Public-key cryptography

In an asymmetric key encryption scheme, anyone can encrypt messages using the public key, but only the holder of the paired private key can decrypt. Security depends on the private key being kept secret.

Public-key cryptography, also called asymmetric cryptography, is a communication where people send messages that can only be read by those who have the key.

In public key cryptography, each user has a pair of cryptographic keys:

• a public key
• a private key

The private key is kept secret, while the public key may be widely distributed and used by other users.

Incoming messages are encrypted with the recipient's public key and can only be decrypted with their corresponding private key. The keys are related mathematically, but the user's private key cannot be easily got from the widely used public key. The most usual problem with this method arises when private key is accidentally leaked.

The two main branches of public key cryptography are:

• Public key encryption: a message encrypted with a recipient's public key cannot be decrypted except by the recipient private key. This is used to ensure secrecy.
• Digital signatures: a message signed with a sender's private key can be verified by anyone who has the sender's public key. So if the sender signed the message no one can alter it. This is used to get authenticity.

They are often used together on the same message.

Public-key Cryptography Media

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  An unpredictable (typically large and random) number is used to begin generation of an acceptable pair of keys suitable for use by an asymmetric key algorithm.

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  In this example the message is digitally signed with Alice's private key, but the message itself is not encrypted.*1) Alice signs a message with her private key.*2) Using Alice's public key, Bob can verify that Alice sent the message and that the message has not been modified.

Related pages

• Symmetric-key algorithm
• RSA algorithm