A New Time-Memory-Resource Trade-Off Method for Password

RecoveryCommunications and Intelligence Information Security

(ICCIIS), 2010 International Conference Authors: Wei Zhang Coll. of Compute., Nanjing Univ. of

Posts & Telecommun., Nanjing, China Mengyuan Zhang ; Yiyang Liu ; Ruchuan Wang

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Password crackThere are two common ways to crack the password if we know the encrypted password:

•Brute-force attack.• Try every passwords until you find the right one.• Time costs may be large.

•Lookup table.• Create a list of passwords and their encrypted results, then

search them.• Crack Fast but need large storage.

•Time-memory tradeoff

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Rainbow table method

• Reduce function : maps hashes to plaintexts.

• Hash chain

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Rainbow table method

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Rainbow table method

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Example: Hash chain

•Give a hash “3626”1. Can not find 3626 in h32. R2(3626) = 363. H(36) = 4202(match)4. Look up the table and find the p1 is 255. H(25) = 20596. R(2059) = 597. H(59) = 3626 The plaintext is 59!!

The rainbow chain with multi-resources

• Dividing a large rainbow table into several small rainbow sub-tables.

• Server-Client mode– Step1: Initialize, ensure each client has corresponding

rainbow tables; – Step2: Start crack password, generate crack task; – Step3: Collect the information of the clients including

specialized resources; – Step4: According to the Step3 results, generate sub-tasks and

dispatch to clients; – Step5: Coordinate the clients, broadcast cracked hash

message to clients to cancel the cracked job; – Step6: Collect the results form the clients, close the clients’

connection, and end the whole crack task. 6

The rainbow chain with multi-resources

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Result

• CPU: Pentium4 CPU 2.93GHz, Memory: 256MB, Hard Disk: 7200, Windows XP Professional SP2

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Summary

• Large storage space and the requirement of cracking time is rainbow table’s bottleneck in single machine.

• Cracking resources extend the two dimensional ( space and time ) exchanging problems of original rainbow chain.

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Reference

• M. E. Hellman, “A Cryptanalytic Time-Memory Trade-Off’, IEEE Transactions on Information Theory, Vol. IT-26, No.4, 1980 ,pp.401-406.

• http://en.wikipedia.org/wiki/Rainbow_table• http://www.rainbowcrack.com

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