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Topic: Collision attack

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Preimage attack

MD5

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	Cryptography Research - Hash Collision Q&A
		In contrast, a collision attack finds two messages with the same hash, but the attacker can't pick what the hash will be.
		The attacks announced at CRYPTO 2004 are collision attacks, not preimage attacks.
		For example, a devastating attack would be one that enabled adversaries to obtain a legitimate server certificate with a collision to one containing a wildcard for the domain name and an expiration date far in the future.
	www.cryptography.com /cnews/hash.html (1054 words)

	Cryptanalysis: Collision attack in Hashing : Palisade
		In a preimage attack, an attacker tries to guess the input message from which a hash function produces a particular output.
		In a collision attack an attacker finds two messages with the same hashed output and sends the incorrect one to the receiver.
		According to the research carried out by these scientists collision attack on SHA-1 requires an estimated work factor of 2(power)69 (approximately 590 billion) hash computations and it is way beyond the capacity of a normal computer.
	palisade.plynt.com /issues/2005Jun/collision-attack (581 words)

	Hash collision - Wikipedia, the free encyclopedia
		In computer science, a hash collision is a situation that occurs when two distinct inputs into a hash function produce identical outputs.
		In certain specialized applications where a relatively small number of possible inputs are all known ahead of time it is possible to construct a perfect hash function which maps all inputs to different outputs.
		The process of finding two arbitrary values whose hashes collide is called a collision attack; the process of finding one arbitrary value whose hash collides with another, given hash is called a preimage attack.
	en.wikipedia.org /wiki/Hash_collision (450 words)

	[No title]
		It is also important to note that the current collision attacks require at least one of the two messages to have a fair amount of structure in the bits of the message.
		In other words, to thwart a hash collision attack in a non- repudiation protocol where a human is using a signed message as authorization, the signer needs to keep a copy of the original message he/she signed.
		For this attack to work, the attacker needs to be able to predict the contents and structure of the certificate before it is issued, including the identity that will be used, the serial number that will be included in the certificate, and the start and stop dates of the validity period for the certificate.
	www.ietf.org /rfc/rfc4270.txt (3344 words)

	The legal and practical implications of recent attacks on 128–bit cryptographic hash functions
		The attacks on the 128–bit hash functions MD4, MD5, RIPEMD and HAVAL–128 presented at Crypto ’2004 [41] have established that it is no longer secure to use any of these four hash functions for various information processing applications where the collision resistance property is relevant.
		Due to the Xioayun attacks it is now possible for both the signer and the verifier of a digitally signed message that relies upon the MD5 hash algorithm to cheat each other and thus obviate the non–repudiation property that has been continually argued by various researchers as being an essential property of digital signature technology.
		The collisions on the MD5 algorithm described in Section 3 do not apply to its usage as HMAC as the properties required from MD5 are different in the HMAC context [27].
	firstmonday.org /issues/issue11_1/gauravaram (7148 words)

	Hash Integrity - monotone documentation
		Collision is the problem the paper is concerned with.
		The fanciful val1 hash presented in the paper does not have such a property — flipping its first bit when all the rest are zero causes no change to any of the 160 output bits — and is completely unsuited for use as a cryptographic hash, regardless of the general shape of its probability distribution.
		The paper also suggests that birthday paradox probability cannot be used to measure the chance of accidental sha1 collision on “real inputs”, because birthday paradox probability assumes a uniformly random sample and “real inputs” are not uniformly random.
	www.venge.net /monotone/docs/Hash-Integrity.html (961 words)

	RSA Security - Hash Function Update Due to Potential Weakness Found in SHA-1
		This attack seems to have uncovered an unexpected weakness in one of the essential properties of SHA-1, a one-way hash function with a 160-bit output.
		For instance, existing signatures are not at risk due to a collision attack nor are the many applications that rely only on the one-way property or the pseudo-randomness of SHA-1.
		Furthermore, any successful attack on SHA-1 based on the new result would still involve a huge amount of computer processing, so this latest research is unlikely to have any significant impact on current applications, though it remains possible that the results could be improved further.
	www.rsasecurity.com /rsalabs/node.asp?id=2834 (1029 words)

	K2Crypt
		This is an attack on the collision resistance property, which is much more efficient (2000 times more efficient, in fact) than birthday attack.
		A collision example on a reduced-round version is also provided, but very little details are given on the attack.
		The complexity of the attack might be reduced, or extensions of the attack might appear that apply to other contexts.
	www.k2crypt.com /sha1.html (1301 words)

	.Net Security Blog : Further Strengthening Hash Algorithms
		MD4 was discovered to have collisions if either the first or last stages of calculation were left out, and eventually collisions were found for the entire algorithm.
		Cryptographic hash algorithms aim to make it as difficult as possible to create a collision, meaning that their goal is to prevent someone who knows a hash value from being able to produce some data that will create the same hash value.
		Basically the goal of someone mounting an aliasing attack is to find some sequence of inputs that when fed to the hashing algorithm will reset the internal state back to the start state.
	blogs.msdn.com /shawnfa/archive/2004/03/05/84799.aspx (823 words)

	Microsoft Combat Flight Simulator 2 (Site not responding. Last check: 2007-11-05)
		In a situation where you can make an overhead attack from behind, but carry out an overhead attack from the front for which there is no justification, maneuvering for the second pass will be comparatively difficult and you may end up in a disadvantageous position.
		When you have been attacked by the enemy plane first, unless the performance of the enemy plane is inferior or the pilot's ability very poor, it is difficult to regain your position in one counter-attack.
		The enemy will break off the attack because his speed is excessive and firing is difficult; as soon as you see him pulling out, turn the tail toward him, and after making a chandelle, maneuver so that you are in pursuit.
	www.microsoft.com /games/combatfs2/articles_tactics_japan.asp (1617 words)

	White Paper 9: Are SHA-1 Devices Still Secure Enough? - Maxim/Dallas
		This white paper discusses that attack and shows that, although the algorithm is slightly less collision-resistant than previously thought, the security of the SHA-1 memory devices from Dallas Semiconductor Maxim is not affected.
		Consequently, the new attack for finding a collision between any two input messages can not be used to find a collision for a given, fixed input message because it requires selecting the input messages carefully.
		A recent attack showed that the SHA-1 algorithm is slightly less collision-resistant than previously thought, but that attack did not affect the security of the SHA-1 memory devices from Dallas Semiconductor/Maxim.
	www.maxim-ic.com /appnotes.cfm/appnote_number/3522 (1322 words)

	BRIKWARS 2005: Chapter 5: Combat
		Attack Mods can sometimes raise or lower an attacker's effective Skill by a large amount, but remember that the possibilities of Critical Successes and Failures mean that the results of a roll are never guaranteed (1.4: Rolling Dice).
		The main effect of this Combined Attack is that the Damage from all participants is added together and applied in a single massive sum, which is handy for punching through otherwise-impregnable armor or for the utter humiliation of weaker targets.
		Any unit capable of making a ranged attack on the target may join in; he does not need to communicate with the other attackers beforehand or to be able to fire at the same part of the target, unless the attack is against a specific Component of a Creation (7.5: Taking Damage: Component Damage).
	www.brikwars.com /rules/2005/5.htm (7822 words)

	IAIK Krypto Group - Meaningful collisions (Site not responding. Last check: 2007-11-05)
		Attacks of type 3 and type 4 have so far not been shown on members of the MD4 family including SHA-1.
		In (here), a method is demonstrated which uses type-1 meaningful collisions for MD5 to replace a key in an X.509 certificate without changing its signature.
		Faster Herding Attacks: Herding attacks (preprint) are a special kind of 2nd preimage attack on all iterated hash functions.
	www.iaik.tu-graz.ac.at /research/krypto/collision/index.php (962 words)

	Storm brewing over SHA-1 as further breaks are found
		The attack, presented last week at the Crypto conference in Santa Barbara, Calif., would allow a forger to create two documents that return the same digital fingerprint, a short sequence of numbers that represent the contents of a much larger document.
		While experts debate whether the attack is practical, the trend seems to indicate that the Secure Hash Algorithm (SHA-1) is succumbing to less processor-intensive breaks, said William E. Burr, manager of the the Security Technology Group at the National Institute of Standards and Technology (NIST).
		The improved attacks on SHA-1 are the latest break against hash algorithms, mathematical techniques of producing digital fingerprints of files that perform a key function in encryption and digital signatures.
	www.securityfocus.com /print/news/11292 (1042 words)

	Cryptographic Hashes
		The difference between a collision attack and either of the two preimage attacks is crucial.
		The term "construction" is used in addition to "attack" because some researchers prefer "construction" for mechanisms that weaken a cryptographic function in a way that does not directly lead to a useful result.
		Collisions for Hash Functions MD4, MD5, HAVAL-128 and RIPEMD by Xiaoyun Wang, Dengguo Feng, Xuejia Lai, and Hongbo Yu, August 2004.
	www.vpnc.org /hash.html (1933 words)

	heise Security - News - SHA-1 hash function under pressure
		The new method is an attack which, for the first time, allows at least a part of the message to be freely selected, for example as straight text.
		Previous approaches, for example the collision attack by Xiaoyun Wang and her team, which attracted considerable attention, were merely able to produce almost completely different hash twins of the same length, both consisting of meaningless gibberish.
		Christian Rechberger, who developed the new attack together with his colleague Christophe De Cannière, explained to heise Security that, in their experiments, up to one quarter of the message could be freely selected.
	www.heise-security.co.uk /news/77244 (445 words)

	.Net Security Blog : The Difference Between the Strong Name Hash and Hash Evidence (Site not responding. Last check: 2007-11-05)
		Collision attack on assembly hash could only apply when using some convoluted techniques like Dan Kaminsky’s trick which is very easy to spot once you are aware of it.
		Last could be thought as indication of memory requirement of their attack, because they increased complexity bounds for the real attack and also they are not mentioning any massive parallel VLSI boards full of FPGA chips (as DES Cracker).
		Of course, hash collision attacks could be made memoryless by using Floyd’s cycle finding algorithms, but that increases computational complexity of the attack...
	blogs.msdn.com /shawnfa/archive/2005/02/28/382027.aspx (1470 words)

	CypheRix (Site not responding. Last check: 2007-11-05)
		Note that in contexts where the diversity of the inputs is known and restricted, hash functions are inherently insecure with regard to property (a) – the one-way property.
		However, the only attack on this cipher that anyone is known to have implemented is a brute force attack, despite its extensive use commercially.
		Thus, a cipher known to have been broken is not necessarily as insecure as a “break” may suggest, primarily because the typical skill requirement and cost of implementing such an attack is high (generally ignored in estimations), whereas a brute force attack is simple.
	www.cypherix.co.za /CypheRix_SHA-1.htm (1066 words)

	RSA Security - SHA1 Collisions can be Found in 2^63 Operations
		Technical Overview: Such attacks first pinpoint a favorable message differential D, such that two messages m and m XOR D have a higher than expected probability of having the same hash value.
		Status of the Attack: Although it is clear that the approach is viable, the improved message modification calculations have not been confirmed by experts.
		Practical Ramifications: This research has ramifications for applications which require collision resistant hash functions: for example digital signatures (see [R] and [K] for a discussion of the ramifications of earlier collision attacks on SHA-1).
	www.rsasecurity.com /rsalabs/node.asp?id=2927 (755 words)

	Financial Cryptography: Collision Search Attacks on SHA1 - the Shandong note
		In particular, our analysis is built upon the original differential attack on SHA0, the near collision attack on SHA0, the multi-block collision techniques, as well as the message modification techniques used in the collision search attack on MD5.
		This should not be interpreted as meaning that the attack does not apply to full SHA-1 just because of that comment about the padding, "Note that padding rules were not applied to the messages." They are simply pointing to a detail of how they present their results.
		For example, if implementing a message id for every possible combinations of messages in the universe would be a perfect collision free hash function; but that is just too linear and predictable, the id can be traced right back to a message, and it’s also impossible to implement considering the size of the table.
	www.financialcryptography.com /mt/archives/000357.html (1829 words)

	CITS - MD5 Collisions
		One of the main workhorses of modern cryptography are collision resistant hash functions.
		Collision resistance means that it is infeasible to find two different inputs M and M' with the same hash H(M)=H(M').
		Due to the hash collision, Caesar's signature for the letter of recommendation is valid for the order, as well.
	www.cits.rub.de /MD5Collisions (977 words)

	Cryptofile - Hash Cracking
		A: Collisions were announced in SHA-1, SHA-0, MD4, MD5, HAVAL-128, and RIPEMD.
		The other collisions were found by the Chinese researcher Xiaoyun Wang with co-authors Dengguo Feng, Xuejia Lai, and Hongbo Yu.
		A:See a nice md5 collision example at www.x-ways.net/md5collision.html.
	cryptofile.com /hash.php (805 words)

	SecuriTeam™ - Multiple Collisions attack on MD5 and other Hashing Algorithms
		The collision allows an attacker to change a very small amount of data in file without changing its signature.
		The presented attack can find many real collisions which are composed of two 1024-bit messages with the original initial value 0 IV of MD5.
		Attack on a reduced version for HAVAL was given by P. Kasselman and W T Penzhorn, which consists of last rounds for HAVAL-128.
	www.securiteam.com /securityreviews/6N00C0KC0Q.html (972 words)

	[No title]
		This would clearly be a valuable, and therefore devastating, attack: the attacker could fool a CA into issuing a certificate for a "good" identity, and that certificate could be used with a "bad" identity as well.
		Using a stronger hash makes the attack that much harder; even if the better hash function doesn't eliminate the attack, it hopefully forces the attacker to need to perform too many attempts to be feasible.
		On the other hand, if a useful attack is described in the next few years, before the PKIX community has a somewhat-unified proposed solution, it will be very destabilizing for the entire notion of third-party trust in Internet protocols.
	www.proper.com /lookit/PreventingIdentityAttacksInPKIX.html (1947 words)

	[No title]
		If we iterate this with 10 successive 1 Meg blocks, then the probability that Semiramis not being detected 10 times in a row is about 0.013, which is certainly small enough that we can claim to have a distinguisher with only 10 MBytes of output (and using far stronger criteria than is normally used).
		This attack can be generalized by defining a "P Collision" as three values (m, n, a, b) such that the three values (P[m][a], P[m][a+24], P[m][a+55]) are a permutation of the three values (P[n][b], P[n][b+24], P[n][b+55]).
		The attack can be executed analogically to the special case although it requires a lot more memory.
	www.casres.com /WhitePaper_2.html (2490 words)

	Using the MD5 collision attack on zip/gzip/bzip2 and Linux package formats
		Such requirement means (using current knowledge of MD5 collisions), that the hash context must be identical from the point of view of whole package as well as the single file inside.
		To be sure, one would have to inspect rpm installer's source code, but we are quite convinced that there is a place to put the colliding block where it would not be checked.
		Using attack like this, the install scriptlet located inside the rpm package would have to read the original rpm's header, but we don't think that would be a problem.
	cryptography.hyperlink.cz /2004/otherformats.html (1195 words)

	[No title] (Site not responding. Last check: 2007-11-05)
		Such signatures are not susceptible to collision attacks because they are not intended to have any non-repudiation or third-party-verification functionality.
		Protocols in the first category are susceptible to attack if the specified function is later found to be too weak for the stated purpose; protocols in the second category can usually avoid such attacks, but at a cost of increased protocol complexity.
		This is not considered to be a useful attack in IKEv1 or IKEv2: the relying party views the attacker as the same entity because the identity is the same in both certificates.
	www.ietf.org /internet-drafts/draft-hoffman-ike-ipsec-hash-use-03.txt (2895 words)

	Joux found a collision for SHA-0 !
		Thursday 12th, August 2004 We are glad to announce that we found a collision for SHA-0.
		The complexity of the attack was about 2^51.
		The three others authors ported and optimized the attack on the TERA NOVA supercomputer, using CAPS Entreprise tools.
	www.mail-archive.com /cryptography@metzdowd.com/msg02554.html (169 words)

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