What is Public Key Cryptography: Complete Explanation

Public Key Cryptography is a type of cryptography that uses pairs of keys. In this system, one key is public, meaning that it can be known by anyone. The second key is the private key, and it is known only by the owner. In this system, a person uses the public key to encrypt a message. That message is then decrypted by the private key. As you can imagine, the generation of such keys involve intensive and extensive knowledge of mathematical and computer algorithms for the purposes of decryption and authentication.

Public Key Cryptography depends on the owner of the private key also having access to a server that can generate public keys. That public key can then be encoded via that public key, also known as an asymmetric key. However, the message will appear as gibberish to anyone who doesn’t actually possess the private key.

This system comes with many advantages, including:

  • Since the messages can only be deciphered by someone who has possession of the private key, they can be sent over an insecure channel – even regular email.
  • Because the private key never has to be revealed, there is a limited risk of the encryption being broken. Possession of the private key is required for authentication, and it is next to impossible to crack the encryption otherwise. 
  • Public key cryptography engages digital signatures that are computer-generated, and the odds of these signatures being cracked via brute force attack are extremely low. As such, this method is considered to be largely secure. 

Public Key Cryptography: An exact definition

Public Key Cryptography is a type of encryption system. It involves the use of pairs of keys – one public, one private – that allow for the encryption of data. 

It is also known as one-way authentication or asymmetric cryptography. It is known as asymmetric cryptography because only one person holds the private key that is necessary to decode the message, hence enabling the asymmetric nature of the encryption. 

How does Public Key Cryptography Work?

The basics behind this concept are relatively simple regardless of the specific method used. 

Public Key

This key can be possessed by anyone and is usually created by a computer, using some sort of mathematical algorithm.

Data – such as a file or word document – is scrambled using this algorithm. It thus becomes unreadable and inaccessible to anyone who comes across it. 

Because the data can be encrypted by anyone who possesses the public key – but only decrypted by someone who possesses the private key – Public Key Cryptography is also known as a one-way function. 

Public Key Cryptography diagram
This diagram simplifies the intricacies of how cryptography — including public key cryptography — works.

Private Key

While anyone can possess the public key, the private key is required to decode the message, and possession of the private key must be kept secret. The private key is used to decode the message and transmit it back to an insecure (and thus readable) state. 

Where did Public Key Cryptography come from?

Public Key Cryptography was first developed in 1976 by Martin Hellman, Ralph Merkle, and Whitfield Diffie. The three men were at Stanford university and attempting to come up with a more secure alternative to Private Key Cryptography. In this form of cryptography, pairs of keys – known as cryptographic keys – are possessed by two individuals. These keys are used to code and decode text. The weakness is obvious: If the key falls into the wrong hands, the code can be broken. Indeed, this is responsible for some of the more famous code-breaking instances in history.

How do you create Public Key Cryptography?

Unlike other systems, Public Key Cryptography cannot be created without the help of specialized computers that can create the algorithms that will be necessary to encode and decode information. 

In order to create Public Key Cryptography, a user will need to:

  • Generate the public key and private key.
  • Establish a method for key exchange. This method should be secure.
  • Encrypt the data using the public key.
  • Transmit the data. This can be on an insecure channel, as the information that has been encrypted cannot be broken without the private key.
  • Decrypt the data. 

What Are the Applications of Public Key Cryptography?

There are many applications when it comes to Public Key Cryptography. 

Encrypting confidential messages

This is arguably the most popular and easily accessible of the various uses for Public Key Cryptography. By using the public and private keys, data can be encrypted, sent, and decrypted by the individual to whom it is intended.

Digital cash

Many mobile payment options are based largely on Public Key Cryptography. This includes payment made via mobile devices, deposited via a mobile device with a bank, or third-party programs, like PayPal or Venmo.

The setup is simple enough: In this case, the public key is held by the app that can be downloaded from anywhere. However, accessing the actual financial services requires possessing the private key, which is held by the financial services provider. Such a model allows for easy consumer access but makes actually breaking into the app and stealing money impossible without actually having the private key.

third party apps utilize public key cryptography
Apps like Paypal, Venmo, Cash App and Google Pay utilize public key cryptography.

Time-stamping services

Time stamping, like financial services, can be easily done with a public and private key. The model is relatively simple: Anyone can use the software, but time-stamping itself is only done via the private key. This guarantees that the date and time of the time-stamping service cannot be tampered with. 

Examples of Public Key Cryptography In the Real World

Private key cryptography continues to create new examples and methods of working. All of these examples utilize the same basic core of private key cryptography and require a private key for authentication purposes. However, there are many differences of specific examples here, and they vary widely. 

Examples include:

Digital Signature Standard

Digital Signature Standard is used to create a digital signature. It has been approved by the United States government and works by taking advantage of Public Key Cryptography.

Digital Signature Standard is used to add a digital signature to a transmission, thus confirming the identity of the individual who is sending the transmission. Furthermore, it can be used to confirm that the information contained in the message has not been altered from the time in which it was sent, thus acting as an electronic version of signing the seal of an envelope. 

Elliptic-Curve Cryptography

Elliptic-Curve Cryptography is a type of Public Key Cryptography that uses elliptical curves. More specifically, it is viewed as more secure than other forms of Public Key Cryptography because finding the appropriate point on the elliptical curve is essentially impossible.

Paillier Cryptosystem

The Paillier Cryptosystem is another type of cryptosystem that takes advantage of residue classes. By using resident classes, the Paillier Cryptosystem is virtually unbreakable. 

The Complete Guide to Public Key Cryptography FAQs (Frequently Asked Questions) 

What is Public Key Cryptography?

Public Key Cryptography is a type of encryption system that takes advantage of two keys – one public, one private. Also known as a one-way function, this cryptography allows for anyone to encode a message if they possess the public key, but ensures that the data cannot be decoded by anyone who does not possess the private key, thus making it a one-way function.

Keys are generated via mathematical algorithms that are created by computers. Cracking these codes is virtually impossible for anyone who does not hold a private key.

Public Key Cryptography uses how many keys?

Public Key Cryptography uses two keys:

  • A public key, which can be known by anyone.
  • A private key, which can only be known by the recipient of the message.

How does Public Key Cryptography work?

There are two keys: A public one or a private one. The public key can be accessed by anyone. In real terms, this means that any person can download the software that will give them access to the public key. The private key – the actual encryption and decryption portion of the app – can only be possessed by the authorized user. This ensures that the only person who will be able to decrypt the data, and thus access it, are authorized users.

What are Public Key Cryptography techniques?

There are literally dozens of different techniques that have been developed for use of Public Key Cryptography. These include Diffie-Hillman key exchange protocol, ElGamal, YAK, and more. Some of these techniques also merge Public and Private key techniques.

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