Ching-Te Wang

Research note: Threshold signature schemes with traceable signers in group communications

We propose a new group-oriented (t,n) threshold signature scheme that can withstand conspiracy attacks without attaching a secret number. The groups public key is determined by all members, each member signs a message independently and transmits the individual signature to a designated clerk who checks and integrates them into a group signature. A verifier can authenticate the group signature and trace back to find the signers. Further, we develop another threshold signature scheme without a trusted center. The proposed schemes possess all of the characteristics listed in Harns scheme and are more difficult to break.

A new audio watermarking based on modified discrete cosine transform of MPEG/audio layer III

This paper proposes a solution to authenticate copyrights of audio signals. The musical file in MP3 format is very popular on Internet due to its characteristically high compression ratio and tone quality. Still, problems occur in the protection function of musical file, which can be illegally duplicated. A new watermarking technique can resolve this problem. We can simultaneously accomplish embedding procedures when performing compression of MP3. As the processes of compression and embedding are finished at the same time, incidence of distorted musical files is also reduced. In the proposed method, a few values of coefficients are slightly modified in the frequency domain; the musical file of MP3 is still undetectable by human hearing. Hence the digital watermark is successfully embedded in MP3, thereby achieving the goal. In experimental results, an audio signal is compressed by MP3 at a ratio of 64 kbps; the detection ratio of extracted watermark is 96%. Even if these signals are truncated 75% in the latter part, the detection ratio of extracted watermark still remains 64%, with watermarks discernible to the human ear.

A New Micro-Payment System Using General Payword Chain

In recent years electronic commerce has grown rapidly as Internet and web technologies have progressed. Therefore, a secure and efficient payment system for general-purpose applications is undoubtedly becoming an important issue. Rivest and Shamir have proposed a micro-payment scheme which is user-specific and vendor-specific. However, in their scheme, it is required that the user generates a new payword chain for each vendor from which the user makes a purchase. In this paper, we propose a new micro-payment system that enables users to make purchases from multiple vendors. Only one payword chain has to be generated which makes this system very efficient. A sequence of payword chains which represents a set of small payments can be authenticated and payment can be made by an efficient method. A lower computation cost and improved system performance is also achieved. Therefore, the new micro-payment system has multiple practical applications.

A method for computing Lucas sequences

Abstract Most of public-key cryptosystems rely on one-way functions, which can be used to encrypt and sign messages. Their encryption and signature operations are based on the computation of exponentiation. Recently, some public-key cryptosystems are proposed and based on Lucas functions, and the Lucas sequences are performed as S = V ( d )mod N . In this paper, we will transform the concept of addition chains for computing the exponentiation evaluations to the Lucas chains for computing the Lucas sequences. Theoretically, the shorter Lucas chain for d is generated, the less computation time for evaluating the value V ( d ) is required. Therefore, we proposed a heuristic algorithm for evaluating a shorter Lucas chain and then use it to compute the Lucas sequence with less modular multiplications.

A group-oriented (t, n) undeniable signature scheme without trusted center

We shall propose a new group-oriented undeniable signature scheme without the assistance of any trusted center in this paper. A single group public key, instead of all public keys of individual members, is used to represent the group. A transformation is applied to convert the group public key and the message to be signed into a public parameter and thus been transmitted out. With this public parameter, a paying customer will be able to authenticate the validity of the signature with the consent of all signers. It is worth mentioning that the new group-oriented undeniable signature possesses all of the characteristics that listed in Harn and Yangs. Besides, Harn and Yangs scheme is generalized in this research.

Using IC cards to remotely login passwords without verification tables

A new remote password authentication scheme based on IC cards is proposed in this paper. By using the scheme, a remote password can be authenticated without either a password file or a verification table. A user first applies for an account in the financial organization and then uses the given IC card to login. In the login phase, a user inputs the identity and password, transmits the generated values to the center. In the authentication phase, the system uses the secret key and remotely submitted message to verify whether the request is legal or not. A one-time-used random number and a timestamp are supplied to protect the potential attacks, which may replay a previously intercepted login request. Further, by using the characteristics of IC cards, the proposed scheme is very suitable for authenticating passwords remotely.

Detecting and restoring the tampered images based on iteration-free fractal compression

In current research, fractal image compression scheme has been used to compress images. In this paper, we apply this technique to refine characteristic values of a specific image and embed the characteristic values into the least significant bits of pixels in the image. Once the picture is damaged by an intruder, the system can detect the tampered blocks and restore them using characteristic values without requiring the original image. From experimental results, we see that the proposed scheme can precisely achieve the detection of a damaged image and improve the performance of image restoration.

Signature schemes based on two hard problems simultaneously

Harn (1994) proposed a signature scheme based on the modified ElGamal scheme and claimed that the security relies on both the factorization and the discrete logarithm. That is, his scheme cannot be broken unless both of the above two problems can be solved simultaneously. Lee and Hwang (1996) showed that an attacker could generate a forged signature on the assumption when the discrete logarithm is solved. Recently, Shao (1998) proposed another two signature schemes, which the security rests on the two problems. In this paper, we propose two improved signature schemes that are really based on two hard problems simultaneously. In addition, the numbers of parameters and computations are reduced in comparison with those of Shao.

The image high capacity and reversible data hiding technique based on pixel frequency of block

The data communication is becoming more and more rapidly and conveniently due to the information technology and Internet expeditious development. Therefore, the protections of information security and integrity are becoming very important in the network transmission. And the data hiding schemes are raised in the image research. The image data hiding technique is to embed secret message into a cover image and produce a stego-image, which can be securely sent to the receiver without revealing the secret message in the image. In this paper, we will propose an image high capacity and reversible data hiding scheme based on the frequency of block pixels. This method explores the frequency of pixels in each block and uses them as the predictive values. Because the neighboring pixels of blocks have the similar characteristics and the differences of prediction pixels are approximately. Thus, the peak values of prediction difference histogram are increased greatly, and the embedding capacity can be effectively enlarged on the cover image. From the experimental results, the stego-image not only has good PSNR values of image quality, but also has reversible characteristics for data hiding.

The image multiple secret sharing schemes without pixel expansion

In this paper, two secret sharing schemes were proposed. The two schemes both have the characteristic that the share images they produced are with no pixel expansion. In encoding phase, the rotated share scheme creates two share images for hiding three secret images, whereas the Exclusive OR rotated scheme achieve three share images for hiding four secret images. In decoding phase, the first scheme get secret information by stacking images and rotating image with different angles (0°, 90°, 180°). The second scheme get secret information by doing XOR operation, stacking, and rotating image with different angles (0°, 90°, 180°, 270°). Compare with other schemes of Visual Cryptography, our schemes not only increase the quantity of secret information, but also enhance quality of share image without increasing embed data.