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very difficult to determine a password that matches a given hash. However, this presents a problem for many (but not all) challenge-response algorithms, which require both the client and the server to have a shared secret. Since the password itself is not stored, a challenge-response algorithm will usually have to use the hash of the password as the secret instead of the password itself. In this case, an intruder can use the actual hash, rather than the password, which makes the stored hashes just as sensitive as the actual passwords.
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application is vulnerable to a delayed message attack. This attack occurs where an attacker copies a transmission whilst blocking it from reaching the destination, allowing them to replay the captured transmission after a delay of their choosing. This is easily accomplished on wireless channels. The time-based nonce can be used to limit the attacker to resending the message but restricted by an expiry time of perhaps less than one second, likely having no effect upon the application and so mitigating the attack.
36:
325:, the challenge value and the secret may be combined to generate an unpredictable encryption key for the session. This is particularly effective against a man-in-the-middle attack, because the attacker will not be able to derive the session key from the challenge without knowing the secret, and therefore will not be able to decrypt the data stream.
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is controlling access to some resource, and Alice is seeking entry. Bob issues the challenge "52w72y". Alice must respond with the one string of characters which "fits" the challenge Bob issued. The "fit" is determined by an algorithm defined in advance, and known by both Bob and Alice. The correct
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on a password authentication can authenticate themselves by reusing the intercepted password. One solution is to issue multiple passwords, each of them marked with an identifier. The verifier can then present an identifier, and the prover must respond with the correct password for that identifier.
307:
can generate challenges that are highly unlikely to occur more than once. It is sometimes important not to use time-based nonces, as these can weaken servers in different time zones and servers with inaccurate clocks. It can also be important to use time-based nonces and synchronized clocks if the
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TRIAD numeral cipher to authenticate and encrypt some communications. TRIAD includes a list of three-letter challenge codes, which the verifier is supposed to choose randomly from, and random three-letter responses to them. For added security, each set of codes is only valid for a particular time
454:
rather than storing the password itself. During authentication, the system need only verify that the hash of the password entered matches the hash stored in the password database. This makes it more difficult for an intruder to get the passwords, since the password itself is not stored, and it is
184:. In reality, the algorithm would be much more complex. Bob issues a different challenge each time, and thus knowing a previous correct response (even if it is not obfuscated by the means of communication) does not allow an adversary to determine the current correct response.
269:. A hash function can also be applied to a password and a random challenge value to create a response value. Another variation uses a probabilistic model to provide randomized challenges conditioned on model input.
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Such encrypted or hashed exchanges do not directly reveal the password to an eavesdropper. However, they may supply enough information to allow an eavesdropper to deduce what the password is, using a
284:, where a malicious intermediary simply records the exchanged data and retransmits it at a later time to fool one end into thinking it has authenticated a new connection attempt from the other.
156:
Assuming that the passwords are chosen independently, an adversary who intercepts one challenge-response message pair has no clues to help with a different challenge at a different time.
204:. In early CAPTCHAs, the challenge sent to the user was a distorted image of some text, and the user responded by transcribing the text. The distortion was designed to make automated
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a similarly encrypted value which is some predetermined function of the originally offered information, thus proving that it was able to decrypt the challenge. For instance, in
220:, when the user could be sure that the system asking for the password was really the system they were trying to access, and that nobody was likely to be eavesdropping on the
280:. The use of information which is randomly generated on each exchange (and where the response is different from the challenge) guards against the possibility of a
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is a family of protocols in which one party presents a question ("challenge") and another party must provide a valid answer ("response") to be
196:, for example, are meant to allow websites and applications to determine whether an interaction was performed by a genuine user rather than a
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is performed using a challenge-response handshake in both directions; the server ensures that the client knows the secret, and the client
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224:. To address the insecure channel problem, a more sophisticated approach is necessary. Many cryptographic solutions involve
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Challenge-response authentication can help solve the problem of exchanging session keys for encryption. Using a
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ensures that the server knows the secret, which protects against a rogue server impersonating the real server.
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authentication, where the challenge is asking for the password and the valid response is the correct password.
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response might be as simple as "63x83z", with the algorithm changing each character of the challenge using a
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Advances in
Practical Applications of Agents, Multi-Agent Systems, and Social Good. The PAAMS Collection
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as the challenge to ensure that every challenge-response sequence is unique. This protects against
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Ahmed, Ibrahim H.; Hanna, Josiah P.; Fosong, Elliot; Albrecht, Stefano V. (2021).
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Non-cryptographic authentication was generally adequate in the days before the
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Challenge-response protocols are also used in non-cryptographic applications.
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208:(OCR) difficult and prevent a computer program from passing as a human.
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691:. Lecture Notes in Computer Science. Vol. 12946. pp. 14–26.
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Another basic challenge-response technique works as follows.
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is a challenge-response algorithm that avoids this problem.
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To avoid storage of passwords, some operating systems (e.g.
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both the user and the system must verify that they know the
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299:. If it is impractical to implement a true nonce, a strong
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key to transmit some randomly generated information as the
232:(the password), without the secret ever being transmitted
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The simplest example of a challenge-response protocol is
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a kind of challenge-response authentication that blocks
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One way this is done involves using the password as the
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cryptographically secure pseudorandom number generator
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Henk C.A. van
Tilborg; Sushil Jajodia (8 July 2014).
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611:Salted Challenge Response Authentication Mechanism
514:Salted Challenge Response Authentication Mechanism
467:Examples of more sophisticated challenge-response
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782:
261:, while the response is the encrypted integer
329:Simple example mutual authentication sequence
249:, whereupon the other end must return as its
62:introducing citations to additional sources
561:Challenge-handshake authentication protocol
502:, OCRA: OATH Challenge-Response Algorithm (
486:Challenge-Handshake Authentication Protocol
434:This particular example is vulnerable to a
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393:and ensures the server responded correctly
384:and ensures the client responded correctly
287:Authentication protocols usually employ a
666:. Springer Science & Business Media.
663:Encyclopedia of Cryptography and Security
387:Client calculates the expected value of
378:Server calculates the expected value of
257:, the challenge is an encrypted integer
52:Relevant discussion may be found on the
14:
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757:: CS1 maint: archived copy as title (
530:'s challenge-response system based on
343:Client sends a unique challenge value
334:Server sends a unique challenge value
172:period which is ordinarily 24 hours.
606:Password-authenticated key agreement
29:
772:"Challenge-Response Authentication"
478:and key agreement systems (such as
441:
73:"Challenge–response authentication"
24:
25:
807:
566:Challenge–response spam filtering
414:is the client-generated challenge
406:is the server-generated challenge
375:+ secret) and sends to the server
362:+ secret) and sends to the client
188:Other non-cryptographic protocols
131:challenge-response authentication
236:over the communication channel.
45:relies largely or entirely on a
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27:Type of authentication protocol
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1:
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476:Zero-knowledge password proof
206:optical character recognition
163:methods are unavailable, the
480:Secure Remote Password (SRP)
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576:Cryptographic hash function
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305:cryptographic hash function
10:
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621:Distance-bounding protocol
596:Needham–Schroeder protocol
697:10.1007/978-3-030-85739-4
636:Man-in-the-middle attack
601:Wide Mouth Frog protocol
212:Cryptographic techniques
159:For example, when other
796:Computer access control
538:Some people consider a
323:key derivation function
226:two-way authentication;
161:communications security
791:Authentication methods
556:Countersign (military)
430:is the server response
422:is the client response
312:Mutual authentication
222:communication channel
452:hash of the password
58:improve this article
733:www.cag.lcs.mit.edu
591:Otway–Rees protocol
581:Cryptographic nonce
289:cryptographic nonce
739:on 14 October 2004
295:with a subsequent
278:brute-force attack
18:Challenge–response
706:978-3-030-85738-7
673:978-1-4419-5906-5
626:Reflection attack
436:reflection attack
274:dictionary attack
127:computer security
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16:(Redirected from
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735:. Archived from
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56:. Please help
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631:Replay attack
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182:Caesar cipher
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135:authenticated
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114:February 2019
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75: –
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43:This article
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741:. Retrieved
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198:web scraper
785:Categories
743:19 October
647:References
469:algorithms
242:encryption
84:newspapers
715:237611496
516:(SCRAM) (
247:challenge
169:AKAC-1553
167:uses the
153:eavesdrop
149:adversary
54:talk page
753:cite web
641:WebAuthn
586:Kerberos
571:CRAM-MD5
550:See also
544:spambots
500:CRAM-MD5
488:(CHAP) (
463:Examples
255:Kerberos
251:response
218:Internet
194:CAPTCHAs
151:who can
142:password
540:CAPTCHA
371:= hash(
358:= hash(
98:scholar
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397:where
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711:S2CID
471:are:
457:SCRAM
263:N + 1
105:JSTOR
91:books
759:link
745:2022
701:ISBN
668:ISBN
616:SQRL
522:5802
508:6287
494:1994
448:Unix
316:also
303:and
77:news
693:doi
532:RSA
528:ssh
518:RFC
504:RFC
490:RFC
276:or
202:bot
200:or
177:Bob
147:An
125:In
60:by
787::
755:}}
751:{{
731:.
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427:sr
419:cr
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403:sc
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267:N
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
