What’s Public Key Cryptography?

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Public key cryptography is a type of encryption architecture known as public key cryptography that uses two keys or a pair of keys to encrypt and decrypt data. One of the two keys is a public key, which anyone can use to encrypt a message for the owner of that key. The encrypted message is sent and the recipient uses their private key to decrypt it. This is the basis of public key cryptography.

This type of encryption is considered very secure because it does not require a secret shared key between the sender and the recipient. Other encryption technologies that use a single shared key to encrypt and decrypt data rely on both parties deciding on a key in advance without any other party finding out what that key is. However, the fact that it must be shared between both parties opens the door to third parties who intercept the key. This type of encryption technology is called symmetric encryption, while public key encryption is known as asymmetric encryption.

A “key” is simply a small piece of text code that activates the associated algorithm to encode or decode the text. In public key cryptography, a key pair is generated using a cryptographic program and the pair is associated with a name or email address. The public key can then be made public by sending it to a key server, a computer that hosts a database of public keys. Alternatively, the public key can be shared in a discriminatory way by emailing it to friends and colleagues. Those who possess the public key can use it to encrypt messages to the person or email address with which it is associated. After receiving the encrypted message, the person’s private key will decrypt it.

Public key encryption is especially useful for keeping emails private. All messages stored on mail servers, which can persist for years, will be unreadable, and messages in transit will also be unreadable. This degree of privacy may seem overwhelming until you realize the open nature of the Internet. Sending unencrypted emails is equivalent to making them public for anyone to read now or at some future date.

The best known and most respected public key encryption program is PGP (Pretty Good Privacy), which offers military-grade encryption. PGP has plug-ins for most major email clients so that clients work in concert with PGP to encrypt outgoing messages and automatically decrypt incoming messages. PGP maintains a “ring of keys” or file of collected public keys. An email address can be associated with a key so that the email client automatically extracts the correct public key from the PGP keyring to encrypt the message upon sending. It will also automatically use a private key to decrypt your incoming mail. To use public key cryptography for e-mail, both the sender and recipient must have encryption software installed.

Programs like PGP also have built-in digital signature capability. With this feature, sent messages can be digitally signed with the click of a button, so the recipient knows the message hasn’t been tampered with en route and is authentic, or from the designated sender. Public key cryptography can also be used for secure storage of data files. In this case, the public key is used to encrypt the files while the private key decrypts them.

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