• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.15 no.8
• /
• pp.2865-2878
• /
• 2021

As a current popular technology, the blockchain has a serious issue: the private key cannot be retrieved due to force majeure. Since the outcome of the blockchain-based Bitcoin, there have been many occurrences of the users who lost or forgot their private keys and could not retrieve their token wallets, and it may cause the permanent loss of their corresponding blockchain accounts, resulting in irreparable losses for the users. We propose a recoverable private key scheme for consortium blockchain based on the verifiable secret sharing which can enable the user's private key in the consortium blockchain to be securely recovered through a verifiable secret sharing method. In our secret sharing scheme, users use the biometric keys to encrypt shares, and the preset committer peers in the consortium blockchain act as the participants to store the users' private key shares. Due to the particularity of the biometric key, only the user can complete the correct secret recovery. Our comparisons with the existing mnemonic systems or the multi-signature schemes have shown that our scheme can allow users to recover their private keys without storing the passwords accurately. Hence, our scheme can improve the account security and recoverability of the data-sharing systems across physical and virtual platforms that use blockchain technology.

• Current Optics and Photonics
• /
• v.3 no.2
• /
• pp.119-127
• /
• 2019

A new secret-key-sharing cryptosystem using optical phase-shifting digital holography is proposed. The proposed secret-key-sharing algorithm is based on the Diffie-Hellman key-exchange protocol, which is modified to an optical cipher system implemented by a two-step quadrature phase-shifting digital holographic encryption method using orthogonal polarization. Two unknown users' private keys are encrypted by two-step phase-shifting digital holography and are changed into three digital-hologram ciphers, which are stored by computer and are opened to a public communication network for secret-key-sharing. Two-step phase-shifting digital holograms are acquired by applying a phase step of 0 or ${\pi}/2$ in the reference beam's path. The encrypted digital hologram in the optical setup is a Fourier-transform hologram, and is recorded on CCDs with 256 quantized gray-level intensities. The digital hologram shows an analog-type noise-like randomized cipher with a two-dimensional array, which has a stronger security level than conventional electronic cryptography, due to the complexity of optical encryption, and protects against the possibility of a replay attack. Decryption with three encrypted digital holograms generates the same shared secret key for each user. Schematically, the proposed optical configuration has the advantage of producing a kind of double-key encryption, which can enhance security strength compared to the conventional Diffie-Hellman key-exchange protocol. Another advantage of the proposed secret-key-sharing cryptosystem is that it is free to change each user's private key in generating the public keys at any time. The proposed method is very effective cryptography when applied to a secret-key-exchange cryptosystem with high security strength.

• IEIE Transactions on Smart Processing and Computing
• /
• v.2 no.5
• /
• pp.266-276
• /
• 2013

LSB-based steganography is a simple and well known information hiding technique. In most LSB based techniques, a secret message is embedded into a specific position of LSB in the cover pixels. On the other hand, the main threat of LSB-based steganography is steganalysis. This paper proposes an asynchronous-cellular-automata(ACA)-based steganographic method, where secret bits are embedded into the selected position inside the cover pixel by ACA rule 51 and a secret key. As a result, it is very difficult for malicious users to retrieve a secret message from a cover image without knowing the secret key, even if the extraction algorithm is known. In addition, another layer of security is provided by almost random (rule-based) selection of a cover pixel for embedding using ACA and a different secret key. Finally, the experimental results show that the proposed method can be secured against the well-known steganalysis RS-attack.

• Journal of IKEEE
• /
• v.25 no.1
• /
• pp.42-46
• /
• 2021

A novel key exchange cryptographic method utilizing biometric finger print as a user's private key is proposed. Each unknown users' finger print is encrypted by optical phase-shifting interferometry principle and is changed into two ciphers, which are exchanged with the other party over a public communication network for secret key sharing. The transmitted ciphers generate a complex hologram, which is used to calculate a shared secret key for each user. The proposed method provides high security when applied to a secret key sharing encryption system.

• Journal of the Korea Society of Computer and Information
• /
• v.10 no.3 s.35
• /
• pp.189-199
• /
• 2005

Now it is increasing the necessity for micropayment system according to activation for trade on internet. Because of the reason, it is requesting safety for personal information as well as for payment cost. But current micropayment systems cannot support anonymity or have heavy overheads in payment process. This paper suggests a micropayment system to keep anonymity of users and also to keep payment cost safe. The proposed system is to use blind signature anonymous ID which is combined nonce with an encryption of personal information. It also keeps payment cost of users by reconfirmation payment cost and product from certification and increases the computational efficiency by using secret key and session key instead of public key.

• The KIPS Transactions:PartC
• /
• v.8C no.2
• /
• pp.122-127
• /
• 2001

1998년 A. Young등은 공개키 기반구조(PKI)를 이용한 키 복구 시스템인 ARC를 제안하였다. 그리고 1999년 P.Paillier 등은 ARC를 개선하여 사용자의 증명서 저장공간이 필요 없는 SE-PKI 키 복구 시스템을 제안하였다. 또한 2001년 유희종 등은 Paillier가 제안한 SE-PKI 키 복구 시스템에 비밀분산 개념을 추가하여 다수의 키 위탁 기관이 참여하는 키 복구 시스템을 제안했다. 본 논문에서는 새로운 scheme을 추가하여 사용자의 비밀키를 사용자만이 인증기관의 도움을 받아 키 위탁 기관으로부터 온 라인 상에서 안전하게 복구할 수 있는 키 복구 시스템을 제안한다. 이 키 복구 시스템에서는 사용자가 비밀키를 자주 변경하는 경우 이전 암호문을 복호화하기 위해 필요한 비밀키 관리가 용이하다.

• Journal of Internet Computing and Services
• /
• v.23 no.3
• /
• pp.21-33
• /
• 2022

This paper is to suggest the secure secret sharing system in order to outstandingly reduce the damage caused by the leakage of the corporate secret. This research system is suggested as efficient P2P distributed system kept from the centrally controlled server scheme. Even the bitcoin circulation system is also based on P2P distribution scheme recenly. This research has designed the secure circulation of the secret shares produced by Threshold Shamir Secret Sharing scheme instead of the shares specified in the torrent file using the simple, highly scalable and fast transferring torrent P2P distribution structure and its protocol. In addition, this research has studied to apply both Shamir Threshold Secret Sharing scheme and the securely strong multiple user authentication based on Collaborative Threshold Autentication scheme. The secure transmission of secret data is protected as using the efficient symmetric encryption with the session secret key which is safely exchanged by the public key encryption. Also it is safer against the leakage because the secret key is effectively alive only for short lifetime like a session. Especially the characteristics of this proposed system is effectively to apply the threshold secret sharing scheme into efficient torrent P2P distributed system without modifying its architecture of the torrent system. In addition, this system guaranttes the confidentiality in distributing the secret file using the efficient symmetric encryption scheme, which the session key is securely exchanged using the public key encryption scheme. In this system, the devices to be taken out can be dynamically registered as an user. This scalability allows to apply the confidentiality and the authentication even to dynamically registerred users.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.13 no.3
• /
• pp.1502-1522
• /
• 2019

Leakage of secret keys may be the most devastating problem in public key cryptosystems because it means that all security guarantees are missing. The forward security mechanism allows users to update secret keys frequently without updating public keys. Meanwhile, it ensures that an attacker is unable to derive a user's secret keys for any past time, even if it compromises the user's current secret key. Therefore, it offers an effective cryptographic approach to address the private key leakage problem. As an extension of the forward security mechanism in certificate-based public key cryptography, forward-secure certificate-based signature (FS-CBS) has many appealing merits, such as no key escrow, no secure channel and implicit authentication. Until now, there is only one FS-CBS scheme that does not employ the random oracles. Unfortunately, our cryptanalysis indicates that the scheme is subject to the security vulnerability due to the existential forgery attack from the malicious CA. Our attack demonstrates that a CA can destroy its existential unforgeability by implanting trapdoors in system parameters without knowing the target user's secret key. Therefore, it is fair to say that to design a FS-CBS scheme secure against malicious CAs without lying random oracles is still an unsolved issue. To address this problem, we put forward an enhanced FS-CBS scheme without random oracles. Our FS-CBS scheme not only fixes the security weakness in the original scheme, but also significantly optimizes the scheme efficiency. In the standard model, we formally prove its security under the complexity assumption of the square computational Diffie-Hellman problem. In addition, the comparison with the original FS-CBS scheme shows that our scheme offers stronger security guarantee and enjoys better performance.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39A no.12
• /
• pp.708-717
• /
• 2014

In this paper, we present a secret key distribution protocol without resorting to a key management infrastructure targeting at providing a low-complexity distributed solution to wireless network. The proposed scheme extracts a secret key from the random fluctuation of wireless channels. By exploiting time division duplexing transmission, two legitimate users, Alice and Bob can have highly correlated channel gains due to channel reciprocity, and a pair of random bit sequences can be generated by quantizing the channel gains. We propose a novel adaptive quantization scheme that adjusts quantization thresholds according to channel variations and reduces the mismatch probability between generated bit sequences by Alice and Bob. BCH codes, as a low-complexity and pratical approach, are also employed to correct the mismatches between the pair of bit sequences and produce a secret key shared by Alice and Bob. To maximize the secret key extraction rate, the parameters, quantization levels and code rates of BCH codes are jointly optimized.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.17 no.2
• /
• pp.471-485
• /
• 2023

As data sharing increases explosively, such information encoded in QR code is completely public as private messages are not securely protected. This paper proposes a new 'PROMISE' framework for hiding information based on the QR code projection matrix by using image segmentation without modifying the essential QR code characteristics. Projection matrix mapping, matrix scrambling, fusion image segmentation and steganography with SEL(secret embedding logic) are part of the PROMISE framework. The QR code could be mapped to determine the segmentation site of the fusion image as a binary information matrix. To further protect the site information, matrix scrambling could be adopted after the mapping phase. Image segmentation is then performed on the fusion image and the SEL module is applied to embed the secret message into the fusion image. Matrix transformation and SEL parameters should be uploaded to the server as the secret key for authorized users to decode the private message. And it was possible to further obtain the private message hidden by the framework we proposed. Experimental findings show that when compared to some traditional information hiding methods, better anti-detection performance, greater secret key space and lower complexity could be obtained in our work.