Cryptocurrency
Crypto currencies are private scooped money or fiat money in the form of digital cash. With them principles of cryptography are used to implement a distributed, decentralized and secure system of a digital complementary currency. The first publicly -traded currency of this kind is the traded since 2009 Bitcoin. Since then, numerous other crypto currencies have been implemented ( see table). In addition to the better known are modeled after the Bitcoin now about 100 other crypto currencies in use.
Just as the currently prevailing fiat or central bank money crypto currencies other than the use value lack some or internal ( intrinsic ) value. The only comes from the acceptance of trading partners ( payers recipients ). The results from the uses and the benefits that result from it. In place of a printed piece of paper ( bill ) or an embossed piece of metal ( coin) for the representation of the exchange value of the possession of a cryptographic key occurs at a cryptologically also signed credit in a collaborative accounting.
Besides the cryptographic implementation is a major difference of most crypto currencies as commonplace familiar money that nobody is able to accelerate its production, impair or abuse significantly in any way. Crypto currencies do not require central banks and subject to any authority or other organization. Through its decentralized structure they have, in contrast to central bank money is no single point of failure that could jeopardize the currency or even manipulate. Instead, a certain amount of currency is produced jointly by the entire system, where the rate is pre- determined and published or limited by the cryptographic mode of production. However, this is to the effect into perspective that some crypto currencies are entirely produced quasi- centrally from owner-managed private companies, such as the Ripple, where the for-profit company Ripple Labs holds 80 percent of new issues and distributed by their own rules.
By cryptographically secure protocols and decentralized data storage crypto currencies allow cashless digital payments without central entities such as banks.
- 3.1 The problem
- 3.2 The approach
- 3.3 Divisible blocks
- 5.1 anonymization
- 5.2 Zerocoin
- 6.1 Software Errors
- 6.2 Specialized Hardware
- 6.3 majority decision by computing power
- 6.4 Data Loss and Data Theft
- 6.5 distribution
- 6.6 rate fluctuations and price manipulation
- 6.7 Other
Operation
A currency without intrinsic value can only work if a sufficient degree of confidence is given to the parties involved. In conventional fiat money the central bank must be trusted. In cryptographic currencies new issues and transactions are confirmed by a majority of fundamentally distrustful and mutually controlling participants.
Since binary information are freely reproducible, it must also be ensured that the amount in circulation does not increase as with any other cashless payment system. A transaction is thus only valid when the sum of the inputs ( of which account is withdrawn an amount ) is equal to the sum of the outputs ( on account, an amount is added ) is. The only exception are new issues, which also in turn pre-set and comprehensible for all rules must be followed in order to achieve the necessary confidence.
In ordinary non-cash payments of participants in a instance must be operated (bank, credit card company, etc.) trust that these monitors compliance with the rules and enforces. In crypto currencies the task of the community of all stakeholders is transmitted. Corrections to the system are possible only if the majority of the participants agree to these by application. For example, a noncompliant transaction due to a software error was mostly automatically accepted at Bitcoin on August 15, 2010. This transaction resulted in a credit of 184 billion BTC ( Bitcoins ) on two accounts. This corresponded to a sudden multiplication of the money supply and thus a drastic inflation of existing assets. Fixed could be this error by creating a new corrected software was put into circulation, which rejected this transaction to be non- compliant. But since no one can correct the distributed database of all transactions, the error was only resolved when a majority of the participants, the new software long enough were applying to build a new longer and thus higher priority block chain with transaction confirmations.
With the exception of the above already mentioned privately operated crypto currencies in which a company gives a special role that work jointly operated on a democratic basis. Here, however, we come to the next fundamental problem. Democracies in the traditional sense based on the equal distribution of voting rights over a defined group of people. On the Internet, people are not clearly identifiable. For reasons of discretion, an identification is also not desirable. Crypto currencies must therefore distribute the voting rights in a different way. Here, predominantly two principles apply. Proof of work (English proof-of -work ) and the proof of Shares (English proof-of- stake ). In the detection by working more influence the participant receives on the overall system by solving arithmetic problems and is able to detect time spent computing power. By solving the largest possible number of tasks the participants will not only have more influence on the system, but also increases its chances of profiting by new issues and transaction fees. Through these incentives to deliver computing power at the same time also ensures that there is always a sufficient number of participants sufficient computing power to expend in order to keep the system in operation. The tasks are therefore designed so that they do the bookkeeping of the system in its entirety.
In the detection of shares he receives more influence and perks that already holds large shares of the credit. Not only the balance, but will be evaluated in part its age. An example of this is the Peercoin. Jointly operated crypto currencies are therefore using a special, strongly deviates from the everyday notion of democracy.
The Expend highest possible computational performance to greater chances to have to take advantage of new issues is also referred to as mining. Transferred to the German one also speaks to mine crypto currencies. Since with crypto currencies are traded in real goods and they are exchanged in conventional currencies, there is a real economic incentive to solve the math problems for digging provided as efficiently as possible. This led to progressively using specialized hardware. First, normal processors, how they work in PCs, used, and soon after there were implementations took advantage of the graphics processors. Meanwhile, based equipment is traded on FPGAs and ASICs that have been specially developed for this purpose. This resulted in a massive increase in computing power. As an example, rose at Bitcoin the time spent computing power from January 2013 to January 2014 on the 660fache. For the individual user of an ordinary PC, it is so attractive for crypto currencies in which a competition between the computing power prevails, become almost impossible in new issues or transaction fees to have part.
To this effect, the increasing number of participants and the Moore 's law to meet, have crypto currencies via customizable difficulty levels ( engl. difficulty ) in the provided computing tasks. So only those solved tasks are accepted by the participants, which correspond to a pre-determined and regularly adapted difficulty. This emission rate can be kept constant and the cost will be raised for a possible manipulation. The principles of proof-of -work and the holding of Shares may also be combined. So may Holder great, old as possible balances with Peercoin submit solutions with reduced difficulty. The resulting higher chance of allocation of new issues or transaction fees will be considered by the creators of this crypto currency as a kind of return on these assets.
Realization
There are dozens of specifications for achieving crypto currencies. Most of them operate according to similar principles as Bitcoin and have a common structure varies only the design in detail at the usually.
Signed P2P networking of participants
All participants are communicating with each other via a peer-to - peer network. Each message is that a participant in this network sends available for each other. However, it will not be sent as a broadcast, but gradually passed usual as in P2P networks. A message that is sent in this network corresponds to a publication to all participants.
First, each new participant generates a pair of keys of an asymmetric cryptosystem. The public key is possibly also published elsewhere over the P2P network. The private secret key now allows to sign orders for transactions cryptographically the participants. Each user can open itself in this way an account. The account has a newly created account on a balance of zero. The release key is virtually the account number and is referred to in English as Account Address. The private key ensures the power of disposal over the account. Since each participant can basically create any number of such key pairs, this file designated as a wallet (English for wallet ) are kept.
Will now another participant to transfer an amount to the newly established account, so he creates a transfer order with the amount that the public key of the target account and signed this contract with his secret key. This order is published on the P2P network. He now needs to be verified and authenticated in the joint accounts as transaction and archived.
Each participant can verify on the basis of the public key that the transfer order was actually created by the sender legitimate. This theft is prevented from foreign accounts. Can then be checked against the previously archived accounting, whether the despatching account also has the necessary funds. Thus the coating of an account, or the double output of the balance is prevented. Only when the transfer order has been accepted compliant with the rules, a participant will try to have him registered in the accounting department.
Accounting
Until now, the crypto- currency consists only of a P2P network in which signed messages are published with asymmetric cryptography. The essential part is the particular form of accounting. This consists of data blocks each reference their predecessors, thus forming a chain. Each data block forms a new side of the common accounting. Each participant of this accounting would add a new block is dropped therein may also enter a transaction out of nowhere on his own account, apart from the confirmatory newly incurred transactions. The consumer is thus bound to this block specified by the rules component of the new issue. For this reason, many participants are eager to create such new blocks and publish.
To reduce the risks of new issues this creation of new blocks is associated with a difficulty. For this purpose, a realized as a cryptologic hash function one-way function must be calculated from the block. This hash must meet a generally accepted condition to be recognized as a valid new block. In the simplest case, the value is below a predetermined threshold must occur. The smaller the threshold is, the lower the probability that the re- calculated hash value is less. Accordingly, it is difficult to create such a block. The participant must now change as long as until he has created a valid block whose hash value is below the threshold the block. To each block contains a value called a nonce, whose only function is to be changed to the hash value of the entire block as long as the condition is fulfilled characterized. Since there is a one-way function, it is not possible to calculate the required nonce directly. The difficulty, then, is as long as the hash value of changed blocks to calculate until happened to have a value less than the specified threshold is reached. As a hash function of various crypto currencies, inter alia, SHA -2 ( Bitcoin, Peercoin ), SHA -3 ( Copperlark ) Scrypt ( Litecoin, Worldcoin ), ECDSA (ripple ) and POW ( Proto shares) used.
To document the complete sequence of blocks tamper-proof, each new block must also contain the hash value of its predecessor. This form a chain the blocks later the gapless unchanged context for each is easily verifiable. The high overhead of creating new blocks of regulated not only limits the rate of new issues, but simultaneously increases the effort to create a fake. If a user has created the first valid new block he may publish it in the P2P network. The other participants can test it and if it meets the agreed rules, it is added to the current block chain and accepted as a new last block in the chain.
The transactions contained in the new block are thus initially confirmed only by this one participant who produced the block. They are thus limited credibility. If the block but also accepted by the other participants as valid, this its Hash value will enter in their newly created blocks. Keeps the majority of participants for the block is valid, the chain so the fastest grow further, starting from this block. Does it not consider it valid for the chain is starting to grow further from the last block so far. Thus, the blocks do not form a simple chain but a tree. Only the first block from the ( root ) longest chain contained in the tree is considered to be valid. This is automatic this form of accounting from those blocks that have the majority accepted as valid. This first block with a crypto currency will also be launched is called based on the biblical story of creation as Genesis block. It is included in many cases in the operating software of the crypto currency already and the only block that does not contain a hash value of a predecessor.
Each participant generated based on a block a new, accepts and confirms the previous blocks compliant with the rules. The more these blocks are generated based on an existing block, the better the operations contained therein are collectively confirmed, and thus irreversibly recorded in the network. By adjusting the level of difficulty at the time spent by the users computing power, the rate can be successfully created using the new blocks can be adjusted. With Bitcoin, this value is adjusted after 2016 blocks that average with a new block every 10 minutes can be expected. The adaptation thus takes place approximately every two weeks. Who wants to carry out a transaction and this needs to confirmed by the network of participants, so you have an average of 10 minutes till it has been entered in a new block. After about an hour this block were added five more. Who wanted to now, these transactions in question would have to spend six times as much computing power as the entire rest of the participants to establish a valid alternative branch in the block chain worldwide. This makes it nearly impossible once to delete registered transactions or to change.
Transaction fees
To avoid attacks on the operation of a crypto currency due to overload (Denial -of -service attacks ), transaction charges are levied to avoid the pointless transfers of small amounts. This transaction fees will be charged by the creator of a new block in it, may register the transfer of the agreed amount on his own account. The transaction fees form so that in addition to the new issues as an incentive to participate in the creation of new blocks. They still make even an economic incentive to participate, if not profitable new missions take place any more.
Since block sizes are limited, it is possible that transactions have to wait longer to be included in a new block. Will the initiator of the transaction he may accelerate this process voluntarily enter a higher transaction fee in its transfer order. The other participants are then preferably install this transaction in their new blocks to record these higher transaction fee for itself.
Summary
The steps in the operation of a decentralized crypto- currency are:
The steps to run it from overlapping. It searches continuously for new blocks and just continuously new transactions are created. For each node change in the likelihood of finding a new block by inserting a new transaction not. Since each node preferred his own public key for the reception of the new issue enters, the blocks are worked on simultaneously worldwide is all different.
Scalability
The problem
The application of current crypto currencies in the manner described here comes in practice to restrictions with regard to the time behavior as well as the communication and memory requirements. If you want to check the credibility of a transfer or an Account balances must be the current block chain right back to Genesis know block. To this end, each participant a complete copy of the current global accounting needs to store in the P2P network of currency. The practical application of a crypto currency with the same self-evident, such as a credit card, would drive the accounting quickly in difficult to handle proportions.
By comparison, the top-selling Bitcoin crypto- currency had an average of 30 transactions per minute in December 2013. The Visa Inc., with an accounting system that was tested in August 2013 to 47,000 transactions per second compared 200,000. Despite the comparatively small booking volumes, the memory requirement of the block chain of Bitcoin rose in 2013 by about 8.8 GB to 12.6 GB. Each participant should now at constant conditions approx. 24,7 MB upload daily from the net and make the P2P concept and corresponding again to others.
The limited rate to produce new blocks and the indeterminism of the process lead to unpredictable long confirmation times. For example, the difficulty level is adjusted only once every two weeks, and then to generate as exactly every 10 minutes a new block at the Bitcoin. Fluctuations actually operated computing power and the principle immanent scattering lead while waiting the transaction acknowledgments from 5 to 20 minutes. Therefore Newer crypto currencies work with modified adaptations of the difficulty level and partly elevated rates for block production.
The approach
Must be abandoned after all do the same in order to achieve workable rates for a widespread everyday use cash the P2P approach. The immense memory requirement could then be realized with archive servers that store as only the entire block chain. Build on this work fully validating server by working initially the block chain from the archive servers but downloaded in only a part of it. You assume the actual load of the resulting bookings. Participants could then software to simplify the verification of payments ( engl. simplified payment verification (SPV ) ) operate to and received from the servers only partial information.
In practice, service providers would be conceivable that similar to an insurance policy to a transfer order to carry out inspections and ensure that the residual risk. A customer just needs to know his account and can with its private crypto keys ( the wallet ) without a copy of the block chain create a transfer order and digitally sign. The dealer could send him to his service to review and would like a quick result as in other non-cash means of payment. The immediate payment for example using a smartphone at the checkout of a retailer is thus conceivable.
These approaches lead but again the introduction of a service layer, and would give up the original idea of a currency which is without a trusted third party (german trusted third party ). However, the entire procedure, unlike banks would still be transparent to everyone. How could also access the full extent of the archive server, if he sees a reason to date whenever necessary. With the described hereinafter concept divisible blocks, individual bookings with SPV applications can be checked without a service layer to have to trust.
Divisible blocks
If in each block, the hash value over the complete predecessor is stored, each one also needs the full block to check the completeness of the chain. So you need the entire accounting, even if you are not interested in every individual booking. Hash trees are used to prevent this. Rather than determining a hash value of the entire block, one can also calculate the hash values of individual transactions and organize them as a hash tree. At the root of the tree is thus obtained again a hash that protects all transactions summarized. Thus, a block header can be created that contains only the hash value of its predecessor, the nonce and the hash value of the root - own tree.
The single block becomes larger but the completeness of the chain can be checked now, using only the comparatively small block header. These headers can be so easy to store and are not dependent on the number of transactions carried out in their memory requirements. When the Bitcoin 80 bytes every 10 minutes or about 4 MByte per year.
The block chain is thus a series of hash trees where initially only the root and the chain of interest. Want an SVP application check a single transaction, so it needs only for relevant sub-tree to the hash value of the transaction to be able to check this subtree to the root based on the values . The fully validated server or archive servers from which the subtree must be based are not familiar with. The subtree is with its hashes the verifiable link between the individual transaction and the block header of the block in which it was booked dar. This process allows for very little effort, the validity of a company to control without the rest of bookkeeping to know. A SVP application is such that the minimum solution for the receipt of payments.
The relatively small block headers are one of the reasons that specialized hardware can be used very efficiently for the mining. Is calculated for each new nonce only the hash value of the small block header and not of the entire block. The memory requirement is therefore very low. Just try newer hash functions to avoid such Scrypt by increasing the memory requirements and thus artificially reduce the influence of special hardware on the currency.
Mining pools
With increasing interest in crypto- currency naturally increases the number of those who wish to invest in the new issues. The individual participant competes with the growing computing power of all the other participants. At the same time increases with growing interest in the rule, the exchange value of the currency. This leads to the situation that the new issues for new blocks are always valuable and there but is also far less likely to get these as individual participants.
Mining pools are the motivation comparable to communities in the lottery game. Several participants jointly invest to increase the chance of winning, and then divide this among themselves. In crypto currencies computing power is combined in order to later share the profit ( new issues, transaction fees).
A central service allows participants to register with him. With special applications, the participants make their own computing power of the service provider. This determines a new block and shares to be searched intervals of the nonce to each participant. All operate by parallel on the same problem, which usually tries to solve a single node. Find a participant doing a nonce which leads to a valid block, the block can be published and the profits will be shared.
Because all work on the same subscriber with different values of the block nonce, the search space of the participant is distributed and thus the search is successful much faster in average. As in the block, the target account is included for the gains already and the hash value would inevitably change when the address would be changed, it is possible that a participant recognized a successful new block on its own. If divisible blocks used with hash trees ( see above) to each subscriber also not aware of the transactions of the new block in the rule. He only gets the template for the new block header and looks for the matching nonce.
If each participant ( regularly or after a new block was found) reports its own best nonce, the operator of the mining pools can it assess the actual time worked by each participating computing power. He focused on ensuring that the nonce in the collectively edited block header and calculates the hash value. The smaller this is, or the closer it comes to the current difficulty, the higher the time spent computing power. Due to the statistical scatter of the proof-of -work task, this estimated computing power must be averaged over multiple processed new blocks. A fraudulent fake actually unpaid balance of computing power is thus largely excluded. The prize can be divided in proportion to the payments made computing power among the participants.
Problematic mining pools are by the loss of control of the participants. The API of many pools does not allow the participants, the transactions that confirms the operator with the new block for the general public to also examine themselves. In particular, when participants receive only templates of the block header, it is impossible to review. Thus, the operator of the pool receives from the participants not only their computing power, but also its majority -forming vote. The principle of democracy by computing power is subverted it. The participants in a mining pool is figuratively his ballot provided to the operator (see risks, a majority vote by computing power ).
Informational self-determination
Crypto currencies are working with a public accounting. Each competitor has unrestricted access to all transactions since the introduction of the currency. There is not a bank and therefore no banking secrecy. However, there is no bank, no instance of a subscriber ever registered as a person. Anyone can generate a key pair and participate with the public key of the two in the payment process. This public key is the pseudonym of the participant. Crypto currencies in the form described here are thus by its very nature a pseudonym for already. In Germany, service providers are required in accordance with § 13 paragraph 6 Teleservices Act, " to allow the use of tele- media and their pay anonymously or under a pseudonym ." A crypto currency fulfills this requirement already by their construction.
Anonymization
To prevent the traceability of payments are offered as a service accounts that allow transactions to be undertaken through them that the recognition of a link between the incoming and outgoing transactions is more difficult as possible. This is the one achieved by many participants settle payment orders on the same account and only the operator knows the connection between the incoming and outgoing transactions. In order to avoid correlations of employee hire additional measures. Payment can be, for example, delayed, broken down into components and / or to multiple recipients accounts ( which in turn may belong to the same person ) are divided. Such services are as a mixing service (Eng. mixing service) or on the basis of the offense of money laundering as a laundry service (Eng. laundry) respectively.
The main disadvantage is that the operators of these services must be trusted, both in terms of anonymity and the actual execution of the payment. It is again a central service before similar to a bank must be trusted. The running of the basic concept of a crypto- currency counter. Laundry services also can be implemented as a decentralized service of the community of participants in a crypto- currency. With Commitment method, cryptographic accumulators and zero- knowledge proofs can be a kind of digital bulletin board produce, deposited at the anonymous funds to be picked up again. To prevent that deposited amounts are removed from the bulletin board, it must be organized in the same way as the accounting of crypto currency itself. One can thus consider the bulletin board as a kind of anonymous parallel currency to the original crypto currency and integrated into their accounting.
Zerocoin
The approach of a digital bulletin board as anonymous parallel currency tracked the original as an extension of the Bitcoin protocol Zerocoin imaginary concept. After this extension for months by the community of Bitcoin participants was not accepted, the developers have decided to operate it as a separate crypto currency is expected in May 2014.
Participants can deposit amounts anonymously as a credit on the bulletin board. They keep a secret that allows anonymous just to get that amount later from the bulletin board again. The result is a transaction from one account to another without intervening a relationship is evident. The sequence of anonymous transaction:
By using a zero-knowledge proof, neither the C nor the commitment in question matching value z is known.
Threats and criticism
Software errors
Also crypto currencies are not safe from software faults like all powered by software systems. Examples:
So far, all accidents could be solved by software corrections and cooperative behavior of the participants in the Bitcoin. However, there is no guarantee that this will be so for all crypto currencies and for all time. In this sense, also the initially statement made about the need not be provided a single point of failure into perspective. If a crypto- currency is almost exclusively operated with software from a source and there is no independent implementations, then this code is a single point of failure;
Specialized hardware
The massive use of special hardware to obtain new issues is highly distorting to the general competition for these. With Bitcoin, in this way at present computing power of 15 PH / s so spent 15 quadrillion calculations per second hash function ( in the 7 -day average) (as of January 16, 2014 ). If you want to calculate a single valid block with the current distribution of 25 BTC within a year, that would at constant conditions ( which it could hardly be ) to spend a computing power of 286 GH / s. Since BTC mining is increasingly unprofitable, resourceful businessmen are now offering their hardware as rentable mining processing power. With newly designed crypto currencies is increasingly trying to reduce the influence of specialized hardware. We used hash functions that increase due to high memory requirements, the hardware cost ( Scrypt ) or tried to make them so that they are as unsuitable for GPUs and FPGAs and ASICs in cause as high costs (POW ).
Majority decision by computing power
By a majority vote by computing power such crypto currencies are exposed to danger, by organizations that manage to apply to be manipulable 51 percent of the computing power. One speaks in this context of a 51 - % attack. The mining pool GHash.IO reached in January 2014 briefly when bitcoin mining 42 percent. The two mining pools GHash.IO (about 34 percent) and BTC Guild ( about 24 percent ) would be a total of about 58 percent currently to jointly control the Bitcoin able (as of January 19, 2014 ). The original idea of the proof- of- concept work to distribute the control of currency evenly over the number of CPU's world is so not succeeded.
Data Loss and Data Theft
Since the control over a credit balance in a crypto- currency consists exclusively by the secret private key, credit is irretrievably lost by data loss in the past. A refund by other means is usually excluded, since lost balance principle can not be distinguished from parked and currently unused assets. This also means that the actual tradable money supply is not known.
The memory footprint relatively small key for the disposal of a credit are also an easy target for cybercriminals. They can be similar to spy on passwords with malicious programs. The global operation with pseudonyms, a criminal prosecution of such thefts of crypto credit is hardly promising. As a consequence, have been providing companies in the safe custody of crypto credit as a service.
Distribution
Some crypto currencies are the general public against unfair by significant parts of the new issues have already been made by the founders (English pre -minded ), or start with the highest yields was not made sufficiently long known. Often even the rules are included, the participants of the start-up phase so-called early adopters give special discounts. If it assumed the founders of selfish intent, such as crypto currencies are also designated as Scamcoins (Eng. fraud coins). But pre -mining can also be open documented part of the concept, as in the planned as a pure exchange currency Ripple.
Also in the initial experimentally observed Bitcoin exist imbalances of the start time. The Bitcoin is designed so that with the first 210,000 blocks ( ie, within about four years ), half of all Bitcoins (ie 10.5 million) are emitted. Since reaching this block on 28 November 2012, the new issue is halved and is further halved in the same way every four years. On this day there was a single account with a balance of 111,111 BTC, a little over 1 percent of all Bitcoins.
A year later, in December 2013 it turned out that 47 persons hold 28.9 percent of the emitted 12 million BTC. More 880 accounts holding 21.5 percent. Half of all previously mined Bitcoins thus include more than 927 people. Another 10,000 persons hold another 25 percent, so that the remaining approximately 1,000,000 participants share the remaining quarter.
Price fluctuations and price manipulation
Comparatively few of the world's operated crypto currencies are tradable in regular currencies. Often they are tradable at most other crypto currencies. They are usually ignored by banks.
Those that are convertible, can be risky due to their high volatility and provide a potential target for pump-and- dump attacks dar. as large distributed machines without any ability to market, where they are to serve as means of payment to respond, they are unsuitable to provide a stable currency. In particular, at relatively low volumes provide crypto currencies represents an object of speculation, with the stable exchange rate regimes to conventional currencies are unlikely.
The often present highly non-uniform distributions (see above ) is also in this context is a threat to the stability of the exchange rate dar. to established currencies if very few people have a very large part of the currency ( the Bitcoin have approximately 1,000 people, over half of the currency), the exchange rate is significantly affected when only a part of this group of people in order to become active. These people can enable a " dump " without previous "pump" but perform with equal effect.
The crypto- currency backs up only their own inventory. It documents which key belongs to which credit, limited and regulates new issues and preventing double spending. The exchange rates arise entirely outside of this system. The exchange rate data over other ( insbesonderen conventional ) currencies are details of dealers or stock exchanges and in principle also be manipulated. They constitute no warranty that the crypto currency is actually exchanged at this price.
Other
Cryptologic Security: The security of a crypto- currency is essentially determined by the security of the method used therein. For example, SHA- 2 was developed as a reaction to become known attacks against SHA-1. If something similar repeat with SHA -2 or another hash function, based crypto currencies would it be manipulated.
Credibility: Many crypto currencies are only slightly varied duplicates of existing currencies without significant technical progress. They are in some cases not at all meant seriously as the example of " Coinye West" showed with the rapper Kanye West should be played.
Regulators: In some countries, regulators have spoken out against the use of crypto currencies, and partly already taken concrete regulatory measures in order to prevent their use.
Reversal: Because transactions are irreversible, there is the exchange back bookable payment methods ( debit, credit card, PayPal, etc.) for traders of crypto currencies the risk to remain seated after a chargeback on the loss.