A novel encryption scheme based on complex chaotic networks is proposed in this paper. Compared with a single chaotic system, a network of chaotic systems possesses complex dynamic characteristics, which can be used in encryption to enhance security. We adopt the drive-response synchronization method to synchronize two identical chaotic networks at the transmitter and receiver. Analysis on encryption security shows that key space is enlarged exponentially with respect to the number of nodes in the drive network, and also shows that the encryption system is highly sensitive to parameter mismatch. The proposed scheme is competent in carrying out encryption tasks of large data. Both theoretical and numerical results demonstrate that the proposed scheme is feasible for implementation in image and data encryption.

An Encryption Scheme Based on Synchronization of Two-Layered Complex Dynamical Networks

A strong designated verifier signature (SDVS) scheme only allows a designated veri- fier to validate signer's signatures for ensuring confidentiality. At the same time, the des- ignated verifier can not transfer the signature to any third party, since he can also generate another computationally indistinguishable SDVS, which is referred to as non-transfer- ability. A proxy signature scheme is a special type of digital signature schemes, which en- ables an authorized proxy signer to create a valid proxy signature on behalf of the original one. The resulted proxy signature is publicly verifiable by anyone. In this paper, we elabo- rate on the merits of SDVS schemes and proxy signature schemes to propose an efficient strong designated verifier proxy signature (SDVPS) scheme in which only a designated verifier can be convinced of the proxy signer's identity. The proposed scheme has crucial benefits in organizational operations and electronic commerce. Compared with related schemes, ours has not only shorter signature length, but also lower computational costs. Moreover, the security requirement of unforgeability against existential forgery under adaptive chosen-message attacks (EF-CMA) is proved in the random oracle model.

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An efficient strong designated verifier proxy signature scheme for electronic commerce

We present a new signature scheme which is existentially unforgeable under chosen message attacks, assuming some variant of the RSA conjecture. This scheme is not based on "signature trees", and instead it uses the so called "hash-and-sign" paradigm. It is unique in that the assumptions made on the cryptographic hash function in use are well defined and reasonable (although non-standard). In particular, we do not model this function as a random oracle.

We construct our proof of security in steps. First we describe and prove a construction which operates in the random oracle model. Then we show that the random oracle in this construction can be replaced by a hash function which satisfies some strong (but well defined!) computational assumptions. Finally, we demonstrate that these assumptions are reasonable, by proving that a function satisfying them exists under standard intractability assumptions.

Secure Hash-and-Sign Signatures without the Random Oracle.

The advancement of public-key cryptography in recent years has offered strong background support for the invention of numerous new system applications vastly employed in electronic business as well as other fields. However, that does not change the fact that the one-and-only Internet still remains open and unprotected. Therefore, for the sake of information security, confirming the legality of an entity’s public key is always critical. Typically, a key authentication scheme needs one or more authorities to authenticate keys. To make a difference, in this study, we have developed a new key authentication scheme using generalized discrete logarithm problem and integer factorization problem for cryptosystems. Although the new scheme works pretty much the same way as regular certificate-based techniques, it differs in that it needs no authority. Taking the password/secret key pair as the certificate of public key for an entity, the new key authentication technique is very simple but profoundly secure.

A secure key authentication scheme for cryptosystems based on GDLP and IFP

Several certificateless short signature and multisignature schemes based on traditional public key infrastructure (PKI) or identity-based cryptosystem (IBC) have been proposed in the literature; however, no certificateless short sequential (or serial) multisignature (CL-SSMS) or short broadcast (or parallel) multisignature (CL-SBMS) schemes have been proposed. In this paper, we propose two such new CL-SSMS and CL-SBMS schemes based on elliptic curve bilinear pairing. Like any certificateless public key cryptosystem (CL-PKC), the proposed schemes are free from the public key certificate management burden and the private key escrow problem as found in PKI- and IBC-based cryptosystems, respectively. In addition, the requirements of the expected security level and the fixed length signature with constant verification time have been achieved in our schemes. The schemes are communication efficient as the length of the multisignature is equivalent to a single elliptic curve point and thus become the shortest possible multisignature scheme. The proposed schemes are then suitable for communication systems having resource constrained devices such as PDAs, mobile phones, RFID chips, and sensors where the communication bandwidth, battery life, computing power and storage space are limited.

Certificateless short sequential and broadcast multisignature schemes using elliptic curve bilinear pairings

Strong designated verifier signature scheme could make it possible for a signer to convince only the designated verifier that the signature is made by the signer. In 2007, Lee et al. proposed a designated verifier signature scheme with message recovery, attaching target message with signature, to prevent any attack by eavesdropping. In this paper, we propose an efficient strong designated verifier signature scheme, using key distribution mechanism where both sender and designated receiver share encryption/decryption key to fulfill encryption/decryption algorithm with low cost of communication and computation: 30% and 50% of Lee et al. scheme, respectively. We would prove its security based on public problem-Gap Diffie-Hellman (GDH) assumption.

A Provably Secure and Efficient Strong Designated Verifier Signature Scheme

Researchers have proposed an effective RSA multisignature scheme based on Shamir’s identity-based signature (IBS) scheme. Despite being a multisignature, the proposed scheme’s signature length is comparable to Shamir’s IBS scheme. Also, only one/two extra increments of l-1 modular multiplications are added to the verification/signature time, whereby l represents the number of signers. This greatly reduced the computational load and communication costs compared to the previously proposed multisignature schemes. However, this study discovers security loopholes in the previous schemes. This study analyzes and highlights the loopholes’ origins, and it proposes improvements to the original schemes, preserves the scheme’s merits and enhances their security. The resultant protocol is thus suitable for wireless communications because it not only possesses security but also saves computation resources and communication bandwidth.

http://ir.lib.cyut.edu.tw:8080/bitstream/310901800/16027/2/J-25-Improving%20an%20efficient%20ID-based%20RSA%20multisignature.pdf

Improving an efficient ID-based RSA multisignature

In 2008, Harn and Ren proposed an effective RSA multisignature scheme based on the identity-based signature (IBS) scheme of Shamir. In spite of being a multisignature, the signature length of Harn and Ren’s scheme is comparable to that in Shamir’s IBS scheme. Also, only two/one extra increments of l-1 modular multiplications are added to the signature/verification time, whereby l represents the number of signers. This enabled a large reduction of computational load and communication costs compared to the multisignature schemes formerly proposed. However, we discovered two security loopholes in their schemes. The purpose of this paper is to analyze and highlight the origins of the loopholes, as well as to put forth proposed improvements, preserve the merits of the original schemes, and enhance their security. The resultant protocol thus is suitable for wireless communications because it is not only possessing security but also saving computation resources and communication bandwidth.

Improvement of an Efficient ID-Based RSA Multisignature

The popularization and conveniences of Internet have changed traditional auction transactions into electronic auction via Internet. In 2006, Chang and Chang proposed an anonymous auction that enabled bidders to bid in anonymous cases without any bonds. However, in the initiation phase, the bidder is unable to be anonymous as there is no mechanism to protect his (her) identity. Therefore, the lawless person might take this chance to do something illegal. Once the latter, who participates in the auction activity, knows the bidder’s identity, he may threaten the honest bidder to become the bid winner. This situation may make bidders refuse to bid to avoid damages. To solve the above mentioned matter, in this paper, we propose an efficient anonymous auction protocol, to protect all bidders’ identities in both initiation and auction phases with low levels of computation and communication: only 27% and 50% of Chang and Chang protocol, respectively. A problem in anonymous auction protocol is that bidder A impersonates bidder B to participate an auction. This may be harmful to bidder B. We prove the proposed auction protocol is secure against this attack as it is based on the Gap Diffie-Hellman (GDH) assumption. Key word: Electronic auction, Anonymous auction, Public-key cryptosystem, Gap Diffie-Hellman assumption, Deniable authentication

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An Anonymous Auction Protocol Based on GDH Assumption.

Three-party password authenticated key exchange (3PAKE) protocol is capable of reducing the number of required keys stored by users in a conference. In 2007, Lu and Cao proposed a simple three-party password authenticated key exchange (S-3PAKE) protocol for assisting users to complete business negotiations and agreements during a communication process without requiring a public server key, and the S-3PAKE protocol can resist all known attacks. However, in 2008, Cuo et al. pointed out the protocol proposed by Lu et al. still cannot resist man-in-the-middle attacks and online dictionary attacks thus further proposed an improved solution as follows. Two parties execute the 2-PAKE protocol to obtain an agreement key first, so that when they execute the 3PAKE protocol, they can authenticate the real identity with each other. An effective three-party password authenticated key exchange (3PAKE) protocol was proposed for authenticating the real identity of both parties without requiring an execution of the 2-PAKE protocol to obtain the agreement key first, but simply adding the real identity of the opposite party in the communication

http://ir.lib.cyut.edu.tw:8080/bitstream/310901800/8441/1/%E6%8A%BD%E5%8D%B0%E6%9C%AC8.pdf

Cai-Ming Liao

Papers

A Provably Secure and Efficient Strong Designated Verifier Signature Scheme

Improving an efficient ID-based RSA multisignature

Improvement of an Efficient ID-Based RSA Multisignature

An Anonymous Auction Protocol Based on GDH Assumption.

An enhanced of Simple Three-Party Key Exchange Protocol