certspotter VS certificate-transparency-go

> 1. Is this proactively monitored for? And how? And by whom?

Yes, security researchers and domain owners use Certificate Transparency Monitors to search for certificates. e.g.:

https://crt.sh/ - allows you to search for certificates for a domain

https://github.com/SSLMate/certspotter/ - open source tool which notifies you when a certificate is issued for one of your domains

https://sslmate.com/certspotter/ - commercial service that does the same, operated by my company

> 2. If a major state-level CA was discovered to have issued a mitm cert, would browser vendors really take the commercial hit of removing or distrusting their root cert?

In 2017, Chrome and Firefox distrusted Symantec, which was at the time the world's largest certificate authority: https://security.googleblog.com/2017/09/chromes-plan-to-dist...

Symantec hadn't even issued MitM certs - they were just grossly incompetent. Distrusting them was very painful, but necessary to upload the integrity of the CA system, and demonstrated conclusively that there is no such thing as a too-big-to-fail CA.

Indeed, a CT monitor which sends alerts about legitimate certificates is pretty much useless due to noise. My service, Cert Spotter, provides an API endpoint[1] which you can upload your CSRs to, so you don't get alerted about certificates using the same key as the CSR. The open source version of Cert Spotter can invoke a script[2] when a certificate is discovered, and the script can cross reference against a list of legitimate certs.

[1] https://sslmate.com/help/reference/certspotter_authorization...

[2] https://github.com/SSLMate/certspotter/blob/master/man/certs...

If you're talking about a certificate honored by a browser, these days they'd have to put it in a CT log, or at least obtain a "signed certificate timestamp" from a CT log: https://certificate.transparency.dev/

>This feels like this might actually be a use-case for a blockchain or a Merkle Tree.

A few years ago, this idea[0] had been explored by Google as a possible application of their Trillian[1] distributed ledger, which is based on Merkle Trees.

I don't know if they've advanced adoption of Trillian for firmware, however, the website lists Go packaging[2], Certificate Transparency [3], and SigStore[4] as current applications.

have used Trillian as the basis for their Certificate Transparency implementation.[2]

[0] https://github.com/google/trillian-examples/tree/master/bina...

[1] https://transparency.dev/

[2] https://go.googlesource.com/proposal/+/master/design/25530-s...

[3] https://certificate.transparency.dev/

[4] https://www.sigstore.dev/

You can find more about certificate monitoring and who are involved here

https://certificate.transparency.dev/

Excellent question! The sctcheck command from https://github.com/google/certificate-transparency-go/ can be used to check the signatures of embedded SCTs.

I've also got an online tool which you can use to test a site for CT policy compliance: https://sslmate.com/labs/ct_policy_analyzer/

Example of a working site: https://sslmate.com/labs/ct_policy_analyzer/?sslmate.com

Example of one of the sites affected by the Let's Encrypt incident: https://sslmate.com/labs/ct_policy_analyzer/?thecandyshake.c...

The x509 package has unfortunately burned me several times, this one included. It is too anal about non-fatal errors, that Google themselves forked it (and asn1) to improve usability.

https://github.com/google/certificate-transparency-go

ogClient, err := client.New( l.URI, &http.Client{ Timeout: 10 * time.Second, Transport: &http.Transport{ TLSHandshakeTimeout: 30 * time.Second, ResponseHeaderTimeout: 30 * time.Second, MaxIdleConnsPerHost: 10, DisableKeepAlives: false, MaxIdleConns: 100, IdleConnTimeout: 90 * time.Second, ExpectContinueTimeout: 1 * time.Second, }, }, jsonclient.Options{UserAgent: "ct-go-scanlog/1.0"}, ) if err != nil { fmt.Fprintf(os.Stderr, "%s -> Failed to create new client: %s\n", l.Name, err) return } sth, err := logClient.GetSTH(context.TODO()) if err != nil { fmt.Fprintf(os.Stderr, "%s -> Failed to get SignedTreeHead: %s\n", l.Name, err) return } fmt.Printf("%s -> Number of logs: %d\n", l.Name, sth.TreeSize) index := uint64(0) // Logs MAY return fewer than the number of leaves requested. Only complete // if we actually got all the leaves we were expecting. // See more: https://github.com/google/certificate-transparency-go/blob/52d94d8cbab94d6698621839ab1a439d17ebbfb2/scanner/fetcher.go#L263 for index <= sth.TreeSize { fmt.Printf("%s -> New fetch start with index %d-%d\n", l.Name, index, index+100) entries, err := logClient.GetRawEntries(context.TODO(), int64(index), int64(index)+100) if err != nil { fmt.Fprintf(os.Stderr, "%s -> Failed to get raw entries: %s\n", l.Name, err) return } if entries == nil { fmt.Fprintf(os.Stderr, "%s -> entries is nil", l.Name) return } if DEBUG { fmt.Printf("%s -> Got %d leaf entry\n", l.Name, len(entries.Entries)) } for i := range entries.Entries { rawLogE, err := ct.RawLogEntryFromLeaf(int64(index), &entries.Entries[i]) if err != nil { fmt.Fprintf(os.Stderr, "%s -> Failed to parse leaf to raw entry at index %d: %s\n", l.Name, index, err) index++ continue } logE, err := rawLogE.ToLogEntry() if err != nil { fmt.Printf("%s -> Failed to convert raw log to log at index %d: %s\n", l.Name, index, err) index++ continue } /* * This check is true most of the time. */ if logE.X509Cert == nil { fmt.Printf("%s -> Failed to read log cert at index %d: X509Cert is nil\n", l.Name, index) index++ continue } if DEBUG { fmt.Printf("%s -> Leaf entry at %d is parsed successfuly!\n", l.Name, index) } entryChan <- *logE index++ } }

Yes, you can use the certificate-transparency go code to pull down from the trillian API https://github.com/google/certificate-transparency-go/blob/m...

You would need to know the index, or you could just iterate over a range