To encrypt a document the option --encrypt is used. You must have the public keys of the intended recipients. The software expects the name of the document to encrypt as input or, if omitted, on standard input. The encrypted result is placed on standard output or as specified using the option --output. The document is compressed for additional security in addition to encrypting it.
alice% gpg --output doc.gpg --encrypt --recipient blake@cyb.org doc |
To decrypt a message the option --decrypt is used. You need the private key to which the message was encrypted. Similar to the encryption process, the document to decrypt is input, and the decrypted result is output.
blake% gpg --output doc --decrypt doc.gpg You need a passphrase to unlock the secret key for user: "Blake (Executioner) <blake@cyb.org>" 1024-bit ELG-E key, ID 5C8CBD41, created 1999-06-04 (main key ID 9E98BC16) Enter passphrase: |
Documents may also be encrypted without using public-key cryptography. Instead, only a symmetric cipher is used to encrypt the document. The key used to drive the symmetric cipher is derived from a passphrase supplied when the document is encrypted, and for good security, it should not be the same passphrase that you use to protect your private key. Symmetric encryption is useful for securing documents when the passphrase does not need to be communicated to others. A document can be encrypted with a symmetric cipher by using the --symmetric option.
alice% gpg --output doc.gpg --symmetric doc Enter passphrase: |