description = [[
Retrieves a server's SSL certificate. The amount of information printed
about the certificate depends on the verbosity level. With no extra
verbosity, the script prints the validity period and the commonName,
organizationName, stateOrProvinceName, and countryName of the subject.

<code>
443/tcp open  https
|  ssl-cert: Subject: commonName=www.paypal.com/organizationName=PayPal, Inc.\
/stateOrProvinceName=California/countryName=US
|  Not valid before: 2009-05-28 00:00:00
|_ Not valid after:  2010-05-01 23:59:59
</code>

With <code>-v</code> it adds the issuer name and fingerprints.

<code>
443/tcp open  https
|  ssl-cert: Subject: commonName=www.paypal.com/organizationName=PayPal, Inc.\
/stateOrProvinceName=California/countryName=US
|  Issuer: commonName=VeriSign Class 3 Extended Validation SSL CA\
/organizationName=VeriSign, Inc./countryName=US
|  Not valid before: 2009-05-28 00:00:00
|  Not valid after:  2010-05-01 23:59:59
|  MD5:   c5b8 7ddd ccc7 537f 8861 b476 078d e8fd
|_ SHA-1: dc5a cb8b 9eb9 b5de 7117 c536 8c15 0e75 ba88 702e
</code>

With <code>-vv</code> it adds the PEM-encoded contents of the entire
certificate.

<code>
443/tcp open  https
|  ssl-cert: Subject: commonName=www.paypal.com/organizationName=PayPal, Inc.\
/stateOrProvinceName=California/countryName=US/serialNumber=3014267\
/1.3.6.1.4.1.311.60.2.1.3=US/streetAddress=2211 N 1st St\
/1.3.6.1.4.1.311.60.2.1.2=Delaware/postalCode=95131-2021\
/localityName=San Jose/organizationalUnitName=Information Systems\
/2.5.4.15=V1.0, Clause 5.(b)
|  Issuer: commonName=VeriSign Class 3 Extended Validation SSL CA\
/organizationName=VeriSign, Inc./countryName=US\
/organizationalUnitName=Terms of use at https://www.verisign.com/rpa (c)06
|  Not valid before: 2009-05-28 00:00:00
|  Not valid after:  2010-05-01 23:59:59
|  MD5:   c5b8 7ddd ccc7 537f 8861 b476 078d e8fd
|  SHA-1: dc5a cb8b 9eb9 b5de 7117 c536 8c15 0e75 ba88 702e
|  -----BEGIN CERTIFICATE-----
|  MIIFxzCCBK+gAwIBAgIQX02QuADDB7CVjZdooVge+zANBgkqhkiG9w0BAQUFADCB
...
</code>
]]

---
-- @output
-- 443/tcp open  https
-- |  ssl-cert: Subject: commonName=www.paypal.com/organizationName=PayPal, Inc.\
-- /stateOrProvinceName=California/countryName=US
-- |  Not valid before: 2009-05-28 00:00:00
-- |_ Not valid after:  2010-05-01 23:59:59

author = "David Fifield <david@bamsoftware.com>"

license = "Same as Nmap--See http://nmap.org/book/man-legal.html"

categories = { "safe", "discovery" }

require("nmap")
require("nsedebug")
require("stdnse")

local stringify_name
local date_to_string
local table_find

local LIKELY_SSL_PORTS = { 443, 465, 989, 990, 992, 993, 994, 995, 587, 8443 }

portrule = function(host, port)
    return port.version.service_tunnel == "ssl"
        or table_find(LIKELY_SSL_PORTS, port.number)
end

action = function(host, port)
    local s = nmap.new_socket()
    local status, error = s:connect(host.ip, port.number, "ssl")
    if not status then
        if nmap.verbosity() > 0 then
            return error
        else
            return nil
        end
    end
    local cert = s:get_ssl_certificate()
    s:close()

    local lines = {}
    lines[#lines + 1] = "Subject: " .. stringify_name(cert.subject)

    if nmap.verbosity() > 0 then
        lines[#lines + 1] = "Issuer: " .. stringify_name(cert.issuer)
    end

    lines[#lines + 1] = "Not valid before: " ..
        date_to_string(cert.validity.notBefore)
    lines[#lines + 1] = "Not valid after:  " ..
        date_to_string(cert.validity.notAfter)

    lines[#lines + 1] = "MD5:   " .. stdnse.tohex(cert:digest("md5"), { separator = " ", group = 4 })
    lines[#lines + 1] = "SHA-1: " .. stdnse.tohex(cert:digest("sha1"), { separator = " ", group = 4 })

    if nmap.verbosity() > 1 then
        lines[#lines + 1] = cert.pem
    end

    return stdnse.strjoin("\n", lines)
end

-- Find the index of a value in an array.
function table_find(t, value)
    local i, v
    for i, v in ipairs(t) do
        if v == value then
            return i
        end
    end
    return nil
end

-- These are the subject/issuer name fields that will be shown, in this order,
-- without a high verbosity.
local NON_VERBOSE_FIELDS = { "commonName", "organizationName",
    "stateOrProvinceName", "countryName" }

function stringify_name(name)
    local fields = {}
    local _, k, v
    if not name then
        return nil
    end
    for _, k in ipairs(NON_VERBOSE_FIELDS) do
        v = name[k]
        if v then
            fields[#fields + 1] = string.format("%s=%s", k, v)
        end
    end
    if nmap.verbosity() > 1 then
        for k, v in pairs(name) do
            -- Don't include a field twice.
            if not table_find(NON_VERBOSE_FIELDS, k) then
                if type(k) == "table" then
                    k = stdnse.strjoin(".", k)
                end
                fields[#fields + 1] = string.format("%s=%s", k, v)
            end
        end
    end
    return stdnse.strjoin("/", fields)
end

function date_to_string(date)
    if not date then
        return "MISSING"
    end
    if type(date) == "string" then
        return string.format("Can't parse; string is \"%s\"", date)
    else
        return os.date("%Y-%m-%d %H:%M:%S", os.time(date))
    end
end