a range of extension protocols (e.g., SPF, DKIM, DMARC) designed to protect against the spoofing of email sender domains. These protocols are complex as is, but are further complicated by automated email forwarding -- used by individual users to manage multiple accounts and by mailing lists to redistribute messages. In this paper, we explore how such email forwarding and its implementations can break the implicit assumptions in widely deployed anti-spoofing protocols. Using large-scale empirical measurements of 20 email forwarding services (16 leading email providers and four popular mailing list services), we identify a range of security issues rooted in forwarding behavior and show how they can be combined to reliably evade existing anti-spoofing controls. We show how this allows attackers to not only deliver spoofed email messages to prominent email providers (e.g., Gmail, Microsoft Outlook, and Zoho), but also reliably spoof email on behalf of tens of thousands of popular domains including sensitive domains used by organizations in government (e.g., state.gov), finance (e.g., transunion.com), law (e.g., perkinscoie.com) and news (e.g., washingtonpost.com) among others

Comparative Efficacy of Video and Text Instructional Modalities for an Oral Surgery Technique among Dental Students

Purpose: To gauge the efficacy of video media in pre-doctoral oral and maxillofacial surgery education and compare it to traditional text-based learning materials. Methods: Twenty novice dental students were randomly divided into two groups to place an Erich arch bar to the maxillary dentition of a dentoform. Group A was given a 10 minute video instruction while Group B was given 10 minutes to review written text instruction. All participants were given 45 minutes to place the arch bar on a dentoform while being recorded. This session concluded with a survey of student perceptions using the SEEQ. The students then alternated instructional modalities and again evaluated using the SEEQ. Two double-blinded clinical OMS faculty evaluated the recordings in accordance with the standards detailed in the ABPAS. Results: The difference in the post-instructional skill scores of Group A and Group B students was deemed not significant (p = 0.46). Overall, the students expressed significant preference for the video modality compared to the textual modality. The difference of the scores in each preference category between the video and text modalities were all found to be significant with p-values well below 0.05. Conclusion: Educators must remain cognizant towards the benefits of new technology and continue to explore newer, potentially more efficacious modalities such as interactive teaching materials. These benefits may be utilized to help increase student engagement and increase long-term retention of the material. It is imperative to understand the limits of each method and balance them strategically to offer comprehensive healthcare training

Modelling, inference and big data in biophysics

Letter to the editorIn recognition of the increasing importance of big data in biophysics, a new session called 'Modelling, inference, big data' is incorporated into the IUPAB/EBSA Congress on 18 July 2017 at Edinburgh, UK