S/MIME

S/MIME (Secure/Multipurpose Internet Mail Extensions) is defined as a standard used for the encryption of public keys and the signing of email messages. It encapsulates data in MIME formats. S/MIME offers the following cryptographic services for electronic messages: the integrity of messages, authentication, non-repudiation, privacy and data encryption. It is built into a large number of email clients and effectively functions in between them. Before S/MIME can be used, an individual must obtain and implement an individual key or certificate from a reputable CA (Certificate Authority). The best approach is to use separate private keys for the purposes of signature authentication and encryption. This enables escrow of the encrypted key without comprising the non-repudiation of the signature key. Though it is possible to transmit encrypted data without ownership of a digital certificate, most S/MIME clients require a user to install one before allowing encryption to others. In most cases, the information on a certificate such as email details, are viewable by the public.