When an application code is downloaded from an unknown server to the mobile device, it is important to authenticate the code. Usually, code execution is overlapped with downloading to reduce transfer/invocation delay. In this letter, we present an efficient code authentication scheme that permits overlapping of execution and downloading when the sequence of code execution is determined during the execution time. The proposed scheme is based on authentication trees. Compared with the tree chaining scheme, the proposed scheme has lower communication overhead and shorter average verification delay. Also, the computation cost of the proposed scheme on the receiver is much smaller than that of the tree chaining scheme.

The security vulnerabilities of a number of provable secure proxy signature schemes are examined with the assumption that users can register their public keys without having corresponding private keys. This assumption is different from that of a standard proxy signature in which the public keys of users are authentic. Under this assumption, both the Triple Schnorr scheme and Kang et al's scheme are shown to be vulnerable to a rogue public key registration attack. This attack gives an adversary the ability to generate a proxy signature without the valid agreement of the original signer. Moreover, it is shown that an adversary can manipulate the description of a delegated signing right at will. This work can be considered as an awakening to the importance of Proof of Possession (PoP) in the PKI environment, as in many cases certificate authorities do not require the PoP protocol, as has been stated [1].

We present an efficient stream authentication scheme using authentication stars. The computation overhead of the proposed scheme on the sender is almost the same as that of the scheme with the smallest overhead. On the receiver's side, the verification probability of the proposed scheme is much higher than that of any other scheme. To show this, we first conducted a mathematical analysis on the verification probability of our scheme and then performed simulation to compare the verification probability of our scheme with those of the previous schemes. Simulation results shows that when the packet loss rate is 50%, the verification probability of our scheme is 73% whereas those of the previous schemes are below 41%.

A burst of social network services increases the need for in-depth analysis of network activities. Privacy breach for network participants is a concern in such analysis efforts. This paper investigates structural and property changes via several privacy preserving methods (anonymization) for social network. The anonymized social network does not follow the power-law for node degree distribution as the original network does. The peak-hop for node connectivity increases at most 1 and the clustering coefficient of neighbor nodes shows 6.5 times increases after anonymization. Thus, we observe inconsistency of privacy preserving methods in social network analysis.

This paper presents a fully self-organized key management scheme for mobile ad hoc networks. Unlike most previous schemes, there is no priori shared secret or no priori trust relationship in the proposed scheme; every node plays the same role and carries out the same function of key management. The proposed scheme consists of (1) Handshaking (HS) and (2) Certificate request/reply (CRR) procedures. In HS, a node acquires the public key of the approaching node via a secure side channel. In CRR, a node requests certificates of a remote node via a radio channel to the nodes that it has HSed. If the number of received valid certificates that contain the same public key exceeds a given threshold, the node accepts the remote node's public key as valid. Security is rigorously analyzed against various known attacks and network costs are intensively analyzed mathematically. Using this analysis, we provide parameter selection guideline to optimize performance and to maintain security for diverse cases. Simulation results show that every node acquires the public keys of all other nodes at least 5 times faster than in a previous scheme.

In this letter, we present an efficient stream authentication scheme that is an improvement of SAIDA. It is shown that under the same communication overhead its verification probability is higher than that of SAIDA. Moreover, its computation cost is lower than that of SAIDA.

People expose their personal information on social network services (SNSs). This paper warns of the dangers of this practice by way of an example. We show that the residence registration numbers (RRNs) of many Koreans, which are very important and confidential personal information analogous to social security numbers in the United States, can be estimated solely from the information that they have made open to the public. In our study, we utilized machine learning algorithms to infer information that was then used to extract a part of the RRNs. Consequently, we were able to extract 45.5% of SNS users' RRNs using a machine learning algorithm and brute-force search that did not consume exorbitant amounts of resources.

To control various access privileges in group-oriented applications having multiple data streams, we present a novel reactive key management scheme where each member can obtain the key of a data stream from public parameters only when necessary. Compared with the previous schemes, this scheme significantly reduces the amount of rekey messages for dynamic membership change due to its reactive nature.

In this study, a novel binary image authentication scheme is proposed, which can be used to detect any alteration of the host image. In the proposed scheme, the watermark is embedded into a host image using a Hamming-code-based embedding algorithm. A performance analysis shows that the proposed scheme achieves both smaller distortion and lower false negative rates than the previous schemes.