Secure/Multipurpose Internet Mail Extensions, or short S-MIME, is a standard for public key encryption and signing of MIME data.
S/MIME provides the following cryptographic security services for electronic messaging applications:
- message integrity,
- non-repudiation of origin (using digital signatures),
- privacy and data security (using encryption).
S/MIME specifies the MIME type application/pkcs7-mime (smime-type "enveloped-data") for data enveloping (encrypting) where the whole (prepared) MIME entity to be enveloped is encrypted and packed into an object which subsequently is inserted into an application/pkcs7-mime MIME entity.