# Public Key Cryptography (PKC) Explained

Public key cryptography is a framework that relies on a pair of keys instead of a single key, as seen in symmetric cryptography. PKC offers a distinctive set of features and abilities that are useful in solving problems associated with other cryptographic methods. It has become an essential tool for securing modern digital systems, including blockchain and cryptocurrency technology. PKC has several advantages, including enhanced computer security and message integrity verification, but also has limitations associated with it. Despite these limitations, PKC plays a critical role in everything from computer security to verifying cryptocurrency transactions.

## Basics

Asymmetric cryptography, also known as Public Key Cryptography (PKC), implements a framework that relies on a pair of keys instead of a single key as seen in symmetric cryptography. By using both a private and public key, PKC offers a distinctive set of features and abilities that are useful in solving problems associated with other cryptographic methods. PKC has emerged as a vital element in modern computer security and is a significant part of the rapidly expanding cryptocurrency industry.

## How Does PKC Work?

One of the keys in a PKC system encrypts data, while the other one decrypts it. Unlike symmetric cryptography, PKC utilizes two different keys. The public key can be safely distributed without compromising the private key's safety, ensuring that only the individual who owns the corresponding private key can access the encrypted message.

Asymmetric encryption algorithms create key pairs that are mathematically linked, which results in a longer key length (usually between 1,024 and 2,048 bits) than that used in symmetric cryptography. Because of this longer length, computing a private key from its public equivalent is extremely difficult. One of the most commonly used asymmetric encryption algorithms is RSA.

The RSA scheme generates keys using a modulus derived from two numbers (often two large prime numbers). The modulus generates two keys: one public that can be shared and one private that should be kept secret. The RSA algorithm was introduced in 1977 by Rivest, Shamir, and Adleman (hence, RSA) and is still a significant element of public key cryptography systems.

### Encryption Tool

Symmetric algorithms have long had a communication problem when it comes to the key that is used for both encryption and decryption. Sharing this key over an insecure connection can expose it to third parties, who can then read any messages that were encrypted with the shared key. While cryptographic techniques exist to solve this issue, they are still vulnerable to attacks (such as the Diffie-Hellman-Merkle key exchange protocol). Public key cryptography, on the other hand, securely shares the encryption key over any connection, resulting in a more secure approach than symmetric algorithms. Asymmetric algorithms provide a higher level of protection compared to symmetric ones.

### Digital Signatures

Digital signatures are another use of asymmetric cryptography algorithms, allowing data to be authenticated. A digital signature is essentially a hash that is created using the data contained in a message. When the message is sent, the recipient can check the signature using the sender's public key. This ensures that the message has not been tampered with and that the source of the message is authentic. In some cases, encryption and digital signatures may be applied together, with the hash being encrypted as part of the message. However, it should be noted that not all digital signature schemes use encryption.

## Limitations

The use of PKC has several advantages, including enhanced computer security and message integrity verification. However, there are also some limitations associated with it. Asymmetric encryption algorithms can be quite slow when dealing with large amounts of data due to the complex mathematical operations involved in encryption and decryption. Additionally, the security of PKC depends on the private key remaining secret. If the private key is accidentally shared or exposed, all messages that have been encrypted with its corresponding public key are at risk of being compromised. It is also possible to lose private keys, which makes it impossible for users to access encrypted data.

## PKC Applications

Public key cryptography has various applications in modern computer systems for safeguarding sensitive data. It can be used to encrypt emails and make secure connections to websites via SSL protocol. It has been researched as a means of secure electronic voting, which could enable voters to participate in elections from their home computers.

PKC is also widely used in blockchain and cryptocurrency technology, where new cryptocurrency wallets are set up with a pair of keys generated. The public key generates the wallet address, while the private key is used for creating digital signatures and verifying transactions. Only the person who holds the private key can move the funds, as the digital signature verifies the transaction.

It is important to note that the asymmetric cryptography used in cryptocurrency applications, such as Bitcoin and Ethereum, differs from those used for computer security. These cryptocurrencies use a specific algorithm for verifying transactions, known as the Elliptic Curve Digital Signature Algorithm (ECDSA), which creates digital signatures without the use of encryption. Therefore, unlike many believe, blockchain does not require encryption.

Despite its benefits, PKC has some limitations, such as being slow when handling large amounts of data due to the complex mathematical operations involved. Additionally, PKC relies heavily on the private key remaining confidential. If a private key is exposed, all messages encrypted with its corresponding public key will be vulnerable to attacks. It is also possible to lose private keys, which can lead to the loss of access to encrypted data.

## Conclusion

The asymmetric cryptography algorithms provided by public key cryptography have become an essential tool for securing modern digital systems. Using paired public and private keys, PKC resolves fundamental security concerns posed by symmetric ciphers. While PKC has been in use for years, new applications are regularly developed, particularly in the blockchain and cryptocurrency space. As a result, PKC plays a critical role in everything from computer security to verifying cryptocurrency transactions.