Previous Work. Information-theoretically secure secret-key agreement from correlated information has first been proposed by Xxxxxx in [11]. He considered a setting where Alice, Bob, and Eve hold many indepen- dent realizations of correlated random variables X, Y , and Z, respectively, with joint probability distribution PXY Z. The (two-way) secret-key rate S(X; Y Z), i.e., the rate at which Xxxxx and Xxx can generate secret-key bits per realization of (X, Y, Z), has further been studied in [1] and later in [12], where the intrinsic information I(X; Y Z) is defined and shown to be an upper bound on S(X; Y Z), which, however, is not tight [13]. | − | | For one-way communication, it is already implied by a result in [3] and has later been shown in [1] that the secret-key rate S→(X; Y Z) is given by the supremum of H(U ZV ) H(U Y V ), taken over all possible random variables U and V obtained from X.1 However, as this is a purely information-theoretic result, it does not directly imply that there exists an efficient key-agreement protocol. | − |
Previous Work. Reputation mechanisms are being used to increase the reliability and perfor- xxxxx of virtual societies (or organisations) while providing mechanisms for exchanging reputation values. In centralised reputation models, a reputation system receives feedback about the interactions among the agents. Each agent evaluates the behaviour of the agents with whom it interacts and informs the reputation system. The system puts together all evaluations and stores such rep- utations. In contrast, in distributed reputation models, each agent evaluates and stores the reputations of the agents with whom it has interacted with and is able to provide such information to other agents. With the aim to cope with the problems of centralised and distributed rep- utation mechanisms3, we proposed the use of a hybrid mechanism [12]. In the distributed part of such a mechanism, agents evaluate the behaviour of other agents by exchanging opinions and storing such information. An opinion has to be justified by providing, for instance, the set of violated norms that contribute to that opinion. X A R ON (A A X {ON R }) A This work is framed in organisational environments that provide a minimum set of organisational mechanisms to regulate agents’ interactions. Formally, an organisation is defined as a tuple g, , , φ, x0, ϕ, om, om where g represents the set of agents participating within the organisation; is the set of actions agents can perform; stands for the environmental states space; φ is a function describing how the system evolves as a result of agents actions; x0 represents the initial state of the system; ϕ is the agents’ capability function describing the actions agents are able to perform in a given state of the environ- ment; om is an organisational mechanism based on organisational norms; and om is an organisational mechanism based on roles that defines the positions agents may enact in the organisation (see [5] for more details). (A R A ) (A A T ) Agents participating in the field of such organisations are involved in different situations. A situation is defined as a tuple g, , , T , that represents an agent g, playing the role , while performing the action , through a time period T . As detailed in [5], different types of situations can be defined following this definition. For instance, situations in which an agent performs an action, regardless of the role it is playing – g, , , –, or situations in which an agent is playing a role along a time period, regardless the acti...
Previous Work. Broadcast: For the standard communication model with a complete synchro- nous network of pairwise authenticated channels, Pease, Shostak, and Xxx- port [PSL80] proved that perfectly secure broadcast is achievable if and only if less than a third of the players is corrupted: t < n/3. This tight bound more generally holds with respect to a network of secure channels and unconditional security, i.e., when even allowing a negligible error probability, as proven by Xxxxxx and Yao [KY]. The first optimally resilient protocol that is efficient was proposed by Dolev et al. [DFF+82]. For the case that broadcast among ev- ery subset of three players is possible (in contrast to the standard model with only pairwise communication), Fitzi and Xxxxxx [FM00] proved that (global) broadcast is possible if and only if t < n/2. In another line of research, Xxxx- Xxxxxxx, Pfitzmann, and Xxxxxxx [BPW91,PW92] proved that broadcast during some precomputation stage allows to later achieve broadcast that tolerates any number of corrupted players (t < n), i.e., that the functionality of the prior broadcast can be preserved for any later time. Multi-party computation: The concept of general multi-party computation (MPC) was introduced by Yao [Yao82] with a first complete solution given by 3 That is, interpreting ⊥ as “invalid”, this condition expresses that no two correct players may decide on valid values that are distinct. Goldreich, Micali, and Wigderson [GMW87] — though with computational se- curity. Ben-Or, Xxxxxxxxxx, and Wigderson [BGW88], and, Xxxxx, Xx´epeau, and Damg˚ard [CCD88], proved that, in the standard model with pairwise se- cure channels, unconditionally secure MPC is achievable if and only if t < n/3 by giving efficient protocols for the achievable cases. Beaver [Bea89], and inde- pendently, Xxxxx and Xxx-Or [RB89] later proved that, when additionally given global broadcast among the players, unconditionally secure MPC is achievable if and only if t < n/2 (see also Xxxxxx et al. [CDD+99]). The result in [FM00] hence implies that broadcast among three players (i.e., 2-cast) is sufficient in order to achieve MPC for t < n/2.
Previous Work. In 2006 [1] introduced a key agreement protocol based in group theory (specifically the braid group) that with- stood several attacks over the past decade. First [18] determined that if braids are too short then it’s possible to find the conjugating factor and use that to break the system. However it was pointed out in [12] that in practice the braids are long enough that this attack can never succeed in practice. It’s akin to using Fermat to factor short RSA keys. Second, [15] showed a linear algebra attack (KTT) that would allow an attacker to determine part of the private key data. However, [10] showed that this is just a class of weak keys and by choosing the private key data in a specific way this attack is defeated. More recently [6] built upon the defeated KTT attack, and using all of the public information were able to, after a large precomputation, spend several hours to reconstruct the shared secret. This attack not only required access to the public parameters but also both public keys (including their permutations). It was shown in [2] that the attack work grows as the size of the permutation order grows as well as the size of the braid group. Still, none of these attacks targeted the underlying hard problems in the braid group, or attempted to at- tack the one-way function introduced in [1] called E- Multiplication. Our Contribution This paper introduces the Ironwood meta key agree- ment and authentication protocol whose security is based on hard problems in group theory. Ironwood leverages the one-way function, E-Multiplication, but creates a different construction that removes some of the public information required to mount any of the previous attacks. In addition to being immune from previous attacks, Ironwood is also quantum resistant. Specifically, Shor’s quantum algorithm [20] which has been shown to break RSA, ECC, and sev- eral other public key crypto systems does not seem appli- cable for attacking Ironwood. Further, Xxxxxx’x quantum search algorithm [21] is not as impactful on Ironwood due to the fact that the running time of Ironwood is linear in the key length. This paper first reviews the braid group and colored Xxxxx represtation. Next it reviews E-Multiplication, and then introduces the meta key agreement and authentica- tion protocol. Following that it introduces Ironwood and presents a security analysis.
Previous Work. In 2006 [1] in joint work with X. Xxxxxx and X. Xxxxxxx two of us (IA and DG) introduced a key agreement protocol based in group theory (specifically the braid group) that has withstood several attacks over the past decade. First Myasnikov–Ushakov [20] determined that if braids are too short then one can find the conjugating factor and use that to break the system. However it was pointed out by one of us (PG) [14] that in practice the braids are long enough that this attack can never succeed: the method in [20] is analogous to using Fermat’s technique to factor short RSA keys, which becomes impractical at secure sizes. Second, Kalka–Xxxxxxx–Tsaban [16] described a linear algebra attack (KTT) that would allow an attacker to determine part of the private key data. However, two of us (DG and PG) [12] showed that this attack succeeds only on a class of weak keys, and that choosing the private key data more carefully defeats this attack. Subsequent to the KTT attack, Xxx-Xxx–Xxxxxxxxx–Tsaban [7], using all of the available public information of the protocol, were able to reconstruct the shared secret, after a large precomputation and several hours of runtime. We later showed [2] that the work necessary to carry out the attack increases as the size of the permutation order grows as well as the size of the braid group. We remark that the current review of WalnutDSA [3], a group theoretic based digital signature, does not apply to the Ironwood protocol. In particular the (exponential) attack on reversing E-multiplication requires data not available to an attacker, and hence the underlying hard problems considered in these approaches do not impact the Ironwood security (see §VI).
Previous Work. Describe the previous studies of the study area. Studies related to groundwater extraction, groundwater levels, river flow, precipitation, water quality and their correlations should be thoroughly investigated and documented. If there have been previous groundwater flow models for the aquifers in the region, review and describe those models. These models may not necessarily cover exactly the same area or have the same objective; however, the previous groundwater models and their associated data sources may provide useful information for this project. Thus, the existing models and related databases/files shall also be reviewed and investigated.
Previous Work. The Gunung Silubat area forms part of what was known as the Chinese district of Western Borneo (Kalimantan Barat), encompassing the sub-districts of Sambas, Bengkajang, Pamangkat, Singkawang and mempawah. Consequently it has been subjected to much exploitation by the Chinese since the 1800's. Understandly no records of production have been kept due to tax evasion.
Previous Work. If the Candidate we supply or propose to supply has previously worked for you, details of any previous work engagement/s where the Candidate's previous engagement ended (a) due to maternity and/or (b) within the previous 6 months, the details in either case including the dates of the engagement, the capacity in which the Candidate was engaged, and the reason for the engagement ending. Comparator Terms - information to enable us to determine the pay and basic working and employment conditions as set out in R.6 of the AWR that are ordinarily in force within your business and which would have been applicable had the Candidate been engaged directly by you on the first day of their assignment to do the same job.
Previous Work. Figure 1: First safe gripper design, originating from the SME‐Robot project. The first prototype of a safe gripper design originates from the SME‐Robot project, in which safety tests have been performed using a modified crash test dummy and a light‐weight robot, focusing on blunt impacts and usage of sharp tools. Since the SCHUNK commercial gripper available at that time had several sharp edges and turned out to pose substantial safety risks to the users manually interacting with the robot, a rubber cover has been designed. In this way, a consistent safety level was achieved for the arm and the gripper. However, it quickly turned out that a major drawback for interaction still was the fact that the user had to release the robot during teaching tasks in order to trigger simple actions on a keyboard, such as storing individual robot configurations, starting and stopping trajectory recording or switching between control modes.
Previous Work. Byzantine Agreement Since its introduction in the work of Xxxxx et al.[20], the problem of Byzantine Agreement has been a source of enormous attention. Xxxxx et al. proved (in [20] itself) that no deterministic algorithm can achieve Byzantine Agreement among n players in the presence of t faults if n ≤ 3t 1The meaning of which players are non-faulty depends on the adversary. (This bound was later extended to the case of randomized algorithms by Xxxxxx and Xxx [19]). They also constructed a (deterministic) algorithm that solves BA for any n > 3t, in a synchronous full-information network. Once the feasibility of BA was shown, further attempts concentrated on reducing the complexity of achieving agreement. The standard complexity measures of interest are the number of rounds, and the total communication and computational complexity of the protocol, the former being the most interesting of them. The protocol of [20] had a round complexity of t + 1 rounds, which was shown to be optimal for deterministic protocols by Xxxxxxx and Xxxxx [14]. However, the communication complexity of the protocol was exponential in n. Following a series of works [5, 6], Xxxxx and Xxxxx [15] constructed a BA protocol that runs for t + 1 rounds, with a polynomial communication.
