Adversarial Model Sample Clauses

Adversarial Model. A A In the real world, a protocol determines how principals behave in response to signals from their environment. In the model, these signals are sent by the adver- sary . For simplicity, only passive adversaries are considered in the definitions. A passive adversary is assumed to merely eavesdrop all communication in the network. An adversary ’s interaction with the principals in the network (more specifically, with the various instances) is modeled by the following oracles: – – Parameter(1λ): On A’s query λ, respond with common parameters denoted by π, including two polynomial time algorithms E(·, ·) and D(·, ·). ık Setup(P0): On A’s query P0, start the protocol Σ and output the initial group P0 = {U1, · · · , UA}. For 1 ≤ k ≤ A, initialize Sidık ← 0, Pid ← ık ık Uk ∅, Dkidık ← NULL, Ekid ← NULL, Fid ← 1, S ← 0. Uk – ExecuteU(k , · · · , U ): ExecUukte the protocol beUtkween unused instances of play- {U1, U1 · · · , Un} n = Pv ⊆ P0 and output the transcript of the execution. Here, v changes whenever the group changes and hence is the group sequence num- ber. The number of group members and their identities are chosen by the ık ık Uk adversary. For 1 ≤ k ≤ n, update Sidık ık ık ← Sid + 0, Xxxxx ← Xx \ {Xx}, Xxxxxx ← dk , Ekid ← ek , S S + 0.Xx is the sUekssion sequence numbUekr to recUokrd the rUuknning tiUmk es of← . S – Ek-Reveal(Πıi ): Output Ekidıi . Execute i i i – Dk-Reveal(ΠUı i ): Output DkidUı i . Update Fidı ← 0. We allow the encryp- tion key to beUidifferent from thUei decryption kUeiy and hence the Ek-Reveal oracle and the Dk-Reveal oracle are distinguished. – Xxxx(Xxx , x0, x0): This query is used to define the advantage of an ad- versary Ui . A executes this query on a fresh instance Πıi (see Definition 4 below) aAt any time, but only once (other queries have noUri estriction). When A asks this query, it receives a challenge ciphertext c∗ = E(mρ, ekıi ), where ρ is the result of a coin flip. Finally, A outputs a bit ρj. Ui
Sample 1
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Adversarial Model. ← The launch and send oracles. We adapt the security model of [5,6] and [22]. We assume that the powerful adversary can launch instances of the prepar- ing/repairing protocol on chosen inputs by making a chosen participant to play the (chosen) role of Xxxxx or Bob with a chosen input. For instance, the Π launch(n, Xxxxx, ID) query creates an instance π of Xxxxx with input ID, played by node n. We assume that the adversary can play with all participants in a con- ← current way and basically run the protocol step by step. The adversary is the cen- tral node of the communication channels, can send an arbitrary message to any instance and get the response message in return. For instance, y send(Π, x) sends the message x as being the current protocol message to instance Π, makes this instance step the protocol, and tells the protocol answer y of Π. The test oracle. We assume that the adversary can make test(n, k, ID) oracle calls which tell whether (k, ID) is an entry of the database of node n. We say that an adversary wins if one test query positively answered. Note that contrarily to the traditional Xxxxxxx-Xxxxxxx [5,6] model, the adversary can make as many test queries as he wants. The reason is that, in practice, information leaks so that the adversary can simulate this oracle in an offline way. Every key K in a database can be seen as a random variable. In that case, every (unsuccessful) test query reduced the entropy by telling the adversary that K is not equal to a given k. The remove oracle. We also assume that the adversary can make remove(n, ID) oracle queries which make node n remove any entry with ID from its database. This simulates a user managing the database of paired devices. ←
Sample 1
Adversarial Model. The adversary interacts with the user instances via a set of oracles Execute, Send, Reveal, Corrupt and Test. We call the adversary passive if no access to the Send- and Corrupt-oracle is granted. { } Execute( X0, X0, . . . , Xx ) This query executes a protocol run between unused instances Πs of the specified users and returns a transcript of all messages sent during the protocol execution. { } Send(Ui, s, M ) This query sends the message M to instance Πs and returns the reply generated by this instance. A special message M = U1, . . . , Ur sent to an unused instance will set pids := M , useds := true and provoke Πs to begin with the protocol execution. i Reveal(Ui, s) returns the session key sks. Corrupt(Ui) returns the long-term secret key SKi that Ui holds. We will refer to a user Ui as honest if no query of the form Corrupt(Ui) was made. i Test(Ui, s) The adversary is allowed to use this query only once. Provided that sks = null, a random bit b is drawn and depending on b with probability 1/2 the session key sks and with probability 1/2 a uniformly chosen random session key is returned. The adversary is allowed to query other oracles after its Test-query, but no query that would repeal the freshness of Πs is allowed.
Sample 1

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