David H. Ackley

Building diverse computer systems

Diversity is an important source of robustness in biological systems. Computers, by contrast, are notable for their lack of diversity. Although homogeneous systems have many advantages, the beneficial effects of diversity in computing systems have been overlooked, specifically in the area of computer security. Several methods of achieving software diversity are discussed based on randomizations that respect the specified behavior of the program. Such randomization could potentially increase the robustness of software systems with minimal impact on convenience, usability, and efficiency. Randomization of the amount of memory allocated on a stack frame is shown to disrupt a simple buffer overflow attack.

Randomized instruction set emulation

Injecting binary code into a running program is a common form of attack. Most defenses employ a “guard the doors” approach, blocking known mechanisms of code injection. Randomized instruction set emulation (RISE) is a complementary method of defense, one that performs a hidden randomization of an applications machine code. If foreign binary code is injected into a program running under RISE, it will not be executable because it will not know the proper randomization. The paper describes and analyzes RISE, describing a proof-of-concept implementation built on the open-source Valgrind IA32-to-IA32 translator. The prototype effectively disrupts binary code injection attacks, without requiring recompilation, linking, or access to application source code. Under RISE, injected code (attacks) essentially executes random code sequences. Empirical studies and a theoretical model are reported which treat the effects of executing random code on two different architectures (IA32 and PowerPC). The paper discusses possible extensions and applications of the RISE technique in other contexts.

Beyond efficiency

Esteem for efficiency should be tempered with respect for robustness.

A practical method for code generation based on exhaustive search

An original method for code generation has been developed in conjunction with the construction of a compiler for the C programming language on the DEC-10 computer. The method is comprehensive, determining evaluation order and doing register allocation and instruction selection simultaneously. It uses exhaustive search rather than heuristics, and is table-driven, with most machine-specific information isolated in the tables. Testing and evaluation have shown that the method is effective, that the search process is not too time consuming, and that the compiler is capable of producing code as good as that of other optimizing compilers.

Modeling the effects of prior infection on vaccine efficacy

We performed computer simulations to study the effects of prior infection on vaccine efficacy. We injected three antigens sequentially. The first antigen, designated the prior, represented a prior infection or vaccination. The second antigen, the vaccine, represented a single component of the trivalent influenza vaccine. The third antigen, the epidemic, represented challenge by an epidemic strain. For a fixed vaccine to epidemic strain cross-reactivity, we generated prior strains over a full range of cross-reactivities to the vaccine and to the epidemic strains. We found that, for many cross-reactivities, vaccination, when it had been preceded by a prior infection, provided more protection than vaccination alone. However, at some cross-reactivities, the prior infection reduced protection by clearing the vaccine before it had the chance to produce protective memory. The cross-reactivities between the prior, vaccine and epidemic strains played a major role in determining vaccine efficacy. This work has applications to understanding vaccination against viruses such as influenza that are continually mutating.

Open-ended evolution: Perspectives from the oee workshop in york

We describe the content and outcomes of the First Workshop on Open-Ended Evolution: Recent Progress and Future Milestones (OEE1), held during the ECAL 2015 conference at the University of York, UK, in July 2015. We briefly summarize the content of the workshops talks, and identify the main themes that emerged from the open discussions. Two important conclusions from the discussions are: (1) the idea of pluralism about OEE—it seems clear that there is more than one interesting and important kind of OEE; and (2) the importance of distinguishing observable behavioral hallmarks of systems undergoing OEE from hypothesized underlying mechanisms that explain why a system exhibits those hallmarks. We summarize the different hallmarks and mechanisms discussed during the workshop, and list the specific systems that were highlighted with respect to particular hallmarks and mechanisms. We conclude by identifying some of the most important open research questions about OEE that are apparent in light of the discussions. The York workshop provides a foundation for a follow-up OEE2 workshop taking place at the ALIFE XV conference in Cancún, Mexico, in July 2016. Additional materials from the York workshop, including talk abstracts, presentation slides, and videos of each talk, are available at http://alife.org/ws/oee1.

Bespoke physics for living technology

In the physics of the natural world, basic tasks of life, such as homeostasis and reproduction, are extremely complex operations, requiring the coordination of billions of atoms even in simple cases. By contrast, artificial living organisms can be implemented in computers using relatively few bits, and copying a data structure is trivial. Of course, the physical overheads of the computers themselves are huge, but since their programmability allows digital “laws of physics” to be tailored like a custom suit, deploying living technology atop an engineered computational substrate might be as or more effective than building directly on the natural laws of physics, for a substantial range of desirable purposes. This article suggests basic criteria and metrics for bespoke physics computing architectures, describes one such architecture, and offers data and illustrations of custom living technology competing to reproduce while collaborating on an externally useful computation.

A Movable Architecture for Robust Spatial Computing

Foropen-endedcomputationalgrowth,wearguethat:(i)insteadofhardwiringandhidingcomponent spatial relationships, computer architecture should soften and expose them; and (2) instead of relegating reliability to hardware, robustness must climb the computational stack toward the end users.Wesuggestthateventuallyalltrulylarge-scalecomputerswillberobustspatialcomputers—even if intended neither for spatial tasks nor harsh environments. This paper is an extended introduction for the spatial computing community to the Movable Feast Machine (MFM), a computing model in the spirit of an object-oriented asynchronous cellular automata. We motivate the approach and then present the model, touching on robustness mechanisms such as redundancy, compartmentalization and homeostasis. We provide simulation data from prototype movable elements such as self-healing wire for data transport and movable ‘membrane’ rings for spatial segregation, and illustrate how some larger computations like sorting or evaluating a lambda expression can be reconceived for robustness and movability within a spatial computing architecture.

Artificial life programming in the robust-first attractor

Despite mounting awareness of the liabilities of deterministic CPU and RAM computing, across industry and academia there remains little clear vision of a fundamental, generalpurpose alternative. To obtain indefinitely scalable computer architectures offering improved robustness and security, we have advocated a realignment of the roles of hardware and software based on artificial life principles. In this paper we propose an active media computational abstraction to underlie such a hardware-software renegotiation. The active media framework is much in the spirit of probabilistic cellular automata, but designed for indefinite scalability and serious programmability, rather than simplicity and analytic tractability. We discuss active media programming techniques based on living systems principles, and present anecdotal data from sample programs to introduce a new programming language called ulam, that we are developing as an underlying language for active media.

Antisocial computing: exploring design risks in social computing systems

Social media has become globally ubiquitous, transforming how people are networked and mobilized. This forum explores research and applications of these new networked publics at individual, organizational, and societal levels. ---Shelly Farnham, Editor