Sturm auf den Reichstag: Ermittlungen gegen Aufwieglerin ...

2016-02-10: I qualified as an expert witness on Bitcoin in federal criminal court in the USA.

A public defender, for whom I have worked in the past, called me late the week before, asking if I could explain Bitcoin to the judge and jury in a case being tried in federal criminal court in West Palm Beach. (I have not read the government's complaint, but I gather that the case involved alleged drug importation and distribution, paid for with bitcoins.)
This is in addition to a different state criminal case in Miami involving the selling of bitcoins via LocalBitcoins, for which I was hired as an expert witness last year. That one is still awaiting trial.
I was particularly impressed by how well the prosecutor understood Bitcoin. I had expected the usual Sturm und Drang that one fears in such situations, but he knew about Gyft, Newegg, Overstock, etc., and was generally positive. Of course, he asked during my cross-examination, whether Bitcoin could be used for illegal activity, and I acknowledged that, like bottles of Liquid Tide, Bitcoin can be used to purchase illegal goods.
I was fascinated at how interested the jurors were in my testimony. While I was waiting for the IT expert witness for the prosecution ahead of me to finish his testimony, most were reasonably attentive, but some seemed to be a bit distracted. However, once we got past the preliminaries during my testimony, I noticed that they were watching me closely, and nodding as I invoked metaphors like boxes of poker chips that cannot be counterfeited and unimaginably wide spreadsheets that get updated every ten minutes, and described some of the work that my students and I do with Bitcoin entrepreneurs in Africa through Conscious Entrepreneurship Foundation.
All in all, it was pretty straightforward.
Given that I am in South Florida—former home of Cryptsy—I expect that we'll be seeing more of this kind of thing in the future.
submitted by pecuniology to btc [link] [comments]

Compact Multi-Signatures for Smaller Blockchains

Cryptology ePrint Archive: Report 2018/483
Date: 2018-06-10
Author(s): Dan Boneh, Manu Drijvers, Gregory Neven

Link to Paper


Abstract
We construct new multi-signature schemes that provide new functionality. Our schemes are designed to reduce the size of the Bitcoin blockchain, but are useful in many other settings where multi-signatures are needed. All our constructions support both signature compression and public-key aggregation. Hence, to verify that a number of parties signed a common message m, the verifier only needs a short multi-signature, a short aggregation of their public keys, and the message m. We give new constructions that are derived from Schnorr signatures and from BLS signatures. Our constructions are in the plain public key model, meaning that users do not need to prove knowledge or possession of their secret key.
In addition, we construct the first short accountable-subgroup multi-signature (ASM) scheme. An ASM scheme enables any subset S of a set of n parties to sign a message m so that a valid signature discloses which subset generated the signature (hence the subset S is accountable for signing m). We construct the first ASM scheme where signature size is only O(k) bits over the description of S, where k is the security parameter. Similarly, the aggregate public key is only O(k) bits, independent of n. The signing process is non-interactive. Our ASM scheme is very practical and well suited for compressing the data needed to spend funds from a t-of-n Multisig Bitcoin address, for any (polynomial size) t and n.

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submitted by dj-gutz to myrXiv [link] [comments]

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