Catálogo de publicaciones - libros

Providing data confidentiality and integrity is essential to ensure secure or trusted computing. Designs for such purpose always face substaintial difficulties, as providing solid security will be contrary to achieving satisfied performance. Basing on a less rigor precondition that will be tenable in many cases, such designs can be implemented with smaller endeavors. The core idea is to let a trusted agent to trustworthily hold one unique timestamp for each untrusted data block; and encrypts each block, as well as the related integrity code, through the corresponding timestamp. In such way, any malicious disclosure and tamper can be prevented. At the same time, each block can be directly verified by the associated timestamp without requiring additional data to minimize the cost of integrity checking, and OTP encryption scheme can pre-computes keystream to remove most encryption latencies.

A ( t , n ) threshold proxy signature scheme enables an original signer or a group of original signers to delegate the signature authority to a proxy group of n members such that not less than t proxy signers can cooperatively sign messages on behalf of the original signer or the original signer group. In the paper, we show that Sun’s and Yang et al.’s threshold proxy signature schemes are insecure against the original signer’s forgery, and that Tzeng et al.’s threshold multi-proxy multi-signature scheme is vulnerable against the actual original signer group’s forgery. We also show that Hsu et al.’s threshold proxy signature scheme suffers from the conspiracy of the original signer and the secret share dealer SA, and that Hwang et al.’s threshold proxy signature scheme is universally forgeable. In other words, none of the above-mentioned schemes holds the unforgeability and provides non-repudiation.

“Token-controlled public key encryption” is a public key encryption scheme where individual message can be encrypted and sent to every receiver, but the receiver cannot decrypt the message until he/she is given an extra piece of information called a “ token ”. The token will not reveal any information about the messages that the sender originally sent and the communication overhead for releasing the token is very small. Also, it is possible that a single token can control the decryption of a number of ciphertexts sent to multiple receivers. We formalize security model for such scheme and show efficient and provably secure constructions based on known computational assumptions in the random oracle model.

In this paper we discuss the problem of collusion secure fingerprinting. In the first part of our contribution we prove the existence of equidistant codes that can be used as fingerprinting codes. Then we show that by giving algebraic structure to the equidistant code, the tracing process can be accomplished by passing a modified version of the Viterbi algorithm through the trellis representing the code.

In this paper, we focus on lowering the complexity of t -out-of- n string/bit OTs for large t . The notion of oblivious public-key cryptosystem (OPKC) is introduced, in which Bob possesses n public keys but only t private keys and no one knows which t private keys Bob possesses. If the sender, say, Alice, encrypts each message using the n oblivious public keys, resp., the receiver, Bob, can obtain only t messages by t decryptions with his known t private keys. This approach can be directly applied to t -out-of- n bit OT. However, it is very inefficient due to heavy message expansion and many encryption/decryption operations. To construct t -out-of- n bit OT, we introduce bit oblivious public-key cryptosystem (BOPKC), which is a special public-key cryptosystem with a message space of n bits, and the private key only enables its owner to decrypt t bits of n secret bits. After an offline generation of such a BOPKC, it requires only one encryption, one decryption and one ciphertext. Finally, we show the concrete implementations of OPKC/BOPKC based on ElGamal/Paillier cryptosystem, and efficient t -out-of- n string/bit OTs are achieved.