Finding Safety in Numbers with Secure Allegation Escrows

For fear of retribution, the victim of a crime may be willing to report it only if other victims of the same perpetrator also step forward. Common examples include 1) identifying oneself as the victim of sexual harassment, especially by a person in a position of authority or 2) accusing an influential politician, an authoritarian government, or ones own employer of corruption. To handle such situations, legal literature has proposed the concept of an allegation escrow: a neutral third-party that collects allegations anonymously, matches them against each other, and de-anonymizes allegers only after de-anonymity thresholds (in terms of number of co-allegers), pre-specified by the allegers, are reached. An allegation escrow can be realized as a single trusted third party; however, this party must be trusted to keep the identity of the alleger and content of the allegation private. To address this problem, this paper introduces Secure Allegation Escrows (SAE, pronounced "say"). A SAE is a group of parties with independent interests and motives, acting jointly as an escrow for collecting allegations from individuals, matching the allegations, and de-anonymizing the allegations when designated thresholds are reached. By design, SAEs provide a very strong property: No less than a majority of parties constituting a SAE can de-anonymize or disclose the content of an allegation without a sufficient number of matching allegations (even in collusion with any number of other allegers). Once a sufficient number of matching allegations exist, the join escrow discloses the allegation with the allegers' identities. We describe how SAEs can be constructed using a novel authentication protocol and a novel allegation matching and bucketing algorithm, provide formal proofs of the security of our constructions, and evaluate a prototype implementation, demonstrating feasibility in practice.Comment: To appear in NDSS 2020. New version includes improvements to writing and proof. The protocol is unchange

A Certificateless One-Way Group Key Agreement Protocol for Point-to-Point Email Encryption

Over the years, email has evolved and grown to one of the most widely used form of communication between individuals and organizations. Nonetheless, the current information technology standards do not value the significance of email security in today\u27s technologically advanced world. Not until recently, email services such as Yahoo and Google started to encrypt emails for privacy protection. Despite that, the encrypted emails will be decrypted and stored in the email service provider\u27s servers as backup. If the server is hacked or compromised, it can lead to leakage and modification of one\u27s email. Therefore, there is a strong need for point-to-point (P2P) email encryption to protect email user\u27s privacy. P2P email encryption schemes strongly rely on the underlying Public Key Cryptosystems (PKC). The evolution of the public key cryptography from the traditional PKC to the Identity-based PKC (ID-PKC) and then to the Certificateless PKC (CL-PKC) provides a better and more suitable cryptosystem to implement P2P email encryption. Many current public-key based cryptographic protocols either suffer from the expensive public-key certificate infrastructure (in traditional PKC) or the key escrow problem (in ID-PKC). CL-PKC is a relatively new cryptosystem that was designed to overcome both problems. In this thesis, we present a CL-PKC group key agreement protocol, which is, as the author\u27s knowledge, the first one with all the following features in one protocol: (1) certificateless and thus there is no key escrow problem and no public key certificate infrastructure is required. (2) one-way group key agreement and thus no back-and-forth message exchange is required; (3) n-party group key agreement (not just 2- or 3-party); and (4) no secret channel is required for key distribution. With the above features, P2P email encryption can be implemented securely and efficiently. This thesis provides a security proof for the proposed protocol using ``proof by simulation\u27\u27. Efficiency analysis of the protocol is also presented in this thesis. In addition, we have implemented the prototypes (email encryption systems) in two different scenarios in this thesis

Building Secure and Anonymous Communication Channel: Formal Model and its Prototype Implementation

Various techniques need to be combined to realize anonymously authenticated communication. Cryptographic tools enable anonymous user authentication while anonymous communication protocols hide users' IP addresses from service providers. One simple approach for realizing anonymously authenticated communication is their simple combination, but this gives rise to another issue; how to build a secure channel. The current public key infrastructure cannot be used since the user's public key identifies the user. To cope with this issue, we propose a protocol that uses identity-based encryption for packet encryption without sacrificing anonymity, and group signature for anonymous user authentication. Communications in the protocol take place through proxy entities that conceal users' IP addresses from service providers. The underlying group signature is customized to meet our objective and improve its efficiency. We also introduce a proof-of-concept implementation to demonstrate the protocol's feasibility. We compare its performance to SSL communication and demonstrate its practicality, and conclude that the protocol realizes secure, anonymous, and authenticated communication between users and service providers with practical performance.Comment: This is a preprint version of our paper presented in SAC'14, March 24-28, 2014, Gyeongju, Korea. ACMSAC 201

A Certificateless One-Way Group Key Agreement Protocol for End-to-End Email Encryption

Over the years, email has evolved into one of the most widely used communication channels for both individuals and organizations. However, despite near ubiquitous use in much of the world, current information technology standards do not place emphasis on email security. Not until recently, webmail services such as Yahoo\u27s mail and Google\u27s gmail started to encrypt emails for privacy protection. However, the encrypted emails will be decrypted and stored in the service provider\u27s servers. If the servers are malicious or compromised, all the stored emails can be read, copied and altered. Thus, there is a strong need for end-to-end (E2E) email encryption to protect email user\u27s privacy. In this paper, we present a certificateless one-way group key agreement protocol with the following features, which are suitable to implement E2E email encryption: (1) certificateless and thus there is no key escrow problem and no public key certificate infrastructure is required; (2) one-way group key agreement and thus no back-and-forth message exchange is required; and (3) n-party group key agreement (not just 2- or 3-party). This paper also provides a security proof for the proposed protocol using proof by simulation . Finally, efficiency analysis of the protocol is presented at the end of the paper

Leak-Free Mediated Group Signatures

Group signatures are a useful cryptographic construct for privacy-preserving non-repudiable authentication, and there have been many group signature schemes. In this paper, we introduce a variant of group signatures that offers two new security properties called leak-freedom and immediate-revocation. Intuitively, the former ensures that an insider (i.e., an authorized but malicious signer) be unable to convince an outsider (e.g., signature receiver) that she indeed signed a certain message; whereas the latter ensures that the authorization for a user to issue group signatures can be immediately revoked whenever the need arises (temporarily or permanently). These properties are not offered in existing group signature schemes, nor captured by their security definitions. However, these properties might be crucial to a large class of enterprise-centric applications because they are desirable from the perspective of the enterprises who adopt group signatures or are the group signatures liability-holders (i.e., will be hold accountable for the consequences of group signatures). In addition to introducing these new securit

A survey on wireless body area networks: architecture, security challenges and research opportunities.

In the era of communication technologies, wireless healthcare networks enable innovative applications to enhance the quality of patients’ lives, provide useful monitoring tools for caregivers, and allows timely intervention. However, due to the sensitive information within the Wireless Body Area Networks (WBANs), insecure data violates the patients’ privacy and may consequently lead to improper medical diagnosis and/or treatment. Achieving a high level of security and privacy in WBAN involves various challenges due to its resource limitations and critical applications. In this paper, a comprehensive survey of the WBAN technology is provided, with a particular focus on the security and privacy concerns along with their countermeasures, followed by proposed research directions and open issues

Development of a certificate less digital signature scheme & implementation in e-cash system

Today’s wireless communication systems having limited computational resources and communication bandwidth find certificate less public-key cryptosystems very attractive and vital to their operations in the sense that they help in reducing a significant amount of data load on the network. To eliminate the need of public key digital certificates Shamir proposed ID based cryptosystems in which the user’s identity (e.g. name or email id) is used as the public key. However this method had a major drawback of the key escrow problem as a result of which certificate less digital signature (CDS) came into light. The main idea behind CDS is that there’s a private key generator (PKG) which generates a partial private key for the user .Then using that key and some of its own private information the user computes its actual private key. PKG’s public parameters and the user’s private key together calculate the user’s public key. Harn, Ren and Lin in 2008 proposed a CDS model which consisted of four generic modules namely PKG, user key generation, signature generation and verification. In this paper, we propose an improvement of the aforesaid CDS scheme in terms of time complexity and signature length and implement the new scheme in an e-cash model proposed by Popescu and Oros. Performance analysis of both the schemes has been carried out in details