S/MIME (Secure Multipurpose Internet Mail Extensions. RFC 2311)

S/MIME (Secure Multipurpose Internet Mail Extensions. RFC 2311) Internet E-mail by an email head and an optional mail subject composition, including mail containing the head email sender and receiver of relevant information. For mail subject, it is especially important in RFC 2045 ~, IETF RFC 2049 defined in MIME regulation, mail subject except ASCII characters type besides, still can contain a variety of data types. User can use MIME increase the text object, such as putting images, audio, formatted text or Microsoft Word document added to mail subject. MIME the data type is generally of compound, also called composite data. By allowing composite data, users can use different types of data is embedded into the same email subject. In include composite data mail subject, with boundary symbol, it indicate each type data begin and end.

S/MIME in terms of security function and expand, it can make the MIME entity (for example, digital signatures and encrypted information etc encapsulation into security object. RFC 2634 defines enhanced security services, for example with the recipient acknowledges receipt function, which can ensure the receiver can't deny that has received the mail. Microsoft will in future Office 2000 new version contains these services. S/MIME added new MIME data types that can be used to provide data confidentiality, integrity, protection, authentication and appraisal services, and other functions, these data types including "application/pkcs7 - MIME" apply/pkcs7 - MIME), "composite/signed" (multipart/counter-offer) and "application/pkcs7 - signature" apply/pkcs7 - our) etc. If the mail contains the MIME composite with relevant data, the mail will MIME accessories. In the email client, the receiver in reading email before, S/MIME application processing these accessories. As shown in table 1, annex extensions for complex data types provided by the S/MIME service and varies. In MIME head, marking the MIME annex name. Some mail client, if not installed with S/MIME ability systems, or is installed, the early S/MIME version, also needs through these accessories to identify email S/MIME related content. Other mail client is completely dependent on composite data information identification MIME entity.

S/MIME only protect the mail subject to mail the header information is not encrypt, so that the mail successfully in the sender and receiver's gateway between relay.

MIME messages can contain text, image, sound, video and other application specific data. Specifically, MIME allow email include:

A single message may contain multiple objects,

Text document does not limit line length or full length;

Transfer outside the character set, allow ASCII non-english languages news,

Many font information;

Binary or specific application documents,

Image, sound, video and multimedia news.

MIME composite news directory letterhead with boundary logo, the boundary mark can never appear in the news of the other position, it can only be in each other as well as news body the beginning and end of the place.

MIME safety version S/MIME (Secure/Internet E-mail Multipurpose Extensions) designed to support email encryption. Based on MIME standard, S/MIME for electronic message application providing the following encryption security service: the authentication, integrity, protection, identification and data confidential, etc.

The traditional mail user agent (MUA) can use S/MIME encryption and decryption to send mail E-mail. However, S/MIME is not limited to the use of email, it also can be applied to any can transmit MIME data transmission mechanism, such as HTTP. Similarly, S/MIME using MIME object-oriented feature allows in hybrid transmission system in exchange of safe news.

In addition, S/MIME can also be used in news automatic transfer agent, they use does not need any artificial operation encryption security services, such as software documentation signature, and send to online tlx.number encryption, etc.