• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.136-139
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• 2000

In this paper, we propose a prime code and a new cryptographic algorithm for encryption and decryption as its application. The characteristics of prime numbers with irregular distribution and uniqueness are used to generate the prime code. Based on the prime code, an encryption algorithm for secret key is presented. Since the algorithm requires simpler operations than existing encryption such as DES, the burden for hardware implementation of the encryption and decryption process is alleviated.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.216-219
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• 2008

It is necessary to study encryption for protection and safe transmission of the important information. Specially, the security in satellite data is also getting more and more important. This paper introduces DES and TDES algorithm, studies how to apply to satellite data with those algorithms and process of encryption and decryption for satellite data. Proposed encryption process in this paper will be utilized in satellite data for encryption in many satellites.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1991.10a
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• pp.100-102
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• 1991

In this paper, we use LFSR(Linear Feedback Shift Register) as a kind of pseudo-random one-time pad. Key generator is constructed using r separate LFSR's with IP(Irreducible Polynominal) which are relatively prime. Key generated in this method has high linear complexity. And also, file cryptosystem for file encryption and decryption is constructed.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.207-210
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• 2002

We suggest binary image decryption system using two-wave mixing in photorefractive crystal. Compared with a conventional method, this method can make optical alignment easily, and brighten the encrypted image even if a small input signal, by index grating of photorefractive crystal. Also it can reconstruct the encrypted image by only reference beam in real time.

• Journal of Internet of Things and Convergence
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• v.2 no.3
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• pp.43-51
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• 2016

In this paper, we have developed Crypft+ as an enhanced file encryption/decryption system to improve the security of IoT system or individual document file management process. The Crypft+ system was developed as a core security module using Python, and designed and implemented a user interface using PyQt. We also implemented encryption and decryption function of important files stored in the computer system using AES based symmetric key encryption algorithm and SHA-512 based hash algorithm. In addition, Cx-Freezes module is used to convert the program as an exe-based executable code. Additionally, the manual for understanding the Cryptft+ SW is included in the internal program so that it can be downloaded directly.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.1
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• pp.20-34
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• 2009

We newly propose a multiple and unlinkable identity-based public key encryption scheme which allows the use of a various number of identity-based public keys in different groups or applications while keeping a single decryption key so that the decryption key can decrypt every ciphertexts encrypted with those public keys. Also our scheme removes the use of certificates as well as the key escrow problem so it is functional and practical. Since our public keys are unlinkable, the user's privacy can be protected from attackers who collect and trace the user information and behavior using the known public keys. Furthermore, we suggest a decryption key renewal protocol to strengthen the security of the single decryption key. Finally, we prove the security of our scheme against the adaptive chosen-ciphertext attack under the random oracle model.

• Journal of Korea Multimedia Society
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• v.11 no.8
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• pp.1093-1100
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• 2008

Feistel and SPN are the two main structures in designing a block cipher algorithm. Unlike Feistel, an SPN has an asymmetric structure in encryption and decryption. In this paper we propose an SPN algorithm which has a symmetric structure in encryption and decryption. The whole operations in our SPN algorithm are composed of the even numbers of N rounds where the first half of them, 1 to N/2, applies function and the last half of them, (N+1)/2 to N, employs inverse function. Symmetry layer is executed to create a symmetry block in between function layer and inverse function layer. AES encryption and decryption algorithm, whose safety is already proved, are exploited for function and inverse function, respectively. In order to be secure enough against the byte or word unit-based attacks, 32bit rotation and simple logical operations are performed in symmetry layer. Due to the simplicity of the proposed encryption and decryption algorithm in hardware configuration, the proposed algorithm is believed to construct a safe and efficient cipher in Smart Card and RFID environments where electronic chips are built in.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1892-1903
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• 2016

Mobile social network is becoming more and more popular with respect to the development and popularity of mobile devices and interpersonal sociality. As the amount of social data increases in a great deal and cloud computing techniques become developed, the architecture of mobile social network is evolved into cloud-based that mobile clients send data to the cloud and make data accessible from clients. The data in the cloud should be stored in a secure fashion to protect user privacy and restrict data sharing defined by users. Ciphertext-policy attribute-based encryption (CP-ABE) is currently considered to be a promising security solution for cloud-based mobile social network to encrypt the sensitive data. However, its ciphertext size and decryption time grow linearly with the attribute numbers in the access structure. In order to reduce the computing overhead held by the mobile devices, in this paper we propose a new Outsourcing decryption and Match-then-decrypt CP-ABE algorithm (OM-CP-ABE) which firstly outsources the computation-intensive bilinear pairing operations to a proxy, and secondly performs the decryption test on the attributes set matching access policy in ciphertexts. The experimental performance assessments show the security strength and efficiency of the proposed solution in terms of computation, communication, and storage. Also, our construction is proven to be replayable choosen-ciphertext attacks (RCCA) secure based on the decisional bilinear Diffie-Hellman (DBDH) assumption in the standard model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.3231-3249
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• 2014

Deniable encryption, introduced in 1997 by Canetti, Dwork, Naor, and Ostrovsky, guarantees that the sender or the receiver of a secret message is able to "fake" the message encrypted in a specific ciphertext in the presence of a coercing adversary, without the adversary detecting that he was not given the real message. Sender - side deniable encryption scheme is considered to be one of the classification of deniable encryption technique which defined as resilient against coercing the sender. M. H. Ibrahim presented a sender - side deniable encryption scheme which based on public key and uncertainty of Jacobi Symbol [6]. This scheme has several problems; (1) it can't be able to derive the fake message $M_f$ that belongs to a valid message set, (2) it is not secure against Quadratic Residue Problem (QRP), and (3) the decryption process is very slow because it is based dramatically on square root computation until reach the message as a Quadratic Non Residue (QNR). The first problem is solved by J. Howlader and S. Basu's scheme [7]; they presented a sender side encryption scheme that allows the sender to present a fake message $M_f$ from a valid message set, but it still suffers from the last two mentioned problems. In this paper we present a new sender-side deniable public-key encryption scheme with fast decryption by which the sender is able to lie about the encrypted message to a coercer and hence escape coercion. While the receiver is able to decrypt for the true message, the sender has the ability to open a fake message of his choice to the coercer which, when verified, gives the same ciphertext as the true message. Compared with both Ibrahim's scheme and J. Howlader and S. Basu's scheme, our scheme enjoys nice two features which solved the mentioned problems: (1) It is semantically secure against Quadratic Residue Problem; (2) It is as fast, in the decryption process, as other schemes. Finally, applying the proposed deniable encryption, we originally give a coercion resistant internet voting model without physical assumptions.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.6
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• pp.81-92
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• 2005

A novel public key cryptosystem that provides a double decryption mechanism is proposed at Asiacrypt '03 by Bresson, Catalano and Pointcheval based on the scheme proposed by Clamor and Shoup at Eurocrypt '02. Previous double decryrtion scheme is designed based on $Z_n^2$ where n=pq for two primes p,q. In this paper, we propose an efficient public key scheme with double decryption mechanism based on $Z_p^2_q$ for two primes p,q. Our scheme is more efficient an the previous schemes. Moreover, we review the previous schemes in a privacy point of view and propose a privacy enhanced double decryption scheme.