In today’s internet landscape, security and privacy are more critical than ever. Two technologies that play a pivotal role in safeguarding our browsing activity are DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH). These protocols were designed to protect DNS queries from being exposed, eavesdropped on, or tampered with by encrypting them. While they share the same core goal of securing DNS traffic, they have different underlying mechanics and implementations. In this blog post, we will break down DoT and DoH, exploring how they work, the benefits they provide, and the nuances between the two technologies.
The Need for Secure DNS
Before diving into DoT and DoH, let’s briefly review what DNS (Domain Name System) is. DNS is often referred to as the “phone book of the internet” because it translates human-readable domain names (like www.example.com) into IP addresses that computers use to identify each other on the network.
Traditionally, DNS queries are sent in plaintext, which makes them vulnerable to several threats:
- Eavesdropping: Third parties, including ISPs or attackers, can easily monitor and log DNS traffic to determine which websites users are visiting.
- Man-in-the-middle (MITM) attacks: Unencrypted DNS queries can be intercepted and tampered with, potentially redirecting users to malicious sites (DNS spoofing or cache poisoning).
To mitigate these risks, DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH) were introduced, providing encrypted channels for DNS queries.
DNS-over-TLS (DoT)
What is DoT?
DNS-over-TLS is a protocol that encrypts DNS queries using Transport Layer Security (TLS), the same cryptographic protocol used in HTTPS connections. By leveraging TLS, DoT ensures that DNS requests are encrypted in transit, preventing third parties from snooping or modifying the communication.
How DoT Works
- Client Initiation: The client (typically your device or DNS resolver) initiates a TLS connection to a DNS resolver that supports DoT on a dedicated port (usually port 853).
- TLS Handshake: The client and server undergo a TLS handshake, during which cryptographic keys are exchanged. This process ensures that future communication is encrypted and secure.
- Encrypted DNS Query: Once the TLS session is established, the client sends its DNS query through this encrypted channel.
- Response: The DNS resolver processes the query, retrieves the corresponding IP address, and sends it back through the same encrypted connection.
The encryption provided by TLS protects the contents of the DNS queries and responses, ensuring privacy between the client and the resolver.
Benefits of DoT
- Encryption and Security: DoT provides robust encryption using TLS, making DNS queries impervious to eavesdropping and MITM attacks.
- Privacy: Since DNS queries are encrypted, third parties like ISPs cannot easily track or log user activity.
- Explicit Port and Protocol Handling: DoT operates on a dedicated port (853), allowing firewalls and network administrators to easily identify and manage DNS traffic over DoT.
Drawbacks of DoT
- Port Blocking: Because DoT uses a well-known port (853), some network administrators or ISPs might block it or throttle its traffic.
- Performance Overhead: Establishing and maintaining a TLS connection adds overhead to DNS resolution, which might introduce some latency.
- Limited Port Flexibility: Since DoT runs on a dedicated port, it can be more easily filtered or blocked by networks that enforce restrictive security policies.
DNS-over-HTTPS (DoH)
What is DoH?
DNS-over-HTTPS is another protocol designed to encrypt DNS traffic, but instead of using a dedicated port, it runs over the HTTPS protocol on port 443. The use of HTTPS provides encryption and also makes DoH traffic indistinguishable from regular web traffic, making it harder to block or censor.
How DoH Works
- Client Initiation: The client (such as a web browser or an operating system) sends a DNS query over an HTTPS connection, using port 443.
- HTTPS Encryption: The DNS query is embedded in an HTTPS request, meaning it is encrypted as part of the standard TLS session between the client and the DoH-enabled DNS server.
- Response: The DNS resolver processes the query, retrieves the IP address, and sends the result back over the HTTPS connection.
Since DoH is essentially a form of HTTPS traffic, it benefits from all the security mechanisms associated with modern web encryption.
Benefits of DoH
- Privacy and Encryption: Like DoT, DoH encrypts DNS traffic, providing protection from snooping and tampering.
- Harder to Block: DoH traffic is indistinguishable from regular HTTPS traffic, making it harder for ISPs or network administrators to block or throttle.
- Widespread Adoption: Many popular browsers (like Chrome and Firefox) support DoH natively, offering seamless integration for end-users.
Drawbacks of DoH
- Increased Complexity: DoH requires DNS to be embedded in HTTPS requests, which can add complexity to the DNS resolution process.
- Performance Overhead: Similar to DoT, DoH introduces some latency due to the overhead of HTTPS encryption. The performance impact may vary depending on network conditions and server infrastructure.
- Loss of Control for Network Administrators: DoH can bypass traditional DNS management tools, making it difficult for administrators to monitor or control DNS traffic on their networks. This is particularly concerning in enterprise environments where DNS filtering and monitoring are important for security and compliance.
DoT vs. DoH: Key Differences
While both DoT and DoH offer encryption and privacy for DNS queries, they differ in several key ways:
| Aspect | DoT | DoH |
|---|---|---|
| Encryption Protocol | TLS (dedicated to DNS traffic) | HTTPS (shared with regular web traffic) |
| Port Used | Port 853 | Port 443 |
| Traffic Appearance | Easily identifiable as DNS traffic | Looks like regular HTTPS traffic |
| Network Management | Easier to monitor/filter | Harder to manage/filter |
| Performance | Slight overhead due to TLS | Potentially more overhead from HTTPS |
| Adoption | Supported by certain DNS servers | Natively supported in most browsers |
DoT and DoH: Performance Considerations
Both DoT and DoH introduce some performance overhead due to the added encryption, but the impact is typically minimal for most users. DoT is generally more efficient because it maintains persistent TLS connections for DNS queries, while DoH may initiate new HTTPS requests for each query, depending on how it is implemented.
DoH can sometimes offer better performance in environments where HTTPS traffic is prioritized or optimized (such as content delivery networks), but in scenarios with heavy traffic or constrained bandwidth, the extra layer of encapsulation can introduce more latency than DoT.
Security and Privacy Trade-offs
Both DoT and DoH offer excellent security features, but DoH has a slight edge in evading censorship since it uses the same port as HTTPS traffic. On the other hand, network administrators often prefer DoT because it allows them to maintain visibility and control over DNS traffic without sacrificing security. The choice between the two often depends on the specific security, privacy, and performance needs of the user or organization.
Conclusion
DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH) are powerful protocols designed to secure DNS traffic, providing essential privacy and security in today’s digital world. While both serve the same core function of encrypting DNS queries, their different implementations give them unique strengths and weaknesses.
- DoT is ideal for environments where explicit control over DNS traffic is necessary, and where performance considerations make the use of dedicated ports more manageable.
- DoH is perfect for situations where bypassing censorship, ensuring privacy, and blending DNS traffic with regular web traffic is crucial.
Ultimately, the choice between DoT and DoH will depend on specific use cases, network environments, and privacy needs. Both protocols represent a significant step forward in securing DNS, helping to protect users from increasingly sophisticated threats on the internet.
As more organizations and individuals adopt these technologies, the internet will continue to become a safer and more private place to explore.