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Determining Key Size Range for Scalable Ciphers

Ibrahim, Subariah and Maarof, Mohd Aizaini (2006) Determining Key Size Range for Scalable Ciphers. WSEAS Transactions on Computers, 5 (1). pp. 97-104.

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Key is an important element in a cryptographic algorithm since it is one of the parameters that determine the security level of the algorithm. The larger the key size, the better security it can provide. Debates on key sizes were discussed in many literature and documents of software vendors that provide cryptographic solutions. Since NIST call for a new symmetric cipher to replace DES in 1997, most ciphers are designed with scalable parameters such as key size and block size. We call these ciphers as scalable ciphers. Most scalable ciphers were designed to have the same key sizes as required by NIST for AES which are 128, 192 and 256 bits. Variable key sizes are required so that security can be increased when needed. However, there is no formal derivation to justify the range of key sizes as specified in AES. The aim of this paper is to determine the key size range for scalable block ciphers. We employed Lenstra’s and Blaze et al.’s recommendations for adequate key size and applied them to Lenstra’s model with some enhancements. Our first proposed model includes a lifespan of information to be encrypted. We also proposed a second model which takes quantum computing into consideration. The key size computation using the first model shows that AES key sizes are adequate for various lifespan of information. However our second model shows that AES key sizes are not adequate to protect very long term information. From these models we then define the key size range for scalable block ciphers.

Item Type:Article
Subjects:Q Science > QA Mathematics > QA75 Electronic computers. Computer science
Divisions:Computer Science and Information System (Formerly known)
ID Code:3254
Deposited By: Subariah Ibrahim
Deposited On:11 Jun 2007 09:02
Last Modified:11 Jun 2007 09:02

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