Public key
Public key
In public-key cryptography, a public key is one of a pair of mathematically related keys. Unlike the private key in the pair, which must be kept secret by its owner, the public key is designed to be shared openly with anyone.
The primary purpose of a public key is to allow anyone who possesses it to perform specific cryptographic operations related to the key's owner, without being able to perform the reverse operations that require the secret private key.
Role and Function
The public key has two main roles in public-key cryptography, working in conjunction with its paired private key:
1. **Encryption for Confidentiality:** If someone wants to send a confidential message to the owner of a Key pair, they use the recipient's public key and a public-key encryption algorithm (like RSA or ECC) to encrypt the message. Only the recipient's corresponding private key can decrypt this message. This ensures that only the intended recipient can read the message, even if it is intercepted by others. 2. **Verifying Digital Signatures:** If the owner of a Key pair creates a digital signature for a piece of data using their secret private key, anyone can use the owner's public key to verify that signature. This verification confirms that the signature was indeed created by the holder of the corresponding private key and that the data has not been altered since it was signed.
The mathematical relationship within the Key pair is such that operations performed with the public key can only be reversed or proven correct using the corresponding private key, and vice versa, but the private key cannot be easily derived from the public key.
Distribution and Trust
Because the public key is meant to be shared, its secure distribution is important. A common way to distribute and manage trust in public keys is through a PKI. In a PKI, a trusted third party, called a CA, issues digital certificates. A Digital certificate cryptographically binds a specific public key to an identity (like a person, organization, or website). When you trust the CA that issued a certificate, you can trust that the public key within that certificate belongs to the identity claimed. This is how your web browser trusts the public key of a website when you visit an HTTPS page.
Public keys are also exchanged or distributed in other ways depending on the application, such as in SSH `authorized_keys` files for server authentication or shared via key servers in systems like PGP.
See Also
- Public-key cryptography
- Private key
- Key pair
- Digital certificate
- PKI
- CA
- Digital signature
- Encryption (cryptography)
References
- Template:Cite book - Standard textbook defining and explaining the role of public keys.
- Template:Cite book - Explains the concept as part of asymmetric cryptography.
- Cloudflare - What is Public Key Cryptography? - Includes an explanation of the public key's role.
- DigiCert - What is Public Key Cryptography? - Explains public keys in the context of digital certificates.
