Public Key Cryptography (PKC), also called asymmetric cryptography, is a field of cryptography that uses both a private key and a public key, as opposed to the single key used in symmetric cryptography. The use of key pairs gives PKC a unique set of features and functionality that can be used to solve problems inherent in other cryptographic techniques. This form of cryptography has become an important part of modern computer security, as well as an essential part of the ever-evolving cryptocurrency ecosystem.

How does public key cryptography work?

In a PKC scheme, the public key is used by a sender to encrypt information, while the private key is used by a recipient to decrypt it. As the two keys are different, the public key can be shared securely without compromising the security of the private key. Each asymmetric key pair is unique, ensuring that a message encrypted using a public key can only be read by the person who has the corresponding private key.

Because asymmetric encryption algorithms generate mathematically related key pairs, their length is much longer than that used in symmetric cryptography. This incremented length - typically between 1,024 and 2,048 bits - makes it extremely difficult to calculate a private key from its public equivalent. One of the most popular algorithms for asymmetric encryption used today is known as RSA. In the RSA scheme, keys are generated using a modulus obtained by multiplying two numbers (often two large primes). In other words, the module generates two keys: one public which can be shared and the other being private and which must be kept secret). The RSA algorithm was first described in 1977 by Rivest, Shamir and Adleman (hence, RSA) and remains a major component of public key cryptography systems.

PKC as an encryption tool

Public key cryptography solves one of the recurring problems of symmetric algorithms, namely the communication of the key used for both encryption and decryption. Sending this key over an insecure connection risks exposing it to third parties, who can then read any messages encrypted with the shared key. Although cryptographic techniques (such as the Diffie-Hellman-Merkle key exchange protocol) exist to address this problem, they remain vulnerable to attacks. In public-key cryptography, on the other hand, the key used for encryption can be securely shared over any connection. As a result, asymmetric algorithms provide a higher level of protection than symmetric algorithms.

Use in generating digital signatures

Another application of asymmetric cryptography algorithms is that of data authentication using digital signatures. Basically, a digital signature is a hash created using data from a message. When this message is sent, the recipient can verify the signature using the sender's public key to authenticate the source of the message and ensure that it has not been tampered with. In some cases, digital signatures and encryption are applied together, with the hash itself possibly encrypted as part of the message. It should be noted, however, that not all digital signature systems use encryption techniques.

Limits

Although it can be used to improve computer security and enable verification of the integrity of messages, PKC encryption has some limitations. Due to the complex mathematical operations involved in encryption and decryption, asymmetric algorithms can be quite slow when forced to process large amounts of data. This type of cryptography also relies heavily on the assumption that the private key will remain secret. If a private key is accidentally shared or exposed, the security of all messages encrypted with the corresponding public key will be compromised. It is also possible that users accidentally lose their private keys, in which case it becomes impossible for them to access the encrypted data.

Applications of public key cryptography

This type of cryptography is used by many modern computer systems to secure sensitive information. Email messages, for example, may be encrypted using public key cryptography techniques to keep their contents confidential. The Secure Sockets Layer (SSL) protocol that makes secure connection to websites possible also uses asymmetric cryptography. PKC systems have even been explored as a way to create a secure electronic voting environment that would potentially allow voters to participate in elections from their home computers.

PKC technology also occupies an important place in blockchain and cryptocurrency technology. When a new cryptocurrency wallet is set up, a key pair is generated (public and private keys). The public address is generated using the public key and can be securely shared with third parties. The private key, on the other hand, is used to create digital signatures and verify transactions and must therefore be kept secret. Once a transaction has been verified by confirming the hash contained in the digital signature, that transaction can be added to the blockchain ledger. This digital signature verification system ensures that only the person with the private key associated with the corresponding cryptocurrency wallet can release funds. It should be noted that asymmetric encryptions used in cryptocurrency applications are different from those used for computer security purposes. Bitcoin and Ethereum, for example, use specialized encryption called the Elliptic Curve Digital Signature Algorithm (ECDSA) to verify transactions.

From computer security to verifying cryptocurrency transactions, public key cryptography plays an important role in securing modern digital systems. By using coupled public and private keys, asymmetric cryptography algorithms resolve the fundamental security problems presented by symmetric ciphers. Although PKC encryption has been used for many years, new uses and applications are regularly developed, particularly in the areas of blockchain and cryptocurrencies.