8 Ways to Prevent Replay Attacks

Posted on Jun 18, 2022 by Kristin Hassel

How to Stop the Interception and Retransmission of Data

Around 16% of all global companies work remotely, with no indication the trend will slow anytime soon. While remote working can save companies money in the long run, the lack of digital security used to secure remote networks creates an issue that’s incredibly costly. 

A rise in remote working means many companies face increased cyber threats and attacks. Unsecured public networks, weak security measures, and use of personal devices for remote access create vulnerabilities. Cybercriminals use replay attacks to exploit these security holes, intercepting traffic to steal important company data. 

Thankfully, you can prevent replay attacks. We’ve rounded up the best ways to secure your networks (both remote and physical), so your company’s sensitive data won’t end up in the hands of cybercriminals.

How to Secure Remote Access Networks

Most companies and employees don’t use security software that’s capable of safeguarding remote access to critical network resources. When companies do use a Secure Remote Access (SRA) method, it’s generally one of the following: 

✅ Virtual Private Network (VPN).

✅ Two-Factor Authentication (TFA).

✅ Device Risk Posture Check (RPC).

✅ Zero-Trust Network (ZTN) access.

Each of these SRA methods has its benefits but, for now, companies prefer using a VPN over all others. Yet, according to cybertalk.org, 11% of companies don’t use any type of SRA method. A total lack of network security measures for remote workers leaves the door wide open for cybercriminals to perform replay attacks

What Is a Replay Attack and How Does It Work?

In a replay attack, the attacker gains access to communication (e.g. a financial transaction) between the origin server and the destination server. This gives the attacker the ability to delay a transmission or replicate it. 

Replay attacks are passive because an attacker takes the information during the verification process, when it’s still unaltered.

A replay attack is a Man-in-the-Middle (MitM) type of attack, as hackers intercept the transmission or communication as it travels between two servers. Unfortunately, replay attacks are one of the easiest and most difficult to detect data breaches, as they happen in real-time. 

Once a replay attack begins, you can’t stop it unless you terminate your connection to the destination server. This is hardly a reliable solution, however, as the damage has likely already been done. As such, using SRA methods and other preventative measures is vital to protecting employee and company information in a remote work age. 

What Are the Security Risks of Replay Attacks?

The financial impact of replay attacks is high but so are the security risks. In 2020, the average cost of a data breach was $3.86 million, which includes both direct and indirect expenses as a result of recovering lost data, repairing system damage, and paying fines. 

Unfortunately, an attacker doesn’t need any special tools or skills to perform a replay attack. Usually, the intercepted data isn’t encrypted, making this form of attack even easier to pull off. Unless you secure your network access points, you may end up dealing with some costly damages. Let’s look at some of the more scary security risks associated with replay attacks.

Replay Attackers Can Gain Access to Your Network

Once an attacker has access to your network, they can hijack the data of anyone connected to the network or even cripple the network. 

In a replay attack, most cybercriminals aren’t looking to destroy your network, rather use it for some type of gain. For instance, sensitive information can be used against you or to make money. That said, a replay attack can also be used to cripple your network.

Replay Attack Example 1: Ted completes financials for his tractor and mower business online. He receives and pays an invoice from Becky’s Landscaping for $100,000 via PayPal. After gaining access to the network, the cybercriminal replicates this transaction but places their own PayPal email in place of Becky’s. Ted pays an extra $100,000 out of pocket, and the attacker receives a huge payment.

Unauthorized Parties Intercept Confidential Information

At a time when 50% of all meetings happen on video conference, it’s not unusual for transcripts and important files to be shared remotely

Without proper network security measures in place, any sensitive project files or meeting notes you upload to the web or share through email are easy to manipulate. Attackers who intercept this information can infer reputational or financial harm to a company. 

Replay Attack Example 2: A remote employee uses their company email to transfer private files regarding a possible merger with an equally large competitor. The private information is intercepted by the attacker and posted on a public forum or an interested third-party is CC’d for a price. This causes the merger to fall through or happen faster than anticipated. Both scenarios are financially devastating to the company.

Identity Fraud

Companies with online services can undergo a replay attack that results in consumer identity theft and account hijacking.

During this type of attack, the attacker may intercept a purchase transaction and duplicate the order. They only need to change one detail of information such as the delivery address. Many e-commerce sites allow you to change the delivery address, so it doesn’t seem strange to have the same order going to different locations. This way, the attacker gets whatever was in the original order and the customer ends up paying the bill. 

Replay Attack Example 3: Margie wants to buy new furniture for her home office, so she goes on Home Depot’s site. She enters all relevant information including billing, delivery address and credit card details, and then hits send. As the data is transmitted from her server to the Home Depot server, an attacker captures the information. 

The attacker uses the information to duplicate the order and changes the delivery address. Margie gets her credit card bill and is shocked to find the double order. The attacker has new furniture and Margie has to call the bank.

8 Ways to Prevent Replay Attacks

I’m going to use the word session quite a bit here, so let’s start with what that is exactly. In the context of replay attacks, a session is two devices acknowledging each other via a network connection for the purposes of data sharing or transmission. The session ends when one or both devices terminate the connection or if times out due to inactivity. Think of a phone call — one person calls another, and the call (session) ends when one party hangs up or the call drops.

Just as a third party can listen in on a call to gain private information, cybercriminals can intercept sensitive account information during a session

Replay attacks may be as simple as spamming an inbox with repeat emails, or more advanced like committing identity fraud. Fortunately, you can use the following methods to protect all of your session data and avoid replay attacks:

  1. Require a Session Key

Session keys can only be used once within a specific time period to encrypt and decrypt data. When the message is sent, the session key is randomly generated. This way, only the sender and receiver have access to the communication. Any subsequent sessions require a different session key. 

The use of session keys is beneficial because even if attackers discovered the key, it’s useless. Duplicating it doesn’t make sense, as the key is for one use only.

  1. Encrypt Your Online Traffic

The use of 256-bit AES encryption for all data transmission is one of the best ways to help prevent replay attacks. Encrypting the traffic between your device and chosen server hides your data by scrambling it, so no one can interfere with your connection. 

A VPN is one of the best ways to encrypt your traffic as it travels between client and destination (VPN) servers. 

Reliable VPNs use military-grade encryption to scramble your data and secure VPN tunneling protocols, like OpenVPN and WireGuard®. VPN protocols protect your traffic as it moves between your device and the server your session interacts with. That way, even if a cybercriminal gains access to your session data, they can’t decrypt it.

Use Private Internet Access to secure your connections with 256-bit AES encryption and stay safe from replay attacks. 

  1. Create Timestamps

A timestamp is a digital record that can include the time and date of data transmission. Most documents and images include a basic timestamp, including the creation date and when they were last edited. Timestamps are created by the sender, device, system, or a trusted third party.

Timestamping Authorities (TSAs) use a public key infrastructure (PKI) to enable data encryption and signing, which ensures that timestamps are legitimate and unaltered. A timestamp allows you to track:

✅ When an account/file was last accessed or edited

✅ The validity of financial transactions

✅ The quality and integrity of data

✅ When documents were signed

Secure timestamps assign a sequence order for sessions. That way, you can void a session immediately if a failure occurs. For example, evidence of tampering or someone attempting to duplicate a session transaction.

  1. Use One-Time Passwords (OTPs)

If you’ve ever forgotten the password to your email, you’ve probably used an OTP. The process is simple: you get a code on your recovery email or phone so you can access your account. 

Single-use passwords can consist of characters, numbers, and punctuation marks. OTPs, like session keys, are usually only valid for a short amount of time. OTP is also used as a form of two-factor authentication, which is one of the methods used by companies for SRA network connections.

Types of OTP Tokens
Soft TokenSMS MessageText with an OTP, common for password recovery, sent to a mobile phone, often used for TFA.
Soft TokenPush NotificationPrompt sent when accessing email from an unknown device, often sent to a phone, often used for TFA.
Soft TokenEmail VerificationEmail containing an OTP, commonly sent to recovery email, mostly used for password reset.
Hard TokenUSB-ConnectedKey fob or smart card used to gain secure access, physical token.
Hard TokenBiometricsUsing a fingerprint, voice, or retinal, to gain secure access to sensitive data, often used for TFA.
Hard TokenContactlessRecognizes you via a Bluetooth device associated with the account to gain secure access, often used for TFA.
  1. Pay Attention to Security Protocols

Enable SSL and/or TLS in your browser settings. These protocols generate the equivalent of four session keys between the origin and destination servers during transmission, which makes it harder for attackers to use replay attacks. You can enable these protocols in your browser easily using the instructions below.

How to Enable SSL/TLS In Your Browser

Chrome: Open the browser > Press Alt F > Settings > Scroll to Advanced Settings> Scroll to System > Click Open Proxy Settings > Select the Advanced tab > Scroll to Security > Check ‘SSL 3.0 and TLS 1.2’ > Press OK > Close browser > Restart the browser.

Safari: New Safari versions automatically use TLS 1.2, SSL is unavailable.

Firefox: Open the browser > Type ‘about:config’ in the address bar> Press Enter > Type ‘TLS’ in Search > Find ‘security.tls.version.min’ and double click > Set integer to 3 for TLS 1.2 > Press OK > Close Firefox > Restart Firefox.

Edge: Open the browser >Internet Options > Internet Properties > Advanced > Security > Select ‘Use SSL 3.0 and TLS 1.2’ > Press OK > Close browser > Restart the app.

Using a VPN is easier than modifying your browser settings, especially if you change devices a lot. VPNs offer tough security protocols like OpenVPN and WireGuard® for secure data transfer.  A VPN encrypts your traffic for maximum protection against replay attacks. The added benefit is that it covers everything, not just browsers. 

Get Private Internet Access for secure access to all your apps anywhere. 

  1. Ask for a Digital Signature

Use digital signatures to authenticate and verify a message or transaction’s origin, status, and validity

A digital signature is encrypted by its creator using a private key, so only the recipient (signer) receives a linked public key. 

One key is useless without the other, ensuring the intended party is the only one who can access the contents protected by the private key. I’ve given a brief overview of some of the most common digital signature methods below.

PINs, OTPs, or SMS codes for authentication

A PIN is used the same way one uses OTPs and SMS codes to authenticate access to networks, files, and accounts.

Cyclic redundancy check (CRC)

A CRC is an error-detecting code that’s used for verification on storage devices and digital networks. It detects any modification of raw data, such as reversed bits or bits lost during transmission. Bits are the smallest unit of data measurement, so in theory nothing slips past CRC. If an anomaly is found, an error window pops up with the text ‘Data error (cyclic redundancy check)’.

  1. Digital Certificates

Digital certificates are managed by certificate authority (CA) verification to avoid the creation of false digital certifications

Timestamps are commonly included on digital signature certificates and are highly traceable, making it harder for replay attacks to occur. 

The infrastructure of digital signatures follows a standard PKI method, so vendor keys are made and stored securely. This ensures they are legally valid and makes them incredibly popular as a form of securing sensitive information worldwide. Three classes of digital signature certificates exist: Class 1, Class 2, and Class 3.

Classes of Digital Signature Certificates
Class Security Level Example Proofing Process Use Case
1 > Basic E-signing documents. Validated via email ID and username. Low risk of data manipulation or compromisation.
2 > Moderate Taxes E-filing. Authenticates signers identity against a verified database of users. Moderate risk of data compromise.
3 > Maximum Court filings E-tendering Requires the signer to identify themselves in front of certifying authorities. High-risk threat to data, or consequences of security breach.
  1. Secure Your Network Connections 

A rise in remote work and office locations makes it more important than ever to secure any network connections you use. Many home networks aren’t adequately secured and most companies do little to stress the importance of SRA. 

The easiest way to ensure secure access to network resources remotely is a VPN. VPNs scramble your data with high-level encryption and use the toughest, most secure tunneling protocols during transmission. 

Stay Vigilant to Prevent Replay Attacks

Access management requires vigilance, especially in the remote office era. Otherwise, you leave your company, yourself, and your co-workers open to replay attacks and other cyber threats. 

Using methods like SMS authentication or OTPs isn’t enough. You need to make sure your networks (remote and physical) are adequately protected. That includes properly protecting data traffic during transmission. Using one, or combining several, of the methods in this article can help you prevent replay attacks and regain data security

Download PIA and stop cybercriminals from tracking your online activity. We even offer a malware and tracker blocker to prevent sites from downloading malicious software to your device. 


What is a replay attack in cybersecurity?

A replay attack is when an attacker invades a transmission or communication between the client server and the destination server. The attacker delays or replicates the valid transmission. Replay attacks are passive attacks that happen in real-time, and are difficult to detect due to a lack of data alteration.

Counter the attack by protecting your data during transmission with a VPN that provides high-level encryption. VPNs also provide strong, stable connections using protocols like WireGuard®

Is a replay attack a man-in-the-middle (MitM) attack?

Yes. Replay attacks fall into the category of MitM attacks. Replay attacks happen while servers are communicating with each other. Any attack where hackers intercept traffic as it’s traveling between two servers is considered an MitM attack. 

Download Private Internet Access to encrypt your data transmissions with 256-bit AES encryption, making sure your connections are secure and cybercriminals can’t read or manipulate your communications. 

How can you prevent replay attacks?

Preventing replay attacks takes a strong focus on access management security, both in-house and remotely. It’s important to use strong protocols and encrypt transmissions whenever possible. You can also make use of OTPs, digital signatures, timestamps, and session keys.

However, the best way to prevent replay attacks is with a VPN. PIA gives you several SRA tools in one, including strong encryption to scramble your communications and tough protocols. Why not test us out? It’s completely risk-free with our 30-day money-back guarantee!

What is the best VPN for online security?

Private Internet Access is the best VPN to secure your network connections in-home and office. We use 256-bit AES encryption to mask your online traffic and secure tunneling protocols, including OpenVPN and WireGuard. When you connect to our VPN, you’re completely invisible online, which means no one can target you with replay attacks. 

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