120 research outputs found
Lime: Data Lineage in the Malicious Environment
Intentional or unintentional leakage of confidential data is undoubtedly one
of the most severe security threats that organizations face in the digital era.
The threat now extends to our personal lives: a plethora of personal
information is available to social networks and smartphone providers and is
indirectly transferred to untrustworthy third party and fourth party
applications.
In this work, we present a generic data lineage framework LIME for data flow
across multiple entities that take two characteristic, principal roles (i.e.,
owner and consumer). We define the exact security guarantees required by such a
data lineage mechanism toward identification of a guilty entity, and identify
the simplifying non repudiation and honesty assumptions. We then develop and
analyze a novel accountable data transfer protocol between two entities within
a malicious environment by building upon oblivious transfer, robust
watermarking, and signature primitives. Finally, we perform an experimental
evaluation to demonstrate the practicality of our protocol
Distributed Key Generation for the Internet
Although distributed key generation (DKG) has been studied for some time, it has never been examined outside of the synchronous setting. We present the first realistic DKG architecture for use over the Internet. We propose a practical system model and define an efficient verifiable secret sharing scheme in it. We observe the necessity of Byzantine agreement for asynchronous DKG and analyze the difficulty of using a randomized protocol for it. Using our verifiable secret sharing scheme and a leader-based agreement protocol, we then design a DKG protocol for public-key cryptography. Finally, along with traditional proactive security, we also introduce group modification primitives in our system.
Using Sphinx to Improve Onion Routing Circuit Construction
This paper presents compact message formats for onion routing circuit construction using the Sphinx methodology developed for mixes. We significantly compress the circuit construction messages for three onion routing protocols that have emerged as enhancements to the Tor anonymizing network; namely, Tor with predistributed Diffie-Hellman values, pairing-based onion routing, and certificateless onion routing. Our new circuit constructions are also secure in the universal composability framework, a property that was missing from the original constructions. Further, we compare the performance of our schemes with their older counterparts as well as with each other
Asynchronous distributed private-key generators for identity-based cryptography
An identity-based encryption (IBE) scheme can greatly reduce the complexity of sending encrypted messages over the Internet. However, an IBE scheme necessarily requires a private-key generator (PKG), which can create private keys for clients, and so can passively eavesdrop on all encrypted communications. Although a distributed PKG has been suggested as a way to mitigate this problem for Boneh and Franklin’s IBE scheme, the security of this distributed protocol has not been proven and the proposed solution does not work over the asynchronous Internet. Further, a distributed PKG has not been considered for any other IBE scheme. In this paper, we design distributed PKG setup and private key extraction protocols in an asynchronous communication model for three important IBE schemes; namely, Boneh and Franklin’s IBE, Sakai and Kasahara’s IBE, and Boneh and Boyen’s BB1-IBE. We give special attention to the applicability of our protocols to all possible types of bilinear pairings and prove their IND-ID-CCA security in the random oracle model. Finally, we also perform a comparative analysis of these protocols and present recommendations for their use.
Introducing Accountability to Anonymity Networks
Many anonymous communication (AC) networks rely on routing traffic through
proxy nodes to obfuscate the originator of the traffic. Without an
accountability mechanism, exit proxy nodes risk sanctions by law enforcement if
users commit illegal actions through the AC network. We present BackRef, a
generic mechanism for AC networks that provides practical repudiation for the
proxy nodes by tracing back the selected outbound traffic to the predecessor
node (but not in the forward direction) through a cryptographically verifiable
chain. It also provides an option for full (or partial) traceability back to
the entry node or even to the corresponding user when all intermediate nodes
are cooperating. Moreover, to maintain a good balance between anonymity and
accountability, the protocol incorporates whitelist directories at exit proxy
nodes. BackRef offers improved deployability over the related work, and
introduces a novel concept of pseudonymous signatures that may be of
independent interest.
We exemplify the utility of BackRef by integrating it into the onion routing
(OR) protocol, and examine its deployability by considering several
system-level aspects. We also present the security definitions for the BackRef
system (namely, anonymity, backward traceability, no forward traceability, and
no false accusation) and conduct a formal security analysis of the OR protocol
with BackRef using ProVerif, an automated cryptographic protocol verifier,
establishing the aforementioned security properties against a strong
adversarial model
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
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