Private Messages Research Articles

On the capacity of a class of K ‐user Gaussian broadcast channel with states known at the transmitter

This studies the capacity of a class of K-user Gaussian broadcast channels with additive i.i.d. Gaussian state sequences which are non-causally known at the transmitter (GBC-SKT). The transmitter wishes to reliably communicate both a common and a private message to each receiver, thus attempting to simultaneously pre-code the common message against different states presented in channel outputs. The authors first derive the approximate capacity for the 2-user GBC-SKT to within 1.25 bits per channel use (bpcu) for all channel parameters and state variances. Then they extended the result to derive the approximate capacity for a class of K-user GBC-SKT to within 1.5 bpcu. In the capacity-approaching strategy, the channel input is obtained as the superposition of two codewords: a bottom codeword treating the channel state as noise and a top codeword pre-coded against the channel state at each user for a portion of the transmission block length or power. For the outer bound, they use the fact that the capacity should be decreasing in state variance in order to get to the tighter outer bound for high values of state variances.

Sudoku-based secret sharing approach with cheater prevention using QR code

QR codes as public patent are widely used to acquire the information in various fields. However, the characteristic of its public readability hinders its usage for delivering private messages. To overcome this weakness, we propose a Sudoku-based secret sharing scheme to protect the privacy QR code message with the functionality of cheater prevention. The secret messages will be divided into several shadows and concealed to the QR code by replacing the QR code public message bits. And the private messages can be faithfully reproduced when all the involved participants cooperate. In our secret sharing scheme, the QR code public message still can be fully decoded publicly from the marked QR codes via a QR code reader, which helps to reduce uninvolved users’ curiosity. Experiments show that the proposed scheme is feasible, with high security protection level, and resistant to common image post-processing attacks.

Just between us: Exclusive communications in online social networks

ABSTRACTSocial media websites such as Facebook are used for relationship development and maintenance often through self-disclosure and sharing of personal information. However, not all forms of social media communication may be equally suitable for this task. This paper explores users’ norms about the appropriateness of using private vs. public Facebook messages to communicate different kinds of personal information, and the effectiveness of these types of communication in building relationships. Study 1, a survey, revealed that users endorse conflicting expectations about preferences for receiving information publicly or privately. Study 2, a field experiment testing the effects of private versus public Facebook communications on actual relationship development using participants’ own Facebook pages, suggested that private messages lead to greater closeness.

Push Attack: Binding Virtual and Real Identities Using Mobile Push Notifications

Popular mobile apps use push notifications extensively to offer an “always connected” experience to their users. Social networking apps use them as a real-time channel to notify users about new private messages or new social interactions (e.g., friendship request, tagging, etc.). Despite the cryptography used to protect these communication channels, the strict temporal binding between the actions that trigger the notifications and the reception of the notification messages in the mobile device may represent a privacy issue. In this work, we present the push notification attack designed to bind the physical owners of mobile devices with their virtual identities, even if pseudonyms are used. In an online attack, an active attacker triggers a push notification and captures the notification packets that transit in the network. In an offline attack, a passive attacker correlates the social network activity of a user with the received push notification. The push notification attack bypasses the standard ways of protecting user privacy based on the network layer by operating at the application level. It requires no additional software on the victim’s mobile device.

“Anyone free to chat?” Using technological features to elicit quality support online

ABSTRACTThis study examines how support seekers can integrate verbal and nonverbal cues in social network sites (SNSs) to elicit quality support from others. Building from sensitive interaction systems theory and verbal person centeredness (VPC), participants (N = 579) evaluated a SNS profile that contained manipulated levels of directness in status updates used to seek support and nonverbal emotional expression in profile pictures. To capture the transaction of support, participants provided supportive messages in public and private conditions that were coded for their level of VPC. Negative emotional cues in profile pictures increased VPC in private messages, whereas directness in status updates negatively predicted VPC in private messages. Participants produced messages with higher levels of VPC after they viewed profiles that incorporated more features to disclose distress effectively. Broadly, this study addresses whether the content people post on SNS profiles shapes the quality of the supportive messages they receive.

A Probabilistic Privacy Preserving Strategy for Word‐of‐Mouth Social Networks

An online social network (OSN) is a platform that makes people communicate with friends, share messages, accelerate business, and enhance teamwork. In the OSN, privacy issues are increasingly concerned, especially in private message leaks in word‐of‐mouth. A user’s privacy may be leaked out by acquaintances without user’s consent. In this paper, an integrated system is designed to prevent this illegal privacy leak. In particular, we only use the method of space vector model to determine whether the user’s private message is really leaked. Canary traps techniques are used to detect leakers. Then, we define a trust degree mechanism to evaluate trustworthiness of a communicator dynamically. Finally, we set up a new message publishing system to determine who can obtain the message of publisher. Secrecy performance analysis is provided to verify the effectiveness of the proposed message publishing system. Accordingly, a user in social networks can check whether other users are trustworthy before sending their private messages.

The Effects of Official and Unofficial Information on Tax Compliance

The administration of tax policy has shifted its focus from enforcement to complementary instruments aimed at creating a social norm of tax compliance. In this paper we provide an analysis of the effects of the dissemination of information regarding the past degree of tax evasion at the social level on the current individual tax compliance behavior. We build an experiment where, for given levels of audit probabilities, fines and tax rates, subjects have to declare their income after receiving either a communication of the official average tax evasion rate or a private message from a group of randomly matched peers about their tax behavior. We use the experimental data to estimate a dynamic econometric model of tax evasion. The econometric model extends the Allingham-Sandmo-Yitzhaki tax evasion model to include self-consistency and endogenous social interactions among taxpayers. We find four main results. First, tax compliance is very persistent. Second, the higher the official past tax evasion rate the higher the degree of persistence: evaders are more likely to evade again, and compliant individuals are more likely to comply again. Third, when all peers communicate to have evaded (complied) in the past, both evaders and compliant individuals are more likely to evade (comply). Fourth, while both treatments, and especially the unofficial information treatment, are associated, in the context of our experiment, with a significantly larger growth in evasion intensity, the aggregate effect depends on the characteristics of the population. In countries with inherently low levels of tax evasion, official information can have beneficial effects by consolidating the behavior of compliant individuals. However, in countries with inherently high levels of tax evasion, official information can have detrimental effects by intensifying the behavior of evaders. In both cases, the impact of official information is magnified in the presence of strong peer effects.

Anonymous Communication via Anonymous Identity‐Based Encryption and Its Application in IoT

Under the environment of the big data, the correlation between the data makes people have a greater demand for privacy. Moreover, the world has become more diversified and democratic than ever before. Freedom of speech is considered to be very important; thus, anonymity is also a very important security demand. The research of our paper proposes a scheme which can ensure both the privacy and the anonymity of a communication system, that is, the protection of message privacy while ensuring the users’ anonymity. It is based on anonymous identity‐based encryption (IBE), by which the users’ metadata are protected. We implement our scheme in JAVA with Java pairing‐based cryptography library (JPBC); the experiment shows that our scheme has significant advantage in efficiency compared with other anonymous communication system. Internet‐of‐Things (IoT) involves many devices, and privacy of devices is very significant. Anonymous communication system provides a secure environment without leaking metadata, which has many application scenarios in IoT.

Public Perceptions of Government Speech

The Supreme Court accords starkly different treatment to private expression and government speech for First Amendment purposes. While regulation of private speech generally must be viewpoint neutral, the government is subject to no such requirement when it engages in speech of its own. But the line between private expression and government speech is often fuzzy. To draw this distinction, the Supreme Court has placed increasing emphasis on whether members of the public reasonably perceive the relevant expression to be private or government speech. We think this turn toward public perception is a welcome development: government intervention in the marketplace of ideas is especially dangerous when it is nontransparent, so before allowing government officials to escape the viewpoint-neutrality requirement, courts should verify that the public actually perceives the speech in question to emanate from the government. But the Court has so far failed to develop a reliable method for determining how ordinary citizens distinguish between private and government messages, relying instead on armchair speculation. Meanwhile, scholars have not yet mustered any evidence as to when and why individuals understand messages to be private expression or government speech. To begin to fill this empirical void, we presented a variety of speech scenarios to a nationally representative sample of more than 1200 respondents and asked the respondents to assess whether the speech in question was the government’s. Some of the speculative claims made by the justices in recent government speech cases are borne out by our survey, but others prove less accurate. We further find that respondents are somewhat more likely to attribute messages to the government if they agree with those messages themselves; in this respect, lay people may be little different from judges, whose decisions in government speech cases sometimes seem to be influenced by ideology. We end by considering whether courts should consult survey evidence in resolving cases that involve government speech claims. An advantage of survey experiments is that they can be used to disentangle the effects of medium from the effects of message, reducing the risk that government speech doctrine will systematically favor some messages over others. To be sure, the use of survey evidence raises a number of implementation issues that require careful thought, but we ultimately conclude that an empirically informed government speech doctrine would protect First Amendment values more successfully than a doctrine dependent upon judicial guesswork.

A new two-level QR code with visual cryptography scheme

The Quick Response (QR) code is designed for information storage recognizable by machine vision. With the popularity of QR code applications, the security of QR codes becomes hot issues concerned by many scholars. In this paper, a novel QR code with two-level information storage is designed to protect private messages. In the meantime, the public level can be directly decoded by any standard QR reader. In contrast to other studies, the computational complexity of the proposed scheme is reduced by combining with the theory of visual cryptography scheme (VCS). In addition, an important characteristic of the QR code, error correction capability, is preserved in this paper, guaranteeing the robustness to QR code damage. Experimental results and analysis show that the proposed scheme is both feasible and reasonably secure, further enriching the application fields and outperforming the previous schemes significantly.

Content-Based Classification of Sensitive Tweets

Online Social Networks (OSNs), such as Facebook and Twitter, provide open platforms for users to easily share their statuses, opinions, and ideas, ranging from personal experiences/activities to breaking news. With the increasing popularity of online social networks and the explosion of blog and microblog messages, we have observed large amounts of potentially sensitive or private messages being published to OSNs inadvertently or voluntarily. The owners of these messages may become vulnerable to online stalkers or adversaries, especially considering that many online social network platforms (e.g. Twitter) provide open access to the public, including unregistered users and search engine bots. Studies show that users often regret posting sensitive or private messages. However, it is very difficult to completely erase such messages from the Internet, especially when the messages have been indexed by the search engines or forwarded (e.g. re-tweet in Twitter) by other users. Therefore, it is critical to identify messages that reveal private/sensitive information, and warn users before they post the messages to the public. However, the definition of sensitive information is subjective and different from user to user. For example, some users may feel comfortable sharing political opinions, while others do not. To develop a privacy protection mechanism that is customizable to fit the needs of diverse audiences, it is essential to accurately and automatically classify potentially sensitive messages into topic categories, such as health, politics, family, relationship, religion, etc. In this paper, we make the first attempt to classify sensitive tweets into 13 pre-defined topic categories. In particular, we model the semantic content of tweets with term distribution features as well as users’ topic-preferences based on personal tweet history. We also add domain-specific features, i.e. domain knowledge, to improve classification performance. Experiments show that our method can boost classification accuracy compared with the well-known Bag-of-Words and TF-IDF methods. a

Joint Feedback and Artificial Noise Design for Secure Communications Over Fading Channels Without Eavesdropper's CSI

Secure communication with noisy feedback is studied in this correspondence. Unlike the majority of previous research efforts where the eavesdropper's channel state information (CSI)—either instantaneous or statistical CSI, is known by the legitimate users, a joint feedback and artificial noise scheme without any eavesdropper's CSI is proposed. The proposed scheme lets the source and the legitimate destination alternatively transmit private messages and degrade the eavesdropper's channel quality in all transmission phases. An insightful discovery is that if the transmit power is lager than a certain threshold, a positive secrecy capacity can be achieved, which overcomes the problem that the secrecy cannot be achieved when the legitimate user's CSI is worse than the eavesdropper's. The secrecy capacity maximization problem is investigated by adaptive power allocation for the private signals and the artificial noise where a near optimal solution of the power of artificial noise is obtained under the high SNR situation. Finally, the numerical results verify the theoretical analysis and illustrate the secrecy performance of the proposed scheme.

Multiple-Layer Power Allocation for Two-User Gaussian Interference Channel

Interference has been a key challenge to wireless networks. As a fundamental transmission unit, the Gaussian interference channel (GIC) provides much insight on understanding the optimal transmission policy and the transmission limit over wireless networks. This paper investigates the multiple-layer power allocation of GIC that maximizes the system sum-rate. First, we derive the optimal signal-layer power allocation and the corresponding sum-rate in closed form for all cases of weak interference GIC based on the rate splitting scheme. Theoretical result indicates that: 1) In low power and asymmetric power regimes, the rate splitting scheme degrades to the pure public or private message transmission at transmitters and simple successive decoding process is efficient enough at receivers and 2) the signal-layer sum-rate is not concave for weak interference GIC and a frequency division scheme brings strict positive sum-rate gain for some power constraints. Second, we specify the relationship between the optimal bandwidth-power allocation of the frequency division scheme and the concave envelope of signal-layer sum-rate in the subband-layer. Finally, considering general GIC with time-varying flat fading, we present an optimal channel-state-layer power allocation associated with rate splitting and frequency division. Numerical results demonstrate that the comprehensive power allocation over the signal-layer, the frequency subbands, and the channel states can largely increase the sum-rate of weak interference GIC in most scenarios.

Durable coalitions and communication: Public versus private negotiations

We present a laboratory experiment to study the effect of communication on durable coalitions — coalitions that support the same allocation from one period to the next. We study a bargaining setting where the status quo policy is determined by the policy implemented in the previous period. Our main experimental treatment is the opportunity for subjects to negotiate with one another through unrestricted cheap-talk communication before a proposal is made and comes to a vote. We compare committees with no communication, committees where communication is public and messages are observed by all committee members, and committees where communication is private and any committee member can send a private message to any other committee member. We find that the opportunity to communicate has a significant impact on outcomes and coalitions. When communication is public, there are more universal coalitions and fewer majoritarian coalitions. With private communication, there are more majoritarian coalitions and fewer universal coalitions. With either type of communication coalitions occur more frequently and last longer than with no communication. The volume and content of communication is correlated with coalition type. These findings suggest a coordination role for communication that varies with the mode of communication.

Multi-Terminal Two-Hop Untrusted-Relay Networks With Hierarchical Security Guarantees

We consider a two-source two-destination two-hop relay network, where all data communication must be kept secret from the relay node. The model considered is the simplest primitive that embodies a multi-transmitter multi-receiver network that needs to communicate sharing an untrusted relay node. We focus on two scenarios. In the first scenario, each source aims to send two messages to be kept secret from the relay: a common message that should be decoded by both destinations, and a private message that should be decoded by the first destination while kept secret from the second one. We define an achievable rate region by utilizing stochastic encoding at the sources, the Gaussian noise cooperative jamming from the destinations, and compress-and-forward at the relay. In the second scenario, each source aims to send a confidential message to its intended destination, which should be kept secret from the other one as well as the relay. We define an achievable rate region using a combination of nested lattice codes and random binning at the sources, structured cooperative jamming from destinations, and scaled compute-and-forward at the relay. We also derive genie-aided outer bounds on the secrecy rate regions. We present numerical results that demonstrate the performance of the proposed achievable schemes. Overall, this paper provides insights into how to utilize an untrusted relay to communicate to destinations with different levels of security clearance, and how intentional interference is an enabler of communication.

Secrecy Capacity Achievable Time Reversal Pre-filter in MISO Communication System and the Unequal Secrecy Protection Application

Classical time reversal (TR) pre-filtering has been considered as one of the key physical layer security techniques for wireless communication applications in the last decade. This paper proposes a secrecy capacity achievable time reversal pre-filter to further enhance the confidentiality of a multi-input single-output (MISO) wireless communication system. In addition, an unequal secrecy protection (UESP) MISO broadcast configuration is constructed in frequency selective channels by exploiting classical and secrecy capacity achievable TR pre-filters, so that UESP wireless communication services can be offered. Theoretical proofs and simulation results show that the proposed TR pre-filter achieves the secrecy capacity in frequency selective channels (HIPERLAN/2 BranA), and the MISO broadcast configuration can provide mobile users with three levels of UESP hierarchical services in terms of public, private and confidential messages.

Broadcast Channels With Privacy Leakage Constraints

The broadcast channel (BC) with one common and two private messages with leakage constraints is studied, where leakage rate refers to the normalized mutual information between a message and a channel symbol string. Each private message is destined for a different user and the leakage rate to the other receiver must satisfy a constraint. This model captures several scenarios concerning secrecy, i.e., when both, either or neither of the private messages are secret. Inner and outer bounds on the leakage-capacity region are derived when the eavesdropper knows the codebook. The inner bound relies on a Marton-like code construction and the likelihood encoder. A Uniform Approximation Lemma is established that states that the marginal distribution induced by the encoder on each of the bins in the Marton codebook is approximately uniform. Without leakage constraints the inner bound recovers Marton's region and the outer bound reduces to the UVW-outer bound. The bounds match for semi-deterministic (SD) and physically degraded (PD) BCs, as well as for BCs with a degraded message set. The leakage-capacity regions of the SD-BC and the BC with a degraded message set recover past results for different secrecy scenarios. A Blackwell BC example illustrates the results and shows how its leakage-capacity region changes from the capacity region without secrecy to the secrecy-capacity regions for different secrecy scenarios.

Probabilistic-constrained robust secure transmission for energy harvesting over MISO channels

In this paper, we consider a system supporting simultaneous wireless information and power transfer (SWIPT),where the transmitter delivers private message to a destination receiver (DR) and powers to multipleenergy receivers (ERs) with multiple single-antenna external eavesdroppers (Eves). We study secure robust beamformer and powersplitting (PS) design under imperfect channel state information (CSI).The artificial noise (AN) scheme is further utilized at the transmitter to provide strong wireless security.We aim at maximizing the energy harvested by ERs subject to the transmission power constraint, a range of outageconstraints concerning the signal-to-interference-plus-noise ratio (SINR) recorded at the DR and the Eves, as well as concerningthe energy harvested at the DR. The energy harvesting maximization (EHM) problem is challenging to directly solve,we resort to Bernstein-type inequality restriction technique to reformulatethe original problem as a tractable approximated version. Numerical results show that our robust beamforming schemeoutperforms the beamforming scheme relying on the worst-case design philosophy.

Special issue on Big Data Security and Intelligent Data in Clouds (BDS‐IDC)

Special issue on Big Data Security and Intelligent Data in Clouds (<scp>BDS‐IDC</scp>)

No place for negative emotions? The effects of message valence, communication channel, and social distance on users’ willingness to respond to SNS status updates

The present study contributes to the investigation of communicative norms and social support in Social Network Sites (SNSs). We suggest that a positivity bias restricts the availability of social support users receive from others via public responses to negative status updates. Moderated mediation analyses of the data of an online experiment (N = 870, Mage = 25.16 years, 64% female) show that users are less willing to comment on negative status updates than on positive ones. In contrast, users are more willing to respond to negative status updates with private messages. These effects are moderated by the strength of the relationship between sender and receiver of the status update and mediated by perceived message appropriateness and support urgency. The results suggest that SNS users canalize supportive reactions to negative experience of their close SNS friends through private modes of communication.