Paper 2022/220

Cache-22: A Highly Deployable End-To-End Encrypted Cache System with Post-Quantum Security

Keita Emura, Shiho Moriai, Takuma Nakajima, and Masato Yoshimi


Cache systems are crucial for reducing communication overhead on the Internet. The importance of communication privacy is being increasingly and widely recognized; therefore, we anticipate that nearly all end-to-end communication will be encrypted via secure sockets layer/transport layer security (SSL/TLS) in the near future. Herein we consider a catch-22 situation, wherein the cache server checks whether content has been cached or not, i.e., the cache server needs to observe it, thereby violating end-to-end encryption. We avoid this catch-22 situation by proposing an encrypted cache system which we call Cache-22. To maximize its deployability, we avoid heavy, advanced cryptographic tools, and instead base our Cache-22 system purely on traditional SSL/TLS communication. It employs tags for searching, and its design concept enables the service provider to decide, e.g., via an authentication process, whether or not a particular user should be allowed to access particular content. We provide a prototype implementation of the proposed system using the color-based cooperative cache proposed by Nakajima et al. (IEICE Trans. 2017) under several ciphersuites containing post-quantum key exchanges in addition to ECDHE (Elliptic Curve-based). We consider NIST Post-Quantum Cryptography round 3 finalists and alternate candidates: lattice-based (Kyber, SABER, NTRU), code-based (BIKE), and isogeny-based (SIKE). Compared to direct HTTPS communication between a service provider and a user, employing our Cache-22 system has a merit to drastically reduce communications between a cache server and the service provider (approximately 95%) which is effective in a hierarchical network with a cost disparity.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. MAJOR revision.ISITA2020
Encrypted Cache SystemSSLTLSPost Quantum Security
Contact author(s)
k-emura @ nict go jp
yoshimi masato @ tis co jp
2022-02-25: received
Short URL
Creative Commons Attribution


      author = {Keita Emura and Shiho Moriai and Takuma Nakajima and Masato Yoshimi},
      title = {Cache-22: A Highly Deployable End-To-End Encrypted Cache System with Post-Quantum Security},
      howpublished = {Cryptology ePrint Archive, Paper 2022/220},
      year = {2022},
      note = {\url{}},
      url = {}
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