Email Security

    Outlook Digital Signature for Secure Messaging

    Digital signatures in Outlook are an effective line of defense against email from unknown sources and phishing attacks. We break down the mechanism behind digital signatures, how to set them up and how they secure Outlook.

    by Daniel Argintaru

    Key Points

    • An Outlook digital signature is a digital identifier that validates the authenticity of an email, protecting both the data and recipients against fraud.
    • Unlike electronic signatures, which can easily be copied, digital signatures are unique to each individual and cannot be reproduced or altered by a third party.
    • Digital signatures can be combined with email encryption, thus ensuring both the authenticity and privacy of email exchanges.

    Microsoft Outlook is one of the world’s most popular email services, with more than 400 million active users as of 2018.[1] Even as enterprise email fraud becomes a bigger threat, Outlook continues to evolve its data security features. One of the most effective lines of defense is the digital signature, which combines identity algorithms, traceability and encryption to improve email security for all users, no matter their level of tech-savviness.

    What Is a Digital Signature?

    A digital signature is a unique identifier that validates the authenticity of a person’s outgoing email messages and assures recipients they have come from that person, as opposed to a cybercriminal or unknown sender. Unlike a simple electronic signature, digital signatures cannot be replaced or altered, thus giving recipients peace of mind that the contents of the incoming message are safe before opening it.

    Digital signatures are derived from a person’s Outlook digital ID, also known as a signing certificate. This ID is like a digital passport in that it’s issued by a trusted organization and only its owner can use it to prove their identity. Email recipients also need a valid digital ID of their own to access messages sent to them with a digital signature.

    This approach offers many advantages, in addition to helping with authentication and fraud protection. For one, digital signatures allow companies to exchange official documents online and from personal devices. This is more convenient than sending paper documents for completion, waiting for them to be filled out, and then waiting even longer for them to be couriered back. What’s more, digital document exchanges also speed up business processes, which in turn drives down costs and makes employees more productive.

    What are the Benefits of Digital Signatures?

    Digital signatures provide organizations with better security, timestamping, global acceptance, legal compliance, time savings, cost savings, positive environmental impacts, and traceability.

    What is the Role of Digital Signatures in Enhancing Email Cybersecurity?

    Digital signatures and encryption work together to make email more secure, protecting user and organization privacy. Digital signatures ensure email recipients that the email they received is really from the sender listed on the email.

    How Are Digital Signatures Different Than Electronic Signatures?

    It’s important to distinguish between digital signatures and the electronic signatures most people add to the end of their business emails. The latter is no more than a digital stamp used to personalize a person’s message. It’s as easy to copy as it is to create, requires no authentication and provides zero assurances to the recipient that an email has indeed come from a known sender.

    Conversely, digital signatures are unique identifiers. They include the certificate and public key associated with each person’s digital ID, proving the authenticity and source of every message they send. Just as importantly, Outlook emails sent with a digital signature cannot be altered by third parties, making them more trustworthy and less susceptible to fraud.

    How to Add a Digital Signature in Outlook

    Adding digital signatures in Outlook only needs to be completed only per user. It requires two basic steps: First, a person must obtain an Outlook digital ID, and, second, they need to set up their signing certificate.

    Here is a quick breakdown of these steps, with a few key points to keep in mind: 

    • Step 1: Obtain an Outlook digital ID
      • Digital IDs must be obtained from an independent certificate authority.
      • Companies might encourage employees to source their digital ID from a Microsoft-recommended provider, such as GlobalSign or IdenTrust. But many others are available, and each business will have its own policies.
      • In addition to validating and securing Outlook messages, a digital ID protects documents created in other Microsoft applications, such as Excel, Word and PowerPoint.
    • Step 2: Set up a signing certificate
      • The exact steps of this process will depend on which version of Outlook an organization uses.
      • Once a digital ID is issued, it needs to be installed in Outlook in the correct file format.
      • From there, the digital signature can be activated in the Microsoft Trust Center.
      • The cryptography format selected will depend on which type of signing certificate has been issued, so be sure to choose the correct one.

    With these two pieces in place, a person can elect to automatically include a digital signature with every message they send or add them on an ad-hoc basis. They will also need to add the digital IDs of their trusted recipients to ensure the security of emails to and from each of these contacts. Finally, it’s also worth noting that recipients won’t be able to read an email sent with a digital signature unless they also have their own digital ID.

    How Do Outlook Digital Signatures Work?

    An Outlook digital signature is a numeric string that validates a sender’s identity when added to a digital certificate or document. The analog equivalent would be an engineer’s signature on official building plans or a dean’s signature on a medical school diploma.

    Behind the digital signatures scenes, three algorithms work together to protect an organization’s email communications: A key generation algorithm randomly selects two keys — one private and one public — that are then associated with the digital signature. The private key is fed into the signing algorithm, which produces the signature. Finally, the signature-verifying algorithm accepts or rejects messages on the recipient’s end after scrutinizing them for authenticity.

    Is a Digital Signature Sufficient for Secure Messaging?

    Digital signatures allow companies to protect the integrity of their emails and any data they contain. Like a passport or official piece of ID, they are unique to each individual and rely on identity as an effective defense against fraud. This makes Outlook digital signatures a powerful security measure that virtually anyone can use.

    Identity-based defenses are also more relevant than ever now that spear-phishing and ransomware attacks are on the rise. These attacks aim to spoof senders or sender domains, impersonating executives, colleagues, business partners or well-known brands to extract money or data from unsuspecting email recipients. Digital signatures reduce the risk of fraudulent emails tricking employees, even if they slip through incoming message filters.

    For added security, some businesses combine Outlook digital signatures with email encryption. Where digital signatures prove that a message has come from a trusted source, email encryption makes its contents indecipherable to anyone but the sender and recipient. Any other party who tries to read the encrypted message will see it in a completely obscured format. In fact, digital signatures from Outlook work with digital signatures from other email programs provided the Outlook user chooses the proper Outlook email encryption add-in.[2]  

    Of course, digital signatures also have some disadvantages. For one, the digital certificates beyond them have an expiration date, so it’s important to keep them up to date to ensure the highest level of security. Second, they require both senders and recipients to buy those digital certificates from a trusted authority, which can be a deterrent for cost-conscious organizations. Both of these disadvantages are relatively minor but are worth keeping in mind when setting up a business’ email defenses.

    The Bottom Line

    As companies embrace more flexible and remote-working structures, email security has risen to the top of their IT security agenda. Digital signatures in Outlook offer a simple yet effective solution to this challenge. That said, they only work if both the sender and recipient have Outlook and digital IDs and are aware that each other has one. As the threat of email fraud grows and becomes more complex, digital signatures nonetheless serve as a crucial first line of defense for the millions of people who rely on Outlook to communicate each day.

    Outlook Digital Signature FAQs

    Common Types of Digital Signature Attacks

    • In a chosen-message attack, the attacker tricks the victim into digitally signing a document or obtains the victim's public key.
    • In a known-message attack, the attacker forges the victim's signature on documents by obtaining messages the victim sent and the victim's key.
    • In a key-only attack, the attacker only has access to the victim's public key but recreates the victim's signature.

    Can Digital Signatures Prevent Email Spoofing and Phishing Attacks?

    Digital signatures can protect email from cyber threats, inclusing spoofing and phishing, which both attempt to trick victims into believing malicious emails have been sent by a trusted source.

    What Encryption Methods are Involved in Outlook Digital Signatures?

    Outlook can encrypt messages using AES-256, AES-192, AES-128, and 3DES.



    [1]How Many People Use Email Worldwide,” Lifewire

    [2]Three Ways to Encrypt Email in Outlook: Comparison and Setup Instructions,” Encyro

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