T0RTT: Non-Interactive Immediate Forward-Secret Single-Pass Circuit Construction

Lauer, Sebastian; Gellert, Kai; Merget, Robert; Handirk, Tobias; Schwenk, Jörg

doi:10.2478/popets-2020-0030

Cited by 7 publications

(2 citation statements)

References 42 publications

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“…Puncturable encryption [32] was used to construct forward-secure instant messaging [32] and 0-RTT protocols [19,20,33,45], for instance. Green and Miers [32] first proposed puncturable encryption as a practical building block for the case of asynchronous messaging.…”

Section: Related Workmentioning

confidence: 99%

Session Resumption Protocols and Efficient Forward Security for TLS 1.3 0-RTT

2021

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The TLS 1.3 0-RTT mode enables a client reconnecting to a server to send encrypted application-layer data in “0-RTT” (“zero round-trip time”), without the need for a prior interactive handshake. This fundamentally requires the server to reconstruct the previous session’s encryption secrets upon receipt of the client’s first message. The standard techniques to achieve this are session caches or, alternatively, session tickets. The former provides forward security and resistance against replay attacks, but requires a large amount of server-side storage. The latter requires negligible storage, but provides no forward security and is known to be vulnerable to replay attacks. In this paper, we first formally define session resumption protocols as an abstract perspective on mechanisms like session caches and session tickets. We give a new generic construction that provably provides forward security and replay resilience, based on puncturable pseudorandom functions (PPRFs). We show that our construction can immediately be used in TLS 1.3 0-RTT and deployed unilaterally by servers, without requiring any changes to clients or the protocol. To this end, we present a generic composition of our new construction with TLS 1.3 and prove its security. This yields the first construction that achieves forward security for all messages, including the 0-RTT data. We then describe two new constructions of PPRFs, which are particularly suitable for use for forward-secure and replay-resilient session resumption in TLS 1.3. The first construction is based on the strong RSA assumption. Compared to standard session caches, for “128-bit security” it reduces the required server storage by a factor of almost 20, when instantiated in a way such that key derivation and puncturing together are cheaper on average than one full exponentiation in an RSA group. Hence, a 1 GB session cache can be replaced with only about 51 MBs of storage, which significantly reduces the amount of secure memory required. For larger security parameters or in exchange for more expensive computations, even larger storage reductions are achieved. The second construction combines a standard binary tree PPRF with a new “domain extension” technique. For a reasonable choice of parameters, this reduces the required storage by a factor of up to 5 compared to a standard session cache. It employs only symmetric cryptography, is suitable for high-traffic scenarios, and can serve thousands of tickets per second.

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Section: Related Workmentioning

confidence: 99%

Session Resumption Protocols and Efficient Forward Security for TLS 1.3 0-RTT

2021

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“…Aviram et al [3] study practical forward secrecy for 0-RTT in TLS 1.3 and in particular the session resumption feature of TLS 1.3. Lauer et al [40] introduce a single-pass circuit construction protocol with forward secrecy for Tor, called Tor 0-RTT (T0RTT), which they construct from BFE. Dallmeier et al [21] use BFE to implement the first fully forward-secret 0-RTT key exchange in Google's QUIC protocol and analyze its performance.…”

Section: Follow-up Workmentioning

confidence: 99%

Bloom Filter Encryption and Applications to Efficient Forward-Secret 0-RTT Key Exchange

Derler¹,

Gellert

Jager

et al. 2021

J Cryptol

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Forward secrecy is considered an essential design goal of modern key establishment (KE) protocols, such as TLS 1.3, for example. Furthermore, efficiency considerations such as zero round-trip time (0-RTT), where a client is able to send cryptographically protected payload data along with the very first KE message, are motivated by the practical demand for secure low-latency communication. For a long time, it was unclear whether protocols that simultaneously achieve 0-RTT and full forward secrecy exist. Only recently, the first forward-secret 0-RTT protocol was described by Günther et al. (Eurocrypt, 2017). It is based on puncturable encryption. Forward secrecy is achieved by “puncturing” the secret key after each decryption operation, such that a given ciphertext can only be decrypted once (cf. also Green and Miers, S&P 2015). Unfortunately, their scheme is completely impractical, since one puncturing operation takes between 30 s and several minutes for reasonable security and deployment parameters, such that this solution is only a first feasibility result, but not efficient enough to be deployed in practice. In this paper, we introduce a new primitive that we term Bloom filter encryption (BFE), which is derived from the probabilistic Bloom filter data structure. We describe different constructions of BFE schemes and show how these yield new puncturable encryption mechanisms with extremely efficient puncturing. Most importantly, a puncturing operation only involves a small number of very efficient computations, plus the deletion of certain parts of the secret key, which outperforms previous constructions by orders of magnitude. This gives rise to the first forward-secret 0-RTT protocols that are efficient enough to be deployed in practice. We believe that BFE will find applications beyond forward-secret 0-RTT protocols.

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