What is Public Key Cryptography?
Public key cryptography (PKC), also known as asymmetric cryptography, is a structure that uses both a private 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 characteristics and capabilities that can be used to solve problems inherent in other cryptographic methods. This form of cryptography has become an important element of modern computer security, as well as a critical component of the growing cryptocurrency ecosystem.
How does Public Key Cryptography Work?
In the PKC scheme, the public key is used by the sender to encrypt information, while the private key is used by the recipient to decrypt it. Because the two keys are different from each other, the public key can be shared securely without compromising private security. 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 key pairs that are mathematically related, the length of these keys is much longer than those used in symmetric cryptography. These longer ones - typically 1024 to 2048 bits - make it extremely difficult to calculate the private key from its public counterpart. One of the most common asymmetric encryption algorithms used today is known as RSA. In the RSA scheme, keys are generated using a modulus that is obtained by multiplying two numbers (often two large prime numbers). Basically, the module generates two keys (one public, which can be shared, and the other private, which must be kept secret). The RSA algorithm was first described in 1977 by Rivest, Shamir and Adleman (hence RSA) and remains a fundamental component of public key cryptographic systems.
PKC as an Encryption Tool
Public key cryptography solves one of the long-standing problems of symmetric algorithms, which is the transmission of a key that is used for both encryption and decryption. Sending this key over an insecure connection is risky and could be disclosed to a third party, who could then read any messages encrypted with this key. Although there are cryptographic methods (such as the Diffie-Hellman-Merkle key exchange protocol) to solve this problem, they are still vulnerable to attacks. In public key cryptography, it's the opposite. The key used for encryption can be transmitted securely over any connection. As a result, asymmetric algorithms provide a higher level of protection compared to symmetric ones.
Using Digital Signatures
Another application of asymmetric cryptography algorithms is data authentication using digital signatures. Essentially, a digital signature is a hash created using the data in the message. When this message is sent, the recipient can verify the signature using the sender's public key to verify the origin of the message and ensure that it has not been tampered with. In some cases, digital signatures and encryption are used together, since the hash itself may be encrypted as part of the message. It should be noted that not all digital signature schemes use an encryption method.
Limits
Although it can be used to improve computer security and verify message integrity, PKC has some limitations. Due to the complex mathematics involved in encryption and decryption, asymmetric algorithms can be quite slow when they have to work with large amounts of data. This type of cryptography also relies heavily on the assumption that the private key will remain secret. If the private key was accidentally shared or disclosed, the security of all messages that were encrypted with the corresponding public key would be compromised. Users may also accidentally lose their private keys, in which case they will not be able to access encrypted data.
Applications of Public Key Cryptography
This type of cryptography is used by many modern computer systems to ensure the security of sensitive information. For example, emails can be encrypted using public key cryptography techniques to ensure the confidentiality of their contents. The Secure Sockets Layer (SSL) protocol, which enables secure connections to websites, also uses asymmetric cryptography. PKC systems have even been used as a means to provide a secure electronic voting environment that would potentially allow voters to participate in elections from their home computers.
PKC also figures prominently in blockchain and cryptocurrency technologies. When creating a new cryptocurrency wallet, a key pair (public and private key) is generated. The public address is generated using a public key and can be shared securely with others. On the other hand, the private key is used to create digital signatures and verify transactions, and therefore must be kept secret. Once a transaction has been confirmed by validating the hash contained in the digital signature, the transaction can be added to the blockchain ledger. This digital signature verification system ensures that only the person who has the private key associated with the corresponding cryptocurrency wallet can withdraw funds from it. It should be noted that asymmetric ciphers used in cryptocurrency applications are different from those used for computer security purposes. For example, Bitcoin and Ethereum use a special cipher known as 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 protecting modern digital systems. Using paired public and private keys, asymmetric cryptography algorithms solve the fundamental security problems presented by symmetric ciphers. Although PKC has been in use for many years, new applications and applications are regularly developed for it, especially in blockchain and cryptocurrencies.
