Christopher W. Fletcher
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Research


I am a computer architect that uses hardware structures to enable novel systems in other application domains. During my Ph.D., I designed and built secure (yet high performance) hardware systems, and developed new cryptographic primitives to serve as the foundation for those systems. Starting Fall 2016, I have been working at the intersection of computer architecture, security and machine learning (or subsets of these three). I also worked on architecture combined with machine learning in my undergraduate, so I seem to enjoy these waters! Here is my CV and Google scholar profile.


Public Material


Extra Cool Stuff

Chip thumbnail
In March 2015, in a collaboration with David Wentzlaff's group at Princeton, we taped out a 25 core Ascend (aka Piton) processor in a 32nm process. Click the picture to get a blowup. The ORAM controller came out to about 1mm^2. For the final layout, we were very conservative at the top level, so the 'real' area is somewhere between .5-1mm^2.

Bring-up: The ORAM successfully passed its self tests on bring-up! The ORAM runs at 857 MHz, dissipating 166 mW @ 1.1V! To verify functionality, we have a traffic generator on the chip that simulates a last level cache miss pattern and supplies the ORAM with requests. The ORAM/chip then talks to a Spartan6 FPGA which is connected over UART to a laptop. The UART/laptop simulates a memory substrate such as DRAM. For power measurements, we have a mode where the ORAM loops data back on itself (thus, 166 mW doesn't include the back-end I/O (e.g., DRAM) controller--it is made up of the logic and SRAM power in the ORAM core itself). See here for a chip selfie and here for a video. See here for the transcript of the first 2 accesses ("received from chip..." is ciphertext received from the ORAM).

Stay tuned for updates on booting Linux on ORAM!

Peer-Reviewed


Color code: Blue: conference, Green: journal, Purple: workshop.

Top architecture conferences: ISCA, ASPLOS, MICRO, HPCA
Top security conferences: Oakland/SP, USENIX Security, NDSS, CCS

  1. UCNN: Exploiting Computational Reuse in Deep Neural Networks via Weight Repetition; Kartik Hegde, Jiyong Yu, Rohit Agrawal, Mengjia Yan, Michael Pellauer, Christopher W. Fletcher; ISCA, 2018

  2. Attack Directories, Not Caches: Side Channel Attacks in a Non-Inclusive World; Mengjia Yan, Read Sprabery, Bhargava Gopireddy, Christopher W. Fletcher, Roy Campbell, Josep Torrellas; Oakland/SP, 2018

  3. Path ORAM: An Extremely Simple Oblivious RAM Protocol; Emil Stefanov, Marten van Dijk, Elaine Shi, T-H Hubert Chan, Christopher W. Fletcher, Ling Ren, Xiangyao Yu, Srinivas Devadas; JACM, 2018

  4. ZeroTrace: Oblivious Memory Primitives from Intel SGX; Sajin Sasy, Sergey Gorbunov, Christopher W. Fletcher; NDSS, 2018

  5. Design and Implementation of the Ascend Secure Processor; Ling Ren, Christopher W. Fletcher, Albert Kwon; Marten van Dijk; Srinivas Devadas; TDSC, 2017

  6. Asymptotically tight bounds for composing ORAM with PIR; Kartik Nayak, Ling Ren, Christopher W. Fletcher, Ittai Abraham, Benny Pinkas; PKC, 2017

  7. HOP: Hardware makes Obfuscation Practical; Kartik Nayak, Christopher W. Fletcher, Ling Ren, Nishanth Chandran, Satya Lokam, Elaine Shi, Vipul Goyal; NDSS, 2017

  8. Onion ORAM: A Constant Bandwidth Blowup Oblivious RAM; Srinivas Devadas, Marten van Dijk, Christopher W. Fletcher, Ling Ren, Elaine Shi, Daniel Wichs; TCC, 2016; (Alphabetical authors, L. Ren and I shared lead author)

  9. Constants Count: Practical Improvements to Oblivious RAM; Ling Ren, Christopher W. Fletcher, Albert Kwon, Emil Stefanov, Elaine Shi, Marten van Dijk, Srinivas Devadas; USENIX Security, 2015

  10. PrORAM: Dynamic Prefetcher for Oblivious RAM; Xiangyao Yu, Syed Kamran Haider, Ling Ren, Christopher W. Fletcher, Albert Kwon, Marten van Dijk, Srinivas Devadas; ISCA, 2015

  11. A Low-Latency, Low-Area Hardware Oblivious RAM Controller; Christopher W. Fletcher, Ling Ren, Albert Kwon, Marten van Dijk, Emil Stefanov, Dimitrios Serpanos, Srinivas Devadas; FCCM, 2015

  12. Freecursive ORAM: [Nearly] Free Recursion and Integrity Verification for Position-based Oblivious RAM; Christopher W. Fletcher, Ling Ren, Albert Kwon, Marten van Dijk, Srinivas Devadas; ASPLOS, 2015
    Open source release here

  13. Suppressing the Oblivious RAM Timing Channel While Making Information Leakage and Program Efficiency Trade-offs; Christopher W. Fletcher, Ling Ren, Xiangyao Yu, Marten van Dijk, Omer Khan, Srinivas Devadas; HPCA, 2014

  14. Path ORAM: An Extremely Simple Oblivious RAM Protocol; Emil Stefanov, Marten van Dijk, Elaine Shi, Christopher W. Fletcher, Ling Ren, Xiangyao Yu, Srinivas Devadas; CCS, 2013
    Best Student Paper Award

  15. Generalized External Interaction with Tamper-Resistant Hardware with Bounded Information Leakage; Xiangyao Yu, Christopher W. Fletcher, Ling Ren, Marten van Dijk, Srinivas Devadas; CCSW, 2013

  16. A Framework to Accelerate Sequential Programs on Homogeneous Multicores; Christopher W. Fletcher, Rachael Harding, Omer Khan, Srinivas Devadas; VLSI SoC, 2013

  17. Integrity Verification for Path Oblivious-RAM; Ling Ren, Christopher W. Fletcher, Xiangyao Yu, Marten van Dijk, Srinivas Devadas; HPEC, 2013

  18. Design Space Exploration and Optimization of Path Oblivious RAM in Secure Processors; Ling Ren, Xiangyao Yu, Christopher W. Fletcher, Marten van Dijk, Srinivas Devadas; ISCA, 2013

  19. Towards an Interpreter for Efficient Encrypted Computation; Christopher W. Fletcher, Marten van Dijk, Srinivas Devadas; CCSW, 2012

  20. A Secure Processor Architecture for Encrypted Computation on Untrusted Programs; Christopher W. Fletcher, Marten van Dijk, Srinivas Devadas; STC, 2012

  21. HORNET: a cycle-level multicore simulator; Pengju Ren, Mieszko Lis, Myong Hyon Cho, Keun Sup Shim, Christopher W. Fletcher, Omer Khan, Nanning Zheng, Srinivas Devadas; TCAD, Vol. 31, No. 6, June 2012

  22. A Low-overhead Dynamic Optimization Framework on Multicores; Christopher W. Fletcher, Rachael Harding, Omer Khan, Srinivas Devadas; PACT (short paper), 2012

  23. Exploring Many-core Design Templates for FPGAs and ASICs; Ilia Lebedev, Christopher Fletcher, Shaoyi Cheng, James Martin, Austin Doupnik, Daniel Burke, Mingjie Lin, John Wawrzynek; IJRC, Article ID 439141, Volume 2012

  24. Scalable Accurate Multicore Simulation in the 1000 core era; Mieszko Lis, Pengju Ren, Myong Hyon Cho, Keun Sup Shim, Christopher W. Fletcher, Omer Khan, Srinivas Devadas; ISPASS, 2011

  25. Brief Announcement: Distributed Shared Memory based on Computation Migration; Mieszko Lis, Keun Sup Shim, Myong Hyon Cho, Christopher W. Fletcher, Michel Kinsy, Ilia Lebedev, Omer Khan, Srinivas Devadas; SPAA (short paper), 2011

  26. Bridging the GPGPU-FPGA Efficiency Gap; Christopher W. Fletcher, Ilia Lebedev, Narges B. Asadi, Daniel R. Burke, John Wawrzynek; ISFPGA (short paper), 2011

  27. MARC: A Many-Core Approach to Reconfigurable Computing; Ilia Lebedev, Shaoyi Cheng, Austin Doupnik, James Martin, Christopher W. Fletcher, Daniel Burke, Mingjie Lin, John Wawrzynek; ReConFig, 2010

  28. ParaLearn: A Massively Parallel, Scalable System for Learning Interaction Networks on FPGAs; Narges B. Asadi, Christopher W. Fletcher, Greg Gibeling, Karen Sachs, Eric Glass, Daniel Burke, Zoey Zhou, John Wawrzynek, Wing H. Wong, Garry P. Nolan; ICS, 2010; (N. Asadi and I shared lead author)
    Best Student Paper Award

Patents


  1. Technique for secure computation; Srinivas Devadas, Christopher W. Fletcher, Marten Van Dijk; Patent No. 8909967. (Note: there is currently a bug where only Marten is listed as inventor. The lawyers are fixing it...)

Theses


  1. Oblivious RAM: From Theory to Practice; Christopher W. Fletcher; Ph.D. Thesis; [Thesis]
    George M. Sprowls Award for outstanding Ph.D. thesis in CS at MIT

  2. Ascend: An Architecture for Performing Secure Computation on Encrypted Data; Christopher W. Fletcher; S.M. Thesis; [CSG Technical Memo 508]

Other Tech Reports/Articles


  1. [Author Retrospective] AEGIS: Architecture for Tamper-Evident and Tamper-Resistant Processing; G. Edward Suh, Christopher W. Fletcher, Dwaine Clarke, Blaise Gassend, Marten van Dijk, Srinivas Devadas; 25 Years of the International Conference on Supercomputing, 2014.

  2. Let's Stop Trusting Software With Our Sensitive Data; Christopher W. Fletcher, Marten van Dijk, Srinivas Devadas; IEEE Design and Test of ICs, March/April 2013. The Last Byte.

Selected Press


  1. Cybersecurity Factory nurtures early-stage startups in a tough field; Fortune [article]

  2. The Quest to Rescue Security Research From the Ivory Tower; Wired [article]

  3. Cloud security reaches silicon; MIT News [article]

  4. Hardware Trick Could Keep Cloud Data Safe; IEEE Spectrum [article]

  5. Devadas hardware disguises cloud servers memory-access patterns thwarting timing attacks; CSAIL News [article]

  6. Protecting data in the cloud; MIT News [article]

  7. A New Type of Security Chip Guards Against Big Data Snooping; Scientific American, Ascend has been named a "World Changing Idea"! [article]

Posters


  1. Ascend: An Architecture for Performing Secure Computation on Encrypted Data; Presented at the ACSC Annual Conference, Boston, 11/12/2013 (and numerous other places ...)
    [poster]
    Best Poster Presentation Award, Second Place

  2. A Low-overhead Dynamic Optimization Framework on Multicores;
    Presented at:
    1. International Conference on Very Large Scale Integration, Istanbul, 10/6/2013
    2. the 21st IEEE/ACM International Conference on Parallel Architectures and Compilation Techniques, Minneapolis, 9/20/2012
    [poster]

  3. Bridging the GPGPU-FPGA Efficiency Gap; Presented at the 19th International Symposium on Field-Programmable Gate Arrays, Monterey, 2/28/2011
    [poster]

  4. Scalable FPGA Solutions for Learning Bayesian Networks
    Presented at:
    1. the BWRC Winter Retreat, Lake Tahoe, 1/10/2010
    2. the BWRC Summer Retreat, U.C. Berkeley, 6/6/2010 (with an updated results pane)
    [poster]

  5. Curing Cancer with RCBIOS; Presented at the RAMP Summer Retreat, U. T. Austin, 6/23/2009
    [poster]

  6. flint; Presented at the RAMP Winter Retreat, U.C. Berkeley, 1/10/2009
    [poster]

Talks (ordered by project, then time)


  1. Cryptography Can Outmaneuver Hardware; Hardware Security Workshop at Columbia University, New York City, 8/31/2016

  2. The Ascend Secure Processor: Concept to Silicon Implementation
    1. University of Illinois at Urbana-Champaign, 2/15/2016
    2. Stanford University, 2/23/2016
    3. Harvard University, 3/6/2016
    4. University of California--San Diego, 4/25/2016
    5. Nvidia Research, 7/14/2016

    I also gave subsets of this talk at:
    1. CHASE Conference (Conference on Secure/Trustworthy Systems and Supply Chain Assurance), University of Connecticut, 6/1/2016
    2. DIMACS Workshop (Center for Discrete Mathematics and Theoretical Computer Science), MIT, 6/11/2016

  3. Constants Count: Practical Improvements to Oblivious RAM; "ORAMorama" Technical Session at the 24th Usenix Security Symposium, Washington D.C., 8/13/2015
    [slides]

  4. Tiny ORAM: A Low-Latency, Low-Area Hardware Oblivious RAM Controller; "Implementation I" Technical Session at the 23rd IEEE Intl. Sym. on Field-Programmable Custom Computing Machines, Vancouver, Canada, 5/2/2015
    [slides]

  5. Onion ORAM: Constant Bandwidth ORAM using Additively Homomorphic Encryption;
    1. ORAM Day at Boston University, Boston, Massachusetts, 1/30/2015
    2. Charles River Crypto Day at Northeastern University, Boston, Massachusetts, 4/17/2015
    3. UBC Seminar, Vancouver, Canada, 5/3/2015
    4. ORAM Technical Session at the 13th Theory of Cryptography Conference, 1/13/2016
    [slides, shorter slides (with whole talk written out in comments section)]

  6. Hardware Security in Cloud Computing
    Presented at the Annual CSAIL Alliance Program meeting, Cambridge, 4/30/2014

  7. Suppressing the Oblivious RAM Timing Channel While Making Information Leakage and Program Efficiency Trade-offs; "Security and Cloning" Technical Session at the 20th Intl. Sym. on High Performance Computer Architecture, Orlando, Florida, 2/18/2014
    [slides]

  8. Techniques for Performing Secure Computation on Encrypted Data
    Presented at:
    1. the NSA-CSAIL visit, Cambridge, Massachusetts, 9/19/2012
    2. the MIT CSAIL security seminar series, Cambridge, Massachusetts, 10/1/2012
    3. 7th ACM Workshop on Scalable Trusted Computing (STC), Raleigh, North Carolina, 10/15/2012 (second half)
    4. 4th ACM Cloud Computing Security Workshop (CCSW), Raleigh, North Carolina, 10/19/2012 (first half)
    5. the Northrop Grumman-CSAIL visit, Cambridge, Massachusetts, 10/25/2012
    6. the Boston University security (BUSec) seminar series, Cambridge, Massachusetts, 12/10/2012
    7. MIT Lincoln Laboratory, Lexington, Massachusetts, 2/4/2013
    [slides]

  9. Bridging the GPGPU-FPGA Effciency Gap; "FPGA Architectures and Technology" Technical Session at the 19th Intl. Sym. on FPGAs, Monterey, California, 2/28/2011
    [slides]

  10. ParaLearn: A massively parallel, scalable system for learning interaction networks on FPGAs; "Applications" Technical Session at the 24th Intl. Conf. on Supercomputing, Tsukuba, Japan, 6/2/2010
    [slides]

    11. The slides for the below talks were subsumed by the ICS'10 and FPGA'11 talks:

  11. Scalable Bayesian Network Discovery with Reconfigurable Hardware
    Presented at:
    1. the BWRC Winter Retreat, Lake Tahoe, 1/10/2010
    2. the RAMP Winter Retreat, U.C. Santa Cruz, 1/28/2010

  12. Reconfigurable Computing & Bayesian Networks
    Presented at the GSRC Annual Research Symposium, San Jose, 9/3/2009

  13. Introduction to GateLib & MCMC on the BEE3
    Presented at the Nolan Lab "All Hands Meeting," Stanford, 6/15/2009