# Blockchain and cryptography

*Kryptos*, which means ‘hidden’ and *graphein*, which means ‘to write’ are the two ancient Greek words that together make up the word cryptography. Cryptography is the process of adopting strategies and procedures to prevent a third party from accessing and obtaining information from the data of private messages whilst a communication process is taking place. This is accomplished through the use of ciphers, which are symbols that a computer is unable to read. The primary goals of cryptography in relation to cryptocurrencies are the protection of users, the integrity of their transactions and the prevention of double spending. In this way, transactions on a blockchain can be protected thus ensuring that only the people for whom the transaction was intended may access, read and handle the data.

Source: Blockchainhub.net

Several words are used often used when discussing cryptography:

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encryption:the process of turning plaintext (or regular text) into ciphertext (random sequence of bits).·

decryption:the opposite of encryption; it is the process of turning ciphertext into plaintext.·

cipher:the mathematical function called a cryptographic algorithm that turns plaintext into ciphertext.·

key:similar to a physical key, it encrypts (locks) data so that only the correct key can decrypt (unlock) the data.

There are two types of cryptography: symmetric-key cryptography and asymmetric-key cryptography.

**Symmetric-key cryptography**

In terms of encryption, this is concerned with using the same key for both purposes. The symmetric-key encryption approach can encrypt data or create secure website connections. It is also known as secret-key cryptography. This is only a problem if the sender and recipient cannot safely exchange keys with one other. Data Encryption Standard is a widely used method of symmetric-key encryption where, in a cipher, the cryptographic algorithm uses the key to encrypt the data which then has to be decrypted (a trustworthy individual can interpret the information). Examples of symmetric-key include Advanced Encryption Standards (AES) and Data Encryption Standard (DES).

Symmetric encryption

Source: 101blockchains.com/blockchain-cryptography

**Properties include:**

· secret-key is another name for this method.

· both parties share the hidden key to maintaining secrets.

· it works well as a mass-encryption solution.

· less processing time and data transfer speed are needed.

**Asymmetric-key cryptography**

In asymmetric-key encryption, the encryption and decryption procedures use a unique key. Public *and* private key cryptography is at the heart of this system - the private key is used to decode the communications and verify the digital signature whilst the public key encrypts the messages and makes them accessible. Based on the mathematical relationship between the two, the public key cannot be obtained from the private key, and the reverse is also true. Examples of asymmetric-keys are Rivest Shamir Adleman (RSA) the Digital Signature Standard (DSS).

Asymmetric encryption

Source: Medium.com

**Properties include:**

· public-key cryptography is another name for this method.

· the key exchange in symmetric cryptography is commonly accomplished with it.

· it is a time-consuming to process and run.

· it factors heavily on the integrity of the hosting server.

**Advantages of cryptography in blockchain:**

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encryptionAsymmetric encryption is used in cryptography to protect information and communication on a network from being shared or accessed by people who should not have access to the data being transmitted.

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immutabilityThis property of cryptography is essential for blockchains because immutability makes it possible for blocks to be securely linked by other blocks; it also ensures that the data stored in the blockchain is correct. Furthermore, an attacker cannot get a valid signature for a new query by looking at previous queries and their signatures.

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securityCryptography makes it easier to keep track of transactions by encrypting data and using public and private keys to obtain data. Cryptographic hashing makes it impossible to change data, therefore renders blockchains more secure.

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scalabilityCryptography makes it impossible to undo a transaction, so all users can be sure that the digital ledger cannot be manipulated, whilst allowing the network to safely record any number of transactions.

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non-repudiationThe digital signature protects against denial of a message sent by the sender through the non-repudiation service i.e., so neither the sender nor the receiver can later deny having processed the information. This benefit can be linked to collision resistance which means that, since each input value has its hash function, the messages sent do not conflict. It is easy therefore to decipher one message from another. Hackers cannot change the data because the digital signature is no longer valid if the information changes. With the help of cryptography, it prevents hackers from accessing the data and also makes it hard erto stop cryptography in the blockchain.

**Disadvantages of cryptography in blockchain:**

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difficulty in accessing informationData that has been heavily encrypted and digitally signed may be inaccessible, even to a legitimate user, at the most crucial time for making decisions. An unauthorised user can launch an assault that completely cripples the network. There is no way to utilise cryptography to guarantee high availability, although it is a fundamental information security property. More measures are required to protect against dangers such as a denial of service attack or a total collapse of the information systems.

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poorly designed protocols, methods and systemsThese can introduce vulnerabilities not mitigated by cryptography. A well-planned defensive system is essential for addressing these problems.

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expensiveCryptography requires substantial financial and human resources. The public key infrastructure needed for public-key cryptography is costly and complex to set up and keep running. Time lags do actually occur when cryptographic methods convey messages or analyse data.

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flawsThe strength of a cryptographic method's protection is proportional to the difficulty of the underlying mathematical issue. Cryptographic techniques are susceptible to any progress made in solving such mathematical problems, e.g. quantum computing.

The core qualities of blockchain technology are precisely ‘in sync’ with the central tenants of cryptography. Though digital signatures are reliable for encrypting data sent over a blockchain network, cryptographic hashing holds more promise. There is no longer any requirement for secret keys in cryptographic hash functions, as in public-key cryptography. It’s simply a question of accessing suitable materials to understand more about cryptography and its uses in the blockchain.