What Is S/MIME and How Can It Secure Email?
- by Brittany Day
Have you ever given any thought to how secure your email security software is? If you haven’t, you’re not the only one. Nevertheless, we all have to take security seriously in the modern world. This article will give you the low-down on everything you need to know about the S/MIME encryption protocol for email. Let’s dive in.
What is S/MIME Encryption?
If you rely on unsecured emails, they may be accessed, intercepted, and read by people other than the intended recipients. That’s where the S/MIME internet standard comes in.
S/MIME Encryption (Secure/Multipurpose Internet Mail Extensions) is an email security protocol that uses public encryption and data signing to secure email messages against tampering. It does this by providing digital certification of the identity of the individual sending the email.
S/MIME isn't a type of encryption but a standard for using encryption to prevent those without the decryption key from reading the message. It also signs it with a digital signature to uniquely identify the sender. This also prevents the sender from being able to deny they sent it - this is called nonrepudiation. It can help avoid email interception attacks using several different validation levels.
S/MIME Validation Levels
There are three validation levels for S/MIME certificates. However, there’s not a single universally accepted standard. The exact classification of these levels can vary slightly depending on which Certificate Authority (CA) you use, but broadly speaking, it looks like this:
- Email/domain validation checks your email address and domain validity.
- Individual validation: The goal here is to identify individual employees. It requires a government-issued ID (e.g., a driver’s license) and a company email address.
- Organizational validation: This procedure is similar to the one for acquiring an OV SSL certificate. The CA will contact the company and ask to speak to a representative. Once the existence of the company and its email domain has been verified, the certificate will be issued.
How Does S/MIME Encryption Work?
S/MIME uses asymmetric cryptography to prevent unwelcome third parties from reading your emails. This means that it uses a public key to encrypt messages; these are then decrypted using the corresponding private key held by the email recipient. The S/MIME system combines encryption with a digital signature to ensure an organization’s email security.
A two-key system like this is possible because the cryptography keys are mathematically related. A critical exchange between communication partners is fundamental to encrypting email communication successfully. (That’s something to remember if your organization uses email capture for marketing purposes).
This works because anyone can access an organization’s public key. The email's sender encrypts the message using the freely available public key of the intended recipient. Then, the recipient decrypts the message using their private key, which is known only to them.
The digital signature element of S/MIME encryption has three functions:
- Authentication: The digital signature validates the sender’s identity, ensuring they are who they say they are.
- Nonrepudiation: It also ensures neither party can deny their actions under that signature, e.g., sending messages or using the digital signature.
- Data integrity means that emails cannot be changed when they are in transit. If they are, the S/MIME protocol will show that the signature has been invalidated.
S/MIME Encryption: Who Needs It & How To Get It?
Any organization that is concerned about email security should consider implementing S/MIME. However, it can prove a little impractical for essential email use. That’s because implementing it can be pretty expensive and time-consuming. S/MIME certificates must be installed on all devices individually, which can be an intimidating barrier for organizations without a large IT support section.
There’s also the potential issue that a staff member will get locked out of their emails if they lose their private key. Resetting their account will mean retrieving the key securely or even starting the process again and generating a new certificate. Additionally, S/MIME can interfere with other email security software systems, such as antivirus and malware URL scanners, since these won’t be able to scan an encrypted message.
When you add that emails using S/MIME encryption can only be sent to recipients who also use S/MIME, the upside/downside ratio may seem reasonably balanced.
So it’s a judgment call. How large is your organization? How much privacy do you need in your business communications?
As a rough guide, here’s a list of organizations that would probably benefit from using S/MIME:
- Government agencies
- Businesses that employ a primarily remote workforce
- Firms whose sphere of work includes countries that apply GDPR
- Organizations that are legally obliged to maintain data privacy according to HIPPA
- Companies that use email lists (regardless of whether they deploy a standard email list scrubbing protocol or not)
- Organizations that use enterprise-level security protocols
- Companies subject to PCI compliance
If you decide to implement S/MIME, you’ll be relieved to know acquiring certificates is relatively straightforward. First, find a CA with a good reputation. All CAs must document their email security products, features, and certificate requirements and make them publicly available.
What Are the Benefits & Disadvantages of S/MIME Encryption to Your Business?
Let’s look at the upsides and downsides of implementing S/MIME encryption. After all, this isn’t like finalizing software contracts that can be negotiated relatively easily. If you decide to go the S/MIME route, you’ll want to be sure before you start that you’re making the right decision.
Benefits of S/MIME Encryption
Combining digital identity certificates and end-to-end encryption makes your email messages secure. This means that:
- Safeguards against cyberattacks: It makes it more difficult for cybercriminals to attack you through your email communications.
- Increases general email security: You can rest assured your email and important documents are as secure as possible.
- Prevents unwanted third-party access: It stops unauthorized users from spying on your communications.
Disadvantages of S/MIME Encryption
It would be remiss of us not to mention the downsides. You’ll need to give these careful thoughts before you decide.
- Lack of universal adoption: Only some people use S/MIME, which poses a problem because using the S/MIME protocol isn’t like using MLOps software or a data analytics solution. Email, by its nature, is a two-way process. For S/MIME to work, both the sender and recipient must have the system installed. There are some workarounds, but no ideal ones as yet exist.
- File size limits: Often, if you’re sending an attachment by email, the data included in it will be the most essential part of the message. Encrypting this also quickly adds to the overall encrypted file size, putting it beyond the limit many email clients allow.
- Potential security flaws: S/MIME provides excellent email security but has several weaknesses. Using static key pairs means that the system is useless if a key is compromised and won’t be effective again until a new key can be generated. Metadata like the email subject line are sent unencrypted. The so-called “Efail” flaw – if, in the unlikely event, a cybercriminal can intercept and alter an encrypted email, it’s theoretically possible for them to send the decrypted message to a server they control with the help of any number of GUI-based email clients.
- Lack of malware protection through detection: Because the protocol is designed with end-to-end security in mind, S/MIME will encrypt any malware in your email along with the content of the email, and you’ll be sending both to the recipient.
PGP vs. S/MIME: Which Is Better?
We decided to include a quick note about PGP. It’s an alternative encryption protocol and tends to be cheaper than S/MIME.
The main difference is that PGP is more of a general-purpose solution than S/MIME, which specializes in email. Aside from that, PGP uses a different digital signature and is more commonly favored by individual users for encrypting files. Your choice of which to use depends on the purpose you have in mind.
S/MIME Email Protection from Spear Phishing Attacks
We’ll examine how S/MIME helps prevent spear phishing email attacks. Spear phishing emails focus on one individual and generally manifest in one of three ways:
- Spoofed email headers: Attackers spoof the “From” field of an email header, making it look like the sender is within the recipient’s organization.
- Impersonation: The email appears to come from a senior staff member, meaning the recipient is less likely to question its authenticity.
- Fake email chain: an entire fake email chain with multiple messages is set up to make the email seem more legitimate.
If you’re using S/MIME, the recipient will know immediately that the email is fake. That’s because all they have to do is check the email signature to verify the sender. Easy. The same applies to standard spear phishing emails. And this is the great strength of S/MIME: if you can get over the deployment hurdles, it’s pretty easy to use.
Keep Learning About S/MIME & How It Can Secure Email
Ultimately, only you know whether S/MIME will be the right choice for your organization. But if you decide it is, there’s no doubt it will give you great peace of mind. Keeping your business communications secure has never been more critical. And just as you’d expect high security from the available cloud PBX features when selecting a phone system, it goes with email. Maybe it’s time to consider a S/MIME solution for your business.
- By following best practices for email security, you can improve your company’s posture to protect against attacks and breaches.
- Keeping the integrity of your email safe requires securing the cloud with spam filtering and enterprise-grade anti-spam services.
- Get the latest updates on how to stay safe online.
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