Sept. 9, 2024
Did you ever stop to think about how secure--or how lame--SMS authentication really is? In these days of increased digital threats, it's more important than ever to understand the tools we're using to keep our data secure. SMS auth is a 2-factor authentication method that adds an extra layer of security by sending one-time passwords (OTPs) to our mobile devices, but it's not a one-size-fits-all solution. In this post, we'll take a deep-dive into how SMS authentication works, the different 'flavors' available to us, the pros and cons of SMS auth, and how to make it more secure. After you read this sms auth post, you'll be better equipped to safeguard your own online accounts and to make informed security decisions.
SMS auth is a way to secure digital things - like websites - by verifying that you are actually you. It does this by sending you a one-time password (OTP) to your phone via text message, and it's an essential component of two-factor authentication (2FA) in general. But what does it mean to have SMS as your authentication method, and what are the advantages and disadvantages?
SMS is a secure and easy way to add an extra layer of security to your login. SMS authentication is a piece of cake to understand. A user logs in to an account as usual using a username and password. When they click submit, the system sends a random password (the one-time password or OTP) to the user's registered mobile device. They then enter this OTP into the login interface to complete the login process. This two-step process makes it much more secure—if someone gets their password, they still won't be able to log into the account without the OTP that was sent to their phone.
That OTP is usually only good for a very short time and for one use only, so it's very secure against unauthorized access. Although it's commonly used (and for good reason, especially in high-security situations like banking and other life-critical contexts), there are a few reasons users might want to consider alternatives to using SMS. SMS itself is vulnerable and can be intercepted, so it's important to use another authentication factor in addition to SMS. SMS auth is just one of the two possible factors that can be used in a 2FA combination.
SMS authentication is a type of something you have authentication, which means the user has to prove who they are based on something physical that they have in their possession. In this case, the mobile device where they receive the SMS. Something you have is usually an additional security measure in conjunction with something you know, because something you know (like a password) is not generally secure enough on its own.
This is great because it's low-memorability--users don't need to memorize some complex password or security question; they just need to keep their phone safe on their person. But it's also a huge problem. If you lose your phone, or somebody steals it, they can easily log in to your account unless you've done something extra to protect yourself.
When you use SMS to authenticate yourself along with a regular password, you're more secure than you would be with just a password alone. It adds a second layer, so it's a lot harder for anyone else to log in as you. In cybersecurity-speak, you're adding a second layer, an OTP sent to your phone via SMS, so that even if your password is stolen, an attacker can't walk up and just log in as you.
That being said, SMS isn't bulletproof. There are known vulnerabilities. SMS messages can be intercepted because they're sent in clear-text (insecure). With enough social engineering and vulnerabilities in our telecom infrastructure, attackers can hijack SMS messages using methods like SIM swapping or SS7 attacks. And it's things like this that show us why we have to complement SMS authentication with other forms of security, like biometrics, mobile authenticator apps, or email-based authentication.
So now you know this stuff, you and your organization can make informed decisions about how to secure yourselves online, and find the right tradeoff between accessibility and security.
SMS auth is one of the most common ways to verify that a user is who they say they are, typically by prompting them to enter a one-time password (OTP). In this post, I'll break down the different types of SMS auth, what they are, how they differ, and the pros and cons of each.
One way to authenticate via SMS is TOTP (Time-based One-Time Password). This involves generating a random number (using a secure algorithm) and sending it to the user's phone. TOTPs have one key characteristic: they're 'ephemeral'. The number is only valid for a short period of time--usually 30-240 seconds.
The short window for the number to be used is what makes it secure: once that window has passed, the number is invalid. So if someone intercepts the number, there's nothing they can do with it--it will have expired. It also creates a sense of urgency for the user to use the OTP for this login or transaction before it's no longer valid.
In practice, you'll see TOTP used in addition to some platforms that require an added layer of security--like banking or email, as well as certain company-critical software. Because it's time-based, it prevents a "static replay attack"--i.e. intercepted OTPs that can be used repeatedly to gain access.
Another type of SMS auth you often see is HOTP, short for HMAC-Based One-Time Password. Unlike TOTP, HOTP generates a code that's valid as soon as it's generated, so it's a bit more versatile for authentication. Each time an OTP is requested, the system will increment a counter for the user account, and based on this counter a HMAC algorithm will generate a new code.
This can be helpful in some circumstances, particularly if the user can't authenticate immediately on their mobile device because the code isn't as short-lived as TOTP, they can retrieve and use the code at a later time. However, it can also be a liability if someone else manages to get ahold of the HOTP code; they can use it in place of the rightful user until the time for that code to expire.
For organizations using HOTP, they absolutely must have strong controls in place to ensure that codes can't be intercepted and reused; the security of the system is almost entirely dependent on the security of the mobile device. You'll also need to take extra measures to guard against codes being reused in ways that indicate the user is being impersonated.
In addition to TOTP and HOTP, there are other flavors of SMS auth that are good for certain use cases, like Flash SMS. As in a standard OTP setup, the user needs to enter a code. With Flash SMS, the message is pushed directly to the user's phone screen. The code is never "there" to be seen for very long, if at all, and the user can simply view the message, also perfect for immediate alerts or updates.
A use case for flash SMS might be anything from immediate account activity to emergency alerting. The downside is it requires a really robust network to deliver flash SMS rapidly and reliably. And because it's immediate, it's challenging to actually get a user to "engage" or "acknowledge" the alert, particularly in cases where you must confirm receipt for security-critical transactions.
It's not that one SMS auth method is better than the other, only that understanding the trade-offs can help you select the best flavor for your use case. With cyber security becoming an increasing concern, using SMS auth (and knowing when to use it and when to use something else) is just a small part of safeguarding sensitive information. SMS authentication enhances security by reducing the likelihood of unauthorized access through popular attack vectors.
As more and more of our world moves into the digital sphere, secure user authentication has never been more critical. One form you might have seen is SMS auth, which sends a text message to verify a user or user action, adding an extra layer of security and using a mobile phone, something that's always with them. We'll show you a few examples of SMS verification to demonstrate how powerful and versatile it can be.
Banks have been doing it for years and it's a good thing. As we've all moved to online banking, it's been really important for people to feel secure about their money! A lot of the time, banks will use SMS to confirm things like sending you notices, and who you are when you're going to log in. For instance, when you go to log in to your online banking from a new device or location, you might get an SMS that has a one-time password (OTP) in it. That way even if somebody finds out what your login details are, they still can't log in because they don't have that OTP that you got on your phone.
Banks also use SMS to notify you about account activity, like if somebody took money out of your account, or made a purchase, etc. It's immediate and you can check it right then and there, and that just helps you keep an eye on your account. Combined with OTP requests, it's a pretty decent system for keeping people on top of things money-wise.
And another super-common use for SMS auth is account recovery. A lot of times, different websites and platforms, when you're trying to reset your password or trying to get your account back, they'll text your phone number a one-time password, so that someone else can't just do it for you.
In practice, if a user forgets their password, the website usually asks them for their phone number. After they've done that, the website will send them an SMS with an OTP. The user enters that OTP back into the website or application, and they can reset their password. It's super secure because it makes it so that random people can't steal your account, because they'd need to have your actual phone to get the code in the first place.
Big tech companies like Microsoft and Google both use SMS verification as a key security tool. Look at Microsoft Azure; they use it to let people securely log in to their services. SMS verification lets them add a second layer for people to log into their account, and it works well.
For example, if someone tries to log in to their Microsoft account or tries to use something like Microsoft Teams, they'll have to do a second step of verification using SMS. This is especially useful for enterprises where you're protecting sensitive data. Google also has SMS verification for their Gmail and cloud services, so you can add 2-factor authentication to further secure your account.
It's evident how versatile and necessary SMS authentication is in everyday digital functions to protect users. With the rise of more and more cybersecurity threats, we're going to need more multi-layer authentication, and SMS verification will be a linchpin in preventing online fraud.
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SMS auth is easy, plain and simple. While other security methods may require you to download an app or perform a multi-step setup, SMS verification is a cakewalk. You receive a message with a code on your device. Most people are familiar with the process of sending and receiving text messages, so it's a very natural and well-known flow. Because it's so easy, it's accessible to people who might otherwise struggle to secure their accounts and feel put off or overwhelmed.
SMS is also agnostic, so anyone can use it. It's easy for users to enable using their existing phone numbers, and only takes a few taps to turn on for their accounts. Because it's very simple and users can easily adopt it, more people in general are able to use 2FA, which helps raise the security bar across the board on a lot of platforms.
And because SMS codes are almost-instant, giving users SMS authentication in seconds, so they can get into their accounts fast. Almost-instant matters because users are trying to log in and get into their accounts, or approve a transaction quickly. Being able to get in right away reduces frustration and gives a better user experience when and where it's most important, like securing sensitive information or taking a time-sensitive action.
Also, real-time SMS notifications let you alert users to suspicious account activity. In real time, this serves as an early warning for users about a potential threat, and they can respond right away to protect their account.
SMS auth is a mixed blessing. It's convenient, but it also has its drawbacks, one of the biggest being that it's not very secure from a number of different attack vectors. One of the most common types of attack is called a SIM swap. In a SIM swap, attackers trick your mobile provider into giving them your phone number. Once they have control over your phone number, they can intercept SMS messages--including 2FA codes--nullifying the security that SMS 2FA was meant to provide in the first place. Hackers can perform SIM swapping.
Furthermore, if the user's phone is compromised, any 2FA codes sent over SMS can be stolen by bad actors. This exposure can lull users into a false sense of security, thinking they're safe when their accounts are still vulnerable.
Another big issue with SMS is it's not end to end encrypted, so your messages aren't totally secure and could be intercepted. And without that encryption, SMS messages are susceptible to something called spoofing attacks, where hackers can impersonate a legitimate phone number and trick you into giving them your credentials. Hackers can exploit weaknesses in the communication systems to re-route messages and intercept the code and take over your account.
Since they're sent over a potentially vulnerable cellular network, you're at risk of having your authentication codes intercepted. That means if you use SMS to verify your identity, you're already more at risk of being breached than someone who uses a more secure method, like an authentication app, which generates the time sensitive codes without the mobile carrier.
In light of this, it may make more sense for you to consider using a more secure 2FA. One of the more popular forms is an authentication app, because it doesn't have the drawbacks of using SMS, plus it has a higher level of security, like codes that expire quickly so there's a smaller window of time for you to be attacked.
In today's digital age, you need a secure way to verify the identity of your end users. Lots of people use SMS for phone verification, but there are best practices to follow to keep it secure, and neat tricks to make it work better for everyone.
While SMS code verification is a popular method for verifying a user, it should not be the only method you use. Multi-layer verification is more secure than single-layer alone. Biometric verifications like fingerprint or facial recognition are unique to the user and much more difficult to intercept than a code sent via SMS. Hardware-based security like a security token is another good pair with SMS—when a user logs in, their device can ask for both an SMS code and a fingerprint scan. This makes it very difficult for a phishing scam to work.
When you have multiple layers, you not only protect your users' accounts, but you also increase user confidence that their data is safe. It's important to continually evaluate these layers—threats evolve and there are a lot of users to consider.
Finally, the last piece of the SMS authentication security puzzle is user education. The vast majority of SMS attacks are social engineering attacks, where the attacker tricks the user into giving them their authentication code. By teaching users what to look out for, you can help them protect themselves.
You'll want to give examples of what a suspicious text might look like, e.g. "We need your social security number in 5 seconds or your bank account will be suspended" or "Click this link to verify your identity." And tell them that, by and large, no legitimate company is going to request sensitive information via SMS. You'll want to keep them up to date constantly with what the latest phishing tactics are so that they will be on alert.
The other piece of this is making sure there is an easy way for users to get in touch, whether to forward you a suspicious text or to let you know if they believe there has been a security incident.
Using different phone numbers for high-risk accounts is a great way to reduce the risk of interception with SMS authentication. When you use the same number for multiple accounts, that's a potential weakness for any bad actor who does gain access. By using a different phone number for high-risk accounts (e.g., financial, sensitive data, etc.), companies can reduce the attack surface area for unauthorized access.
The same principle applies to temporary telephone numbers per transaction for an added level of security. If a user is doing something high-stakes, use a temporary number so that they have the least amount of exposure. This protects the end user and the integrity of the system.
The cyber threat landscape is always changing, so it's important to stay ahead of the game. By regularly reviewing and updating your SMS authentication, you can make sure it remains effective against modern threat tactics.
You should be listening to your users to understand their SMS authentication experience, so you know what to improve. You should also be discovering and using new tech and techniques to secure your SMS authentication. For example, you could use ML to recognize unusual patterns and flag it as a type of hacking, giving you an additional layer of defense.
Instilling a state of readiness in your organization will ensure your organization is prepared for whatever comes its way. As SMS authentication evolves, so should your security program!
SMS authentication is a popular security feature for digital security. Usually a one-time password (OTP), a user enters their usual credentials, then gets a code sent to their phone to enter on screen. It's a nice extra layer of security, but it's a possession-based security model, so it's not air-tight and is vulnerable to things like interception and SIM swapping. In this post, we're going to look at the different types of SMS authentication, like Time-Based and HMAC-Based One-Time Passwords, and how banks, account recovery, and big tech companies use it. SMS is so convenient which is why everyone loves it, but this also means it's a big target, so you're going to want to use something else as well. We'll cover how you can use SMS in combination with other types of authentication, how to help your users spot and avoid phishing, and keep up with security to stay ahead of the latest threats.
SMS authentication is a way of helping to ensure that the person using the system is really who they say they are. When a user logs in with their username and password, the system sends a one-time password (OTP) to the user's registered mobile device and the user must enter the OTP to gain access to the system. This process of two-step verification makes access more secure by requiring something the user has (in this case, their mobile phone) as well as something they know (in this case, their password).
There are a few different types of SMS authentication. TOTP (Time-based One-Time Passwords) are a type of time-sensitive code that expire after a window of time, whereas HOTP codes do not. Flash SMS is yet another kind of code and is an SMS that is sent to a user's device screen almost immediately and requires no action to view the code. This is useful for different things depending on how immediate or how much user action you need -- for example, if you need to verify someone is a human before they can see a piece of content.
The best thing about SMS authentication is its simplicity and convenience. No additional apps or configuration required. Instant verification codes sent to your phone so you can log in fast. Real-time alerts of potential suspicious activity. That simplicity and speed means more people will use 2FA on their accounts.
2FA, specifically SMS 2FA, is super vulnerable to a variety of attacks, like SIM swapping, where attackers literally steal your phone number to intercept SMS codes! Also, SMS messages are not end-to-end encrypted, so they can be intercepted and even spoofed (meaning attackers can send fake SMS messages on your behalf). And if your mobile device is compromised, then that opens up the authentication codes, putting your account security at risk.
For even greater 2FA security, you can combine it with an additional security measure, such as biometric 2FA, or some form of hardware security tokens. It's also important to educate users about phishing, so that they can identify and fend off attempts to fraudulently obtain their SMS codes. Using unique phone numbers for your high-risk accounts can reduce interception risks even more.
Organizations use SMS authentication because it's extremely effective at securing user accounts, particularly for sensitive applications like bank accounts or online services. It's an extra barrier to entry so that if your password is stolen, someone else still can't get in. This is critical for maintaining user trust and keeping valuable information safe from hackers.
Companies should revisit and update their SMS authentication policies to reflect the changing times and protect against new cyber threats. They should also listen to user feedback on their experience, as they may have new ideas to shake things up. Plus, they should use the latest tech like ML to monitor for unusual patterns and notify them of potential hacks, among other things, to bolster their security system.
sms auth - a person receiving an SMS on their phone
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