Secure/Multipurpose Internet Mail Extensions (S/MIME) is a standard for encrypting and signing electronic messages, such as email messages. It is designed to provide confidentiality, integrity, and authentication for electronic communications.
S/MIME works by using public key encryption to encrypt the message and digital signatures to authenticate the sender and verify the integrity of the message. When a sender wants to send an encrypted and signed message, they will first generate a private/public key pair and then use their private key to sign the message. They will then attach their public key to the message as a certificate, and send the message to the recipient.
When the recipient receives the message, they will use the sender's public key to verify the digital signature and confirm that the message was actually sent by the sender. They will then use their own private key to decrypt the message and read its contents.
By using S/MIME, it is possible to help ensure the confidentiality, integrity, and authenticity of electronic messages, such as email messages. It is commonly used in enterprise environments to secure business-critical communications.