# NAME **certspotter** - Certificate Transparency Log Monitor # SYNOPSIS **certspotter** [`-start_at_end`] [`-watchlist` *FILENAME*] [`-email` *ADDRESS*] `...` # DESCRIPTION **Cert Spotter** is a Certificate Transparency log monitor from SSLMate that alerts you when a SSL/TLS certificate is issued for one of your domains. Cert Spotter is easier to use than other open source CT monitors, since it does not require a database. It's also more robust, since it uses a special certificate parser that ensures it won't miss certificates. Cert Spotter is also available as a hosted service by SSLMate, . You can use Cert Spotter to detect: * Certificates issued to attackers who have compromised your DNS and are redirecting your visitors to their malicious site. * Certificates issued to attackers who have taken over an abandoned sub-domain in order to serve malware under your name. * Certificates issued to attackers who have compromised a certificate authority and want to impersonate your site. * Certificates issued in violation of your corporate policy or outside of your centralized certificate procurement process. # OPTIONS -batch_size *NUMBER* : Maximum number of entries to request per call to get-entries. You should not generally need to change this. Defaults to 1000. -email *ADDRESS* : Email address to contact when a matching certificate is discovered. You can specify this option more than once to email multiple addresses. Your system must have a working sendmail(1) command. -logs *ADDRESS* : Filename or HTTPS URL of a v2 or v3 JSON log list containing logs to monitor. The schema for this file can be found at . Defaults to , which includes the union of active logs recognized by Chrome and Apple. certspotter periodically reloads the log list in case it has changed. -no_save : Do not save a copy of matching certificates. -script *COMMAND* : Command to execute when a matching certificate is found. See certspotter-script(8) for information about the interface to scripts. -start_at_end : Start monitoring logs from the end rather than the beginning. **WARNING**: monitoring from the beginning guarantees detection of all certificates, but requires downloading hundreds of millions of certificates, which takes days. -state_dir *PATH* : Directory for storing state. Defaults to `$CERTSPOTTER_STATE_DIR`, which is "~/.certspotter" by default. -stdout : Write matching certificates to stdout. -verbose : Be verbose. -version : Print version and exit. -watchlist *PATH* : File containing DNS names to monitor, one per line. To monitor an entire domain namespace (including the domain itself and all sub-domains) prefix the domain name with a dot (e.g. ".example.com"). To monitor a single DNS name only, do not prefix the name with a dot. Defaults to `$CERTSPOTTER_CONFIG_DIR/watchlist`, which is "~/.certspotter/watchlist" by default. Specify `-` to read the watch list from stdin. certspotter reads the watch list only when starting up, so you must restart certspotter if you change it. # OPERATION certspotter continuously monitors all browser-recognized Certificate Transparency logs looking for certificates which are valid for any domain on your watch list. When certspotter detects a matching certificate, it emails you (if `-email` is specified), executes a script (if `-script` is specified), and/or writes a report to standard out (if `-stdout` is specified). certspotter also saves a copy of matching certificates in `$CERTSPOTTER_STATE_DIR/certs` ("~/.certspotter/certs" by default) unless you specify the `-no_save` option. When certspotter has not previously monitored a log, it can either start monitoring the log from the beginning, or seek to the end of the log and start monitoring from there. Monitoring from the beginning guarantees detection of all certificates, but requires downloading hundreds of millions of certificates, which takes days. The default behavior is to monitor from the beginning. To start monitoring new logs from the end, specify the `-start_at_end` option. If certspotter has previously monitored a log, it resumes monitoring the log from the previous position. This means that if you add a domain to your watch list, certspotter will not detect any certificates that were logged prior to the addition. To detect such certificates, you must delete `$CERTSPOTTER_STATE_DIR/logs`, which will cause certspotter to restart monitoring from the very beginning of each log (provided `-start_at_end` is not specified). This will cause certspotter to download hundreds of millions of certificates, which takes days. To find preexisting certificates, it's faster to use the Cert Spotter service , SSLMate's Certificate Transparency Search API , or a CT search engine such as . # EXIT STATUS certspotter exits 0 when it receives `SIGTERM` or `SIGINT`, and non-zero when a serious error occurs. # ENVIRONMENT `CERTSPOTTER_STATE_DIR` : Directory for storing state. Overridden by `-state_dir`. Defaults to `~/.certspotter`. `CERTSPOTTER_CONFIG_DIR` : Directory from which any configuration, such as the watch list, is read. Defaults to `~/.certspotter`. `HTTPS_PROXY` : URL of proxy server for making HTTPS requests. `http://`, `https://`, and `socks5://` URLs are supported. By default, no proxy server is used. # SEE ALSO certspotter-script(8) # COPYRIGHT Copyright (c) 2016-2023 Opsmate, Inc. # BUGS Report bugs to .