Generic Internal State Recovery on Strengthened HMAC: n-bit Secure HMAC Requires Key in All Blocks
Date of Issue2016-01-01
Lee Kong Chian School of Medicine
HMAC is the most widely used hash based MAC scheme. Recently, several generic attacks have been presented against HMAC with a complexity between 2n/2 and 2n, where n is the output size of an underlying hash function. In this paper, we investigate the security of strengthened HMAC instantiated with a Merkle-Damgård hash function in which the key is used to process underlying compression functions. With such a modification, the attacker is unable to precompute the property of the compression function offline, and thus previous generic attacks are prevented. In this paper, we show that keying the compression function in all blocks is necessary to prevent a generic internal state recovery attack with a complexity less than 2n. In other words, only with a single keyless compression function, the internal state is recovered faster than 2n. To validate the claim, we present a generic attack against the strengthened HMAC instantiated with a Merkle-Damgård hash function in which only one block is keyless, thus pre-computable offline. Our attack uses the previous generic attack by Naito et al. as a base. We improve it so that the attack can be applied only with a single keyless compression function while the attack complexity remains unchanged from the previous work.
Internal state recovery
Internal state recovery
IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences
© 2016 Institute of Electronics, Information and Communication Engineers. This paper was published in IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences and is made available as an electronic reprint (preprint) with permission of Institute of Electronics, Information and Communication Engineers. The published version is available at: [http://doi.org/10.1587/transfun.E99.A.22]. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.