Public/private key pairs are used for public-key cryptography, also known as asymmetric cryptography. In comparison to its less modern counterpart – symmetric cryptography – asymmetric cryptography uses two distinct keys for encryption and decryption. Asymmetric cryptography is the current industry standard for encryption due to its nature of requiring two keys, and because it requires a 2048-bit or longer key size, which means cracking the encryption is highly infeasible. For a 2048-bit key, there would be 2 to the power of 2048 possible combinations, which would take modern computers around 300 trillion years to crack.  

For asymmetric cryptography, a private key is generated along with its corresponding public key. This means that the public key and private key are mathematically similar, however a private key cannot be generated from a public key. The ‘public key’ is the key a party would share to allow other parties to send them encrypted messages, with no security risk if the key is shared publicly. The ‘private key’ is the key a party would keep to themselves, with an extreme security risk if it were to be made public or leaked. Messages encrypted with a public key can only be decrypted using the corresponding private key, and the private key can only decrypt messages encrypted with its corresponding public key. One example use case of a public/private key pair would be email transfer. When sending an email to a recipient, their public key is used to encrypt the outgoing email so that only the recipient, who holds the corresponding private key, can decrypt and read the contents of the email. Of course, this entire process is handled automatically by the emailing software.  

Asymmetric encryption also enables the use of digital signatures, where the sender uses a signing algorithm to produce a signature from a private key and a desired message, from which the recipient uses a signature verifying algorithm along with the sender’s message and the private key’s corresponding public key to verify the sender’s signature. An example use case of digital signatures would be in videogame systems such as the PS3, where every PS3 contains a public key for software update verification. When Sony sends out a PS3 software update, the updates are signed using a private key which only Sony has access to. A PS3 receiving an update would use the public key to verify the contents of the update, preventing unofficial software updates from being installed. 

Written by Hussain Hamidi – LCF Intern

Find Out More

If you enjoyed this briefing paper, check out our other digital resources which cover a wide range of topics, including quantum computing, social media, and 3D printing.

The Lancashire Cyber Foundry runs a series of business strategy and cyber workshops specifically designed for SMEs in Lancashire. We’re passionate about seeing Lancashire business become more cyber-aware and innovative and so offer funded places for companies to come and learn how to defend, innovate and grow their business. Additionally, we have an experienced technical team ready to help you with your business innovation ideas, particularly around cyber and digital innovation

Interested? Email us

Sign up to our newsletter

Get the latest updates on news and events from the Lancashire Cyber Foundry team.

By filling in this form you register for our e-newsletter, which will help explain the programme and how we could benefit your business. Registering does not place you under any obligation, and you can unsubscribe from communications at any time using the unsubscribe link at the bottom of our newsletters. Lancaster University will hold and use the information which you supply in line with our privacy policy.

Thank you! Your subscription has been confirmed. You'll hear from us soon.