What is S/MIME and How Does It Work?

In this tutorial, we are going to see What is S/MIME and How Does It Work?

S/MIME (for Secure Multipurpose Mail Extension) is a process for securing e-mail exchanges that guarantees the confidentiality and non-repudiation of electronic messages.

S/MIME is based on the MIME standard, whose purpose is to allow the attachment of files other than text files (ASCII) in electronic messages. It is thus thanks to the MIME standard that it is possible to add attachments of all types to e-mails.

S/MIME was originally developed by the company RSA Data Security. Approved in July 1999 by the IETF, S/MIME has become a standard, whose specifications are contained in RFC 2630 to 2633.
 

 

How Does S/MIME Work?

The S/MIME standard is based on the principle of public-key encryption. S/MIME allows the content of messages to be encrypted but does not encrypt the communication.
 

 
The different parts of an electronic message, coded according to the MIME standard, are all encrypted using a session key.

The session key is inserted in each part of the message header and is encrypted with the recipient’s public key. Only the recipient can open the body of the message, using his private key, which ensures the confidentiality and integrity of the message received.

Also, the signature of the message is encrypted using the sender’s private key. Any person intercepting the communication can read the content of the message signature, but this guarantees the identity of the sender to the recipient because only the sender is able to encrypt a message (with his private key) that can be decrypted using his public key.
 
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