Definition

private key

Contributor(s): Michael Cobb

A private key, also known as a secret key, is a variable in cryptography that is used with an algorithm to encrypt and decrypt code. Secret keys are only shared with the key’s generator, making it highly secure. Private keys play an important role in symmetric cryptography, asymmetric cryptography and cryptocurrencies.

The complexity and length of the private key determine how feasible it is for an interloper to carry out a brute force attack and try out different keys until the right one is found.

How does a private key work?

Private key encryption is referred to as symmetric encryption, where the same private key is used for both encryption and decryption purposes. A private key is typically a long, randomly generated number that cannot easily be guessed. Since only one key is involved, the process is fast and simple.

Secret key ciphers generally fall into one of two categories: stream ciphers or block ciphers. A block cipher applies a private key and algorithm to a block of data simultaneously, whereas a stream cipher applies the key and algorithm one bit at a time. Symmetric-key encryption is much faster computationally than asymmetric encryption but requires a key exchange.

Most cryptographic processes use private key encryption to encrypt data transmissions but used public key encryption to encrypt and exchange the secret key.

Challenges of private key encryption

While private key encryption does ensure a high level of security, the following challenges must be considered:

  • Encryption key management can become too complex if each user has their own private key.
  • Private keys need to be changed frequently to avoid being leaked or stolen.
  • If the private key is forgotten or lost, the system is broken and messages stay encrypted.
  • Significant computing resources are required to create long, strong private keys.

Private keys vs. public keys

Asymmetric cryptography, also known as public key encryption, uses two different but mathematically linked keys. The public key is made available to everyone that needs it in an easily accessible repository while the private key is confidential and only shared with its owner. In this method, whatever is encrypted with the public key requires the related private key for decryption and vice versa. Public key encryption is typically used for securing communication channels, such as email.

This was last updated in May 2019

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