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| '''Burrows–Abadi–Needham logic''' (also known as the '''BAN logic''') is a set of rules for defining and analyzing information exchange protocols. Specifically, BAN logic helps its users determine whether exchanged information is trustworthy, secured against eavesdropping, or both. BAN logic starts with the assumption that all information exchanges happen on media vulnerable to tampering and public monitoring. This has evolved into the popular security mantra, "Don't trust the network."
| | Many people have this habit of doing all the stuff by themselves, irrespective of how critical or simple they are! These folks won't let others interfere inside their matters. While this stance will work inside other regions of existence, it's not how to respond when you need to fix a Windows registry. There are some jobs such as removing spywares, virus as well as obsolete registry entries, which are best left to pro softwares. In this article I can tell we why it really is important to fix Windows registry NOW!<br><br>If it is very not because big of a issue as you think it happens to be, it may probably be solved easily by running a Startup Repair or by System Restore Utility. Again it can be as effortless as running an anti-virus check or cleaning the registry.<br><br>System tray icon makes it convenient to launch the system and displays "clean" status or the number of errors in the last scan. The ability to locate and remove the Invalid class keys plus shell extensions is one of the leading blessings of the program. That is not usual function for the different Registry Cleaners. Class keys plus shell extensions which are not functioning may seriously slow down a computer. RegCure scans to find invalid entries plus delete them.<br><br>In purchase to remove the programs on the computer, Windows Installer need to be in a healthy state. If its installation is corrupted we will receive error 1721 in Windows 7, Vista plus XP during the program removal process. Just re-registering its component files would resolve your issue.<br><br>So to fix this, we really have to be capable to make all the registry files non-corrupted again. This can dramatically accelerate the loading time of the computer plus allows we to a big amount of elements on it again. And fixing these files couldn't be easier - you simply should employ a tool called a [http://bestregistrycleanerfix.com/system-mechanic system mechanic].<br><br>Although I always employ the most recent variation of browser, often different extensions plus plugins become the cause of mistakes with my browser and the system. The same is the story with my browser which was crashing frequently perhaps due to the Flash player error.<br><br>By restoring the state of your program to an earlier date, error 1721 might not appear inside Windows 7, Vista and XP. There is a tool called System Restore which we have to employ in this procedure.<br><br>What I would recommend is to look on your for registry cleaners. You are able to do this with a Google search. If you find products, look for ratings plus testimonials regarding the product. Next you can see how others like the product, plus how perfectly it functions. |
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| A typical BAN logic sequence includes three steps:<ref>[http://www.cs.utexas.edu/users/dahlin/Classes/UGOS/readings/BAN.pdf UT Austin CS course material on BAN logic (PDF)]</ref>
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| # Verification of message origin
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| # Verification of message [[Freshness (cryptography)|freshness]]
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| # Verification of the origin's trustworthiness.
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| BAN logic uses [[postulate]]s and [[definition]]s – like all [[axiomatic system]]s – to analyze [[authentication]] [[Protocol (computing)|protocols]]. Use of the BAN logic often accompanies a [[security protocol notation]] formulation of a protocol and is sometimes given in papers.
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| ==Language type and alternatives==
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| BAN logic, and logics in the same family, are [[decidable language|decidable]]: there exists an algorithm taking BAN hypotheses and a purported conclusion, and that answers whether or not the conclusion is derivable from the hypotheses. The proposed algorithms use a variant of [[magic set]]s (Monniaux, 1999).
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| BAN logic inspired many other similar formalisms, such as [[Gong–Needham–Yahalom logic|GNY logic]]. Some of these try to repair one weakness of BAN logic: the lack of a good semantics with a clear meaning in terms of knowledge and possible universes. However, starting in the mid-1990s, crypto protocols were analyzed in operational models (assuming perfect cryptography) using model checkers, and numerous bugs were found in protocols that were "verified" with BAN logic and related formalisms. This has led to the abandonment of BAN-family logics in favor of proof methods based on standard invariance reasoning.
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| ==Basic rules==
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| The definitions and their implications are below (''P'' and ''Q'' are network agents, ''X'' is a message,
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| and ''K'' is an [[encryption key]]):
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| *''P'' believes ''X'': ''P'' acts as if ''X'' is true, and may assert ''X'' in other messages.
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| *''P'' has jurisdiction over ''X'': ''P''<nowiki>'</nowiki>s beliefs about ''X'' should be trusted.
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| *''P'' said ''X'': At one time, ''P'' transmitted (and believed) message ''X'', although ''P'' might no longer believe ''X''.
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| *''P'' sees ''X'': ''P'' receives message ''X'', and can read and repeat ''X''.
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| *{''X''}<sub>''K''</sub>: ''X'' is encrypted with key ''K''.
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| *fresh(''X''): ''X'' has not previously been sent in any message.
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| *key(''K'', ''P''↔''Q''): ''P'' and ''Q'' may communicate with shared key ''K''
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| The meaning of these definitions is captured in a series of postulates:
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| * If ''P'' believes key(''K'', ''P''↔''Q''), and ''P'' sees {''X''}<sub>''K''</sub>, then ''P'' believes (''Q'' said ''X'')
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| * If ''P'' believes (''Q'' said ''X'') and ''P'' believes fresh(''X''), then ''P'' believes (''Q'' believes ''X'').
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| ''P'' must believe that ''X'' is fresh here. If ''X'' is not known to be fresh, then it might be an obsolete message, replayed by an attacker.
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| * If ''P'' believes (''Q'' has jurisdiction over ''X'') and ''P'' believes (''Q'' believes ''X''), then ''P'' believes ''X''
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| * There are several other technical postulates having to do with composition of messages. For example, if ''P'' believes that ''Q'' said <''X'', ''Y''>, the concatenation of ''X'' and ''Y'', then ''P'' also believes that ''Q'' said ''X'', and ''P'' also believes that ''Q'' said ''Y''.
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| Using this notation, the assumptions behind an authentication protocol
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| can be formalized. Using the postulates, one can prove that certain
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| agents believe that they can communicate using certain keys. If the
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| proof fails, the point of failure usually suggests an attack which
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| compromises the protocol.
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| == BAN logic analysis of the Wide Mouth Frog protocol ==
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| A very simple protocol — the [[Wide Mouth Frog protocol]] — allows two agents, A and B, to establish secure communications, using a trusted authentication server, S, and synchronized clocks all around. Using standard notation the protocol can be specified as follows:
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| :<math>A \rightarrow S: A,\{T_A, K_{ab}, B\}_{K_{as}}</math>
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| :<math>S \rightarrow B: \{T_S, K_{ab}, A\}_{K_{bs}}</math>
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| Agents A and B are equipped with keys ''K''<sub>''as''</sub> and ''K''<sub>''bs''</sub>, respectively, for communicating securely with S. So we have assumptions:
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| : ''A'' believes key(''K''<sub>''as''</sub>, ''A''↔''S'')
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| : ''S'' believes key(''K''<sub>''as''</sub>, ''A''↔''S'')
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| : ''B'' believes key(''K''<sub>''bs''</sub>, ''B''↔''S'')
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| : ''S'' believes key(''K''<sub>''bs''</sub>, ''B''↔''S'')
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| Agent ''A'' wants to initiate a secure conversation with ''B''. It therefore invents a key, ''K''<sub>''ab''</sub>, which it will use to communicate with ''B''. ''A'' believes that this key is secure, since it made up the key itself:
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| : ''A'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')
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| ''B'' is willing to accept this key, as long as it is sure that it came from ''A'':
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| : ''B'' believes (''A'' has jurisdiction over key(''K'', ''A''↔''B''))
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| Moreover, ''B'' is willing to trust ''S'' to accurately relay keys from ''A'':
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| : ''B'' believes (''S'' has jurisdiction over (''A'' believes key(''K'', ''A''↔''B'')))
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| That is, if ''B'' believes that ''S'' believes that ''A'' wants to use a particular key to communicate with ''B'', then ''B'' will trust ''S'' and believe it also.
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| The goal is to have
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| : ''B'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')
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| ''A'' reads the clock, obtaining the current time ''t'', and sends the following message:
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| : 1 ''A''→''S'': {''t'', key(''K''<sub>''ab''</sub>, ''A''↔''B'')}<sub>''K<sub>as</sub>''</sub>
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| That is, it sends its chosen session key and the current time to ''S'', encrypted with its private authentication server key ''K''<sub>''as''</sub>.
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| Since ''S'' believes that key(''K''<sub>''as''</sub>, ''A''↔''S''), and ''S'' sees {''t'', key(''K''<sub>''ab''</sub>, ''A''↔''B'')}<sub>''K''<sub>''as''</sub></sub>,
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| then ''S'' concludes that ''A'' actually said {''t'', key(''K''<sub>''ab''</sub>, ''A''↔''B'')}. (In particular, ''S'' believes that the message was not manufactured out of whole cloth by some attacker.)
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| Since the clocks are synchronized, we can assume
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| : ''S'' believes fresh(''t'')
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| Since ''S'' believes fresh(''t'') and ''S'' believes ''A'' said {''t'', key(''K''<sub>''ab''</sub>, ''A''↔''B'')},
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| ''S'' believes that ''A'' actually ''believes'' that key(''K''<sub>''ab''</sub>, ''A''↔''B''). (In particular, ''S'' believes that the message was not replayed by some attacker who captured it at some time in the past.)
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| ''S'' then forwards the key to ''B'':
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| : 2 ''S''→''B'': {''t'', ''A'', ''A'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')}<sub>''K<sub>bs</sub>''</sub>
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| Because message 2 is encrypted with ''K''<sub>''bs''</sub>, and ''B''
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| believes key(''K''<sub>''bs''</sub>, ''B''↔''S''), ''B'' now believes that ''S''
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| said {''t'', ''A'', ''A'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')}.
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| Because the clocks are synchronized, ''B'' believes fresh(''t''), and so
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| fresh(''A'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')). Because ''B''
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| believes that ''S''<nowiki>'</nowiki>s statement is fresh, ''B'' believes that ''S'' believes that
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| (''A'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')). Because ''B''
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| believes that ''S'' is authoritative about what ''A'' believes, ''B'' believes
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| that (''A'' believes key(''K''<sub>''ab''</sub>, ''A''↔''B'')). Because ''B''
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| believes that ''A'' is authoritative about session keys between ''A'' and ''B'', ''B''
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| believes key(''K''<sub>''ab''</sub>, ''A''↔''B''). ''B'' can now contact ''A''
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| directly, using ''K''<sub>''ab''</sub> as a secret session key.
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| Now let's suppose that we abandon the assumption that the clocks are
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| synchronized. In that case, ''S'' gets message 1 from ''A'' with {''t'',
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| key(''K''<sub>''ab''</sub>, ''A''↔''B'')}, but it can no longer conclude
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| that t is fresh. It knows that ''A'' sent this message at ''some'' time
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| in the past (because it is encrypted with ''K''<sub>''as''</sub>)
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| but not that this is a recent message, so ''S'' doesn't believe that ''A''
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| necessarily wants to continue to use the key
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| ''K''<sub>''ab''</sub>. This points directly at an attack on the
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| protocol: An attacker who can capture messages can guess one of the
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| old session keys ''K''<sub>''ab''</sub>. (This might take a long
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| time.) The attacker then replays the old {''t'',
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| key(''K''<sub>''ab''</sub>, ''A''↔''B'')} message, sending it to ''S''. If
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| the clocks aren't synchronized (perhaps as part of the same attack), ''S'' might
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| believe this old message and request that ''B'' use the old, compromised key
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| over again.
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| The original ''Logic of Authentication'' paper (linked below) contains this example and many others, including analyses of the [[Kerberos (protocol)|Kerberos]] handshake protocol, and two versions of the [[Andrew Project]] RPC handshake (one of which is defective).
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| == Notes ==
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| <references/>
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| == References==
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| * David Monniaux, Decision Procedures for the Analysis of Cryptographic Protocols by Logics of Belief, in Proceedings of The 12th Computer Security Foundations Workshop, 1999. [http://citeseer.ist.psu.edu/monniaux99decision.html (Online)].
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| == External links ==
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| * [http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.115.3569 A Logic of Authentication] ([http://ftp.digital.com/pub/DEC/SRC/research-reports/abstracts/src-rr-039.html mirror]), the original paper by [[Michael Burrows|Burrows]], [[Martín Abadi|Abadi]], and [[Roger Needham|Needham]].<!-- http://citeseer.ist.psu.edu/burrows90logic.html -->
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| *Source: [http://web.archive.org/web/20050902032746/http://www.pasta.cs.uit.no/thesis/html/ronnya/node31.html The Burrows–Abadi–Needham logic]
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| * [http://www.cs.utexas.edu/users/dahlin/Classes/UGOS/readings/BAN.pdf BAN logic in context, from UT Austin CS (PDF)]
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| {{DEFAULTSORT:Burrows-Abadi-Needham logic}}
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| [[Category:Theory of cryptography]]
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| [[Category:Automated theorem proving]]
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Many people have this habit of doing all the stuff by themselves, irrespective of how critical or simple they are! These folks won't let others interfere inside their matters. While this stance will work inside other regions of existence, it's not how to respond when you need to fix a Windows registry. There are some jobs such as removing spywares, virus as well as obsolete registry entries, which are best left to pro softwares. In this article I can tell we why it really is important to fix Windows registry NOW!
If it is very not because big of a issue as you think it happens to be, it may probably be solved easily by running a Startup Repair or by System Restore Utility. Again it can be as effortless as running an anti-virus check or cleaning the registry.
System tray icon makes it convenient to launch the system and displays "clean" status or the number of errors in the last scan. The ability to locate and remove the Invalid class keys plus shell extensions is one of the leading blessings of the program. That is not usual function for the different Registry Cleaners. Class keys plus shell extensions which are not functioning may seriously slow down a computer. RegCure scans to find invalid entries plus delete them.
In purchase to remove the programs on the computer, Windows Installer need to be in a healthy state. If its installation is corrupted we will receive error 1721 in Windows 7, Vista plus XP during the program removal process. Just re-registering its component files would resolve your issue.
So to fix this, we really have to be capable to make all the registry files non-corrupted again. This can dramatically accelerate the loading time of the computer plus allows we to a big amount of elements on it again. And fixing these files couldn't be easier - you simply should employ a tool called a system mechanic.
Although I always employ the most recent variation of browser, often different extensions plus plugins become the cause of mistakes with my browser and the system. The same is the story with my browser which was crashing frequently perhaps due to the Flash player error.
By restoring the state of your program to an earlier date, error 1721 might not appear inside Windows 7, Vista and XP. There is a tool called System Restore which we have to employ in this procedure.
What I would recommend is to look on your for registry cleaners. You are able to do this with a Google search. If you find products, look for ratings plus testimonials regarding the product. Next you can see how others like the product, plus how perfectly it functions.