## Cryptology ePrint Archive: Report 2019/506

Forward Integrity and Crash Recovery for Secure Logs

Erik-Oliver Blass and Guevara Noubir

Abstract: Logging is a key mechanism in the security of computer systems. Beyond supporting important forward security properties, it is critical that logging withstands both failures and intentional tampering to prevent subtle attacks leaving the system in an inconsistent state with inconclusive evidence. We propose new techniques combining forward integrity with crash recovery for secure data storage. Our main contribution is a new coding scheme resolving unique design constraints such as forward integrity and most importantly a {single-pass, constant number} of operations per encoding. Our idea is to add a new log item by XORing it to forward-securely selected $k$ cells of a table. If up to a certain threshold of cells is modified by the adversary, or lost due to a crash, we still guarantee the recovery of all stored log items. We instantiate our scheme into an abstract data structure which allows to either detect adversarial modifications to log items or treat modifications like data loss in a system crash. The data structure can recover lost log items, thereby effectively reverting adversarial modifications. The key advantage of this setup is its efficiency: we use spectral graph theory techniques to prove that $k$ is {constant} in the number $n$ of all log items ever stored and small in practice, e.g., $k=5$. Moreover, we prove that to cope with up to $\sqrt{n}$ lost log items, storage expansion is asymptotically constant in $n$ and small in practice. For $k=5$, the total size of the table is only $12\%$ more than the simple concatenation of all $n$ items.

Category / Keywords: cryptographic protocols /

Date: received 15 May 2019, last revised 15 May 2019

Contact author: erik-oliver blass at airbus com

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2019/506

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