Mitigating dictionary attacks on password-protected local storage

Ran Canetti*, Shai Halevi, Michael Steiner

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

24 Scopus citations

Abstract

We address the issue of encrypting data in local storage using a key that is derived from the user's password. The typical solution in use today is to derive the key from the password using a cryptographic hash function. This solution provides relatively weak protection, since an attacker that gets hold of the encrypted data can mount an off-line dictionary attack on the user's password, thereby recovering the key and decrypting the stored data. We propose an approach for limiting off-line dictionary attacks in this setting without relying on secret storage or secure hardware. In our proposal, the process of deriving a key from the password requires the user to solve a puzzle that is presumed to be solvable only by humans (e.g, a CAPTCHA). We describe a simple protocol using this approach: many different puzzles are stored on the disk, the user's password is used to specify which of them need to be solved, and the encryption key is derived from the password and the solutions of the specified puzzles. Completely specifying and analyzing this simple protocol, however, raises a host of modeling and technical issues, such as new properties of humansolvable puzzles and some seemingly hard combinatorial problems. Here we analyze this protocol in some interesting special cases.

Original languageEnglish
Title of host publicationAdvances in Cryptology - CRYPTO 2006 - 26th Annual International Cryptology Conference, Proceedings
PublisherSpringer Verlag
Pages160-179
Number of pages20
ISBN (Print)3540374329, 9783540374329
DOIs
StatePublished - 2006
Externally publishedYes
Event26th Annual International Cryptology Conference, CRYPTO 2006 - Seattle, WA, United States
Duration: 20 Aug 200624 Aug 2006

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume4117 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

Conference26th Annual International Cryptology Conference, CRYPTO 2006
Country/TerritoryUnited States
CitySeattle, WA
Period20/08/0624/08/06

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