# Public Key Cryptography

### From gWebs Support Wiki

## Contents |

## What is Public Key Cryptography?

Public key cryptography is an asymmetric encryption scheme that uses a pair of keys (a public key and a private key) to securely encrypt data.

The public key encrypts data and a corresponding private key decrypts it. People are encouraged distribute their public key widely while keeping their private key secret. Anyone with a copy of "Bob's" public key can securely encrypt data so that only Bob can read it... after decrypting it with his private key.

It is virtually impossible to compute a private key from a public key. Thus, anyone who has a public key can encrypt information but cannot decrypt it. Only the person with the matching private key can decrypt the data.

In practice, MailCloak uses two public keys when encrypting email - the sender's and the recipient's - so that both parties can read the email after it has been sent.

## Why Public Key Cryptography?

Public key cryptography allows people with no prior security agreement to exchange messages securely.

In a symmetric encryption scheme, a secret key must be agreed upon between the two users and the same secret key is used to encrypt and decrypt the messages. In an asymmetric encryption scheme (using public and private keys), the need for the sender and receiver to share the secret key is eliminated.

## Which Public Key Cryptography System does MailCloak use?

MailCloak uses the open-source, open-standard GnuPG encryption system to encrypt email, attachments and drafts.