DOCSLIB.ORG

On the (Non)Universality of the One-Time Pad

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
On the (Non)Universality of the One-Time Pad On the (non)Universality of the One-Time Pad Yevgeniy Dodis Joel Spencer Department of Computer Science Department of Computer Science New York University New York University Email: [email protected] Email: [email protected] Abstract 1 Imperfect Random Sources Randomization is vital in cryptography: secret keys Randomization has proved to be extremely useful and should be randomly generated and most cryptographic fundamental in many areas of computer science, such as primitives (e.g., encryption) must be probabilistic. As a approximation algorithms, counting problems, distributed common abstraction, it is assumed that there is a source of computing, primality testing, as well as cryptographic pro- truly random bits available to all the participants of the sys- tocols (which is the topic of this paper). The common ab- tem. While convenient, this assumption is often highly un- straction used to introduce randomness into computation realistic, and cryptographic systems have to be built based is that the underlying algorithm has access to a stream of on imperfect sources of randomness. Remarkably, this fun- completely unbiased and independent random bits. This ab- damental problem has received little or no attention so far, straction allows one to use randomness in a clean way, sep- despite the fact that a related question of simulating prob- arating out the issue of actually generating such “strong” abilistic (BPP) algorithms with imperfect random sources random bits. Unfortunately, in reality we do not have has a long and rich history. sources that emit perfectly uniform and independent ran- In this work we initiate the quantitative study concerning dom bits. However, there are many sources whose outputs feasibility of building secure cryptographic primitives us- (which need not be bits) are believed to be “somewhat ran- ing imperfect random sources. Specifically, we concentrate dom”. Such sources are generally called imperfect random on symmetric-key encryption and message authentication, sources. We remark that the “imperfectness” of the source where the shared secret key comes from an imperfect ran- does not only come from the fact that it does not generate dom source instead of being assumed truly random. In each uniform random bits, but also because the exact source dis- case, we compare the class of “cryptographic” sources for tribution is usually unknown; instead, only some property the task at hand with the classes of “extractable” and “sim- the distribution is known (like no string is excessively likely, ulatable” sources, where: (1) “cryptographic” refers to etc.), and our proposed usage of a given source should work sources for which the corresponding symmetric-key prim- for any distribution satisfying this property. Thus, “imper- itive can be build; (2) “extractable” refers to a very narrow fect source” literally means “an unknown source from a class of sources from which one can extract nearly perfect given family of probability distributions”. randomness; and (3) “simulatable” refers to a very general A large amount of research has been devoted to filling class of weak random sources which are known to suffice in the gap between such realistic imperfect sources and the for BPP simulation. For both encryption and authentica- ideal sources of randomness that are actually used in de- tion, we show that the corresponding cryptographic sources signing various algorithms and protocols. As we will argue lie strictly in between extractable and simulatable sources, below, the current body of knowledge nevertheless leaves which implies that “cryptographic usage” of randomness is a large gap in understanding the usefulness of imperfect more demanding than the corresponding “algorithmic us- sources for various cryptographic purposes. Indeed, we age”, but still does not require perfect randomness. Inter- can roughly separate the following two major questions that estingly, cryptographic sources for encryption and authen- have been addressed so far in studying imperfect random tication are also quite different from each other, which sug- sources, none of which directly dealing with cryptography: gests that there might not be an elegant way to describe im- perfect sources sufficient for “general cryptographic use”. ¯ Simulation: can we efficiently simulate a probabilis- We believe that our initial investigation in this new area will tic (BPP) algorithm with a given source? inspire a lot of further research. ¯ Extraction: can we extract almost perfect random- ness from a given source? The first question addresses the problem if a given source fixing sources, and already mentioned weak sources (the lat- is acceptable for universal probabilistic computation of ter being significantly more general than the former two). decision or optimization problems (i.e., problems with a STREAMING SOURCES. Like the ideal source, a stream- unique “correct” output which are potentially solved more ing source produces a stream of bits incrementally over efficiently using randomization). The second question goes time, but these bits are not necessarily unbiased or inde- for a conceptually cleaner approach in trying to provide — pendent (exact details depend on the streaming source con- when possible – a “compiler” for a given imperfect source. sidered). The first works [34, 12, 5] considered stream- The complier first extracts almost perfect randomness from ing sources which generated highly independent (but pos- the source, which can then be used for any application orig- sibly biased) random bits. As a result, elegant techniques inally designed to work with ideal random bits. Clearly, were developed to extract many ideal random bits from extraction from a given source is a very desirable prop- such highly “regular” sources. Unfortunately, once the erty to have, since it solves a much broader problem that strong independence requirement was relaxed, many im- BPP simulation. For example, “extractable” sources can be possibility results were obtained. The first quite striking used in any cryptographic application (like secure encryp- negative result was obtained by S´antha and Vazirani [23], tion), but not every “simulatable” source can [19] (see be- who demonstrated that not even a single almost random bit low). Unfortunately, as shown below, the set of extractable can be extracted if every bit of the source can be slightly sources is also dramatically smaller than the set of simulat- biased and depend on all the previous bits. Lichtenstein et able sources. al. [18] showed a mix of positive and (mainly) negative re- SIMULATABLE SOURCES. It turns out that the class of sults when few bits of the source could be arbitrarily biased simulatable sources is extremely large. In particular, more while the rest were truly random. Dodis [10] showed even and more imperfect (so called “weak”) random sources have more negative results for the common generalization of the been shown to be simulatable [32, 30, 8, 9, 35, 2], cul- above two sources. minating in using extremely weak sources [2]. The only thing guaranteed about a weak source is that no particular BIT-FIXING SOURCES. A bit-fixing source produces (at string has a very high probability of occurring. This is char- once) a string of Æ bits, some of which (say, ) are adver- ´Æ µ sarially fixed, but the other are truly random. acterized by a parameter (called the min-entropy of the source) by saying that no string (of some given length) oc- The goal of extraction for such sources is to design a func- tion (called a resilient function) whose output is “close” to curs with probability more than ¾ (for any distribution of the source). The optimal result of [2] then says that BPP random no matter which input bits are fixed. It turns out that there is a huge difference depending on whether the simulation is possible for any Æ -bit weak source of min- ­ “fixed” bits get set before or after the random bits are cho- ­ ¼ entropy at least Æ , for some (arbitrarily small) . Interestingly, we will see that weak sources are typically sen. In the first scenario (studied by [31, 7, 3, 13, 17, 11]), far too general for any randomness extraction (e.g., none of quite positive and by now nearly optimal results are known the sources [32, 30, 8, 9, 35, 2] is extractable). Instead, the for extracting many bits (one perfect bit is trivially ex- works above take advantage of the fact that even though it tracted by the parity function). In particular, close to is impossible to generate almost random bits from the cor- nearly perfect bits can be extracted in this setting [11]. In responding weak sources, it is possible to generate random the second scenario ( fixed bits are set after the ran- strings, a majority of which avoid falling into the negligi- dom bits), even one bit is hard to extract: the optimal ¾ Æ ÐÓ Æ µ bly small set of “bad” strings. Running the given algorithm for this task lies somewhere between ª´ [1] and ´Æ ÐÓ Æ µ many times on varioussuch pseudorandomstrings and com- Ç [16]. puting some statistics, a correct answer is given with high WEAK SOURCES. Originated by Chor and Goldreich [8], probability. much subsequent research has been dedicated to various Unfortunately, most of the above methods are not ap- flavors of the so called weak random sources. Recall, a plicable for cryptographic use, where the randomness is fixed distribution has min-entropy if no element can occur needed by the application itself, and not mainly for the pur- with probability more that ¾ . Generally, a min-entropy poses of efficiency. Indeed, McInnes and Pinkas [19] have of a probability distribution is considered the right measure shown that none of the simulatable sources above can be for the amount of “randomness” it contains. An imperfect used to securely encrypt even a single bit! (See Section 2). source has min-entropy if all of its distributions have min- EXTRACTION FROM IMPERFECT SOURCES. As we will entropy , even though not all such distributions might be- see, extraction is much harder to achieve than simulation, longto the source.
Load more

Recommended publications
  • Topic 3: One-Time Pad and Perfect Secrecy
    Cryptography CS 555 Topic 3: One-time Pad and Perfect Secrecy CS555 Spring 2012/Topic 3 1 Outline and Readings • Outline • One-time pad • Perfect secrecy • Limitation of perfect secrecy • Usages of one-time pad • Readings: • Katz and Lindell: Chapter 2 CS555 Spring 2012/Topic 3 2 One-Time Pad • Fix the vulnerability of the Vigenere cipher by using very long keys • Key is a random string that is at least as long as the plaintext • Encryption is similar to shift cipher • Invented by Vernam in the 1920s CS555 Spring 2012/Topic 3 3 One-Time Pad Let Zm ={0,1,…,m-1} be the alphabet. Plaintext space = Ciphtertext space = Key space = n (Zm) The key is chosen uniformly randomly Plaintext X = (x1 x2 … xn) Key K = (k1 k2 … kn) Ciphertext Y = (y1 y2 … yn) ek(X) = (x1+k1 x2+k2 … xn+kn) mod m dk(Y) = (y1-k1 y2-k2 … yn-kn) mod m CS555 Spring 2012/Topic 3 4 The Binary Version of One-Time Pad Plaintext space = Ciphtertext space = Keyspace = {0,1}n Key is chosen randomly For example: • Plaintext is 11011011 • Key is 01101001 • Then ciphertext is 10110010 CS555 Spring 2012/Topic 3 5 Bit Operators • Bit AND 0 0 = 0 0 1 = 0 1 0 = 0 1 1 = 1 • Bit OR 0 0 = 0 0 1 = 1 1 0 = 1 1 1 = 1 • Addition mod 2 (also known as Bit XOR) 0 0 = 0 0 1 = 1 1 0 = 1 1 1 = 0 • Can we use operators other than Bit XOR for binary version of One-Time Pad? CS555 Spring 2012/Topic 3 6 How Good is One-Time Pad? • Intuitively, it is secure … – The key is random, so the ciphertext is completely random • How to formalize the confidentiality requirement? – Want to say “certain thing” is not learnable by the adversary (who sees the ciphertext).
    [Show full text]
  • Applications of SKREM-Like Symmetric Key Ciphers
    Applications of SKREM-like symmetric key ciphers Mircea-Adrian Digulescu1;2 February 2021 1Individual Researcher, Worldwide 2Formerly: Department of Computer Science, Faculty of Mathematics and Computer Science, University of Bucharest, Romania [email protected], [email protected], [email protected] Abstract In a prior paper we introduced a new symmetric key encryption scheme called Short Key Random Encryption Machine (SKREM), for which we claimed excellent security guarantees. In this paper we present and briey discuss some of its applications outside conventional data encryption. These are Secure Coin Flipping, Cryptographic Hashing, Zero-Leaked-Knowledge Authentication and Autho- rization and a Digital Signature scheme which can be employed on a block-chain. We also briey recap SKREM-like ciphers and the assumptions on which their security are based. The above appli- cations are novel because they do not involve public key cryptography. Furthermore, the security of SKREM-like ciphers is not based on hardness of some algebraic operations, thus not opening them up to specic quantum computing attacks. Keywords: Symmetric Key Encryption, Provable Security, One Time Pad, Zero Knowledge, Cryptographic Commit Protocol, Secure Coin Flipping, Authentication, Authorization, Cryptographic Hash, Digital Signature, Chaos Machine 1 Introduction So far, most encryption schemes able to serve Secure Coin Flipping, Zero-Knowledge Authentication and Digital Signatures, have relied on public key cryptography, which in turn relies on the hardness of prime factorization or some algebraic operation in general. Prime Factorization, in turn, has been shown to be vulnerable to attacks by a quantum computer (see [1]). In [2] we introduced a novel symmetric key encryption scheme, which does not rely on hardness of algebraic operations for its security guarantees.
    [Show full text]
  • NIST SP 800-56: Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography (Superseded)
    ARCHIVED PUBLICATION The attached publication, NIST Special Publication 800-56 (dated July 2005), has been superseded and is provided here only for historical purposes. For the most current revision of this publication, see: http://csrc.nist.gov/publications/PubsSPs.html#800-56A. NIST Special Publication 800-56 Recommendation for Pair-Wise July 2005 Key Establishment Schemes Using Discrete Logarithm Cryptography Elaine Barker, Don Johnson, and Miles Smid C O M P U T E R S E C U R I T Y NIST SP 800-56: Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography DRAFT July 2005 DRAFT Abstract This Recommendation specifies key establishment schemes using discrete logarithm cryptography, based on standards developed by the Accredited Standards Committee (ASC) X9, Inc.: ANS X9.42 (Agreement of Symmetric Keys Using Discrete Logarithm Cryptography) and ANS X9.63 (Key Agreement and Key Transport Using Elliptic Curve Cryptography). Worked examples are provided in Appendix D. KEY WORDS: assurances; Diffie-Hellman; elliptic curve cryptography; finite field cryptography; key agreement; key confirmation; key derivation; key establishment; key management; MQV. 2 NIST SP 800-56: Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography DRAFT July 2005 DRAFT Acknowledgements The National Institute of Standards and Technology (NIST) gratefully acknowledges and appreciates contributions by Rich Davis, Mike Hopper and Laurie Law from the National Security Agency concerning the many security
    [Show full text]
  • Public Key Infrastructure (PKI)
    Public Key Infrastructure Public Key Infrastructure (PKI) Neil F. Johnson [email protected] http://ise.gmu.edu/~csis Assumptions • Understanding of – Fundamentals of Public Key Cryptosystems – Hash codes for message digests and integrity check – Digital Signatures Copyright 1999, Neil F. Johnson 1 Public Key Infrastructure Overview • Public Key Cryptosystems – Quick review – Cryptography – Digital Signatures – Key Management Issues • Certificates – Certificates Information – Certificate Authority – Track Issuing a Certificate • Putting it all together – PKI applications – Pretty Good Privacy (PGP) – Privacy Enhanced Mail (PEM) Public Key Cryptosystems – Quick Review • Key distribution problem of secret key systems – You must share the secret key with another party before you can initiate communication – If you want to communicate with n parties, you require n different keys • Public Key cryptosystems solve the key distribution problem in secret key systems (provided a reliable channel for communication of public keys can be implemented) • Security is based on the unfeasibility of computing B’s private key given the knowledge of – B’s public key, – chosen plaintext, and – maybe chosen ciphertext Copyright 1999, Neil F. Johnson 2 Public Key Infrastructure Key Distribution (n)(n-1) 2 Bob Bob Alice 1 Alice 2 Chris Chris 7 5 8 9 Ellie 3 Ellie 6 David 4 David Secret Key Distribution Directory of Public Keys (certificates) Public Key Cryptosystem INSECURE CHANNEL Plaintext Ciphertext Plaintext Encryption Decryption Algorithm Algorithm Bob’s PUBLIC
    [Show full text]
  • Introduction, Overview, One Time Pad
    University of Illinois, Urbana Champaign LECTURE CS 598DK Special Topics in Cryptography Instructor: Dakshita Khurana Scribe: Joshua Reynolds, Amit Agarwal Date: August 28, 2019 1 Introduction, Overview, One Time Pad 1.1 Introduction This introductory lecture introduces some fundamental goals of cryptography and defines the basic requirement for a useful private key (symmetric) encryption scheme. A basic problem in Cryptography is that of encryption. The encryption problem is that two parties wish to communicate a message without an eavesdropper being able to learn their secret, or even any information about that secret. This problem can be solved with private key (symmetric) encryption under the assumption that both parties already have a shared secret key. This problem can also be solved with public key (asymmetric) key encryption under various other assumptions. These primitives are among the building blocks of more complicated cryptography sys- tems and a useful medium to explore the assumptions made in cryptographic systems. Encryption, in particular, is important because it allows us to communicate secrets safely through an untrusted medium like the Internet. Focusing first on private key encryption, we define the property of correctness. The second necessary property of encryption is security and is covered in part 2 of these lecture notes. 1.2 Notation This set of scribe notes will use the following notation and definitions: • A set will be denoted by a capital letter { M is the set of all possible messages { K is the set of all possible keys { C is the set of all possible ciphertexts • Set subtraction will use the /operator and jSj means the cardinality of set S • An item from a set will be denoted by a lower case letter { m is a message in plaintext (not encrypted) { ct is a ciphertext (encrypted message) { sk is a secret key used as an input in symmetric encryption and decryption • A statistical method of sampling from a set will be denoted with an arrow combined with a description of how the selection is done.
    [Show full text]
  • Solutions Problem 1. the Ipsec Architecture Documents States That
    Homework 5 - Solutions Problem 1. The IPSec architecture documents states that when two transport mode SA are bundled to allow both AH and ESP protocols on the same end-to-end flow, only one ordering of security protocols seems appropriate: performing the ESP protocol before performing the AH protocol. Why is this approach recommended rather than authentication before encryption? Solution This order of processing facilitates rapid detection and rejection of replayed or bogus packets by the receiver, prior to decrypting the packet, hence potentially reducing the impact of denial of service attacks. It also allows for the possibility of parallel processing of packets at the receiver, i.e., decryption can take place in parallel with authentication. Problem 2. Consider the following threats to web security and describe how each is countered by a particular feature of IPSec. a. Brute force cryptoanalitic attack. An exhaustive search of the key space for a conventional encryption algorithm. b. Known plaintext dictionary. Many messages will have predictable plaintext such as HTTP DET command. An attacker can construct a dictionary containing every possible encryption of the known plaintext message. When an encrypted message is intercepted, the attacker takes the portion containing the encrypted known plaintext and looks up the ciphertext in the dictionary. The ciphertext should match against an entry that was encrypted with the same secret key. This attack is especially effective against small key sizes (e.g. 40-bit keys). c. Replay attack. Earlier SSL handshake messages are replayed. d. Man in the middle. An attacker interposes during key exchange, acting as the client to the server and a server to the client.
    [Show full text]
  • Analysing and Patching SPEKE in ISO/IEC
    1 Analysing and Patching SPEKE in ISO/IEC Feng Hao, Roberto Metere, Siamak F. Shahandashti and Changyu Dong Abstract—Simple Password Exponential Key Exchange reported. Over the years, SPEKE has been used in several (SPEKE) is a well-known Password Authenticated Key Ex- commercial applications: for example, the secure messaging change (PAKE) protocol that has been used in Blackberry on Blackberry phones [11] and Entrust’s TruePass end-to- phones for secure messaging and Entrust’s TruePass end-to- end web products. It has also been included into international end web products [16]. SPEKE has also been included into standards such as ISO/IEC 11770-4 and IEEE P1363.2. In the international standards such as IEEE P1363.2 [22] and this paper, we analyse the SPEKE protocol as specified in the ISO/IEC 11770-4 [24]. ISO/IEC and IEEE standards. We identify that the protocol is Given the wide usage of SPEKE in practical applications vulnerable to two new attacks: an impersonation attack that and its inclusion in standards, we believe a thorough allows an attacker to impersonate a user without knowing the password by launching two parallel sessions with the victim, analysis of SPEKE is both necessary and important. In and a key-malleability attack that allows a man-in-the-middle this paper, we revisit SPEKE and its variants specified in (MITM) to manipulate the session key without being detected the original paper [25], the IEEE 1363.2 [22] and ISO/IEC by the end users. Both attacks have been acknowledged by 11770-4 [23] standards.
    [Show full text]
  • Why Passwords Stink White Paper | Why Passwords Stink
    WHITE PAPER WHY PASSWORDS STINK WHITE PAPER | WHY PASSWORDS STINK 01 INTRODUCTION 02 PASSWORDS ARE FUNDAMENTALLY INSECURE 03 THE PROBLEM WITH PASSWORDS IS THAT THEY CONTENTS ARE “SHARED SECRETS” 04 CURRENT ALTERNATIVES AREN’T THE ANSWER 05 A SOLUTION TO THE PASSWORD ISSUE 06 INTRODUCING BEYOND IDENTITY 07 CONCLUSION 02 WHITE PAPER | WHY PASSWORDS STINK There are hundreds of billions of passwords in the world today, with more being created every day. In fact, the average business user maintains an astounding average of 191 passwords.1 Unfortunately, these passwords represent a fundamentally weak link in most organizations because INTRODUCTION they will always be insecure. This white paper examines why that is, investigates some alternative solutions, and introduces a new method of authentication using asymmetric keys and certificates to eliminate passwords altogether. 01 1 https://www.securitymagazine.com/articles/88475-average-business-user-has-191-passwords 03 WHITE PAPER | WHY PASSWORDS STINK Let’s face it: Passwords stink! For employees and customers, they cause friction and frustration when logging in – Who can remember the 16-character combination of letters, symbols, and digits that are indicative of strong passwords, much less come up with them in the first place? When PASSWORDS ARE a password gets lost or stolen (and they invariably do), it places a burden on the help desk. In fact, 20-50% of help FUNDAMENTALLY desk calls are for password resets, with the average call costing the organization $70.2 INSECURE For CISOs, passwords represent corporate assets that can be targeted by bad actors. And that’s a problem because they often transit networks in the clear, are stored in databases that can be and often are hacked, are shared 02 among colleagues, and are reused across multiple apps – making them easy targets for malware, phishing attacks, and other credential-stealing schemes.
    [Show full text]
  • TCP/IP Network Security
    An Intro to Network Crypto Jim Binkley- [email protected] 1 Crypto outline ◆ overview ◆ symmetric crypto (DES ... encryption) ◆ hash/MAC/message digest algorithms ◆ asymmetric crypto (public key technology) ◆ DH - how to start a secure connection ◆ KDC - a little bit on shared secret servers ◆ signatures - authentication with asymmetric keys ◆ certificates - signed public keys ◆ a little bit on authentication 2 overview ◆ there are MANY crypto algorithms and MANY academic network secure protocols ◆ how they are used in network protocols is another matter ◆ traditional IETF RFC said under security considerations (at end of doc) – “not considered here” (another F. Flub) ◆ new IETF POV: must consider here 3 symmetric encryption ◆ both sides know OUT OF BAND shared secret (password, bit string) ◆ encrypt(key, plaintext) -> cybercrud(encrypted) ◆ decrypt(key, cybercrud) -> plaintext ◆ encode/decode use same key (symmetric) – shared secret on both sides ◆ algorithms include: DES, 3DES, IDEA(128), BLOWFISH, SKIPJACK, new AES ◆ ssh uses 128 bit keyed IDEA ◆ DES key 56 bits - 0xdeadbeefdeadbeef 4 DES-CBC ◆ Cipher Block Chaining Mode ◆ DES processes one 64 bit block of data at a time (key is 64 bits (8 bits not important)) ◆ CBC is used so that e.g., two 64 bit blocks in a row that are the same, do NOT produce two 64 encrypted blocks that are the same ◆ C(n) = Ek [C(n-1) xor Plaintext(n)] ◆ requires known IV or initialization vector 5 pros/cons ◆ pros – faster than asymmetric ◆ cons – shared secrets do not scale in general to many users » more people
    [Show full text]
  • Walking the Bifrost: an Operator's Guide to Heimdal & Kerberos on Macos
    Walking the Bifrost: An Operator's Guide to Heimdal & Kerberos on macOS Cody Thomas Objective By The Sea 3.0 March 2020 WHO AM I? Cody Thomas - @its_a_feature_ ● Operator / Instructor at SpecterOps ● Open Source Developer ○ Apfell – Red Team C2 Framework ○ Bifrost – Kerberos Manipulation ○ Orchard – Open Directory Access ○ GitHub: https://github.com/its-a-feature OVERVIEW ● Brief intro to Kerberos ○ What is it / How does it work / Why do we care? ● Attacking Active Directory Kerberos from macOS ○ Credential Storage / Theft ○ Common Attacks ● Other Kerberos details on macOS ○ LKDC KERBEROS INTRODUCTION A brief overview KERBEROS 101 ● What is Kerberos? ○ Authentication mechanism invented by MIT in 1980s ○ Designed for use on insecure networks ○ Uses math and cryptography to provide strong guarantees ○ Based on a client/server model - stateless ○ Uses ASN.1/DER encoding of data ○ Scoped to ‘realms’ of authentication ● Many implementations ○ Traditional MIT (with plugins) ○ Windows ○ macOS KERBEROS 101 – AUTH STEPS 1. Client and Key Distribution Center (KDC) have shared secret ○ Think of the KDC like an all-knowing PKI management server 2. Client makes a request to the Authentication Server (AS) to be authenticated with the shared secret – i.e. an AS-REQ ○ AS forwards request to the KDC, typically these are the same machine 3. AS responds with a ticket to the krbtgt SPN and encrypts a portion with the krbtgt hash. This ticket is called a Ticket Granting Ticket (TGT). This is an AS-REP. ○ The TGT proves you are who you say you are to the KDC because of the encrypted portion ○ Think of this like a new username/password combination KERBEROS 101 – AUTH STEPS 4.
    [Show full text]
  • Security Policy Trapeze Networks
    MX-200R-GS/MX-216R-GS Mobility Exchange WLAN Controllers Security Policy Trapeze Networks August 14, 2009 Copyright Trapeze Networks 2007. May be reproduced only in its original entirety [without revision]. Security Policy TABLE OF CONTENTS 1. MODULE OVERVIEW .........................................................................................................................................3 2. SECURITY LEVEL................................................................................................................................................4 3. MODES OF OPERATION.....................................................................................................................................5 4. PORTS AND INTERFACES .................................................................................................................................5 5. IDENTIFICATION AND AUTHENTICATION POLICY................................................................................6 6. ACCESS CONTROL POLICY..............................................................................................................................7 ROLES AND SERVICES................................................................................................................................................7 DEFINITION OF CRITICAL SECURITY PARAMETERS (CSPS)........................................................................................7 DEFINITION OF CSPS MODES OF ACCESS ..................................................................................................................8
    [Show full text]
  • Security Overview: Key Exchange Protocols, Message
    Security and the Internet Original key design goals of Internet protocols: • resiliency Computer Networks • availability • scalability Security has not been a priority until mid 1990s Designed for simplicity: “on”-by-default Lecture 14: Unfortunately, readily available zombie machines Network Security and Attacks look like normal traffic Cryptographic Algorithms Internet’s federated operation obstructs cooperation for diagnosis/mitigation [after Rexford] Security Attacks Security Requirements Cast of characters: Alice, Bob, and Trudy, three well- Attack against content: known characters in network security world Bob and Alice want to communicate “securely” Data integrity: sender and receiver(s) want to ensure that data is not altered (in transit, or afterwards) or if Trudy (intruder) may intercept, delete, and/or add altered, detectable messages Alice data, control Bob Confidentiality/secrecy: only parties involved, the channel messages sender and the intended receiver(s) should know of secure secure data data (the content of) the transaction sender receiver Trudy Security Requirements Security Requirements Attack against content: Attack against infrastructure: Authentication: sender, receiver(s) want to Access and availability: services must be accessible confirm each other’s identity and available to (authorized) users • compare: authorization (what’s the difference between • destroy hardware (cutting fiber) or software authentication and authorization?) • modify software in a subtle way Non-repudiation: involved parties cannot deny • corrupt
    [Show full text]