H. Dobbertin. The status of MD5 after a recent attack. CryptoBytes, 2(2):1,3--6, 1996.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....a CRHF because (1) it seems easier to build an e#cient and secure UOWHF than to build an e#cient and secure CRHF, and (2) in many applications, most importantly for building digital signature schemes, a UOWHF is su#cient. As evidence for claim (1) we point out the recent attacks on MD5 [dBB93, Dob96] We also point out the complexity theoretic result of Simon [Sim98] that shows that there exists an oracle relative to which UOWHFs exist but CRHFs do not. CRHFs can be constructed based on the hardness of specific number theoretic problems, like the discrete logarithm problem [Dam87] Simon s ....

.... it is hard to find di#erent input x # x such that C(x) C(x # ) This assumption seems to be much weaker than assumption that no collisions in C can be found at all (which as an intractability assumption does not even make sense) Indeed, the techniques used to find collisions in MD5 [dBB93, Dob96] do not appear to help in finding second preimages. 9 Note that from a complexity theoretic point of view, second preimage collision resistance is no stronger than the UOW property. Indeed, if HK (x) is a UOWHF, then the function sending (K, x) to (K, HK (x) is second preimage collision ....

H. Dobbertin. The status of MD5 after a recent attack. RSA Laboratories' CryptoBytes, 2(2), 1996. The main result of this paper was announced at the Eurocrypt '96 rump session.

....directly of the node, depending on which API calls are supported. The direct query can be represented compactly and executed efficiently as a single API call, while the other program cannot. There is some evidence that the collision resistance of MD5 may be broken in the foreseeable future [Dobbertin, 1996, Robshaw, 1996] but to my knowledge no evidence that the one way property is in question. 33 Table 2.1: Node API exported to capsule forwarding routines This suggests that the node API is an important research question in itself. In this thesis, I address the question only so far as it ....

H. Dobbertin. The Status of MD5 After a Recent Attack. RSA Laboratories CryptoBytes, 2(2), 1996.

....DES encryptions, 220 RSA signature verifications and 18 RSA signatures, per second. A logarithmic scale is required to illustrate such huge differences. We observe the difference in hash function speeds, where MD5 is twice as fast as SHA 1. However, SHA 1 is considered the more secure of the two [Dob96], due to collisions having been found for the MD5 compression function. 115284 53590 53045 23261 10288 220 18 1 10 100 1000 10000 100000 1000000 MD5 SHA 1 RC6 DES 3DES RSA verify RSA sign Operations second MD5 SHA 1 RC6 DES 3DES RSA verify RSA sign Figure 4 1 Efficiency ....

....as highlighted in Section 4.2. Storage space and message lengths will depend on key sizes, hash sizes, signature and certificate sizes, all of which depend in turn on the algorithms used. Table B.1 shows the algorithms selected. SHA performs slower than MD5 but has been shown to be more secure [Dob96]. RC6 was selected as one of the faster finalist candidate algorithms [Dra00] for the AES standard, and was shown to perform significantly faster than DES in software in Chapter 4. Recently the Rijndael algorithm, which has a similar performance to RC6 in Java, but with a slower key setup time ....

H. Dobbertin. The status of MD5 after a recent attack. RSA Laboratories' CryptoBytes, 2(2):1-6, 1996.

....of terms, used in this paper. 2. Successful attacks on one way hash functions the background Recent advances in cryptography showed ways to attack three widely used one way hash functions MD2 [8] MD4 [9] and MD5 [10] Besides plain message digest calculation with MD2 [11] MD4 [12] and MD5 [13], this also includes e.g. MD4 usage for MACs [14] It turns out that it is beneficial to treat application of cryptographic techniques and e docs as a whole and this is the main motivation behind the paper. The proposed framework takes into account common principles behind attacks on MD2 and M5, ....

....a non finite universal set will be mapped to elements of a finite one, collisions can not be avoided. The problem is to ensure computational infeasibility for such events. Unfortunately, the existence of collision resistant hash functions (in an idealised strict sense) is still an open question [13]. Moreover, if they were provably existing, infeasibility should be assured for practicable implementations. For the time being, probability based attacks could turn out to be feasible. Basically, two conceptually different approaches are possible: fixed date paradox collision and ....

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Dobbertin H., The Status of MD5 After a Recent Attack, CryptoBytes, RSA Labs, Vol. 2, No. 3, 1996, pp 1-6.

....are available. Among them is MD5 [14] which was designed to be a fast hash algorithm. MD5 generates a 128 bit digest for a given input, which should be a dicult size to break. In 1996, however, Hans Dobbertin discovered that a collision could be generated on the MD5 hash in about 10 hours on a PC [3]. A more secure hash is SHA 1, developed by the NSA and NIST [8] SHA 1 takes a string of arbitrary length and produces a 160 bit digest. Since a SHA 1 hash is four bytes longer than an MD5 hash and is cryptographically secure, it is less susceptible to collisions. 6 5 Performance Figure 2: ....

Hans Dobbertin. The status of MD5 after a recent attack. CryptoBytes Vol.2 No.2, Summer, 1996. Available at http://www.rsasecurity.com/rsalabs/cryptobytes/.

....MD5 digest, we use only the 10 least significant bytes. This truncation has the obvious advantage of reducing the size of MACs and it also improves their resilience to certain attacks [22] This is a variant of the secret suffix method [30] which is secure as long as MD5 is collision resistant [22, 8]. Discussion The advantage of MACs over digital signatures is that they can be computed three orders of magnitude faster. For example, a 200MHz Pentium Pro takes 43ms to generate a 1024 bit modulus RSA signature of an MD5 digest and 0.6ms to verify the signature [31] whereas it takes only 10.3s ....

H. Dobbertin. The Status of MD5 After a Recent Attack. RSA Laboratories' CryptoBytes, 2(2), 1996.

....MD5 digest, we use only the 10 least significant bytes. This truncation has the obvious advantage of reducing the size of MACs and it also improves their resilience to certain attacks [27] This is a variant of the secret suffix method [36] which is secure as long as MD5 is collision resistant [27, 8]. The digital signature in a reply message is replaced by a single MAC, which is sufficient because these messages have a single intended recipient. The signatures in all other messages (including client requests but excluding view changes) are replaced by vectors of MACs that we call ....

H. Dobbertin. The Status of MD5 After a Recent Attack. RSA Laboratories' CryptoBytes, 2(2), 1996.

....to a CRHF because (1) it seems easier to build an ecient and secure UOWHF than to build an ecient and secure CRHF, and (2) in many applications, most importantly for building digital signature schemes, a UOWHF is sucient. As evidence for claim (1) we point out the recent attacks on MD5 [dBB93, Dob96] We also point out the complexity theoretic result of Simon [Sim98] that shows that there exists an oracle relative to which UOWHFs exist but CRHFs do not. CRHFs can be constructed based on the hardness of speci c number theoretic problems, like the discrete logarithm problem [Dam87] Simon s ....

.... it is hard to nd di erent input x 0 6= x such that C(x) C(x 0 ) This assumption seems to be much weaker than assumption that no collisions in C can be found at all (which as an intractability assumption does not even make sense) Indeed, the techniques used to nd collisions in MD5 [dBB93, Dob96] do not appear to help in nding second preimages. 9 Note that from a complexity theoretic point of view, second preimage collision resistance is no stronger than the UOW property. Indeed, if HK (x) is a UOWHF, then the function sending (K; x) to (K; HK (x) is second preimage collision ....

H. Dobbertin. The status of MD5 after a recent attack. RSA Laboratories' CryptoBytes, 2(2), 1996. The main result of this paper was announced at the Eurocrypt '96 rump session.

....use of MD5 in particular has been proposed. The design and properties of HMAC are such that Dobbertin s current techniques that might find collisions for either the compression function or the full hash function of MD5 seem to have little immediate impact on the security of HMAC when MD5 is used [10]. 7. Some Alternative Hash Functions As alternative hash functions, SHA 1, RIPEMD 128 and RIPEMD 160 can still be recommended as being secure for any application. While all three hash functions bear similarities to MD4 and MD5 in their design, the techniques of Dobbertin do not readily extend to ....

....25] Collisions have been demonstrated for MD4 [7, 8] MD4 should not be used. This merely restates a recommendation which has been present in the literature for some time, in fact, its use has not been recommended since the introduction of MD5. MD5 Both pseudo collisions [6] and collisions [9, 10] for the compression function of MD5 have been demonstrated, though collisions for the full MD5 have not yet been achieved. Existing signatures formed using MD5 are not at risk and while MD5 is still suitable for a variety of applications (namely those which rely on the one way property of MD5 ....

H. Dobbertin. The Status of MD5 after a Recent Attack. CryptoBytes, 2(2): 1-6, 1996

.... procedures for registration of new documents, for finding a document given its name, 1 For example, because of recent attacks on MD5, RSA Laboratories recommends that in the future MD5 should no longer be implemented in signature schemes, where a collision resistant hash function is required [Dob 96c] for updating a document s location information, and for validating the integrity of a document. Typically, there is a server that resolves or translates a name into location information, for example into a URL or a list of URLs. The name may include other information about the document, ....

....state of the art advances, it is likely that a function that was once securely one way will eventually cease to be so. For example, Dobbertin s recently announced attacks on MD4 and MD5 have considerably reduced the community s confidence in the strength of these two functions [Dob 96a, Dob 96b, Dob 96c] In x5 below we offer a solution to the problem this poses for certain practical systems whose real world security depends on the actual infeasibility of specific computational tasks. We refer the reader to [Pre 93] for a thorough discussion of one way hash functions. 2.3 Theoretical model We ....

H. Dobbertin. The status of MD5 after a recent attack. CrytoBytes, Vol. 2, No. 2 (Summer 1996).

....to a CRHF because (1) it seems easier to build an efficient and secure UOWHF than to build an efficient and secure CRHF, and (2) in many applications, most importantly for building digital signature schemes, a UOWHF is sufficient. As evidence for claim (1) we point out the recent attacks on MD5 [4, 5]. We also point out the complexity theoretic result of Simon [8] that shows that there exists an oracle relative to which UOWHFs exist but CRHFs do not. CRHFs can be constructed based on the hardness of specific numbertheoretic problems, like the discrete logarithm problem [2] Simon s result is ....

.... input (S 0 ; B 0 ) 6= S; B) such that C(S; B) C(S 0 ; B 0 ) This assumption seems to be much weaker than assumption that no collisions in C can be found at all (which as an intractability assumption is not even well defined) Indeed, the techniques used to find collisions in MD5 [4, 5] do not appear to help in finding second preimages. Note that from a complexity theoretic point of view, second preimage collision resistance is no stronger than the UOW property. Indeed, if HK (x) is a UOWHF, then the function sending (K; x) to (K; HK (x) is second preimage collision resistant. ....

H. Dobbertin. The status of MD5 after a recent attack. RSA Laboratories ' CryptoBytes, 2(2), 1996. The main result of this paper was announced at the Eurocrypt '96 rump session.

....MD5 digest, we use only the 10 least significant bytes. This truncation has the obvious advantage of reducing the size of MACs and it also improves their resilience to certain attacks [27] This is a variant of the secret suffix method [36] which is secure as long as MD5 is collision resistant [27, 8]. The digital signature in a reply message is replaced by a single MAC, which is sufficient because these messages have a single intended recipient. The signatures in all other messages (including client requests but excluding view changes) are replaced by vectors of MACs that we call ....

H. Dobbertin. The Status of MD5 After a Recent Attack. RSA Laboratories' CryptoBytes, 2(2), 1996.

....e mail: dobbertin skom.rhein.de March 21, 1997 In [1] it was shown that there are very effective attacks leading to collisions for the hash function MD4 designed by R. Rivest [3] A summary of the status of hash functions of the MD4 family with respect to collision resistence can be found in [2] and [4] However, attacking the one wayness of a hash function is a much more demanding challenge, and in case of success it has much more devastating consequences. No result along this line is known for MD4 and its successors. Therefore it is worth to explore how the recently developed new ....

H. Dobbertin, The status of MD5 after a recent attack, CryptoBytes, The technical newsletter of RSA Laboratories, vol. 2/2, Sommer 1996, pp. 1-6.

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H. Dobbertin. The status of MD5 after a recent attack. CryptoBytes, 2(2):1,3--6, 1996.

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H. Dobbertin. The status of MD5 after a recent attack. CryptoBytes, RSA Laboratories. Vol.2, #2, 1996.

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H. Dobbertin. The Status of MD5 After a Recent Attack. CryptoBytes, 1996.

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