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### 5.9 Signing and encrypting

Gnus can digitally sign and encrypt your messages, using vanilla PGP format or PGP/MIME or S/MIME. For decoding such messages, see the `mm-verify-option` and `mm-decrypt-option` options (see Security).

Often, you would like to sign replies to people who send you signed messages. Even more often, you might want to encrypt messages which are in reply to encrypted messages. Gnus offers `gnus-message-replysign` to enable the former, and `gnus-message-replyencrypt` for the latter. In addition, setting `gnus-message-replysignencrypted` (on by default) will sign automatically encrypted messages.

Instructing MML to perform security operations on a MIME part is done using the `C-c C-m s` key map for signing and the `C-c C-m c` key map for encryption, as follows.

`C-c C-m s s`
  Digitally sign current message using S/MIME.
`C-c C-m s o`
  Digitally sign current message using PGP.
`C-c C-m s p`
  Digitally sign current message using PGP/MIME.
`C-c C-m c s`
  Digitally encrypt current message using S/MIME.
`C-c C-m c o`
  Digitally encrypt current message using PGP.
`C-c C-m c p`
  Digitally encrypt current message using PGP/MIME.
`C-c C-m C-n`
  Remove security related MML tags from message.

See Security, for more information.