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1  Bitcoin / Development & Technical Discussion / Question about SegWit on: March 24, 2016, 02:19:45 PM
Suppose Alice is running "new" (SegWit-capable) client software, and sends some bitcoin to Bob, who is running an "old" (SegWit-oblivious) client, with a SegWIt transaction T1.

I understand that Bob would still be able to spend that bitcoin with a non-SegWit transaction T2, by providing the proper signature; is that correct?

But would Bob know what signature he must provide, without Alice telling him?  Or will Bob's client believe that the output of T1 is "anyone can spend", and assume that T2 does not require a signature?
2  Economy / Economics / A descriptive sum-of-bubbles model for the price of bitcoin on: April 22, 2015, 06:37:16 AM
Preliminary report - version 2015-05-04. Edits from previous versions:
* 2015-04-22 Fixed caption of Figure 4, added Figure 5.
* 2015-04-23 Added the section "Justification of the model"
* 2015-05-04 Better tuning of parameters (no more rising tails).  Extended price series to 2015-04-20 and added one more "standard" bubble covering the last month.  Added unsmoothed plots (Figures 2 and 8 ).  Added section "Modeling the 2014--2015 price variations" with a 20-bubble model (in blue).
* 2020-10-21 Fixed image links.


A descriptive sum-of-bubbles model for the price of bitcoin

Figure 1 below shows that the price history of bitcoin can be described fairly accurately by a model consisting of the sum of several idealized bubbles, each consisting of an exponential rise, an optional flat plateau, and an exponential tail.


[ Figure 1. A bubble model for the price of bitcoin, showing the smoothed actual price (grey), the modeled price (green), and the individual bubbles.  The brown line near the bottom is the ratio of the actual price to the model price.  Click on the image for a full-size version. ]


[ Figure 2. The same data and model in Figure 1, without smoothing. Click on the image for a full-size version. ]

Figures 3--6 below show three of those bubbles in linear scale.  Note that, on a log scale plot, such as Figure 1, the rise and tail of a single bubble are plotted as straight lines, but they are distorted into curves when added to other bubbles.


[ Figure 3. The bubble "2011-06" that peaked around June 08, 2011. Click on the image for a full-size version. ]


[ Figure 4. The bubble "2012-08" that peaked around 2012-09-09. Click on the image for a full-size version. ]


[ Figure 5. The bubble "2013-04", with a plateau from about April 5th to May 31st, 2013. Click on the image for a full-size version. ]


[ Figure 6. The bubble "2013-11" that peaked on November 28, 2013, 2013 (the all-time high). Click on the image for a full-size version. ]

The above model has 11 such bubbles.  The first one (red) accounts for the price between 2010-07-15 to 2010-09-30, and is essentially flat at about 0.06 $/BTC in that period.  All other bubbles have a relatively fast ascending rise, with the price increasing between 2% and 10% per day, and a tail that decays more gradually. Four of them have a flat plateau.

In the mathematical model each bubble extends over the entire range of dates considered, but is plotted only while it makes a significant contribution to the model price, specifically at least 5% of it.  Under this criterion, each bubble effectively starts to be relevant and noticeable a few months before the peak, and stop being relevant a few months after the peak.

The brown line in Figures 1 shows that the difference between the model price (green) and the actual smoothed price (grey) is rarely 50% down or 100% up, which is actually quite good considering that the price varied by a factor of about 20'000 = ~2'000'000% (from ~0.06 to ~1200 $/BTC) in the span of that plot.  The largest diferences occur just after the peaks of some bubbles (due to the strong oscillations in the price which are not represented in the model), during the rise of the "2011-06" bubble (which may be two nearly coincident bubbles), and in 2014--2015 (when there were large swings due to the MtGOX collapse, and to rumors and anti-rumors about tightening of the Chinese government decrees).  The 2014--2015 swings can be accurately modeled by adding a few more elements to the model; see below.

Justification of the model

There are infinitely many ways to approximate a function by a linear combination of "basis" functions. One may ask what is special about this bubble basis in particular.

For starters, the bubble basis elements are everywhere positive, and the least-squares fit uses them with positive coefficients.  Other general purpose bases -- such as Gaussian humps, wavelets, B-splines -- would probably require both positive and negative coefficients .

Moreover, the bubble basis above yields a fairly god unweighted least-squares fit, with small relative error, even though the target function varies by a factor of 20'000 over the domain considered.  Usually, least-squares approximations would spread the absolute error evenly over the domain, which would result in errors of tens of dollars even in the early years where the price was below 1 dollar.  (The plot above uses weighted least squares to improve the fit in the early years; however, the unweighted least-squares approximation, not shown, is nearly indistiguishable from that plot, except in the first 3 months Jul--Sep 2010.)

The basis is also very economical (only 11 elements with 45 total parameters) and is directly determined by salient features of the price series.  There are ten salient "bubble-like events", characterized by a period of rapidly increasing price, lasting for a month or more and raising the price by 50% or more, that ends abruptly, creating an evident "kink" in the log-scale plot. (The last two, peaking in early June 2014 and April 2015, are somewhat anomalous and less definite, as discussed below; but they still can be included in this description.)  Just before each kink, the log-scale plot is approximately straight and ascending, which means nearly-exponential growth. In all those ten cases, the kink  is followed by a descending line, initially straight; either immediately, or (in four cases) after a period when the price is nearly constant (once one discounts the influence of nearby bubbles).

After rising from January to late April 2013, and oscillating for about one month, the price spent another month at about 120 $/BTC, then gradually dipped between early June and July, gradually recovered by late August, and remained stable at about 120 $/BTC again, until October 2013, when the next bubble started.  This sequence may have been a single bubble-like event spanning those 10 months, with a temporary remission in the middle of its plateau.  However, it can be modeled fairly well by two flat-top bubble functions, with about the same amplitude.  The start of the sencond bubble's tail is not discernible in the data; it was arbitrarily set to begin around the date of PBoC's first decree (early December 2013) and decay with the same rate as the other Chinese bubbles.

There was also a sharp rise starting in 2014-05-20, that lifted the price fron ~450 $/BTC to ~660 $/BTC in about 10 days.  While the peak of this "mini-bubble" was not as sharp as that of other bubbles, the rise and subsequent slow decay can be modeled fairly well by a bubble function "2014-06" with the same rise and decay rates as the main Chinese bubble "2013-11".  Another similar mini-bubble "2015-03", also with approximately the same rise and decay rates, may have started in February 2015 and peaked on  2015-03-08 (althoug this identification is still quite uncertain.)

The basis merely includes one element for each of those bubble-like events, plus a constant term for the part before the first bubble (Jul--Sep 2010). Note that each pronounced discontinuity in the data calls for at least one basis element with a similar discontinuity.  The typical basis element has four adjustable parameters: its magnitude (the coefficient of the linear combination), the date of the peak, and the rates of the two exponentials. The four bubble elements with a constant section have one additional parameter each, the duration of that section.  Thus, the model has 1 + 4 x 10 + 4 = 45 adjustable parameters in all.

Actually, the rise rates of the last three bubble functions were constrained to be equal while fitting the model, and so were the decay rates of the last four.  These constraints were motivated by the conjecture that those bubbles were connected to the Chinese market (see below), and that their decays were equally affected by the Central Bank restrictions starting in December 2013, right after the all-time high.  Therefore, the number of adjustable parameters was only 40, not 45.

Moreover, the date and rate parameters of each basis element were chosen to match the date of the visible kink(s) of the corresponding event, and the slopes of the log-scale plot just before and just after those kink(s).  It is remarkable that the resulting model also approximates remarkably well the concave curved sections of the price plot between successive bubble events --- even though it has no extra parameters to control the shapes of those curves.

Finally, the basis elements can be interpreted in terms of real-world events and processes (see below); and the composition of the elements by addition (rather than, say, multiplication) is compatible with that interpretation.  Note, in particular, that the curved sections of the log-scale plot arise naturally from the additon of simple exponentials, each of them being straight on that plot.

As noted above, the "bubble event" that peaked in early June 2014 was somewhat anomalous, because the rise phase started quite abruptly on 2014-05-20, lasted only 10-15 days, and ended more gradually than previous events.  The last bubble, that peaked on early April 2015, has not lasted long enough to enable its shape to be discerned with confidence.  Even so, those two events can be adequately modeled by standard bubble functions without plateau, with relatively small error.

Descriptive, not predictive

The model is meant to be purely descriptive, not predictive. That is, it aims only to provide a succint description of the historical prices, without attempting to predict future prices.  If anything, it is "anti-predictive", because it implies that the past bubbles have exponentially decreasing relevance for the future prices, and any future bubbles cannot be detected until they are well underway.

Until mid-2014, it was widely claimed that the price would continue to grow, as it has done in the past, by a sequence of bubbles spaced roughly 9 months apart, with exponentially increasing peak amplitudes. However, this model suggests that such "exponential bubble train model" may be just an illusion.  The good fit of our model to the price, particularly between successive bubbles, suggests that bubbles are added rather than multiplied. It follows that each new bubble is only noticeable when its amplitude is substantially greater than the sum of all tails of the previous bubbles.  If a bubble like the "2011-06" one occurred today, for example, lifting the price by only 10 dollars, it would not be discernible at all.  Therefore, if bubbles actually occurred at random intervals and with random amplitudes, this masking effect would give the impression that bubble amplitudes are increasing.

Interpretation of bubbles as market openings

Although the model is not predictive, I believe that it is explanatory as well as descriptive.  Namely, each bubble can be conjectured to represent a surge in demand due to the opening of some new market.  Each market may be another community of users, isolated from the others by national, language, or legal barriers; or a new use of bitcoins.  

The exponential rise part of a bubble would then be due to the spread of demand in that market by "contagion", possibly amplified by media coverage and speculative demand.  The end of the rise would be due to saturation of that market. (In some bubbles one can see oscillations extending for a month or two after the end of the rise, presumably caused by panic and recovery among the speculators. These oscllations have not been included in the model yet.)  The plateau part of each bubble would be due to a period of relatively constant demand after the peak, while a decreasing tail could be due to gradual decrease of the demand, e.g. for disappointment, government repression, etc.

In particular, the bubble labeled "2013-11" ("Beijing 1", Figure 6) was almost certainly due to the opening of the Mainland Chinese market after the major exchanges Huobi and OKCoin started operating in Beijing, and a report about bitcoin was featured in mainstream Chinese media.  Local reports attribute the huge demand to a large contingent of amateur speculators that used to day-trade in commodities like tea or garlic, and found bitcoin more attractive for that purpose because of its higher volatility.  That is one of the fastest-rising bubbles in the model (about 10%/day).  It peaked at 2013-11-29, when the Central Bank of China (PBoC) intervened and banned the use of bitcoin in e-commerce and forbade financial institutions from dealing with it. That bubble then started decaying at about 0.55%/day.  

The earlier bubble "2013-04" ("Sanghai 1", Figure 5), that has a plateau from about April 5th to May 31, 2013, may have been created by demand in China, too; but by BTC-China in Shanghai, possibly catering to a different community.  BTC-China started operating well before that bubble, but in early 2013 it recruited Bobby Lee as CEO, a Stanford alumnus who formerly worked for Walmart. BTC-China's trading volume started growing exponentially in the first 3 months of 2013, and it was leading the price increase during that period.  In the model, it is assumed that the contribution of that demand to the price remained constant for 2 months and then started to decay.

It would be useful to identiy the markets and/or events that caused the other bubbles.  It has been claimed that one of them was caused by an article in the Wired magazine, for example.

Note that the relation between price increase and demand depends on the liquidity of the market, which is not known, and must be non-linear.  Therefore, the magnitude of each bubble should not be interpreted as a measure of the demand, but only of its effect on the price.

This in interpretation would confirm the claim that the model is not predictive, because the opening of markets in the past would hardly influence the opening of new markets in the future.  In particular, to have another bubble with magnitude above 1000 $/BTC, bitcoin woudl have to conquer some market with demand comparable to the Chinese one.  While there are conjectural candidates for such a market, the past history of the price cannot have much influence on that future event.

Modeling the 2014--2015 price variations

After the all-time high of 2013-11-29, the character of the price graph changed noticeably: instead of typical bubbles, there was a succession of sudden rises and dips, superimposed on the slowly decaying tails of the Chinese bubbles.  Most of these changes were clearly connected to news and rumors that affected either the Chinese or the non-Chinese day traders.  

For example, there was a partial recovery of the price in late December 2013, when some Chinese exchanges regained bank access that had ben closed earlier that month; then a sharp drop on 2014-02-10, then Mark Karpelès of MtGOX cleimed that there was a bug in the protocol; then a recovery on 2014-03-15.  There was also a sharp drop on 2014-03-26, when a Chinese newspaper leaked new of further PBoC restrictions; a recovery on 2014-04-15, when the announced deadline passed with no restrictions; then another sudden drop on 2014-04-25, when the restrictions began to be enforced and one major Chinese exchange had to close.  A sharp but smaller drop occurred on 2014-06-12, when the first USMS auction of the SilkRoad bitcoins was announced, which was reversed on 2014-06-30, when it became known that the auction had been won by entrepreneur Tim Draper.  Other short-lived spikes occurred when it became known that Microsoft was "accepting bitcoins" (which turned out to be only for a few digital products), when it was rumored that McDonalds would start accepting bitcoins on Valentine's day (it was "love" instead), when a statement by an OKCoin staffer was misinterpreted as saying that a large hedge fund would start trading bitcoins, and at several other times.  

These events were quite unlike the previous bubbles in that they had very fast rise and decay (often lasting less than a day), with gradually decaying price in between.  The decay could be attributed to the continuing decay of the main Chinese bubbles "2013-11" and "2014-06"; if these two elements are subtracted from the price, the variations in 2014 and 2015 cn be modeled fairly well by some rectangular pulses with nearly flat tops, and some sharp spikes, all with nearly vertical sides.  These pulses and spikes, in turn can be modeled by degenerate bubble functions with very fast rises and decays.  (Due to their short durations, it is not possible to tell whether the sides are indeed exponentials; but their shape has little effect on the goodness of fit.)  

Figures 7 and 8 below show a an extension of the model of Figures 1 and 2 that uses eight such degenerate bubble functions to model the main events in 2014 and 2015, plus one spike-like element "2011-05" to model the "stutter" during the rise of the "2011-06" bubble.  


[ Figure 7. A 20-bubble model for the price of bitcoin, showing the smoothed actual price (grey), the modeled price (green), and the individual bubbles.  The brown line near the bottom is the ratio of the actual price to the model price.  Click on the image for a full-size version. ]


[ Figure 8. The same data and model in Figure 7, without smoothing. Click on the image for a full-size version. ]


How the model was constructed

A typical bubble has 4 parameters: the rate of change per day during the rise part (always greater than 1), the date of the peak, the rate of change per day during the tail (less than 1, except for the "2010-07" and "2012-08" bubbles), and the magnitude at the peak. Some bubbles had one additional parameter, the duration of the plateau phase.

The number of bubbles in the model (11) and all bubble parameters except the peak magnitude were determined initially by hand, inspecting the price chart. They were then tweaked by variosu means to improve the fitting.

Once the other parameters were chosen, the bubble magnitudes were then determined by weighted least squares fitting of their linear combination to the observed prices P(i).  Each price datum P(i) was assigned a weight W(i) = 1/P(i), in order to simulate the effect of fitting the model in log scale, while actually using linear scale.  

The input prices and the component bubbles were smoothed with a Hann window spanning 2 weeks.
3  Other / Meta / Mysterious deletions -- Bitcointalk hacked? [NOT] on: April 19, 2015, 06:18:19 PM
Random posts are being deleted without explanation from the "Wall Observer" thread and perhaps other places.  The deletion messages have no explanations and say
Quote
You have just been sent a personal message by Bitcoin Forum on Bitcoin Forum.

Wild guess: the user name "Bitcoin_Forum" has admin privileges by default, and someone just created that account.

EDIT: No hacking, just some moderator not aware of the "anything goes" culture of that thread.
4  Other / Meta / Bitcointalk.org activity statistics by broad category on: September 26, 2014, 05:10:38 AM
Bitcointalk.org posts by topic, updated

Below is a breakdown of the 239 recently most active threads in this forum, captured a few hours ago.  For comparison, I copied the similar statistics tallied on June/21 and July/25:

2014-06-21    ! 2014-07-25    ! 2014-09-25    !
--------------+---------------+---------------+
Posts !     % ! Posts !     % ! Posts !     % ! Category                      
------+-------+-------+-------+-------+-------+--------------------------------
    8 |   6.7 |    14 |  12.6 |    28 |  11.7 | Off-topic                      
    4 |   3.3 |     7 |   6.3 |    15 |   6.3 | Gambling                      
   18 |  15.0 |    12 |  10.8 |    58 |  24.3 | Bitcoin mining                
   37 |  30.8 |    22 |  19.8 |    23 |   9.6 | Bitcoin non-mining            
   53 |  44.2 |    56 |  50.5 |   115 |  48.1 | Altcoins (including mining)    
------+-------+-------+-------+-------+-------+--------------------------------
  120 | 100.0 |   111 | 100.0 |   239 | 100.0 | TOTAL                          


Explanation

To create the last table, I quickly copied the first 6 pages of the list of most recent topics posted to, spanning about 1 hour, and manually classified the 240 threads listed there (minus one repeated entry) in the above categories. (This is not quite a sample of the recent posts, since each thread was counted only once even if it had several posts within that interval.  So the most active threads are under-represented.)

Comments

In all three epochs, about half of the activity seemed to be related to altcoins.  Activity about bitcoin proper (mining and non-mining) was 46%, 31% , and 34% in the three samples; the difference was taken over by gambling and other threads unrelated to cryptocoins.  

Among the posts about bitcoin proper, the fraction about mining seems to be increasing.

In June, of 37 posts about bitcoin proper, excluding mining, 18 (49%) were in Chinese language.  This time, the proportion was 9 out of 49  (16%) only.  (However, this proportion is likely to vary a lot along the day.  The last sample was taken at about 02:00--03:00 UTC, which is 10:00--11:00 am in China.  I did not record the hour of the previous two samples.)

EDIT: Here are the samples of thread headers used to make those tables:

2014-06-21
2014-07-25
2014-09-25

The headers were edited to remove funny characters and indicate the language (with [CN] or [Chinese], [RU], [DE] etc.).  Titles in some foreign languages were translated through Google.
5  Economy / Service Discussion / BTC stolen from PC wallet on: August 24, 2014, 01:56:30 PM
Moving off-topic discussion from the Tezor thread:

yesterday was some BTC stollen from my wallet (PC). I dont know how or who or how did this happened. [ ... ]
Impossible to say, as you don't know how they were stolen. [ ... ]

All I can found that BTC was sent to 183u3xkUUqpVwJmmLqqt14cchS5Mu9CQk7 and then to 17gH1u6VJwhVD9cWR59jfeinLMzag2GZ43 .. but I had some secure things like firewall antispam .. .etc. on my computer .. but i looks it is not enough .. So I hope trezor will make it safe for next time.

Were you handling that wallet when the first transaction happened, or shortly before?
No, only incoming trancaction All i See is one transaction few hours befonr.

Quote from: JorgeStolfi
Do you use Dropbox or some other external storage?
No external (Inet) devices .. only my own NAS with firewall and restricted IPs

Quote from: JorgeStolfi
Was the wallet totally emptied, or only part of it?
tottlly empty after that attack

Quote from: JorgeStolfi
What software/hardware did you use to generate your private keys?
sorry but I dont understand this queston. Do you mean passwords? Or what type of keys?

I meant, what software do you use to handle your wallet.  How did you create the private keys of the accounts that were emptied.
6  Local / 跳蚤市场 / 为什么今天的交易量如此之低在中国? / Why is trade volume so low in China today? on: June 23, 2014, 01:50:18 AM
这是上午09时半在中国。
贸易额就像是上午06点的。
为什么这么低?

It is 09:30 am in China. 
Trade volume is like at 03:00 am.
Why so low?


7  Economy / Economics / Reliable data on increasing adoption? on: June 21, 2014, 05:35:56 PM
There are recurrent claims that "bitcoin adoption is increasing", but there seems to be few if any reliable numbers suporting the claim, and a few signs that it may not be true.

* The number of stores that "accept bitcoin" through Bitpay or similar service appears to be growing; but since the lowest ("starter") level of merchant registration in Bitpay is free (with a 1% fee on each payment), that number does not imply growing number of clients, or growing volume of payments.  Moreover, it is hard to guess what percentage of the people who use Bitpay are "new adopters", or old adopters that buy more bitcoins specifically to use the service.  It may be that most Bitpay clients are old adopters who use Bitpay to spend their old coins, since that payment method does not seem to have any advantage for the other two categories.

* Bitpay declared that they processed payments totalling 100 M USD in 2013.  However it is not known how much of that is actual commercial payments (bitcoins changing owner in exchange for goods or services other than national  currencies); as opposed to coins being bought or sold for investment and speculation.

*  Blockchain traffic analysis shows subtantial transaction volume: about 100 kBTC/day = 60 M USD/day presently.  However, the evolution of these numbers since January suggests that only a small fraction of that volume is actual commercial payments, the rest being investment/speculation or coins being moved between addresses belonging to the same person.

* The number of new posts on bitcointalk.org had its peak in January 2014 and has then stagnated.  A visual scan of the recent posts page suggests that many of the new posts are now about altcoins. The number of registered members keeps increasing by 15'000 -- 20'000 per month, but there is no data on how many cease to be active.  The number of active members may well be stagnating or decreasing. The number of pages read per month keeps increasing, slowly, but that may be a consequence of the increased number of topics.  In any case, a breakdown of these numbers by geographic country or region and by topic would be necessary to interpret them.
8  Local / 中文 (Chinese) / Payment day in China / 付款日在中国 on: April 25, 2014, 01:45:23 AM
[ Sorry for posting in English but I do not speak Chinese and do not trust Google Translate. ]

Is there a "standard" day of the month when salaries are paid in China?  End of every month? Beginning of every month?  Middle of every month?

The reason for asking is: perhaps more money enters the exchanges on certain days of the month than in others.  That would cause the price of BTC to go up.

[ Google translation follows.  I hope that it makes sense. ]
[谷歌翻译如下。我希望这是有道理的。]

有一个月的工资时支付在中国的一个“标准”的一天?每月结束了吗?开始每月?每个月的中间?

究其原因,问的是:也许更多的资金进入交易所在每月的某几天比其他国家小。这将导致BTC的价格上去。
9  Local / 中文 (Chinese) / Why is the volume so low? 为什么是体积如此之低? on: April 24, 2014, 04:20:15 AM
[ Sorry for posting in English but I do not speak Chinese and do not trust Google Translate. ]

The daily trading volume in the main Chinese exchanges (Huobi and OKCoin) was very low yesterday (Apr/23).  The volume is even lower today (Apr/24).  May be one of the lowest daily volumes of this year.

What could be the cause of the low volume?  Is today a holiday in China?

[ Google translation follows.  I hope that it makes sense. ]
[谷歌翻译如下。我希望这是有道理的。]

[对不起,张贴在英语,但我不会说中国话和不信任谷歌翻译。]

在中国主要的交流(Huobi和OKCoin)的每日成交量很低昨日(Apr/23)。体积甚至更低今日(Apr/24)。可能是最低的日成交量今年之一。

这可能是低量的原因是什么?今天是中国的假期呢?

10  Economy / Economics / Risk of the police misidentifying the owner of an address on: April 22, 2014, 07:27:52 PM
I wonder if the anonimity of bitcoin addresses could create risks of misidentification of address owners by the police, even for people who have never used bitcoins.

Suppose that a "bandit" X generates a new address A1, deposits a pile of "dirty" bitcoins in it.

X then makes some small purchase from a retailer Z, pretending to be some other person Y who has nothing to do with the matter.  He provides Y's physical address for delivery (if the purchase is a physical item) and pays in bitcoins out of address A1 to the retailer's address A2. Then X moves the rest of the dirty coins from A1 to a tumbler, or whatever.

While following the trail of the "dirty" bitcoins, the police gets to address A1, notices the small transaction to address A2, that they recognize as belonging to retailer Z. From the retailer's record of the purchase, they identify Y and conclude that he must be the owner of address A1 and hence of the "dirty" coins.

For bandit X, the purpose of this this ruse would be to delay the police's pursuit, or even permanently derail it.  He could choose the innocent decoy Y so that the suspicion would seem plausible -- eg. someone not very computer-savy and with criminal background, large debts, drug addiction, etc. 

Many variants of this trick seem possible.  Bandit X could do the same with dozens of decoys, to get the police bogged down into checking dozens of false leads. 

Is this risk significant?  If so, how could it be reduced?

Criminals already use this trick with bank accounts. However, the risk for bandit X is very high in the bank version, because he must steal Y's identity and impersonate him when creating the bank account A1.  On the other hand, the police usually can figure out very quickly that Y did not create that account nor issue the payment and transfer orders.  (Here in Brazil, the innocent victim Y is called "an orange" in fraud jargon, and he is usually some poor semi-literate guy who does not even have a bank account and lives far from the branch where the account is opened.)

With bitcoin addresses, however, the risk for X is very small, since he does not have to get Y's documents nor interact with anyone else to pull the trick, other than issue the bitcoin transaction requests and the bogus purchase order in Y's name; while Y can be any person in the world, and he has no way of proving to the police that he is not the owner of address A1 and did not make the fatal purchase.   His only hope is that the police can trace the path of the purchase order and/or the bitcoin transaction requests on the internet, and determine that they could not have been issued from any computer that Y could have accessed.
11  Local / Economia & Mercado / Alerta sobre investimento em bitcoin on: April 15, 2014, 02:23:08 AM
Nas duas últimas semanas aparceram artigos sobre bitcoin nos principais meios de comunicaçãodo Brasil - Folha, Estadão, Globo, Correio Braziliense...  No geral positivos, esses artigos omitem os podres - MtGOX, Neo&Bee, preço em queda, restrições na China e outros países, ...

Em outros threads deste forum li várias refrências à América Latina (algumas bastante ofensivas até) como o último grande repositório de "bobos ricos" que poderiam trazer novo dinheiro para o mercado e levantar o preço do Bitcoin, compensando a perda gradual (e talvez, em breve, súbita) da China.  E infelizmente já estão atacando: ja há muitos "vendedores" de bitcoin no Brasil prometendo mil e umas virtudes, só falta curar câncer e trazer de volta a namorada.  Saiu até no Wall Street Journal, por exemplo, que na Agentina tem uma dona prometendo que bitcoin vai valer um milhão de dólares algum dia.

Quaisquer que sejam as virtudes reais do bitcoin, hoje ele é  um péssimo investimento.  O preço não está amarrado a nada (porque é 450 dólares, e não 4.50 ou 45000?) caiu mais de 60% desde novembro,  e tem caído continuamente desde fevereiro.  A taxa de "inflação" do bitcoin desde janeiro foi de 350% ao ano, muito mais que a do Real (6.5%), a do Peso argentino (11%) e até mesmo do Bolívar venezuelano (53%).  As razões da queda são conhecidas (estrangulamento do mercado da China, falência de exchanges, ...) e não há previsão de fatos positivos que possam reverter essa queda -- exceto a possível exploração dos "bobos ricos" na América Latina.

Mesmo a longo prazo, o sucesso do bitcoin está mais nebuloso que nunca.  Muitos países estã banindo ou restringindo seu uso comercial.   A maioria das bolsas e outras empresas baseadas em bitcoin opera fora de qualquer estrutura legal, e ninguém sabe como regulamentá-las sem estragar a idéia.   Sua suposta imunidade contra interferência do governo foi desmentida.  Sua suposta escassez foi negada pelo surgimento e sobrevivência das moedas alternativas.  A mineração está ficando concentrada empoucas empresas e está cada vez menos rentável.  E por aí vai.

Todo adulto que não seja incapacitado mentalmente tem direito de fazer o que quiser com seu dinheiro, inclusive jogar fora.  Se alguém quiser apostar nessa loteria doida que é o preço do bitcoin, conhecendo os fatos e os riscos, tudo bem, é problema dele.  Mas tentar vender bitcoin a pessoas sem conhecimento avançado de computação, como "bom investimento" -- sem avisar o freguês sobre todos esses problemas e podres, e mentindo sobre as chances do preço subir às alturas -- isso é vigarice, pura e simples. 
12  Other / Meta / The "delete" button should leave a stub behind on: April 12, 2014, 10:57:33 PM
[ Apologies if this has been suggested before, I did not find it with "search". ]

The "delete" button should not delete the post completely, instead it should leave behind an empty placeholder record.

Currently, when a post is deleted, links to that post are broken in a rather unfriendly way. Also, all subsequent posts in the thread are repaginated, which makes the Google Search cache obsolete from that point on.  (A user recently deleted hundreds of his old posts in many threads, messing up that cache completely.)

This is a link to a deleted post:
[ This is a test post to understand how "delete" works, for a discussion on the "meta" thread. Sorry for the noise, please ignore ]

A reader who clicks on the link in that quotation will be shown a page with unrelated posts, none of them containing that text.  How could he guess what happened?

The suggestion is that "delete" should leave behind an empty placeholder post, which would be rendered as one line saying "[ this post has been deleted by the author ]", with the original date and sequence number.  That way the pagination of subsequent posts would not change, Google Search would point to the correct place, and readers who followed links to that post would not waste time reading the wrong entries and trying to make sense of them.

Even if the deleted post was the last one on its thread, it cannot be "hard deleted" since some reader may have already saved its URL in order to insert it in another post, or some page external to the forum.


Perhaps one should retain a "hard delete" facility, but for administrator use only, with the nderstanding that it may cause the above problems.
13  Bitcoin / Development & Technical Discussion / Would miners ever want to generate "fake" transaction volume? on: April 02, 2014, 03:41:22 AM
(Apologies if this is a stupid question)

Could it be advantageous, in some circumstances, for the miners to collectively generate "bogus" transaction volume?

By that I mean a large number of perfectly valid transactions that merely shuffle coins between two or more addresses owned by the same miner.

Presumably there is no advantage for a single miner to do this, but what about an hypothetical mining cartel that accounted for a sizable percentage of all the mining activity?
14  Other / Meta / Google search returns wrong links on: March 29, 2014, 06:08:50 AM
Google search on the thread Wall Observer BTC/USD - Bitcoin price movement tracking & discussion returns pointers to the wrong pages.

A user recently deleted all his posts (hundreds?) on that thread. Presumably messages moved to different pages, and the Google database needs to be updated/rebuilt.
15  Economy / Speculation / Priice oscillations at MtGox on: January 01, 2014, 02:56:08 PM
There is apeculiar pattern at Mt Gox / USD that does not occur at Bitstamp ot Btc-China. The price oscillates by 5-10 USD between the lowest ask and the highest bid, with one cycle or more per minute. Volume is very low, less than 10 BTC per minute, or less than 5 BTC per transaction. At each cycle the price at both ends usually increases by a few USD.

This pattern has been going on at least since 2013-12-30, except for a few hours in the early morning of 2013-12-31.  Otherwise MtGox/USD seems to have few transacctions; on some days, less than one per hour.

Curiously Mt Gox seems to have been offline for about 1.5h around 2014-01-01 02:00 UTC, yet the price kept inching up during that time.

Presumably that slow creep upwards of the charted price convinces many traders to revise their bids/offers upwards, so as to remain within a preset distance from the current price.

Does this make sense, or am I allucinating?

16  Economy / Marketplace / Market share of major exchanges on: December 15, 2013, 04:34:43 PM
I have seen some pie charts claiming that the market is split roughly equally among BTC-China, Mt.Gox, Bitstamp.  However, by these charts
http://bitcoincharts.com/charts/btcnCNY#rg2zigHourlyztgSzm1g10zm2g25zv
the traded volume (say, per hour) at BTC-China is almost 10 times larger than either of the other two.

What is the truth?
17  Economy / Economics / How many people are trading bitcoins? on: December 10, 2013, 08:12:52 AM
Is is possible to estimate how many distinct people are actually trading bitcoins in a given day (or week, or month)?
18  Economy / Economics / What will the "steady state" look like? on: December 10, 2013, 04:38:32 AM
Let's assume that the bitcoin "network" will be alive 10 years from now.  What will it look like?

Let's say that the "material value" of a bitcoin, at a certain moment, is the amount of materal goods one could buy with it at that moment. (This notion is a bit fuzzy because the demand for different goods like cars and houses may vary in different ways. But we may ignore that problem for this discussion.)

10 years ffrom now, the material value of a bitcoin, like that of any commodity, is likely to be some predictable "trend" plus some unpredictable "noise".   How big will be the noise compared to the trend?   That is, by how much can one expect the material value of a bitcoin to change in addition to the predictable trend in the next hour? In the next day? Month? Year?

What will be the prevailing predictable trend for the material value of a bitcoin:  constant? Increasing (deflation)?  Decreasing (inflation)?  By how much % per year?

Since there are only ~20 million bitcoins, if 2 billion people are using bitcoins, the average wallet will have 1/100 of a bitcoin.  How much would that buy, if translated in today's dollars?
19  Economy / Speculation / Why are prices so different between exchanges? on: December 09, 2013, 04:34:17 PM
Just moments ago, 1 BTC was 900 USD on Mt Gox, 850 USD on Btc-e. 

Why is there such a large price difference between exchanges? What prevents people from making a profit by buying bitcoins on BTC-e and selling them on Mt Gox, until the prices match?  Is it the difficulty of moving dollars between the two countries?
20  Economy / Economics / Bitcoin will one day be superseded by a technically superior NuCoin. What then? on: December 09, 2013, 02:55:50 AM
Bitcoin cannot claim eternal divine perfection, so inevitably there will arise a "NuCoin" that has the same nice properties but is technically better in some respect -- and will therefore replace Bitcoin as  the preferred medium of payment for internet commerce.   

What will happen to the Bitcoin then? Owners of course would like to swap them for equal worth of NuCoins.  But who will agree to the swap?
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