If you understand the TLS protocol and handshake correctly, Go offers everything else you need right out of the box.

Lets run a TLS server that uses a valid and non-revoked certificate: The client-side application connects to the server, receives a TLS certificate, checks the local cache for the CRL file, and searches if the certificate serial ID is present there. On the other hand, applications dont know whether certificates are revoked until they download the newer version of CRL. These domains do not exist, so we will create an alias for localhost (127.0.0.1). CRL extensions can specify other fields of the certificate, not only serial numbers. Who knows how many exciting findings wait for you deep inside all those TLS-related RFCs? For example, CRL cache TTL might differ from CRLs next update date; thus, the application checks for a new CRL more often. Works with SQL / NoSQL and validates TLS certificates. In my case, however, I wanted to control the set of certificates trusted by my client app separately from the system running the client. Let use the key and certificate generated for the server-cert domain to configure TLS on the server. We stand with Ukraine, and we stand for Ukraine. The server gets its certificate from a CA (CA-1).

If the application treats Unknown status as the certificate is still valid, it opens a threat vector.

In my particular case, I control both the server and the client, so I can give the certificate to the client ahead of time so that it can trust (or not trust) the certificate provided by the server. In the playground the time begins at 2009-11-10 23:00:00 UTC Documentation, tutorials, and guides, and a large collection of ready-to-try examples of Cossack Labs' products. We work with companies on demanding markets.Read how we use Acra to protect data in critical infrastructure. The server is actually what it says it is. The interested readers can clone the repository and follow along.

OCSP disadvantages: increased handshake time because of additional network request(s). The client is the same as earlier. However, for performance purposes, it would be better to build a map[bytes]pkix.RevokedCertificate after parsing the CRL for more efficient lookups. The next step is to check the signature. This makes it easier to cache programs by giving them deterministic output. At this point, the server includes a public certificate of CA-2. This is again good news, this means that a certificate issued to domain server-cert cannot be used by other domains (localhost). Acra database security suite is an application that sits between the app and the database and encrypts / decrypts sensitive data. The response from the authority is one of the following: The OCSP response is signed by the CA itself or by another certificate signed by CA and allowed to sign OCSP responses. From the attackers perspective, poisoning (tampering with) the CRL cache is an easy hack.

Otherwise these instructions should suffice. Even with OCSP / CRL support, your solution might be susceptible to design and implementation mistakes, opening a wide attack surface. The ocspResponse.Status represents one of the following: Now, based on ocspResponse.Status, you can return nil or some custom error from the callback. Lets start with crafting the OCSP request. Full implementation for this functionality is available here.

The sequence of checks depends on the desired security and performance properties of the solution. In the most simple scenario, the request contains only the serial number of the certificate were interested in.

Check out the GitHub repo cossacklabs/blogposts-examples with all the scripts to generate TLS certificates, OCSP responder based on OpenSSL, and Golang server-side and client-side apps. Things that I had to Google around for assembled in one place for your convenience. We tell stories to show what security difficulties our customers face, and how we help to solve them. Its essential to verify the CRL response signature to prevent potential attackers from tampering with the list. In the next sections, we will configure the server with these certificates, to encrypt the traffic between the client and the server. You should also check an earlier post where we explored the TLS encryption and security from a theoretical standpoint. runs the program inside a sandbox, then returns the output. If there are any validation errors on either side, the connection will be aborted. Just take verifiedChains[0][0]. After downloading, you parse the CRL (the ParseCRL function is part of the Golang standard library): As description says, this function can parse both PEM-encoded and DER-encoded CRLs, while other libraries may have specific funtions for these two. NOTE : In a production system, it would be wise to use InsecureSkipVerify : true parameter if the normal/secure method failed. Since the CRL is signed, the app can use a simple HTTP request for the download. Feel free to review and run examples to see how the verification works with valid and revoked certificates. If you are, youre not verifying the received certificate at all, leaving you vulnerable to man-in-the-middle attacks. They should be able to verify the servers identity through a CA. Mostly, we rely on cryptography, but it doesnt live in a vacuum. Copyright 2014-2022 Cossack Labs Limited, 113274642861313425704666455845030198894915511470, 547114458127197346809836113712612368226057720033, I consent for this website to store my submitted information and accept, Configuring TLS for OCSP and CRL in Golang, OCSP (Online Certificate Status Protocol), GitHub repo cossacklabs/blogposts-examples, OWASP Transport Layer Protection Cheat Sheet. That should be a good starting place, even if you dont need to allow multiple domains and / or IP addresses. The playground uses the latest stable release of Go. Lets do it! and no main function, the service runs the tests. Apart from a simple socket encryption feature, TLS has dozens of various extensions. If you search around for the right way to use self-signed SSL certificates for establishing secure HTTP connections in Go, youll find a lot of bad advice. Frequently updated technical blog with engineering articles written by Cossack Labs team. I couldt find any good tutorials on this, so I wrote my own. There are a few key things to note in this configuration: The http.Client configuration changes a little for the client as well. Then we call the endpoint using http.Client and print the result. OCSP flow from cossacklabs/blogposts-examples with a server application that uses TLS certificate which client-side application validates using OCSP. Take a look at the OCSP and CRL implementations in Golang weve built for this post using only standard modules.

The OCSP response could have Good, Revoked, or Unknown status for the certificate. The TLS protocol has support for this from the beginning. Below, cert.pem is the PEM-encoded certificate and key.pem is the PEM-encoded private key. In our case, we will use minica to provision this for us. environment with limited resources. Both OCSP and CRL can cause visible delays in the application work, so, developers might be tempted to optimise things.

How exactly will the arguments look like? As the CRL is always growing, the RFC describes delta CRLsshorter files that contain only updates since the last version. Please refer to OWASP Transport Layer Protection Cheat Sheet to learn the best practices configuring TLS in general. and that your service is of benefit to the Go community. The server creates a CA certificate pool to validate all the clients.

In this post, we will learn how to configure TLS encryption in Go. Before we come to that stage, we should set up our public key infrastructure (PKI). The playground can use most of the standard library, with some exceptions. End-to-end secure data storage, processing, and sharing framework with zero trust to storage/exchange infrastructure. It is to handle data retrieval for web server with expired SSL certificates by skipping security check. Lets take a look at ocsp.CreateRequest: The first argument is the certificate we are validating. The application tries to update the CRL or receive the OCSP response, but the responder servers are unreachable. This is good news, which means the server is sending encrypted data. Basically, just a custom HTTP transport client disabled security check.

For example, financial, healthcare or public service industry. Benchmarks will likely not be supported since the program runs in a sandboxed For these scenarios, we can configure mutual TLS between the client and the server so that both parties can trust each other. This may be caused by a misconfiguration or delays in OCSP server database updates. CRL (Certificate Revocation List), RFC5280, is a non-interactive protocol. We will then encrypt the traffic between them by configuring TLS on the server. OCSP advantages: the application finds out the certificate was revoked as soon as possible (time depends only on how often the application performs OCSP requests). I use a Linux machine and setting the domain alias is pretty straightforward. Thats why this post has a security overview, the implementation details, and the what could go wrong section.

Be careful: if the OCSP stapling is used, the Good response may be cached for an extended time on the server-side. The CRL should be signed by the CA of the certificate youre validating. This tutorial is a note from helping a friend today to create a custom HTTP transport client in Golang. contact us first (note this is a public mailing list), (Go by Example is one other instance) You can imagine the consequences. +24k Golang : How to create new XML file ? The application might perform TLS revocation checks in the background while it continues communication with a potentially untrusted service. contact us first (note this is a public mailing list). This post authored by

OCSP and CRL are often considered too advanced to start with. Remember, the TLS certificate may contain CRL URL(s) in its metadata, and its the CRLDistributionPoints field of tls.Certificate. Whenever the app accesses a cached CRL, if it turns out to be outdated, the app has to download the whole CRL again (or download a delta CRLs). As Acra protects sensitive data, it uses strict TLS settings to provide strong security guarantees. When talking to security-sensitive services, applications should validate certificates before every connection. Alternatively, you can also use IP instead of domains with minica to generate your keypairs and certificates. They arent trusted by clients (web browsers, SSL libraries, curl, etc.) - where attribution is required. Typically, in Golang, we create a TLS connection in two steps: As it was mentioned, the standard tls.Conn does not handle either OCSP or CRL. To set up our mini PKI infrastructure, we will use a Go utility called minica to produce root, server, and the client keypairs and certificates. This is precisely what this post is about, but before diving into implementation details, lets talk about OCSP and CRL from the birds eye. +3.9k Golang : Extract unicode string from another unicode string example, +2.9k JavaScript : Rounding number to decimal formats to display currency, +2.6k Golang : Valued expressions and functions example, +6.6k Golang : Send data to /dev/null a.k.a blackhole with ioutil.Discard, +9.6k Golang : Get dimension(width and height) of image file, +5.7k Golang : Create unique title slugs example, +7.9k Golang : Find and draw contours with OpenCV example, +3.1k Golang : Pad file extension automagically, +7.9k Golang : Read file and convert content to string, +6.5k Golang : Launch Mac OS X Preview (or other OS) application from your program example, SocketLoop@Facebook Blogs RSS Feed Tutorials RSS Feed Privacy Policy About, All material here is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. Lets take SHA256 instead of default SHA1: Now the buffer contains the request, serialized in a proper format, ready to be sent to the server. However, implementing OCSP and CRL are a part of the application code. For my specific app, I needed to create a self-signed certificate that could be used for multiple domains and IP addresses. It depends on a threat model and security requirements. Go uses your systems root certificate authority set by default, so if you add your certificate to this root set of certificates, you can use http.Client without modification. As application security is complex, mistakes in implementation could pass undetected and lead to a security compromise while preserving the illusion of security. go.dev's servers.

a certificate from CA. The typical confusions in the TLS configuration are often around using the correct certificates rather than its implementation. In reality, a Certificate Authority (CA) or a Domain Administrator (within an organization) will provide you a keypair and a signed certificate. This way, the client does not need to perform additional network requests, only to validate the attached response. Developers should add code to perform network requests, validate the response, and handle the certificate revocation before continuing the connection to an untrusted service. Stunned by losing their robotic devices, [REDACTED] learnt that they were hijacked by attackers even with communication being encrypted. Dont use it. About Cossack Labs: what we do, who our team is, who our customers are, and how you can contact us. This discussion on GitHub may give you hints about how OCSP might be integrated into the standard library in future. Now, lets try TLS certificate verification using CRL. To meet our security model, we had to implement OCSP / CRL verification in Golang ourselves. If you are on a platform other than Linux, you should Google on how to set it up for your OS. What can we use to implement it? This section hosts presentations and public appearance recaps by Cossack Labs team. (determining the significance of this date is an exercise for the reader). The first step is downloading a CRL (or reading it from a cache). PKI comes in all shapes and sorts: deploying self-signed homebrewed PKIs in Kubernetes, relying on openssl easy-ca, building something unique based on CFSSL, or putting together a bunch of bash scripts.