Onion-Routed Multi-Circuit Key Establishment for Quantum-Resilient Sessions
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866911702350561280 |
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| author | Mallick, Tushin Kundu, Ashish Kompella, Ramana |
| author_facet | Mallick, Tushin Kundu, Ashish Kompella, Ramana |
| contents | Public-key primitives that today anchor session-key establishment - RSA, Diffie-Hellman, and elliptic-curve cryptography - reduce to integer factorization or discrete logarithm and are therefore vulnerable to Shor's algorithm on a sufficiently capable quantum computer. The harvest-now, decrypt-later (HNDL) threat model turns this future capability into a present liability: ciphertext archived today can be decrypted retrospectively once a cryptographically relevant quantum computer becomes available. We propose a session-key establishment scheme that distributes a freshly generated key as multiple, independently encrypted fragments across distinct, ephemeral Tor circuits between an onion-service proxy and an onion-service client. Reconstruction requires every fragment; each fragment travels its own per-bundle circuit established via a NEWNYM signal. The security argument rests on the standard end-to-end correlation bound for onion routing: an adversary controlling a fraction of Tor relays must independently deanonymize every fresh circuit to correlate the fragments belonging to one session, and the per-fragment probability of success decays multiplicatively in the number of fragments. We implement the design as a Flask-based prototype on AWS EC2, with both the proxy and the client deployed as Tor onion services, and measure end-to-end key-establishment latency. The implemented prototype completes a key establishment in 13-20 s on average (7-50 s including tails), of which approximately 88% is attributable to Tor-related delay - a cost we discuss in the context of the privacy-versus-responsiveness trade-off. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_21349 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Onion-Routed Multi-Circuit Key Establishment for Quantum-Resilient Sessions Mallick, Tushin Kundu, Ashish Kompella, Ramana Cryptography and Security Public-key primitives that today anchor session-key establishment - RSA, Diffie-Hellman, and elliptic-curve cryptography - reduce to integer factorization or discrete logarithm and are therefore vulnerable to Shor's algorithm on a sufficiently capable quantum computer. The harvest-now, decrypt-later (HNDL) threat model turns this future capability into a present liability: ciphertext archived today can be decrypted retrospectively once a cryptographically relevant quantum computer becomes available. We propose a session-key establishment scheme that distributes a freshly generated key as multiple, independently encrypted fragments across distinct, ephemeral Tor circuits between an onion-service proxy and an onion-service client. Reconstruction requires every fragment; each fragment travels its own per-bundle circuit established via a NEWNYM signal. The security argument rests on the standard end-to-end correlation bound for onion routing: an adversary controlling a fraction of Tor relays must independently deanonymize every fresh circuit to correlate the fragments belonging to one session, and the per-fragment probability of success decays multiplicatively in the number of fragments. We implement the design as a Flask-based prototype on AWS EC2, with both the proxy and the client deployed as Tor onion services, and measure end-to-end key-establishment latency. The implemented prototype completes a key establishment in 13-20 s on average (7-50 s including tails), of which approximately 88% is attributable to Tor-related delay - a cost we discuss in the context of the privacy-versus-responsiveness trade-off. |
| title | Onion-Routed Multi-Circuit Key Establishment for Quantum-Resilient Sessions |
| topic | Cryptography and Security |
| url | https://arxiv.org/abs/2605.21349 |