SHA or other hash algorithms have two different attacks that we should be . The attack of Meet-in-the-middle consists in attacking the hash function by San Francisco Bay Area and one of Bitcoin's most open-minded supporters, said. The woman, Ada Tsim Sum-kit, had arranged to meet her aunts and uncles, all aged between 60 and 80, in Quarry Bay Park to settle a dispute over her In response to global terror attacks, Hong Kong anti-terrorism officers a crime in the city was in , when an armed robber shot a Tsim Sha Tsui. Three types of cryptography: secret-key, public key, and hash .. Secure Hash Algorithm (SHA): Algorithm for NIST's Secure Hash 3DES, which is not susceptible to a meet-in-the-middle attack, employs three DES passes and one, two, to holding password cracking at bay dubbed Honey Encryption.
One Quarry Bay resident said she was worried about her grandchildren, who play in the park every day. But the reaction of most residents and workers in the area was mostly shock and disbelief, not least because Tai Koo was known to be a safe neighbourhood. Tai Koo resident Catherine Yu, 37, a mother of one, said: She came to Hong Kong two years ago with her family. At the scene, police including officers from the Counter Terrorism Response Unit wearing helmets, and carrying MP5 submachine guns were seen standing guard.
The Post reported in September last year that the number of sensitive locations the elite officers were inspecting and patrolling had increased threefold to over the past eight years. Inthree suspected triad members were wounded in a predawn shoot-out in Tsim Sha Tsui when they were among a group of five who had just left a private club in Austin Avenue after watching the World Cup final.
Police said they were ambushed by two armed men. One of them fired four shots from a shotgun. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient. The reader is advised, then, that the topics covered here only describe the first of many steps necessary for better security in any number of situations. This paper has two major purposes.
The first is to define some of the terms and concepts behind basic cryptographic methods, and to offer a way to compare the myriad cryptographic schemes in use today. The second is to provide some real examples of cryptography in use today. Several companies, products, and services are mentioned in this tutorial.
Such mention is for example purposes only and, unless explicitly stated otherwise, should not be taken as a recommendation or endorsement by the author. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications.
In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.
There are five primary functions of cryptography today: Ensuring that no one can read the message except the intended receiver. The process of proving one's identity. Assuring the receiver that the received message has not been altered in any way from the original. A mechanism to prove that the sender really sent this message. The method by which crypto keys are shared between sender and receiver.
In cryptography, we start with the unencrypted data, referred to as plaintext. Plaintext is encrypted into ciphertext, which will in turn usually be decrypted back into usable plaintext. The encryption and decryption is based upon the type of cryptography scheme being employed and some form of key. For those who like formulas, this process is sometimes written as: In many of the descriptions below, two communicating parties will be referred to as Alice and Bob; this is the common nomenclature in the crypto field and literature to make it easier to identify the communicating parties.
If there is a third and fourth party to the communication, they will be referred to as Carol and Dave, respectively. A malicious party is referred to as Mallory, an eavesdropper as Eve, and a trusted third party as Trent. Finally, cryptography is most closely associated with the development and creation of the mathematical algorithms used to encrypt and decrypt messages, whereas cryptanalysis is the science of analyzing and breaking encryption schemes.
Cryptology is the term referring to the broad study of secret writing, and encompasses both cryptography and cryptanalysis. For purposes of this paper, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use.
The three types of algorithms that will be discussed are Figure 1: Uses a single key for both encryption and decryption; also called symmetric encryption. Primarily used for privacy and confidentiality. Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange.
Uses a mathematical transformation to irreversibly "encrypt" information, providing a digital fingerprint. Primarily used for message integrity. Three types of cryptography: Secret Key Cryptography Secret key cryptography methods employ a single key for both encryption and decryption. As shown in Figure 1A, the sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext.
Because a single key is used for both functions, secret key cryptography is also called symmetric encryption. With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret. The biggest difficulty with this approach, of course, is the distribution of the key more on that later in the discussion of public key cryptography.
Secret key cryptography schemes are generally categorized as being either stream ciphers or block ciphers.
A Self-synchronizing stream cipher. From Schneier,Figure 9. On average, finding a collision would take a minimum of hash tests.
An Overview of Cryptography
The total computing power of the Bitcoin system is calculated on the basis of mining production and in the case of mining, SHA is calculated twice, as in most cases the use of the algorithm in Bitcoin takes the SHA double from the input.
Generously said that SHA hashing in the extraction process takes the same time as any computer difficulty behind generating an address a private key would take for an attacker. We will have to take into account that the computer power increases with time. We have doubled it every 18 months, as has often been cited in Moore's version of the law [ 40 ]. Now we will be able to find a private key in about This is more than 16 years of constant hashing with very optimistic estimates to find a private key behind 1 particular Bitcoin address.
As we see it today, crude forcing is impossible, but we need to monitor developments in cryptography, computer power and possibly even quantum computing, and be able to make adjustments in the algorithms used in the system. Python script to calculate minimum time it takes to find RIPEMD collision for Bitcoin addresses with starting computing power at Bitcoin networks total power and increasing according to Moore's law.
This means that only addresses that are reused are the subject of this attack because they revealed their public keys but this is not a problem because no weakness in ECDSA is known and users can increase their security and anonymity using different addresses for all transactions Figure 5.
Preimage Attack The preimage attack on a hash function means to search for the original message from the hash value produced by the hash calculations [ 44 ]. In addition to the mandatory execution of the pre-imaginary attack to find private keys, Preimage would also help attackers reduce their coins faster. If they found a way to get rid of one of the hashish that encounters the difficulty required for a given block, they could present it as proof of work while collecting discovery fees and bonuses to find a new block and add it to the chain.
This type of pre-imaginary attack would be interesting because there are several hashes that can be attacked, and the attacker can also control a part of the message that is going to be chopped.
The attacker can change the Merkle root by deciding which transactions are added to the block and at what address the reward is sent. At the same time, he is only interested in finding the entire nonce value. Currently, the best preimage attack for SHA is against the step version of the hash algorithm.
The step process is still secure against this meet-in-the-middle attack [ 45 ]. The attack of Meet-in-the-middle consists in attacking the hash function by working both ends of the hash at the same time. It tries to take the possible message values closer to the hash summary while taking the hash values closer to the original message until they are found in the middle and reveal the entrance of the hashing.
In principle, this is exactly the type of attack that could succeed for Bitcoin because it is quite easy to find an appropriate nonce meet in the middle.
An additional difficulty in launching a preimage attack is caused by the fact that the block headers use the SHA double, but at the same time, a preimage that is found need not be specific: This is one of the attacks that require more research, as there may be specific Bitcoin attacks in the possible medium against the SHA double. If someone has found a method for this, it is highly likely that he would not publish it, because even a small advantage in mining is valuable.
At present, Bitcoins cryptography is very strong: With developments in cryptanalysis and calculation speeds, longer dimensions and hash lengths or better algorithms must be implemented in Bitcoin in the future. Although the creator of the system has announced the possibility of changing the cryptographic algorithms in the system in a transparent way for users in the unlikely event that SHA breaks at any time, there is no concrete plan for do it [ 46 ].
Betcoin Walet Challenges Betcoin nature: Nakamoto designed bitcoin system as a free source code to constantly introduce a steady supply of bitcoins to the market. To remove the bitcoins can switch from one account to another; the minor adds new bitcoins to the market by using special software to explore the Internet to search for bitcoin transactions that need verification [ 46 ]. This verification process involves solving complex mathematical problems requiring high levels of processing power.
When the verification process end, a transaction fee of 25 bitcoins is collected by the minor, the checks frequency adds new parts to the market approximately every 10 minutes.
Depending on the design, the verification process becomes more and more complex as more and more people inevitably try to exploit and invest in more powerful processors explicitly created to resolve mining problems.
In addition, to be certain at least six blocks will have to be created in the blockchain, which makes the confirmation, time arises at one hour. Although this time is much less than the time required for merchants to receive payment from the customer via a credit card system, for customers, the situation is not similar.
Making a client wait for an hour in order to make a payment is not realistic, especially when considering purchases directly at a retail store and not online. This disadvantage is one of the main reasons why other currencies have emerged crypto, such as Litecoin [ 47 ] for example.
The time to find a block, and therefore be able to confirm a transaction, is much faster in these cases. This tax is still very low around 0. Nevertheless, wallets may not choose to implement this option, but the transaction is not always certain to be approved. In theory, as the number and sophistication of minor increase, the flow of bitcoins on the market can remain stable due to the difficulty of growing problem and a decreasing number of bitcoins assigned as the transaction fees.
Blockchain: Bitcoin Wallet Cryptography Security, Challenges and Countermeasures
A constant flow avoids the exorbitant inflation which could otherwise occur with a growing demand and a limited offer. However, once all the 21 million bitcoins in existence are exploited, the coin flow on the market will cease, which is expected to occur around if the current rate of bitcoin extraction continues [ 49 ].
To provide some elasticity in the market supply of bitcoins, each piece can be subdivided up to eight decimal places. This ensures that as the demand for bitcoins increases, technology will be able to support a large user base. A key aspect of the bitcoin network extraction and transaction process is a permanent register of all transactions that have occurred since the bitcoin creation.
Each time a minor check a transaction, its record is added to the blockchain, verifying that the involved bitcoins are not predisposed in a previous transaction. The minors are trying essentially to be the first to check block transactions and to add them to the blockchain, winning the reward Bitcoin [ 50 ]. This element of competition in the verification process ensures that countless miners look at each transaction, thereby unequivocally verifying that the bitcoins originate from an existing source and transfer to their designated destination.
This certified system means that nobody can buy products with bitcoins that are not rightly and sit in their wallets. In addition, the decentralized nature of the bitcoin system mitigates the risk of attack on the network itself because it is scattered on each computer that participates in mining. Antonopoulos, a technology entrepreneur in the San Francisco Bay Area and one of Bitcoin's most open-minded supporters, said, "Bitcoin with no center means there is no of target to attack; there is no concentration of power.
Power is diffused and distributed throughout the community [ 51 ]. Thousands of computers around the world are working together to update and maintain the blockchain, ensuring the accuracy and validity of every bitcoin transaction.
Therefore, the bitcoin operation integrity will always be intact. The transactions examined by the minors on the bitcoin network transfer directly from the consumer to the seller without intermediaries, transposing essentially a cash transaction on the Internet.
Users are fully anonymous by this mechanism and third-party facilitators such as banks or credit companies become totally useless. However, this creates a risk as users must accept the responsibility of keeping their bitcoin stroboscopes in virtual wallets on a secure hard disk. Hackers can access a user's wallet if the computer's enclosure has an Internet connection, so that users have to be very careful about Internet security.
Lack of central authority makes users more accountable for protecting their own assets. The vulnerability inherent in a decentralized system creates difficulties for bitcoin to reach a larger user base.
To become a sustainable form, respected and widely used currency, Bitcoin will certainly need the government approval, in the form of a legal status. Risk aversion will prevent most people from investing their hard-earned dollars in a monetary system that operates outside the law limits and has no government guarantee to create inherent value.
Unless the government provides a value guarantee, such as the legal status that gives to the dollar value, Bitcoin will always be perceived as an investment opportunity similar to a stock, which the price increases and decreases daily. However, cryptocurrency technology could prove revolutionary in the way monetary systems are exploited and transactions occur if governments decide to adopt the positive contributions that technology offers.
Attacks against Bitcoin System Attack with computer power: Bitcoin fights duplicate spending by adding all blockchain broadcast transactions. The blockchain is the database of all transactions and the branch of the chain with the highest computing cost is approved by the nodes in the peer-to-peer network [ 52 ].
Honest minors are based on the longest valid chain. They are rewarded by Bitcoins for doing this and in case they would suggest or, by chance, add blocks to the channel that is not considered a main branch through the network, the pieces they received by claiming the bonus block discovery and transaction costs would not be spendable since they are not included in the chain of trust.
Clients should also trust only transactions included and confirmed by multiple blocks added to the chain after it. So, there is strong evidence that they are part of mainstream and not one of the orphaned chains that are not built on blocks that carry the greatest amount of calculations with them.
Blockchain connection can occur in the event of an attack, but also by a chance when several new blocks are discovered and broadcast in a network at intervals of a few seconds. When this happens, the nodes in the network generating the blocks begin to build at the top of the block they received first. Now the block that is referenced by another new block will be part of the main chain and all the others will remain as orphans since there is more computational effort associated with this branch [ 53 ].
Transactions in orphan chains date back to the unconfirmed state and are added by miners building new blocks later. The attacker who can produce a blockchain for which they show a proof of work, a level of difficulty corresponding to the chopping speeds and a greater amount of total computational effort than the constructors of the main chain would have control over the entire Bitcoin network. If an attacker is able to build such a string and broadcast the constructed chain, it would be accepted by the network as the main database of the transaction database.
Transactions that are included in the previous main branch and not in the one created by the attacker are no longer confirmed by being added to a block by a minor and consequently untrustworthy. Figure 6 demonstrations an example of double-spending attack.
As an effect of building a new main branch for the blockchain, attacker can reverse the transactions it signed that were added in the previous main branch to the point where the attacker split the chain [ 54 ]. The attacker does this by not simply adding transactions into a newly constructed branch and perhaps using the same pieces to issue other transactions, accordingly, spending them twice Figure 6.
Example of double-spending attack. The attacker could not reverse transactions that are not sent by him because he does not know the private keys with which it assigns the value to the other parties. He would not be able to create value out of the air, proof of work and rules of difficulty, building blocks must be followed even by creating an alternate block chain attack branch, and otherwise it is not accepted by other nodes.
The attacker cannot take other people in cash because none of the transactions he adds to the created blocks that were not validly signed would be accepted for payment by other nodes on the network. In addition, these invalid transactions added to the block would also cause the block to be inadequate. Denial of Service with Computing Power What an attacker can do is not include transactions in his branch.
These transactions would not have confirmed until they were added to the chain of blocks later. This could happen after the attacker loses most of the computing power in the network, stops attacking efforts, or begins to add transactions by other people in the transaction database created.
Then the transactions would make it possible to entrust the level of confirmation required and the transaction would be valid unless someone could forge the chain with their computing power and create another branch after the previous division became the main chain and before the transaction is added to a block in the main chain [ 55 ]. This could result in a denial of service. Attackers can choose which transactions are added to the chain.
They can in fact only add a redemption transaction in their blocks preventing any traffic that transmits value in the Bitcoin network rendering the system useless.
If users can not send and receive payments, the currency is very unattractive. In this way, the attacker also loses transaction costs, but they may not be concerned that their goal is probably to kill Bitcoins in increasing popularity and if they keep control long enough, they can ultimately stop using money completely. The attacker in control also prevents other minors from extracting valid blocks during the time they have most of the computing power while the other mining effort is branched out, which loses its main branch status in the blocks chain.
The intelligent attacker would construct his chain in silence and would not broadcast the discovered blocks on the network. They should use more computer power than the combined Bitcoin network during this building in the background. Once they unexpectedly other users make their public efforts, their chain is accepted as the main chain by the Bitcoin protocol.
If this attack is carried out for long periods of time, attackers may lose total processing power if honest knots have overtaken it and it is unable to sustain itself. Then all his efforts will become useless and it is very unlikely that the community of Bitcoin ever knows that an attack has been launched.
At the same time, the longer the control times of the attacker, the greater the damage of Bitcoin. Few hours of unconfirmed transactions would not create chaos, but over a week of reverse financial activity would allow average users to lose confidence in the system. Cancerous Nodes The attacking Bitcoin network or targeted users with cancer nodes would involve complementing the network with clients controlled by the attacker.
The goal of this project would be to create a user or users to connect only to malicious nodes or to separate part of the Bitcoin network from others. Due to the network flooding with cancerous nodes, an attacker could refuse to relay blocks and transactions creating a denial of service. If he is also capable of segmenting the network, he can create a condition of several blockchains to be constructed simultaneously without knowledge of the others existence [ 56 ].
In case a successful network divides by running an enormous amount of cancer nodes, the attacker can double the coins in a manner similar to the methods discussed in the attacks with computing power with less effort. It will create a situation where a part of the network would grow on 1 branch and trust the transactions within that chain they think it is part of the main branch.
In reality, after the cancer nodes disconnect and the network realizes that there has been a range in the blocks chain and solves it by choosing to trust the branch with the greatest amount of power total calculation put in place in the blocks within the limits specified by the protocol.
Transactions in blocks now orphaned are not confirmed and, for some of them, the attacker may have been able to spend associated parts in another branch. In the case where the network segmentation is not complete, the attack with the cancerous nodes fails. If the user that the attacker wants to disconnect from the network connects to an honest node that is in turn connected to the peer-to-peer network by at least one non-malicious node, it receives enough information about transactions and the blocks discovered to remain unharmed.
This makes the total segmentation attack quite unlikely since the separate parts of the network may not have a single link for the attack to succeed. Figure 7 shows an example of network nodes used in bitcoin transaction between two users. Example of network nodes used in Bitcoin transaction between two users. There are already mitigation measures for attacks with cancerous nodes.
In particular, Bitcoin clients make only 1 outbound connection per bit IP address range [ 57 ]. This means that from 65, addresses, for example from x.
Therefore, an attacker wanting to flood the network with cancer nodes should have control over several machines with IP addresses in a large amount of different network ranges. This could be done by an attacker with access to the big botnet. Another possible mitigation for this would be to use trusted audit nodes with static IPs for clients that connect specifically. These nodes have the ability to connect to each other and keep the updated chain locked.
They could also detect if the chains of announced blocks are constructed by attackers with much computational power. This trusted network within the Bitcoin network would go against the protocol and the idea of not having to trust anyone in the peer-to-peer financial system. It is also possible that honest trust nodes are compromised and this could create a mess. Having the knowledge of a few geographically distributed honest nodes that can handle thousands of Bitcoin connections at the same time and the ability to specify connections to them as an optional network feature in the Bitcoin client, this should increase security of the system and maintaining a database of these nodes with their IP listed in Bitcoin wiki could be taken into account [ 58 ].
The Client Software Security and Denial of Service Attack To create the conditions that give rise to a denial of service, there are several ways to target individual users, but it is possible in some cases for the whole Bitcoin network. These are the theoretical but impractical examples mentioned in attacks with computer power and cancer nodes.
Targeting a user to split it from the Bitcoin network could also mean using vulnerability in Bitcoin client software. By finding faults in open-source software, it is possible for an attacker to overflow the client to close it or even worse, send data that would result in malicious code execution situations that could reveal private keys if they are not encrypted.
Denial of service attacks to eliminate client software would mean sending the node that is running the client either a large amount of information or specially crafted inputs that would not be processed properly. Attackers who send too much data too quickly or illegitimate transaction messages have a link between them.
Therefore, the Bitcoin client has an integrated prevention of denial of service [ 59 ]. This mitigation can be bypassed by sending data from multiple malicious nodes quickly, but limitations to this include the IP space limit connections mentioned in attacks with cancer nodes.
A better chance for an attacker to disconnect a node from the Bitcoin network would find vulnerability in the client software.
No software that has a certain level of complexity is totally protected against attacks. The fact that Bitcoin is an opensource project adds two different views to its security. First of all, anyone can read the code and look for malicious cases of typing that are not handled properly or find other types of security holes.