Reviewing Elements of Crytography: What Are Private and Public Keys?

What Is a Private Key?

Before we get into the private and public terms, let’s first define a key. In cryptography, a key is a string of randomly generated bits used to scramble and unscramble data. Keys are generated by algorithms that ensure that each key is unpredictable and unique. The more bits used in the key, the harder it is to break.

So, in the context of encryption and decryption, a private key is a key used both for encryption and decryption. Both parties, the sender and receiver, use the private key for encryption and decryption purposes.

The encryption algorithm is the inverse of the decryption algorithm. Thus, if the encryption algorithm was created with multiplication and addition, the decryption algorithm would use division and subtraction to “break” the code.

Private keys are also called “symmetric” because it’s the only key copied and shared by another user to decode the received cipher.

What Is a Public Key?

A public key is an encryption method that uses a pair of private and public keys to secure data communication. First, the public key encrypts the plain text, converting it into ciphertext, then the private key is used for decrypting the converted ciphertext so the recipient can read the message.

The public receives the appropriately named public key, and the receiver gets the private key. Public key cryptography is called asymmetric cryptography.

Some people describe public keys as the same thing as looking up a company’s address on the Internet. Anyone can look up that information and share it as they wish. Each public key is paired with a private key. Using our company address analogy, the private key is like the key to that company’s front door. The public knows the company's location because the address (public key) can be easily found. But only people with a key to the front door of the building (private key) can gain entry.

What’s the Difference Between Private and Public Encryption Keys?

Let's use a comparison chart to quickly show the difference between a public and private key.

How Do Public and Private Key Encryption Work?

The public key encryption technique uses a pair of public and private keys to facilitate confidential, secure data communication. The public key is generated by an algorithm and used to encrypt the plain text, converting it into ciphertext. After the message is sent, the private key is used to decrypt the ciphertext, allowing the recipient to read the message.

On the other hand, in private key encryption, the sender uses the secret key and its algorithm for encryption. The receiver then uses this same key and algorithm to decrypt the message. The algorithm used in the encryption process is the inverse of the algorithm used for decryption.

What Are Public and Private Keys: How to Generate a Public Key and a Private Key

There are many mathematical algorithms available to generate public and private keys. Here are three of the more popular and respected algorithms.

• Digital Signature Standard (DSS): This algorithm is a Federal Information Processing Standard that specifies the algorithms that can be employed to generate digital signatures used by the National Institute of Standards and Technology (NIST).
• Elliptic curve cryptography (ECC): The ECC algorithm uses elliptic curves to generate keys and is typically used for digital signatures and key agreement.
• Rivest-Shamir-Adelman (RSA): This algorithm is the oldest of the public-private key cryptography systems. It’s often used in transmitting shared keys for symmetric key cryptography. RSA is well-regarded due to the difficulty of finding the prime factors of a composite number.

What Are Private and Public Keys: Examples of Public and Private Key Encryption

Here’s an illustration of how these keys work.

Let’s say Karin wants to send John an encrypted e-mail. If she’s using public encryption, she takes John’s public key, encrypts his message, and sends it to him. When John receives Karin’s e-mail, he encrypts it with his private key, which only he has. When John wants to reply to Karin, he repeats the process, encrypting the e-mail with Karin’s public key. When she receives John's e-mail, she decrypts it with her private key, which, like John's, only she knows.

Now, if Karin wants to send John an e-mail that’s been privately encrypted, the entire process only uses one private key for both encryption and decryption. So she uses the private key to encrypt her e-mail and sends it to John, who uses the same private key to decrypt the message.

What Are Private and Public Keys: The Applications

People use public key encryption for:

• Blockchain and cryptography technology, such as generating a pair of keys while setting up a new cryptocurrency wallet
• Creating a digital signature in operating system software such as Red Hat Linux or Ubuntu
• Encrypting e-mails to keep the content confidential
• Secure socket layer (SSL) protocol to secure the connections to websites

Private key encryption can also be used for the above applications, although it’s particularly ideal for handling cryptocurrency transactions. Private keys are also suitable for handling vast amounts of text.

What Are Public and Private Keys: The Business Benefits

Security is a big issue today, and threats lurk around every corner. Today's businesses need to ensure that their data is safe to keep their resources secure and engender strong consumer confidence. Here are the top three benefits of public and private key encryption:

• Authenticity: Since each message sent is signed by a private key, the recipient can rest assured that the source is genuine. The only way to decrypt a sender’s private key is with the sender’s public key, which the recipient can access. By employing a private key, the sender ensures the authenticity of their message and verifies that it really did come from them.
• Confidentiality: Content and messages secured with a public encryption key can only be decrypted with the correct private key. This arrangement means that only the intended recipient can access the message's contents.
• Integrity: Not every cyber-crook or intruder steals data. Some just enjoy ruining things. However, when you use private or public key encryption, integrity is ensured because an essential part of the decryption process requires checking if the received message matches the sent message. This setup shows that the message has not been changed between the source and destination; thus, integrity is preserved.

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