description = [[
Queries Google's Certificate Catalog for the SSL certificates retrieved from target hosts.  The Certificate Catalog provides information about how recently and for how long Google has seen the given certificate.  If a certificate doesn't appear in the database, despite being correctly signed by a well-known CA and having a matching domain name, it may be suspicious. It uses the certificate gotten from ssl-cert.nse script, so that script must be run as well.
]]

---
-- @usage
-- nmap -p 443 --script ssl-cert,ssl-google-cert-catalog <host>
--
-- @output
-- PORT     STATE SERVICE
---443/tcp open  https
---| ssl-google-cert-catalog: 
---|   First/Last time saw: 19 Aug 2011 / 10 Sep 2011
---|_  Days saw between: 20

author = "Vasiliy Kulikov"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = { "safe", "discovery", "external" }
dependencies = { "ssl-cert" }

require("nmap")
require("shortport")
require("stdnse")
require("dns")


local get_cert = function(host, port)
    if nmap.registry[host.ip] and nmap.registry[host.ip][port] then
        return nmap.registry[host.ip][port]["ssl-cert"]
    end
end

local format_date = function(day_num)
    return os.date("%d %b %Y", 60 * 60 * 24 * tonumber(day_num))
end

portrule = shortport.ssl

action = function(host, port)
    local lines, sha1, query
    local cert = get_cert(host, port.number)

    if not cert then
        return nil
    end

    sha1 = stdnse.tohex(cert.digest(cert, "sha1"))
    query = sha1 .. ".certs.googlednstest.com"
    stdnse.print_debug("%s %s", SCRIPT_NAME, query)

    local status, decoded_response = dns.query(query, { dtype = "TXT" })

    lines = {}

    if status then
        local raw_start, raw_stop, delta = string.match(decoded_response, "(%d+) (%d+) (%d+)")
        local date_start, date_stop = format_date(raw_start), format_date(raw_stop)

        table.insert(lines, "First/Last time saw: " .. date_start .. " / " .. date_stop)
        table.insert(lines, "Days saw between: " .. tonumber(delta))
    else
        table.insert(lines, "No DB entry")
    end

    return stdnse.format_output(true, lines)
end