1,895 research outputs found
Keeping Authorities "Honest or Bust" with Decentralized Witness Cosigning
The secret keys of critical network authorities - such as time, name,
certificate, and software update services - represent high-value targets for
hackers, criminals, and spy agencies wishing to use these keys secretly to
compromise other hosts. To protect authorities and their clients proactively
from undetected exploits and misuse, we introduce CoSi, a scalable witness
cosigning protocol ensuring that every authoritative statement is validated and
publicly logged by a diverse group of witnesses before any client will accept
it. A statement S collectively signed by W witnesses assures clients that S has
been seen, and not immediately found erroneous, by those W observers. Even if S
is compromised in a fashion not readily detectable by the witnesses, CoSi still
guarantees S's exposure to public scrutiny, forcing secrecy-minded attackers to
risk that the compromise will soon be detected by one of the W witnesses.
Because clients can verify collective signatures efficiently without
communication, CoSi protects clients' privacy, and offers the first
transparency mechanism effective against persistent man-in-the-middle attackers
who control a victim's Internet access, the authority's secret key, and several
witnesses' secret keys. CoSi builds on existing cryptographic multisignature
methods, scaling them to support thousands of witnesses via signature
aggregation over efficient communication trees. A working prototype
demonstrates CoSi in the context of timestamping and logging authorities,
enabling groups of over 8,000 distributed witnesses to cosign authoritative
statements in under two seconds.Comment: 20 pages, 7 figure
Fair signature exchange via delegation on ubiquitous networks
This paper addresses the issue of autonomous fair signature exchange in emerging ubiquitous (u-) commerce systems, which require that the exchange task be delegated to authorised devices for its autonomous and secure execution. Relevant existing work is either inefficient or ineffective in dealing with such delegated exchange. To rectify this situation, this paper aims to propose an effective, efficient and secure solution to the delegated exchange to support the important autonomy feature offered by u-commerce systems. The proposed work includes a novel approach to symmetric-key based verifiable proxy encryption to make the exchange delegation flexible, efficient and simple to implement on resource-limited devices commonly used in u-commerce systems. This approach is then applied to design a new exchange protocol. An analysis of the protocol is also provided to confirm its security and fairness. Moreover, a comparison with related work is presented to demonstrate its much better efficiency and simplicity
Novel Contract Signature based on Key Exchange
A contract signature is a particular form of digital multi-signature that only involves two signers. Contract signing plays a critical role in any business transaction, particularly in situations where the involved parties do not trust each other. One of the most significant concerns in exchange signatures is the fraudulent and unfair exchange, which occurs when one party gets the signature of another party without giving his own signature. In the view of these security concerns, this thesis presents a secure and fair contract signature scheme based on key exchange protocol. The security and protection of the proposed scheme is based on solving hard computational assumptions such as discrete logarithm problem (DLP). The proposed protocol is abuse-free. The proposed scheme targets to have lesser computational overhead and high-security features than existing scheme[1]. The proposed scheme has wide application in real life scenarios, such as in electronic cash system
Manifesting Unobtainable Secrets: Threshold Elliptic Curve Key Generation using Nested Shamir Secret Sharing
We present a mechanism to manifest unobtainable secrets using a nested Shamir
secret sharing scheme to create public/private key pairs for elliptic curves. A
threshold secret sharing scheme can be used as a decentralised trust mechanism
with applications in identity validation, message decryption, and agreement
empowerment. Decentralising trust means that there is no single point
vulnerability which could enable compromise of a system. Our primary interest
is in twisted Edwards curves as used in EdDSA, and the related Diffie-Hellman
key-exchange algorithms. The key generation is also decentralised, so can be
used as a decentralised secret RNG suitable for use in other algorithms. The
algorithms presented could be used to fill a ``[TBS]'' in the draft IETF
specification ``Threshold modes in elliptic curves'' published in 2020 and
updated in 2022
Comments on "A practical (t, n) threshold proxy signature scheme based on the RSA cryptosystem"
In a (t, n) proxy signature scheme, the original signer can delegate his/her signing capability to n proxy signers such that any t or more proxy singers can sign messages on behalf of the former, but t 1 or less of them cannot do the same thing
A PoW-less Bitcoin with Certified Byzantine Consensus
Distributed Ledger Technologies (DLTs), when managed by a few trusted
validators, require most but not all of the machinery available in public DLTs.
In this work, we explore one possible way to profit from this state of affairs.
We devise a combination of a modified Practical Byzantine Fault Tolerant (PBFT)
protocol and a revised Flexible Round-Optimized Schnorr Threshold Signatures
(FROST) scheme, and then we inject the resulting proof-of-authority consensus
algorithm into Bitcoin (chosen for the reliability, openness, and liveliness it
brings in), replacing its PoW machinery. The combined protocol may operate as a
modern, safe foundation for digital payment systems and Central Bank Digital
Currencies (CBDC)
Evolving Bitcoin Custody
The broad topic of this thesis is the design and analysis of Bitcoin custody
systems. Both the technology and threat landscape are evolving constantly.
Therefore, custody systems, defence strategies, and risk models should be
adaptive too.
We introduce Bitcoin custody by describing the different types, design
principles, phases and functions of custody systems. We review the technology
stack of these systems and focus on the fundamentals; key-management and
privacy. We present a perspective we call the systems view. It is an attempt to
capture the full complexity of a custody system, including technology, people,
and processes. We review existing custody systems and standards.
We explore Bitcoin covenants. This is a mechanism to enforce constraints on
transaction sequences. Although previous work has proposed how to construct and
apply Bitcoin covenants, these require modifying the consensus rules of
Bitcoin, a notoriously difficult task. We introduce the first detailed
exposition and security analysis of a deleted-key covenant protocol, which is
compatible with current consensus rules. We demonstrate a range of security
models for deleted-key covenants which seem practical, in particular, when
applied in autonomous (user-controlled) custody systems. We conclude with a
comparative analysis with previous proposals.
Covenants are often proclaimed to be an important primitive for custody
systems, but no complete design has been proposed to validate that claim. To
address this, we propose an autonomous custody system called Ajolote which uses
deleted-key covenants to enforce a vault sequence. We evaluate Ajolote with; a
model of its state dynamics, a privacy analysis, and a risk model. We propose a
threat model for custody systems which captures a realistic attacker for a
system with offline devices and user-verification. We perform ceremony analysis
to construct the risk model.Comment: PhD thesi
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