RFC5751

RFC 5751, titled "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2", is an Internet Standard that defines the Secure/Multipurpose Internet Mail Extensions (S/MIME) protocol. S/MIME is a standard for sending and receiving digitally signed and encrypted email. It builds upon the Multipurpose Internet Mail Extensions (MIME) standards and provides cryptographic security services for electronic messaging.

The primary goals of S/MIME are to provide authentication, message integrity, non-repudiation of origin, and privacy for email communications. Authentication ensures that the sender of a message is who they claim to be. Message integrity guarantees that the message has not been altered in transit. Non-repudiation prevents the sender from denying that they sent the message. Privacy is achieved through encryption, making the message unreadable to anyone without the appropriate decryption key.

RFC 5751 specifies the data formats for cryptographic messages, including how digital signatures and encryption are applied to email content. It relies on X.509 public-key certificates for key management and distribution. The RFC details the cryptographic algorithms that can be used, such as RSA for encryption and digital signatures, and DES, 3DES, and AES for symmetric encryption. It also outlines the procedures for generating and verifying signatures, as well as for encrypting and decrypting messages.

S/MIME is widely supported by various email clients and servers, allowing for interoperable secure email communication across different platforms and vendors. It is a crucial technology for organizations and individuals requiring secure and trustworthy email exchanges.