It is well known that conventional digital signature algorithms such as RSA and ECDSA are vulnerable to quantum computing attacks. Hash-based signature schemes are attractive as post-quantum signature schemes in that it is possible to calculate the quantitative security level and the security is proven. SPHINCS is a stateless hash-based signature scheme and introduces HORST few-time signature scheme which is an improvement of HORS. However, HORST as well as HORS suffers from pretty large signature sizes. HORSIC is proposed to reduce the signature size, yet does not provide in-depth security analysis. In this paper, we propose HORSIC+, which is an improvement of HORSIC. HORSIC+ differs from HORSIC in that HORSIC+ does not apply f as a plain function to the signature key, but uses a member of a function family. In addition, HORSIC+ uses the chaining function similar to W-OTS${}^{+}$. These enable the strict security proof without the need for the used function family to be a permutation or collision resistant. HORSIC+ is existentially unforgeable under chosen message attacks, assuming a second-preimage resistant family of undetectable one-way functions and cryptographic hash functions in the random oracle model. HORSIC+ reduces the signature size by as much as 37.5% or 18.75% compared to HORS and by as much as 61.5% or 45.8% compared to HORST for the same security level.

In spite of recent remarkable advances in binary code analysis, malware developers are still using complex anti-reversing techniques to make analysis difficult. To protect malware, they use packers, which are (commercial) tools that contain various anti-reverse engineering techniques such as code encryption, anti-debugging, and code virtualization. In this paper, we present x64Unpack: a hybrid emulation scheme that makes it easier to analyze packed executable files and automatically unpacks them in 64-bit Windows environments. The most distinguishable feature of x64Unpack compared to other dynamic analysis tools is that x64Unpack and the target program share virtual memory to support both instruction emulation and direct execution. Emulation runs slow but provides detailed information, whereas direct execution of the code chunk runs very fast and can handle complex cases regarding to operating systems or hardware devices. With x64Unpack, we can monitor major API (Application Programming Interface) function calls or conduct fine-grained analysis at the instruction-level. Furthermore, x64Unpack can detect anti-debugging code chunks, dump memory, and unpack the packed files. To verify the effectiveness of x64Unpack, experiments were conducted on the obfuscation tools: UPX 3.95, MPRESS 2.19, Themida 2.4.6, and VMProtect 3.4. Especially, VMProtect and Themida are considered as some of the most complex commercial packers in 64-bit Windows environments. Experimental results show that x64Unpack correctly emulates the packed executable files and successfully produces the unpacked version. Based on this, we provide the detailed analysis results on the obfuscated executable file that was generated by VMProtect 3.4.

Time-release cryptography is a special encryption technique that allows a message to be hidden for some time. The previous schemes have shortcomings in that the encryptor should predict the decryptor’s computing power precisely or the trusted agent should be always available. In this paper, we propose a new, practical time-release blockchain, and find the key to decrypt the content after a certain time. In order to verify the effectiveness of the blockchain system automatically, which uses the proof-of-work (PoW) and the consensus algorithm in the the proposed technique, we have implemented a prototype version of our blockchain system using Python. The proposed method has the following advantages. First, the decryption time is automatically adjusted, even if the miner’s computing power changes over time. Second, unlike previous time-lock puzzle schemes, our algorithm does not require additional computation work for solving the puzzle. Third, our scheme does not need any trusted agents (third parties). Fourth, the proposed method uses standard cryptographic algorithms.

This letter presents an enhancement of EigenTrust. Using the beta distribution, local trust values can be more correctly evaluated. Simulation shows that the proposed scheme calculates the local trust more correctly by up to 8%. For personalization, the proposed scheme provides cumulative transitive values from the local trust to the global trust with mathematically guaranteed convergence.