Security Analysis of salt||password Hashes

Gauravaram, Praveen (2012) Security Analysis of salt||password Hashes. In Advanced Computer Science Applications and Technologies (ACSAT), 2012 International Conference on, IEEE, Kuala Lumpur, pp. 25-30.

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Abstract

Protection of passwords used to authenticate computer systems and networks is one of the most important application of cryptographic hash functions. Due to the application of precomputed memory look up attacks such as birthday and dictionary attacks on the hash values of passwords to find passwords, it is usually recommended to apply hash function to the combination of both the salt and password, denoted salt||password, to prevent these attacks. In this paper, we present the first security analysis of salt||password hashing application. We show that when hash functions based on the compression functions with easily found fixed points are used to compute the salt||password hashes, these hashes are susceptible to precomputed offline birthday attacks. For example, this attack is applicable to the salt||password hashes computed using the standard hash functions such as MD5, SHA-1, SHA-256 and SHA-512 that are based on the popular Davies-Meyer compression function. This attack exposes a subtle property of this application that although the provision of salt prevents an attacker from finding passwords, salts prefixed to the passwords do not prevent an attacker from doing a precomputed birthday attack to forge an unknown password. In this forgery attack, we demonstrate the possibility of building multiple passwords for an unknown password for the same hash value and salt. Interestingly, password||salt (i.e. salts suffixed to the passwords) hashes computed using Davies-Meyer hash functions are not susceptible to this attack, showing the first security gap between the prefix-salt and suffix-salt methods of hashing passwords.

Impact and interest:

6 citations in Scopus
1 citations in Web of Science®
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ID Code: 81699
Item Type: Conference Paper
Refereed: Yes
DOI: 10.1109/ACSAT.2012.49
ISBN: 978-1-4673-5832-3
Divisions: Current > Schools > School of Electrical Engineering & Computer Science
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2012 IEEE
Deposited On: 09 Feb 2015 03:25
Last Modified: 13 Feb 2015 04:23

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