• Journal of Internet Computing and Services
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• v.21 no.1
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• pp.179-190
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• 2020

In the Unix-like system environment, the GOT overwrite attack is one of the traditional control flow hijacking techniques for exploiting software privileges. Several techniques have been proposed to defend against the GOT overwrite attack, and among them, the Full Relro(Relocation Read only) technique, which blocks GOT overwrites at runtime by arranging the GOT section as read-only in the program startup, has been known as the most effective defense technique. However, it entails loading delay, which limits its application to a program sensitive to startup performance, and it is not currently applied to the library due to problems including a chain loading delay problem caused by nested library dependency. Also, many compilers, including LLVM, do not apply the Full Relro technique by default, so runtime programs are still vulnerable to GOT attacks. In this paper, we propose a GOT protection scheme using the Control Flow Integrity(CFI) technique, which is currently recognized as the most suitable technique for defense against code reuse attacks. We implemented this scheme based on LLVM and applied it to the binutils-gdb program group to evaluate security, performance and compatibility. The GOT protection scheme with CFI is difficult to bypass, fast, and compatible with existing library programs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.5
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• pp.309-316
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• 2014

It is easy to reverse engineer an Android app package file(APK) and get its decompiled source code. Therefore, attackers obtains economic benefits by illegally using the decompiled source code, or modifies an app by inserting malware. To address these problems in Android, we propose an APK overwrite scheme that protects apps against illegal modification of themselves by using a new anti-reverse engineering technique. In this paper, the targets are the apps which have been written by any programmer. For a target app (original app), server system (1) makes a copy of a target app, (2) encrypts the target app, (3) creates a stub app by replacing the DEX (Dalvik Executable) of the copied version with our stub DEX, and then (4) distributes the stub app as well as the encrypted target app to users of smartphones. The users downloads both the encrypted target app and the corresponding stub app. Whenever the stub app is executed on smartphones, the stub app and our launcher app decrypt the encrypted target app, overwrite the stub app with the decrypted target one, and executes the decrypted one. Every time the target app ends its execution, the decrypted app is deleted. To verify the feasibility of the proposed scheme, experimentation with several popular apps are carried out. The results of the experiment demonstrate that our scheme is effective for preventing reverse engineering and tampering of Android apps.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.313-315
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• 2013

Hand-held devices such as smart phones exploit flash memory based storages to store data for processing jobs. Since the flash memory, non-volatile memory, is able to store mass data, it is required to use the index for processing queries. However, the flash memory has the shortcomings that it does not support the overwrite operation and its write operation is very slow. In this paper, we build the fixed grid file, one of the multi-dimensional spatial index, on a flash memory and evaluate the performance test.

• The KIPS Transactions:PartA
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• v.12A no.3 s.93
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• pp.205-214
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• 2005

Flash memory is at high speed used as storage of personal information utilities, ubiquitous computing environments, mobile phones, electronic goods, etc. This is because flash memory has the characteristics of low electronic power, non-volatile storage, high performance, physical stability, portability, and so on. However, differently from hard disks, it has a weak point that overwrites on already written block of flash memory is impossible to be done. In order to make an overwrite possible, an erase operation on the written block should be performed before the overwrite, which lowers the performance of flash memory highly. In order to solve this problem the flash memory controller maintains a system software module called the flash translation layer(FTL). Of many proposed FTL schemes, the log block buffer scheme is best known so far. This scheme uses a small number of log blocks of flash memory as a write buffer, which reduces the number of erase operations by overwrites, leading to good performance. However, this scheme shows a weakness of low page usability of log blocks. In this paper, we propose an enhanced log block buffer scheme, FAST(Full Associative Sector Translation), which improves the page usability of each log block by fully associating sectors to be written by overwrites to the entire log blocks. We also show that our FAST scheme outperforms the log block buffer scheme.

• Electrical & Electronic Materials
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• v.1 no.3
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• pp.219-227
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• 1988

광자기디스크 응용상의 과제로서는 저가격화와 overwrite의 실현, 그리고 고속 기록재생 및 고속 access성을 들 수 있는데 현재 기록매체와 drive공히 다방면으로 연구개발이 집중되고 있어 제2, 제3세대 광자기디스크 장치가 속속 나타날 전망이다. 광자기 디스크의 수요예측은 예측시점이나 예측방법, 예측자에 따라 상당한 차이를 보이나 공통적으로 1990년대레응 20-30억불 시장을 예상하고 있으며 수요증가추세는 2000년까지 기하급수적으로 늘어날 것으로 보고 있다. 광자기 디스크 장치의 수요 예측 결과의 일예를 그림 12에 소개한다.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.6
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• pp.521-531
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• 2009

Flash memory has physical characteristics different from hard disk where two costs of a read and write operations differ each other and an overwrite on flash memory is impossible to be done. In order to solve these restrictions with software, storage systems equipped with flash memory deploy FTL(Flash Translation Layer) software. Several FTL algorithms have been suggested so far and most of them prefer sequential write pattern to random write pattern. In this paper, we provide a new technique to efficiently store and maintain the B-tree index on flash memory. The operations like inserts, deletes, updates of keys for the B-tree generate random writes rather than sequential writes on flash memory, leading to inefficiency to the B-tree maintenance. In our technique, we convert random writes generated by the B-tree into sequential writes and then store them to the write-buffer on flash memory. If the buffer is full later, some sequential writes in the buffer will be issued to FTL. Our diverse experimental results show that our technique outperforms the existing ones with respect to the I/O cost of flash memory.

• Journal of KIISE:Computing Practices and Letters
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• v.13 no.6
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• pp.422-426
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• 2007

Personal mobile devices equipped with non-volatile storage such as MP3 player, PMP, cellular phone, and USB memory require safety for the stored data on the devices. One of the safety requirements is secure deletion, which is removing stored data completely so that the data can not be restored illegally. In this paper, we study how to design the secure deletion on Flash memory, commonly used as storage media for mobile devices. We consider two possible secure deletion policy, named zero-overwrite and garbage-collection respectively, and analyze how each policy affects the performance of Flash memory file systems. Then, we propose an adaptive file deletion scheme that exploits the merits of the two possible policies. Specifically, the proposed scheme applies the zero-overwrite policy for small files, whereas it employs the garbage-collection policy for large files. Real implementation experiments show that the scheme is not only secure but also efficient.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.34-41
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• 2005

We report some recent results in the rewritable Blu-ray Disc with enhanced overwrite cyclability by using the growth dominant eutectic based Ge(Sb70Te30)+Sb recording layer, GeN interface layer and write strategy optimization. We have developed phase-change optical media with appropriate write strategy for 36(i.e., 1X)-72Mbps(i.e., 2X) dual speed Blu-ray Disc system and fur the future high speed optical data storage. For recording layer, eutectic-based Ge(Sb70Te30)+Sb material was used and Sb/Te ratio and Ge content were optimized to obtain proper erasability and archival stability of recorded amorphous marks. The recording layer is wrapped up in GeN interface layers to obtain overwrite cyclability and higher crystallization speed. In addition, we designed appropriate write strategy so called Time-Shifted Multipulse (TSMP) write strategy where starting position of multipulse parts are shined from reference clock. With this write strategy, the jitter characteristics of the disc was improved and we found that leading edge jitter was improved much more than trailing edge jitter in 1X-2X speed recording. Finally, we investigated the higher speed feasibility of 144Mbps(i.e., 4X) by adopting some elemental doping to the eutectic based Ag-In-Sb-Te recording layer and structural optimization of constitution layers in Blu-ray Disc. In the paper, we report the effect of Sn addition for the feasibility of higher speed recording. The addition of Sn shows increases of the crystallization speed of phase change recording layer.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.1
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• pp.36-42
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• 2016

In multi-level-cell based storage devices, TLC NAND has been employed solid state drive due to cost effectiveness. Since TLC has slow performance and low endurance compared with MLC, TLC based storage has adopted SLC buffer scheme to improve performance. To improve SLC buffer scheme, this paper proposes page overwriting method in SLC block. This method provides data updates without erase operation within a limited number. When SLC buffer area is filled up, FTL should execute copying valid pages and erasing it. The proposed method reduces erase counts by 50% or more compared with previous SLC buffer scheme. Simulation results show that the proposed SLC buffer overwrite method achieves 2 times write performance improvement.

• Journal of KIISE:Databases
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• v.36 no.1
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• pp.1-7
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• 2009

Flash memory has its unique characteristics: i.e., (1) the write operation is much more costly than the read operation. (2) In-place updating is not allowed. In this paper, we first analyze how these characteristics affect the performance of record management in flash memory, and discuss the problems with previous methods for record management when they are applied to flash memory environment. Next, we propose a new record management method to be suitable for flash memory environment. The proposed method employs a new concept of a container that makes it possible to overwrite data on flash memory several times when performing insertions, deletions, and modifications of records. As a result, this method reduces the number of overwrite operations, and consequently does the number of erase operations. The results of experiments show that our method improves the performance by up to 34%, compared with the previous one.