What is S/MIME?
S/MIME, or Secure Multipurpose Internet Mail Extension, is an email encryption and signing industry standard widely used by corporations to enhance email security. S/MIME is compatible with most enterprise email clients.
In simple terms, S/MIME is an encryption protocol used to digitally sign and encrypt an email to ensure that the email is authenticated and its content is not altered.
S/MIME works based on asymmetric encryption. This means that this protocol uses a two-key system (Public and Private) that is mathematically related but different, to encrypt and decrypt an email.
A S/MIME certificate needs to be installed on the email clients of both the recipient and the sender to ensure email encryption at both ends. When an email is sent, the sender encrypts the email using the recipient's public key and the recipient decrypts the email using the private key.
S/MIME also attaches a digital signature to an email. This ensures that the sender is authorized to send emails from a specific domain.
The encryption and digital signing of an email ensure that the data transmitted through email is confidential, and true to its sender. S/MIME protects an email in the following methods:
The email content is encrypted using the recipient's public key, the moment the sender hits the Send button. Even if the email gets intercepted by anyone, they cannot view the content of the email unless they have access to the private key of the recipient.
The encryption of the email content ensures the confidentiality of the data and attachments sent through the email. Any attempt to view the content of the email is made void as the data can be decrypted only with the help of a private key unique to the recipient.
The email will be digitally signed along with encryption on installing the S/MIME certificate. The email is signed using the private key of the sender and authenticated by the public key of the recipient. An unaltered digital signature shows that the email content has not been compromised and tampered with.
When the sender digitally signs the email using their private key, the recipient validates and authenticates the signature using their public key to ensure that the email is received from a reliable source.
Non-repudiation by the Sender
The digital signature of each sender is unique and is assigned to the user and the domain when the S/MIME certificate is purchased and installed. This voluntarily provides the non-repudiation of the signature by the sender in case of any legal proceedings.
Content Integrity of the Email
When the recipient of a digitally signed email is validated using the public key of the recipient, they're assured of the absence of any alterations in the content of the email and is intact as and when it was sent.
Getting S/MIME installed on your organization's email client helps prevent you and your organization's data from the following actions:
Phishing and Spoofing
The act of phishing and spoofing via email occurs by impersonation of the sender or sender's domain. The digital signature using S/MIME validates and authenticates the sender's identity and prevents you from becoming a victim of these attacks. Hence, it's imperative to sign the email digitally along with encryption. Mere encryption of the email will not validate the authenticity of the sender.
The email content encrypted using the public key of a recipient can be decrypted and viewed only by the intended recipient with the help of their private key. Hence, the emails encrypted using S/MIME though intercepted by hackers the content of the email cannot be altered unless they have access to the private key of the recipient.
Unauthorized access to confidential data
Since email has become a medium for transaction emails, sharing business quotes, and much more personal data, it is imperative that the email is encrypted end-to-end. S/MIME encrypted emails are hard to decrypt by anyone else other than the intended recipients, thus ensuring the confidentiality of the data transmitted.