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MA Final Talk: Tamper-Evident Publication of Internet Measurements - - PowerPoint PPT Presentation

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Chair of Network Architectures and Services Department of Informatics Technical University of Munich MA Final Talk: Tamper-Evident Publication of Internet Measurements Max Helm Advisors: Oliver Gasser, Benjamin Hof, Quirin Scheitle July 16,

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Chair of Network Architectures and Services Department of Informatics Technical University of Munich

MA Final Talk: Tamper-Evident Publication of Internet Measurements

Max Helm Advisors: Oliver Gasser, Benjamin Hof, Quirin Scheitle

July 16, 2018 Chair of Network Architectures and Services Department of Informatics Technical University of Munich

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Motivation

  • What?
  • Tamper-evident: Cryptographically provable append-only property
  • Publish Internet measurements (e.g. certificates)
  • Why?
  • Documentation of measurement claim, timestamping service, attribution to cryptographic iden-

tity: I found and uploaded this specific certificate at this exact time

  • Ease the joint use of different certificate sources: Certificate Transparency ↔ Active Scans [6]
  • Bind measurement results to their meta data
  • M. Helm — MA: Tamper-Evident Measurements

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Motivation

Requirements:

  • CT compatibility: Upload, download, proofs
  • Extensibility: Add additional modules
  • New spam protection mechanism
  • M. Helm — MA: Tamper-Evident Measurements

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Related Work

  • Data archival and reproducibility guidelines: BSI[2], TUM UB[5], Censys[3]
  • Tamper-evident data structures:
  • Chain-based: Linear hash chains, ...
  • Tree-based: Merkle Trees, Certificate Transparency, Persistent Authenticated Dictionaries, ...
  • Merkle Tree extensions: Revocation Transparency[4], CT for DNSSEC[7], ...
  • M. Helm — MA: Tamper-Evident Measurements

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Background

  • Merkle Tree:
  • Binary hash tree (leaves are certificates, nodes are hashes of children)
  • Root hash gets published
  • Efficient way of proving inclusion of certificates and consistency between tree versions
  • Certificate Transparency (CT):
  • Public, tamper-evident logs of certificates
  • Everyone can submit certificates with a valid chain
  • Supply simple HTTP(S) GET/POST endpoints for up- and download
  • Use Merkle tree to achieve tamper-evident property
  • M. Helm — MA: Tamper-Evident Measurements

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Approach

  • Three leaf types:
  • Certificates (comparable to CT)
  • Scan Data (Meta data about whole scan as well as single scan items)
  • Derived Data (Additional data: e.g. linter results for certificates)
  • Use three Merkle trees in conjunction (additional data, keep CT compatibility)
  • M. Helm — MA: Tamper-Evident Measurements

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Approach

Workflow for researchers:

  • Upload scan meta data → Returns: Inclusion promise for scan + leaf hash of scan
  • Upload scan results → Returns: Inclusion promise for each result
  • Researcher has to store or publish inclusion promises → Possible to prove misbehavior of

log

  • Log triggers derived data collection
  • M. Helm — MA: Tamper-Evident Measurements

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Design

scan2 scan1 scan0

Figure 1: Scan series tree (scan meta data)

  • M. Helm — MA: Tamper-Evident Measurements

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Design

scan2 scan1 scan0

Figure 1: Scan series tree (scan meta data)

cert3 cert2 cert1 cert0

Figure 3: Certificate tree (certificate data)

  • M. Helm — MA: Tamper-Evident Measurements

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Design

scan2 scan1 scan0

Figure 1: Scan series tree (scan meta data)

derived3 derived2 derived1 derived0

Figure 2: Derived data tree (additional data derived from certs)

cert3 cert2 cert1 cert0

Figure 3: Certificate tree (certificate data)

  • M. Helm — MA: Tamper-Evident Measurements

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Design

Scan Data scan2 scan1 scan0 Certificates cert3 cert2 cert1 cert0 Derived Data derived3 derived2 derived1 derived0

Figure 4: The three tree types and their final interconnections. Solid lines represent tamper-evident links, dashed lines represent non-tamper-evident links.

  • M. Helm — MA: Tamper-Evident Measurements

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Implementation

  • Based on github.com/google/trillian (log server)

and github.com/google/certificate-transparency-go (log client)

  • Extended server to support active scans with meta data and derived data
  • Extended client to upload scan data and added different upload modes
  • M. Helm — MA: Tamper-Evident Measurements

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Implementation

add-scan add-cert verifyPGP GPG Public Key Ring addToCache Memcached Instance checkCache Tree Mode startDerivation add-derived createTree queueLeaf DB gRPC Figure 5: Overview of the implementation of the trillian personality.

  • M. Helm — MA: Tamper-Evident Measurements

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Implementation

Big scans cause problems (protobuf restrictions) ⇒ Two modes for different requirements to the size of scans:

  • Default (Scans < 5M entries):
  • Three static trees
  • One scan consists of one node of the scan tree
  • Dynamic Tree Generation (Scans 5M entries):
  • Three static trees + Dynamically generated trees
  • Each scan triggers generation of new tree
  • Those dynamic trees are sub trees of scan tree
  • One scan consists of one node of scan tree + One dynamic tree
  • M. Helm — MA: Tamper-Evident Measurements

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Implementation

Scan Data scan2 scan1 scan0

datum3 datum2 datum1 datum0 datum3 datum2 datum1 datum0 datum3 datum2 datum1 datum0

Figure 6: The scan tree on top with three dynamically generated sub trees for the three scans in the top tree.

  • M. Helm — MA: Tamper-Evident Measurements

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Implementation

Different upload modes for certificates:

  • Default (like in CT):
  • One cert per request
  • Batches:
  • 1,000 certs per request
  • Concurrent batches:
  • Parallel upload of batches
  • M. Helm — MA: Tamper-Evident Measurements

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Evaluation

Setup:

  • Single VM
  • Debian Jessie, 64GB RAM, 8 × 2.67GHz cores

Scan upload (1M entries per scan):

  • Default: Four minutes
  • Dynamic Trees: 165 minutes

Certificate upload (1M certs):

  • Default (like in CT): 660 minutes
  • Batches: 161 minutes
  • Concurrent batches: 70 minutes
  • M. Helm — MA: Tamper-Evident Measurements

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Evaluation

(a) Memory and CPU usage (b) Network usage and number of unsequenced rows

Figure 7: Measurement results for the scan upload in the default mode

  • Short upload time
  • Not resource bound
  • M. Helm — MA: Tamper-Evident Measurements

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Evaluation

(a) Memory and CPU usage (b) Network usage and number of unsequenced rows

Figure 8: Measurement results for the scan upload in the dynamic trees mode

  • Upload takes more time
  • Batch pattern in unsequenced rows
  • M. Helm — MA: Tamper-Evident Measurements

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Evaluation

(a) Rocketeer log size over time[1] (b) Argon 2017 log size over time[1]

Figure 9: CT logs over time

  • Rocketeer: mean of 300,000 per day
  • Argon 2017: maximum of 2,100,000 per day

⇒ Only estimation of lower bound

  • M. Helm — MA: Tamper-Evident Measurements

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Future Work

  • Improve performance:
  • Timeout issues of implementation
  • Contexts get canceled
  • Gossiping:
  • Security goals like tamper-evidence, spam protection, accountability reached
  • Other goals require lots of assumptions → e.g. no split view attacks
  • M. Helm — MA: Tamper-Evident Measurements

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Conclusion

  • CT compatibility: Upload ✗, download ✓, proof ✓
  • Extensibility: Add derived module via git link ✓
  • New spam protection mechanism: GPG ✓

Questions?

  • M. Helm — MA: Tamper-Evident Measurements

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Backup

Implementation details

  • trillian implements highly scalable Merkle-Tree in Go
  • certificate-transparency-go implements CT personality
  • Altered CT personality to work with arbitrary data (not only certs)
  • Added second tree, communication between trees
  • Removed: root store contains valid root certs
  • Added: PGP signature verification on scan upload
  • User store: implemented as Public key ring file
  • Memcache for caching of cert hashes
  • Only accept cert uploads where cert is part of existing scan
  • M. Helm — MA: Tamper-Evident Measurements

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Backup

Design details Roles:

  • Log owner (created and delete log, add admins)
  • Log admin (freeze log, add contributors)
  • Log contributor (upload data)
  • Log user (download data)

Attacker model:

  • External attacker: User of or contributor to log → Alter (own) contributions
  • Internal attacker: Owner or admin of the log → Alter contributions to fit long term measure-

ment results

  • Internal data corruption: Bit flips, accidental overrides, ...
  • M. Helm — MA: Tamper-Evident Measurements

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Backup

Figure 10: Structure of an inclusion promise.

  • M. Helm — MA: Tamper-Evident Measurements

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Bibliography

[1] CT Monitor. ct.grahamedgecombe.com. Accessed: 2018-07-15. [2] BSI. M 4.170. https://www.bsi.bund.de/DE/Themen/ITGrundschutz/ITGrundschutzKataloge/Inhalt/_content/m/m04/m04170.html. [3]

  • Z. Durumeric, D. Adrian, A. Mirian, M. Bailey, and J. A. Halderman.

A search engine backed by Internet-wide scanning. In Proceedings of the 22nd ACM SIGSAC Conference on Computer and Communications Security, pages 542–553. ACM, 2015. [4]

  • B. Laurie and E. Kasper.

Revocation transparency. Google Research, September, 2012. [5]

  • U. TUM.

Forschungsdatenmanagement. https://www.ub.tum.de/forschungsdaten-archivieren. [6]

  • B. VanderSloot, J. Amann, M. Bernhard, Z. Durumeric, M. Bailey, and J. A. Halderman.

Towards a Complete View of the Certificate Ecosystem. In Proceedings of the 2016 ACM on Internet Measurement Conference, pages 543–549. ACM, 2016. [7]

  • D. Zhang.

Certificate Transparency for Domain Name System Security Extensions. Work In Progress, 2016. https://tools.ietf.org/html/draft-zhang-trans-ct-dnssec-03.

  • M. Helm — MA: Tamper-Evident Measurements

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