Ruhe vor dem Sturm?: Anhaltende Seitwärtstendenz beim ...

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.

References
  1. Ahn, J.H., Green, M., Hohenberger, S.: Synchronized aggregate signatures: new definitions, constructions and applications. In: Al-Shaer, E., Keromytis, A.D., Shmatikov, V. (eds.) ACM CCS 10: 17th Conference on Computer and Communications Security. pp. 473–484. ACM Press, Chicago, Illinois, USA (Oct 4–8, 2010)
  2. Andresen, G.: m-of-n standard transactions. Bitcoin improvement proposal (BIP) 0011 (2011)
  3. Bagherzandi, A., Cheon, J.H., Jarecki, S.: Multisignatures secure under the discrete logarithm assumption and a generalized forking lemma. In: Ning, P., Syverson, P.F., Jha, S. (eds.) ACM CCS 08: 15th Conference on Computer and Communications Security. pp. 449–458. ACM Press, Alexandria, Virginia, USA (Oct 27–31, 2008)
  4. Bagherzandi, A., Jarecki, S.: Multisignatures using proofs of secret key possession, as secure as the Diffie-Hellman problem. In: Ostrovsky, R., Prisco, R.D., Visconti, I. (eds.) SCN 08: 6th International Conference on Security in Communication Networks. Lecture Notes in Computer Science, vol. 5229, pp. 218–235. Springer, Heidelberg, Germany, Amalfi, Italy (Sep 10–12, 2008)
  5. Bansarkhani, R.E., Sturm, J.: An efficient lattice-based multisignature scheme with applications to bitcoins. In: Foresti, S., Persiano, G. (eds.) CANS 16: 15th International Conference on Cryptology and Network Security. Lecture Notes in Computer Science, vol. 10052, pp. 140–155. Springer, Heidelberg, Germany, Milan, Italy (Nov 14–16, 2016)
  6. Barreto, P.S.L.M., Lynn, B., Scott, M.: On the selection of pairing-friendly groups. In: Matsui, M., Zuccherato, R.J. (eds.) SAC 2003: 10th Annual International Workshop on Selected Areas in Cryptography. Lecture Notes in Computer Science, vol. 3006, pp. 17–25. Springer, Heidelberg, Germany, Ottawa, Ontario, Canada (Aug 14–15, 2004)
  7. Bellare, M., Namprempre, C., Neven, G.: Unrestricted aggregate signatures. In: Arge, L., Cachin, C., Jurdzinski, T., Tarlecki, A. (eds.) ICALP 2007: 34th International Colloquium on Automata, Languages and Programming. Lecture Notes in Computer Science, vol. 4596, pp. 411–422. Springer, Heidelberg, Germany, Wroclaw, Poland (Jul 9–13, 2007)
  8. Bellare, M., Namprempre, C., Pointcheval, D., Semanko, M.: The one-more-RSAinversion problems and the security of Chaum’s blind signature scheme. Journal of Cryptology 16(3), 185–215 (Jun 2003)
  9. Bellare, M., Neven, G.: Multi-signatures in the plain public-key model and a general forking lemma. In: Juels, A., Wright, R.N., Vimercati, S. (eds.) ACM CCS 06: 13th Conference on Computer and Communications Security. pp. 390–399. ACM Press, Alexandria, Virginia, USA (Oct 30 – Nov 3, 2006)
  10. Boldyreva, A.: Threshold signatures, multisignatures and blind signatures based on the gap-Diffie-Hellman-group signature scheme. In: Desmedt, Y. (ed.) PKC 2003: 6th International Workshop on Theory and Practice in Public Key Cryptography. Lecture Notes in Computer Science, vol. 2567, pp. 31–46. Springer, Heidelberg, Germany, Miami, FL, USA (Jan 6–8, 2003)
  11. Boldyreva, A., Gentry, C., O’Neill, A., Yum, D.H.: Ordered multisignatures and identity-based sequential aggregate signatures, with applications to secure routing. In: Ning, P., di Vimercati, S.D.C., Syverson, P.F. (eds.) ACM CCS 07: 14th Conference on Computer and Communications Security. pp. 276–285. ACM Press, Alexandria, Virginia, USA (Oct 28–31, 2007)
  12. Boneh, D., Gentry, C., Lynn, B., Shacham, H.: Aggregate and verifiably encrypted signatures from bilinear maps. In: Biham, E. (ed.) Advances in Cryptology – EUROCRYPT 2003. Lecture Notes in Computer Science, vol. 2656, pp. 416–432. Springer, Heidelberg, Germany, Warsaw, Poland (May 4–8, 2003)
  13. Boneh, D., Lynn, B., Shacham, H.: Short signatures from the Weil pairing. In: Boyd, C. (ed.) Advances in Cryptology – ASIACRYPT 2001. Lecture Notes in Computer Science, vol. 2248, pp. 514–532. Springer, Heidelberg, Germany, Gold Coast, Australia (Dec 9–13, 2001)
  14. Brogle, K., Goldberg, S., Reyzin, L.: Sequential aggregate signatures with lazy verification from trapdoor permutations - (extended abstract). In: Wang, X., Sako, K. (eds.) Advances in Cryptology – ASIACRYPT 2012. Lecture Notes in Computer Science, vol. 7658, pp. 644–662. Springer, Heidelberg, Germany, Beijing, China (Dec 2–6, 2012)
  15. Budroni, A., Pintore, F.: Efficient hash maps to G2 on BLS curves. Cryptology ePrint Archive, Report 2017/419 (2017), http://eprint.iacr.org/2017/419
  16. Burmester, M., Desmedt, Y., Doi, H., Mambo, M., Okamoto, E., Tada, M., Yoshifuji, Y.: A structured ElGamal-type multisignature scheme. In: Imai, H., Zheng, Y. (eds.) PKC 2000: 3rd International Workshop on Theory and Practice in Public Key Cryptography. Lecture Notes in Computer Science, vol. 1751, pp. 466–483. Springer, Heidelberg, Germany, Melbourne, Victoria, Australia (Jan 18–20, 2000)
  17. Castelluccia, C., Jarecki, S., Kim, J., Tsudik, G.: A robust multisignatures scheme with applications to acknowledgment aggregation. In: Blundo, C., Cimato, S. (eds.) SCN 04: 4th International Conference on Security in Communication Networks. Lecture Notes in Computer Science, vol. 3352, pp. 193–207. Springer, Heidelberg, Germany, Amalfi, Italy (Sep 8–10, 2005)
  18. Certicom Research: Sec 2: Recommended elliptic curve domain parameters. Tech. rep., Certicom Research (2010)
  19. Chang, C.C., Leu, J.J., Huang, P.C., Lee, W.B.: A scheme for obtaining a message from the digital multisignature. In: Imai, H., Zheng, Y. (eds.) PKC’98: 1st International Workshop on Theory and Practice in Public Key Cryptography. Lecture Notes in Computer Science, vol. 1431, pp. 154–163. Springer, Heidelberg, Germany, Pacifico Yokohama, Japan (Feb 5–6, 1998)
  20. Coron, J.S., Naccache, D.: Boneh et al.’s k-element aggregate extraction assumption is equivalent to the Diffie-Hellman assumption. In: Laih, C.S. (ed.) Advances in Cryptology – ASIACRYPT 2003. Lecture Notes in Computer Science, vol. 2894, pp. 392–397. Springer, Heidelberg, Germany, Taipei, Taiwan (Nov 30 – Dec 4, 2003)
  21. Drijvers, M., EdalatNejad, K., Ford, B., Neven, G.: Okamoto beats Schnorr: On the provable security of multi-signatures. Cryptology ePrint Archive, Report 2018/417 (2018), https://eprint.iacr.org/2018/417
  22. Fuentes-Casta˜neda, L., Knapp, E., Rodr´ıguez-Henr´ıquez, F.: Faster hashing to ð2. In: Miri, A., Vaudenay, S. (eds.) SAC 2011: 18th Annual International Workshop on Selected Areas in Cryptography. Lecture Notes in Computer Science, vol. 7118, pp. 412–430. Springer, Heidelberg, Germany, Toronto, Ontario, Canada (Aug 11–12, 2012)
  23. Gentry, C., O’Neill, A., Reyzin, L.: A unified framework for trapdoor-permutationbased sequential aggregate signatures. In: Abdalla, M., Dahab, R. (eds.) PKC 2018: 21st International Conference on Theory and Practice of Public Key Cryptography, Part II. Lecture Notes in Computer Science, vol. 10770, pp. 34–57. Springer, Heidelberg, Germany, Rio de Janeiro, Brazil (Mar 25–29, 2018)
  24. Gentry, C., Ramzan, Z.: Identity-based aggregate signatures. In: Yung, M., Dodis, Y., Kiayias, A., Malkin, T. (eds.) PKC 2006: 9th International Conference on Theory and Practice of Public Key Cryptography. Lecture Notes in Computer Science, vol. 3958, pp. 257–273. Springer, Heidelberg, Germany, New York, NY, USA (Apr 24–26, 2006)
  25. Hardjono, T., Zheng, Y.: A practical digital multisignature scheme based on discrete logarithms. In: Seberry, J., Zheng, Y. (eds.) Advances in Cryptology – AUSCRYPT’92. Lecture Notes in Computer Science, vol. 718, pp. 122–132. Springer, Heidelberg, Germany, Gold Coast, Queensland, Australia (Dec 13–16, 1993)
  26. Harn, L.: Group-oriented (t, n) threshold digital signature scheme and digital multisignature. IEE Proceedings-Computers and Digital Techniques 141(5), 307–313 (1994)
  27. Horster, P., Michels, M., Petersen, H.: Meta-multisignature schemes based on the discrete logarithm problem. In: Information Securitythe Next Decade. pp. 128–142. Springer (1995)
  28. Itakura, K., Nakamura, K.: A public-key cryptosystem suitable for digital multisignatures. Tech. rep., NEC Research and Development (1983)
  29. Komano, Y., Ohta, K., Shimbo, A., Kawamura, S.: Formal security model of multisignatures. In: Katsikas, S.K., Lopez, J., Backes, M., Gritzalis, S., Preneel, B. (eds.) ISC 2006: 9th International Conference on Information Security. Lecture Notes in Computer Science, vol. 4176, pp. 146–160. Springer, Heidelberg, Germany, Samos Island, Greece (Aug 30 – Sep 2, 2006)
  30. Le, D.P., Bonnecaze, A., Gabillon, A.: Multisignatures as secure as the DiffieHellman problem in the plain public-key model. In: Shacham, H., Waters, B. (eds.) PAIRING 2009: 3rd International Conference on Pairing-based Cryptography. Lecture Notes in Computer Science, vol. 5671, pp. 35–51. Springer, Heidelberg, Germany, Palo Alto, CA, USA (Aug 12–14, 2009)
  31. Li, C.M., Hwang, T., Lee, N.Y.: Threshold-multisignature schemes where suspected forgery implies traceability of adversarial shareholders. In: Santis, A.D. (ed.) Advances in Cryptology – EUROCRYPT’94. Lecture Notes in Computer Science, vol. 950, pp. 194–204. Springer, Heidelberg, Germany, Perugia, Italy (May 9–12, 1995)
  32. Lu, S., Ostrovsky, R., Sahai, A., Shacham, H., Waters, B.: Sequential aggregate signatures and multisignatures without random oracles. In: Vaudenay, S. (ed.) Advances in Cryptology – EUROCRYPT 2006. Lecture Notes in Computer Science, vol. 4004, pp. 465–485. Springer, Heidelberg, Germany, St. Petersburg, Russia (May 28 – Jun 1, 2006)
  33. Lysyanskaya, A., Micali, S., Reyzin, L., Shacham, H.: Sequential aggregate signatures from trapdoor permutations. In: Cachin, C., Camenisch, J. (eds.) Advances in Cryptology – EUROCRYPT 2004. Lecture Notes in Computer Science, vol. 3027, pp. 74–90. Springer, Heidelberg, Germany, Interlaken, Switzerland (May 2–6, 2004)
  34. Ma, C., Weng, J., Li, Y., Deng, R.: Efficient discrete logarithm based multisignature scheme in the plain public key model. Designs, Codes and Cryptography 54(2), 121–133 (2010)
  35. Maxwell, G., Poelstra, A., Seurin, Y., Wuille, P.: Simple schnorr multi-signatures with applications to bitcoin. Cryptology ePrint Archive, Report 2018/068 (2018), https://eprint.iacr.org/2018/068/20180118:124757
  36. Maxwell, G., Poelstra, A., Seurin, Y., Wuille, P.: Simple schnorr multi-signatures with applications to bitcoin. Cryptology ePrint Archive, Report 2018/068 (2018), https://eprint.iacr.org/2018/068/20180520:191909
  37. Merkle, R.C.: A digital signature based on a conventional encryption function. In: Pomerance, C. (ed.) Advances in Cryptology – CRYPTO’87. Lecture Notes in Computer Science, vol. 293, pp. 369–378. Springer, Heidelberg, Germany, Santa Barbara, CA, USA (Aug 16–20, 1988)
  38. Micali, S., Ohta, K., Reyzin, L.: Accountable-subgroup multisignatures: Extended abstract. In: ACM CCS 01: 8th Conference on Computer and Communications Security. pp. 245–254. ACM Press, Philadelphia, PA, USA (Nov 5–8, 2001)
  39. Michels, M., Horster, P.: On the risk of disruption in several multiparty signature schemes. In: International Conference on the Theory and Application of Cryptology and Information Security. pp. 334–345. Springer (1996)
  40. Nakamoto, S.: Bitcoin: A peer-to-peer electronic cash system (2008), http://bitcoin.org/bitcoin.pdf
  41. Neven, G.: Efficient sequential aggregate signed data. In: Smart, N.P. (ed.) Advances in Cryptology – EUROCRYPT 2008. Lecture Notes in Computer Science, vol. 4965, pp. 52–69. Springer, Heidelberg, Germany, Istanbul, Turkey (Apr 13–17, 2008)
  42. Ohta, K., Okamoto, T.: A digital multisignature scheme based on the Fiat-Shamir scheme. In: Imai, H., Rivest, R.L., Matsumoto, T. (eds.) Advances in Cryptology – ASIACRYPT’91. Lecture Notes in Computer Science, vol. 739, pp. 139–148. Springer, Heidelberg, Germany, Fujiyoshida, Japan (Nov 11–14, 1993)
  43. Ohta, K., Okamoto, T.: Multi-signature schemes secure against active insider attacks. IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences 82(1), 21–31 (1999)
  44. Okamoto, T.: Provably secure and practical identification schemes and corresponding signature schemes. In: Brickell, E.F. (ed.) Advances in Cryptology – CRYPTO’92. Lecture Notes in Computer Science, vol. 740, pp. 31–53. Springer, Heidelberg, Germany, Santa Barbara, CA, USA (Aug 16–20, 1993)
  45. Park, S., Park, S., Kim, K., Won, D.: Two efficient RSA multisignature schemes. In: Han, Y., Okamoto, T., Qing, S. (eds.) ICICS 97: 1st International Conference on Information and Communication Security. Lecture Notes in Computer Science, vol. 1334, pp. 217–222. Springer, Heidelberg, Germany, Beijing, China (Nov 11–14, 1997)
  46. Pointcheval, D., Stern, J.: Security arguments for digital signatures and blind signatures. Journal of Cryptology 13(3), 361–396 (2000)
  47. Ristenpart, T., Yilek, S.: The power of proofs-of-possession: Securing multiparty signatures against rogue-key attacks. In: Naor, M. (ed.) Advances in Cryptology – EUROCRYPT 2007. Lecture Notes in Computer Science, vol. 4515, pp. 228–245. Springer, Heidelberg, Germany, Barcelona, Spain (May 20–24, 2007)
  48. Schnorr, C.P.: Efficient signature generation by smart cards. Journal of Cryptology 4(3), 161–174 (1991)
  49. Scott, M., Benger, N., Charlemagne, M., Perez, L.J.D., Kachisa, E.J.: Fast hashing to g2 on pairing-friendly curves. In: Shacham, H., Waters, B. (eds.) PAIRING 2009: 3rd International Conference on Pairing-based Cryptography. Lecture Notes in Computer Science, vol. 5671, pp. 102–113. Springer, Heidelberg, Germany, Palo Alto, CA, USA (Aug 12–14, 2009)
submitted by dj-gutz to myrXiv [link] [comments]

Bitcoin & Co. #2: Die Zeichen stehen auf Sturm! Ist jetzt die Zeit von Bitcoin gekommen? BITCOIN Ruhe vor dem Sturm?! Die Ruhe vor dem Sturm?  Bitcoin Update #1 - YouTube Ist es schon zu spät, um zu kaufen? - Die Ruhe vor dem Bitcoin Sturm Bitcoin - Ist das die Ruhe vor dem Sturm? - YouTube

Obwohl die älteste Kryptowährung Bitcoin eigentlich für hohe Volatilität bekannt ist, hat sie in den vergangenen Monaten ausgesprochen stabil tendiert. Verschiedene Indikatoren zeigen nun an ... Bitcoin – Ruhe vor dem Sturm? - Lesen Sie auch weitere News zu Thema (Kryptohandel, Kryptoaktie, Kryptowährung) - ICOs auf BITCOIN • KRYPTO Die Analysefirma ARK Invest hat ihre "Big Ideas 2020" veröffentlicht. Darin geht es neben den Aussichten bei Trendthemen wie Deep Learning, Stream... Das Bitcoin Halving wird in ungefähr 8 Tagen stattfinden und einige Investoren, die das Geschehen bislang von der Seitenlinie verfolgt haben, könnten bald in den Markt treten und Bitcoin kaufen, um von einem möglichen noch bevorstehenden Hype zu profitieren. Wie Crypto News Flash bereits berichtete, gehen die Meinungen stark auseinander ... Ruhe vor dem Sturm: Bullishe Verschnaufpause bei Bitcoin und Co. von Stefan Lübeck. Am 19. Oktober 2020 19. Oktober 2020 · Lesezeit: 7 Minuten. Stefan Lübeck. Stefan Lübeck arbeitet als freiberuflicher Analyst für BTC-ECHO. Stefan ist seit über einem Jahrzehnt Trader und Chartanalyst am klassischen Markt und weiterte seine Analysen Mitte 2017 auf den Kryptomarkt aus. Der studierte ...

[index] [35369] [2208] [30490] [13853] [13480] [18308] [50931] [47698] [29704] [35636]

Bitcoin & Co. #2: Die Zeichen stehen auf Sturm! Ist jetzt die Zeit von Bitcoin gekommen?

Bitcoin Kurs Prognose: Wie tief fällt BTC noch? Bringt das Halving die Wende? BTC in 2020/2021 Bringt das Halving die Wende? BTC in 2020/2021 - Duration: 16:30. Gerade erleben wir die Ruhe vor dem Bitcoin Sturm, darum stellt sich vielen die Frage: Soll ich jetzt kaufen oder ist es schon zu spät? Das Bitcoin-Halving ist mittlerweile 2 Wochen her. Der Kurs ... Bricht Bitcoin bald aus? Wir schauen uns in dem Video den Chart an und analysieren die aktuellen News. Tritt der CoinCheck-Community bei: 👥 ABO! Verpasse kei... This video is unavailable. Watch Queue Queue. Watch Queue Queue * Bitcoin bei 11.000 Dollar diese Woche? „unmittelbarer“ Bull-Run voraus ? * BTC ist ein perfekter Sturm der Technologie, aber XRP ist überlegen * Wie US Ame...

#