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. Right now, my primary focus is Architecture + Security and Architecture + Machine learning/Tensor processing, and cross-overs between these areas. Here is my CV and Google scholar profile.

Here are two recent papers that give a sense of our current work:

  1. Architecture + Security: Data Oblivious ISA Extensions for Side Channel-Resistant and High Performance Computing
  2. Architecture + Machine Learning: UCNN: Exploiting Computational Reuse in Deep Neural Networks via Weight Repetition

On the security/machine learning sides, we are very fortunate to collaborate with Intel/{Intel, NVIDIA}, respectively.

During my PhD, my focus was Architecture + Security, and our work spanned taping out a secure processor to designing asymptotically better cryptography. Here are two representative papers:

  1. Theory: Onion ORAM: A Constant Bandwidth Blowup Oblivious RAM
  2. Practice: Design and Implementation of the Ascend Secure Processor

Also, here is a 1-pager on the Ascend project that expounds my philosophy in secure hardware design.

Navigation

  1. Peer-reviewed papers
  2. Patents
  3. Theses
  4. Misc. papers (e.g., eprints)
  5. Academic blogs
  6. Selected press
  7. Posters
  8. Talks
  9. Funding
  10. Resources

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. See here for the transcript of the first 2 accesses ("received from chip..." is ciphertext received from the ORAM).

A paper describing the design can be found here. The ORAM controller RTL is open source here.

Peer-Reviewed Papers


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

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

  1. MicroScope: Enabling Microarchitectural Replay Attacks; Dimitrios Skarlatos, Mengjia Yan, Bhargava Gopireddy, Read Sprabery, Josep Torrellas, Christopher W. Fletcher; ISCA, 2019
    Open source release coming soon
    Highest ranked paper in double-blind review process

  2. SecDir: Secure Directories to Defeat Directory Side Channel Attacks; Mengjia Yan, Jen-Yang Wen, Christopher W. Fletcher, Josep Torrellas; ISCA, 2019

  3. Buffets: An Efficient and Composable Storage Idiom for Explicit Decoupled Data Orchestration; Michael Pellauer, Yakun Sophia Shao, Jason Clemons, Neal Crago, Kartik Hegde, Rangarajan Venkatesan, Stephen W. Keckler, Christopher W. Fletcher, Joel Emer; ASPLOS, 2019
    Open source release coming soon

  4. Minotaur: Adapting Software Testing Techniques for Hardware Errors; Abdulrahman Mahmoud, Radha Venkatagiri, Khalique Ahmed, Sasa Misailovic, Darko Marinov, Christopher W. Fletcher, Sarita V. Adve; ASPLOS, 2019

  5. Data Oblivious ISA Extensions for Side Channel-Resistant and High Performance Computing; Jiyong Yu, Lucas Hsiung, Mohamad El Hajj, Christopher W. Fletcher; NDSS, 2019
    Open source release here
    Distinguished Paper Finalist

  6. 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, 2019

  7. InvisiSpec: Making Speculative Execution Invisible in the Cache Hierarchy; Mengjia Yan, Jiho Choi, Dimitrios Skarlatos, Adam Morrison, Christopher W. Fletcher, Josep Torrellas; MICRO, 2018
    Open source release here
    IEEE Micro's Top Picks 2019 Honorable Mention

  8. Morph: Flexible Acceleration for 3D CNN-based Video Understanding; Kartik Hegde, Rohit Agrawal, Yulun Yao, Christopher W. Fletcher; MICRO, 2018

  9. 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

  10. 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

  11. ZeroTrace: Oblivious Memory Primitives from Intel SGX; Sajin Sasy, Sergey Gorbunov, Christopher W. Fletcher; NDSS, 2018
    Open source release here

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

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

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

  15. 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)

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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
    Top Picks in Hardware & Embedded Security 2018

  22. 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

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

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

  25. 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

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

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

  28. 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

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

  30. 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

  31. 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

  32. 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

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

  34. 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

  35. 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. Cache telepathy: Leveraging shared resource attacks to learn DNN architectures; Mengjia Yan, Christopher W. Fletcher, Josep Torrellas; arXiv preprint arXiv:1808.04761

  2. Bucket ORAM: Single Online Roundtrip, Constant Bandwidth Oblivious RAM; Christopher W. Fletcher, Muhammad Naveed, Ling Ren, Elaine Shi, Emil Stefanov; Cryptology ePrint Archive (IACR), Report 2015/1065, 2015. http://eprint.iacr.org/

  3. [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.

  4. 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.

Academic Blogging


  1. Approaches to System Security: Using Cryptographic Techniques to Minimize Trust; Sigarch blog [article]; with Simha Sethumadhavan.

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. Hardware Abstractions and Efficient Intersection for Tensor Algebra; Workshop on Compiler Techniques for Sparse Tensor Algebra, 1/26/2019

  2. Data Oblivious Programming and Data Oblivious ISAs
    1. Open Source Enclaves Workshop, Berkeley CA, 8/29/2018
    2. International Workshop on Blockchain/Crypto Winterschool, Xi'an China, 12/10/2018
    3. Intel Research Technical Talk, 1/22/2019
    [slides]

  3. Attack Directories, Not Caches: Side Channel Attacks in a Non-Inclusive World; AMD Weekly Seminar Series, 7/13/2018

  4. Systems-centric aspects in Holistic Defense against Information Leakage; Plenary talk, NSF Workshop on Side and Covert Channels in Computing Systems, Washington D.C., 3/22/2018
    [slides]

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

  6. 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

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

  8. 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]

  9. 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)]

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

  11. 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]

  12. 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]

  13. 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]

  14. 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]

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

  15. 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

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

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

Funding

* All funding amounts are my personal take/total grant budget.

  1. Intel ISRA (2018-2021); 300K/1.5M (awarded as gift), Lead PI
  2. NSF CNS #1817020 (2018-2021); 250K/500K, Co PI
  3. DARPA SDH (2018-2022); 466K/23M, subcontractor under NVIDIA
  4. NSF CCF #1725734 (2017-2020); 250K/500K, Co PI
  5. Travel grants: ISCA'18 4x, MICRO'18 2x

Resources

  1. Crypto-hardware-software bibliography

© Chris Fletcher 2019