Jaeheung Lee

Secure deletion for NAND flash file system

In most file systems, if a file is deleted, only the metadata of the file is deleted or modified and the files data is still stored on the physical media. Some users require that deleted files no longer be accessible. This requirement is more important in embedded systems that employ flash memory as a storage medium. In this paper, we have designed a NAND flash file system that has a secure deletion functionality. We modified YAFFS to support secure deletion. Our method uses encryption to delete files and forces all keys of a specific file to be stored in the same block. Therefore, only one erase operation is required to securely delete a file. The proposed method securely deletes not only keys but also all of the metadata of that file. Our simulation results show that the number of block erases due to file creation and file modification is very low and the amortized number of block erases is lower than the simple encryption method. Even though we applied our method only to the YAFFS, our method can be easily applied to other NAND flash file systems.

HORSIC: An efficient one-time signature scheme for wireless sensor networks

One-time signature schemes are promising candidates for broadcast authentication, which is an essential security primitive in wireless sensor networks. This paper proposes HORSIC, an efficient one-time signature scheme for broadcast authentication in wireless sensor networks. Different from previous one-time signature schemes, HORSIC can reduce the public key size and signature size simultaneously at the cost of increased overhead in key generation and signature verification.

An optimal distributed trigger counting algorithm for large-scale networked systems

Distributed trigger counting (DTC) is a problem related to the detection of w triggers with n nodes in large-scale distributed systems that have general characteristics of complex adaptive systems. The triggers come from an external source, and no a priori information about the triggers is given. DTC algorithms can be used for distributed monitoring and global snapshots. When designing an efficient DTC algorithm, the following goals should be considered: minimizing the overall message complexity and distributing the loads for detecting triggers among nodes. In this paper, we propose a randomized algorithm called TreeFill, which satisfies the message complexity of O ( n log ( w / n ) ) with high probability. The maximum number of received messages to detect w triggers in each node is O ( log ( w / n ) ) with high probability. These results satisfy the lower bounds of DTC problems. We prove the upper bounds of TreeFill. The performance of TreeFill is also evaluated by means of an agent-based simulation using NetLogo. The simulation results show that TreeFill uses about 54–69% of the messages used in a previous work called CoinRand. The maximum number of received messages in each node of TreeFill is also smaller than that in the previous work.

Buffer cache level encryption for embedded secure operating system

A cryptographic file system is the representative way of assuring confidentiality of files in operating systems. For secure embedded operating systems, the cryptographic file system could be a practical technique. In general, cryptographic file systems are implemented using a stackable file system or a device driver. These two mechanisms can provide user transparent encryption/decryption of cryptographic file systems. But these mechanisms sometimes encrypt or decrypt data redundantly or unnecessarily. Embedded systems with a low speed CPU and flash storage are more affected by the problems than general systems. We addressed the above mentioned problems by applying an encryption algorithm on buffer caches and enabling one buffer cache to have both encrypted and decrypted data together. Experimental results show that the proposed mechanisms reduce the redundant or unnecessary operations and it can improve the performance of cryptographic file systems.