What Is a Public Key and How Does It Work

Public-key cryptography (PKC) is an asymmetric encryption technique that relies on a pair of keys to secure data communication. The public key is the encryption key shared with everyone to receive transactions, and the private key is the decryption key that must be kept secret.

This technique is at the heart of cryptocurrencies and ensures the integrity and authenticity of crypto transactions.

What Is Cryptographic Key Encryption?

The encryption algorithm used in blockchains is the cryptographic key encryption method for encrypting and decrypting data. A cryptographic key is a random string of data, such as numbers and letters, generated to encrypt data and decrypt the encrypted data.

Cryptographic encryption can be symmetric key cryptography or asymmetric. In symmetric encryption, only a single key is used to encrypt and decrypt data. While in asymmetric encryption, two keys are required to encrypt and decrypt encrypted messages in a complex mathematical algorithm. The key pairs used in asymmetric cryptography are known as public and private keys. A public key is used to encrypt messages and is widely shared and publicly displayed, similar to your email address or bank account, to receive cryptocurrency. Instead, a private key is the decryption key used to decrypt messages and must be kept in secret, similar to your password, to safeguard your cryptocurrencies.

Public-key cryptography is used in cryptocurrency transactions to ensure that only the intended recipient can access the message. Integrity is ensured through asymmetric encryption because only a private key can decrypt the information encrypted with a public key. The decryption process requires checking that the received message matches the sent message, thereby authenticating that the data is untampered and unaltered.

History and Common Methods

In the early days of cryptography, distributing key pairs between two parties was quite challenging. The parties had first to exchange a key that had to be kept in absolute secrecy using a face-to-face meeting or a trusted courier and then use the key for sharing encrypted messages.

In our days, the Diffie–Hellman key exchange method allows two parties with no prior knowledge of each other to establish a shared secret key together over an insecure channel.  

Some of the most commonly used algorithms for generating public keys are Rivest-Shamir-Adleman (RSA), Elliptic curve cryptography (ECC), and Digital Signature Standard (DSS).

The ECC algorithm uses elliptic curves to generate keys and is used for digital signatures and key agreement. The RSA algorithm is the oldest cryptography system used in transmitting shared keys for symmetric key cryptography. DSS is a Federal Information Processing Standard specifying the algorithms that can be used to generate digital signatures used by NIST.

How Does Public Key Cryptography Work?

In public key cryptography, known as asymmetric encryption, anyone can encrypt messages using a public key, but you need a matching private key to decrypt the message. First, the unencrypted data, or plaintext, is put into a cryptographic algorithm using the public key. Then the plaintext comes out as random-looking data. And finally, anyone with the corresponding private key can decrypt the data and translate it back into plaintext.

For example, Jane (sender) wants to send 1 BTC to Alice (recipient). Jane knows Alice’s public key and uses it to encrypt the transaction. After receiving it, the transaction is decrypted using Alice’s private key. Alice should be the only person who can authorize the transaction, as nobody else knows her private key. 

Public key encryption can also be used to create digital signatures. Here are the steps for generating a digital signature:

1. The sender selects the file to be digitally signed.
2. The sender’s computer calculates the unique hash value for the file content.
3. The hash value is encrypted with the sender’s private key, creating the digital signature.
4. The original file and the digital signature are sent to the recipient.
5. The recipient uses the associated document application, which identifies that the file has been digitally signed.
6. The receiver’s computer decrypts the digital signature using the sender’s public key and verifies that the decrypted hash value matches the hash of the original file.

Differences Between Public and Private Keys

Public Key

The public key is the user’s public address on the blockchain used to receive cryptocurrencies. Anyone can use it to send digital currencies to you; however, only you can spend them using your private key. The public key is used to encrypt messages before sending.

Private Key

A private key is similar to your house’s front door. The public knows its location because the address (public key) can be easily found, but only you with a key to the house’s front door (private key) can enter it. Private keys are used to decrypt messages created with the corresponding public key. The private key is kept secret; if lost, restoring or accessing your funds is impossible.

Risks Associated With Public Key Encryption

While public key cryptography’s indisputable advantage is robust data security, there are still some risks associated with it, such as:

Low-Quality Key

A poorly crafted asymmetric key algorithm, i.e., too short, is a security risk. So, the encryption key issuance, renewal, and revocation should be managed with great care.

Loss of Private Key

As mentioned earlier, private keys can’t be shared publicly and should be kept private and secure. This is because once the private key is lost, there is no way to access data or funds stored in a crypto wallet.

Man-in-the-Middle Attacks

Public Key Encryption is also vulnerable to a Man-in-the-Middle (MitM) Attack in which the communication of public keys is intercepted by a third party (the “man in the middle”) and then modified to provide different public keys instead.

The primary way to establish a secure connection with servers, you must first check their digital certificates.

Secure Socket Layer and Transport Layer Security connections SSL / TLS uses public key encryption to enable the use of Hypertext Transfer Protocol Secure to create a secure connection between the server and client. The communication session is first established using asymmetric encryption to verify the identities of both parties and exchange a shared session key that enables a symmetric cipher.

Conclusion

Cryptography is essential for securing cryptocurrency transactions and ensuring your data hasn’t been tampered with. That’s why private, and public keys are critical in authorizing these transactions.

Remember to keep your private keys private and secure at all times. Write down your phrase on paper and store it in a fireproof safe. Also, go the extra mile by having your private keys engraved on a metal plate to protect them from high temperatures, moisture, and aggressive chemicals!