path: root/acmens.py

#!/usr/bin/env python3
import argparse, subprocess, json, os, urllib.request, sys, base64, binascii, \
    time, hashlib, tempfile, re, copy, textwrap

from urllib.request import urlopen
from urllib.error import HTTPError

def sign_csr(account_key, csr, email=None):
    """Use the ACME protocol to get an ssl certificate signed by a
    certificate authority.

    :param string account_key: Path to the user account key.
    :param string csr: Path to the certificate signing request.
    :param string email: An optional user account contact email
                         (defaults to webmaster@<shortest_domain>)

    :returns: Signed Certificate (PEM format)
    :rtype: string

    """
    #CA = "https://acme-staging-v02.api.letsencrypt.org"
    CA = "https://acme-v02.api.letsencrypt.org"
    DIRECTORY = json.loads(urlopen(CA + "/directory").read().decode('utf8'))

    def _b64(b):
        "Shortcut function to go from bytes to jwt base64 string"
        if type(b) is str:
            b = b.encode()

        return base64.urlsafe_b64encode(b).decode().replace("=", "")

    # helper function - run external commands
    def _cmd(cmd_list, stdin=None, cmd_input=None, err_msg="Command Line Error"):
        proc = subprocess.Popen(cmd_list, stdin=stdin, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        out, err = proc.communicate(cmd_input)
        if proc.returncode != 0:
            raise IOError("{0}\n{1}".format(err_msg, err))
        return out

    # helper function - make request and automatically parse json response
    def _do_request(url, data=None, err_msg="Error", depth=0):
        try:
            resp = urllib.request.urlopen(urllib.request.Request(url, data=data, headers={"Content-Type": "application/jose+json", "User-Agent": "acme-nosudo"}))
            resp_data, code, headers = resp.read().decode("utf8"), resp.getcode(), resp.headers
        except IOError as e:
            resp_data = e.read().decode("utf8") if hasattr(e, "read") else str(e)
            code, headers = getattr(e, "code", None), {}
        try:
            resp_data = json.loads(resp_data) # try to parse json results
        except ValueError:
            pass # ignore json parsing errors
        if depth < 100 and code == 400 and resp_data['type'] == "urn:ietf:params:acme:error:badNonce":
            raise IndexError(resp_data) # allow 100 retrys for bad nonces
        if code not in [200, 201, 204]:
            raise ValueError("{0}:\nUrl: {1}\nData: {2}\nResponse Code: {3}\nResponse: {4}".format(err_msg, url, data, code, resp_data))
        return resp_data, code, headers

    # helper function - make signed requests
    def _send_signed_request(url, payload, err_msg, depth=0):
        payload64 = "" if payload is None else _b64(json.dumps(payload).encode('utf8'))
        new_nonce = _do_request(DIRECTORY['newNonce'])[2]['Replay-Nonce']
        protected = {"url": url, "alg": "RS256", "nonce": new_nonce}
        protected.update({"jwk": jwk} if acct_headers is None else {"kid": acct_headers['Location']})
        protected64 = _b64(json.dumps(protected).encode('utf8'))
        protected_input = "{0}.{1}".format(protected64, payload64).encode('utf8')
        out = _cmd(["openssl", "dgst", "-sha256", "-sign", account_key], stdin=subprocess.PIPE, cmd_input=protected_input, err_msg="OpenSSL Error")
        data = json.dumps({"protected": protected64, "payload": payload64, "signature": _b64(out)})
        try:
            return _do_request(url, data=data.encode('utf8'), err_msg=err_msg, depth=depth)
        except IndexError: # retry bad nonces (they raise IndexError)
            return _send_signed_request(url, payload, err_msg, depth=(depth + 1))

    # helper function - poll until complete
    def _poll_until_not(url, pending_statuses, err_msg):
        result, t0 = None, time.time()
        while result is None or result['status'] in pending_statuses:
            assert (time.time() - t0 < 3600), "Polling timeout" # 1 hour timeout
            time.sleep(0 if result is None else 2)
            result, _, _ = _send_signed_request(url, None, err_msg)
        return result


    # Step 1: Get account public key
    sys.stderr.write("Reading pubkey file...\n")
    out = _cmd(["openssl", "rsa", "-in", account_key, "-noout", "-text"], err_msg="Error reading account public key")
    pub_hex, pub_exp = re.search(
        r"modulus:[\s]+?00:([a-f0-9\:\s]+?)\npublicExponent: ([0-9]+)",
        out.decode('utf8'), re.MULTILINE|re.DOTALL).groups()
    pub_mod = binascii.unhexlify(re.sub("(\s|:)", "", pub_hex))
    pub_mod64 = _b64(pub_mod)
    pub_exp = int(pub_exp)
    pub_exp = "{0:x}".format(pub_exp)
    pub_exp = "0{0}".format(pub_exp) if len(pub_exp) % 2 else pub_exp
    pub_exp = binascii.unhexlify(pub_exp)
    pub_exp64 = _b64(pub_exp)
    jwk = {
        "e": pub_exp64,
        "kty": "RSA",
        "n": pub_mod64,
    }
    accountkey_json = json.dumps(jwk, sort_keys=True, separators=(',', ':'))
    thumbprint = _b64(hashlib.sha256(accountkey_json.encode()).digest())
    sys.stderr.write("Found public key!\n")

    # Step 2: Get the domain names to be certified
    sys.stderr.write("Reading csr file...\n")
    out = _cmd(["openssl", "req", "-in", csr, "-noout", "-text"], err_msg="Error loading {}".format(csr))
    domains = set([])
    common_name = re.search("Subject:.*? CN *= *([^\s,;/]+)", out.decode('utf8'))
    if common_name is not None:
        domains.add(common_name.group(1))
    subject_alt_names = re.search("X509v3 Subject Alternative Name: \n +([^\n]+)\n", out.decode('utf8'), re.MULTILINE|re.DOTALL)
    if subject_alt_names is not None:
        for san in subject_alt_names.group(1).split(", "):
            if san.startswith("DNS:"):
                domains.add(san[4:])
    sys.stderr.write("Found domains {0}\n".format(", ".join(domains)))

    # Step 3: Ask user for contact email
    if not email:
        default_email = "webmaster@{0}".format(min(domains, key=len))
        stdout = sys.stdout
        sys.stdout = sys.stderr
        input_email = input("STEP 1: What is your contact email? ({0}) ".format(default_email))
        email = input_email if input_email else default_email
        sys.stdout = stdout


    # Step 4: Generate the payload for registering user and initiate registration.
    sys.stderr.write("Registering {0}...\n".format(email))
    reg = {
        "termsOfServiceAgreed": True
    }
    acct_headers = None
    result, code, acct_headers = _send_signed_request(DIRECTORY['newAccount'], reg, "Error registering")
    if code == 201:
        sys.stderr.write("Registered!\n")
    else:
        sys.stderr.write("Already registered!\n")


    # Step 5: Request challenges for each domain
    for domain in domains:
        sys.stderr.write("Making new order for {0}...\n".format(domain))
        id = {
            "identifiers": [{
                "type": "dns",
                "value": domain,
            }],
        }
        order, order_code, order_headers = _send_signed_request(DIRECTORY['newOrder'], id, "Error creating new order")

        # Request challenges
        sys.stderr.write("Requesting challenges...\n")
        chl_result, chl_code, chl_headers = _send_signed_request(order['authorizations'][0], None, "Error getting challenges")

        challenge = [c for c in chl_result['challenges'] if c['type'] == "http-01"][0]
        token = re.sub(r"[^A-Za-z0-9_\-]", "_", challenge['token'])
        keyauthorization = "{0}.{1}".format(challenge['token'], thumbprint)

        # build request for the server to test this challenge.
        test_url = challenge['url']
        test_raw = "{}"

        # challenge response for server
        response = {
            "uri": ".well-known/acme-challenge/{0}".format(challenge['token']),
            "data": keyauthorization,
        }

        # Step 6: Ask the user to host the token on their server
        sys.stderr.write("""\
Please update your server to serve the following file at this URL:

--------------
URL: http://{0}/{1}
File contents: \"{2}\"
--------------

Notes:
- Do not include the quotes in the file.
- The file should be one line without any spaces.

""".format(domain, response['uri'], response['data']))

        stdout = sys.stdout
        sys.stdout = sys.stderr
        input("Press Enter when you've got the file hosted on your server...")
        sys.stdout = stdout

        # Step 7: Let the CA know you're ready for the challenge
        sys.stderr.write("Requesting verification for {0}...\n".format(domain))
        _send_signed_request(challenge['url'], {}, "Error requesting challenge verfication: {0}".format(domain))
        chl_verification = _poll_until_not(challenge['url'], ["pending"], "Error checking challenge verification")
        if chl_verification['status'] != "valid":
            raise ValueError("Challenge did not pass for {0}: {1}".format(domain, chl_verification))
        sys.stderr.write("{} verified!\n".format(domain))

        # Step 8: Finalize
        csr_der = _cmd(["openssl", "req", "-in", csr, "-outform", "DER"], err_msg="DER Export Error")
        fnlz_resp, fnlz_code, fnlz_headers = _send_signed_request(order['finalize'], {"csr": _b64(csr_der)}, "Error finalizing order")

        # Step 9: Wait for CA to mark test as valid
        sys.stderr.write("Waiting for {0} challenge to pass...\n".format(domain))
        order = _poll_until_not(order_headers['Location'], ["pending", "processing"], "Error checking order status")

        if order['status'] == "valid":
            sys.stderr.write("Passed {0} challenge!\n".format(domain))
        else:
            raise ValueError("'{0}' challenge did not pass: {1}".format(domain, order))


    # Step 10: Get the certificate.
    sys.stderr.write("Getting certificate...\n")
    signed_pem, _, _ = _send_signed_request(order['certificate'], None, "Error getting certificate")

    sys.stderr.write("Received certificate!\n")
    sys.stderr.write("You can remove the acme-challenge file from your webserver now.\n")

    return signed_pem

if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description="""\
Get a SSL certificate signed by a Let's Encrypt (ACME) certificate
authority and output that signed certificate. You do NOT need to run
this script on your server, it is meant to be run on your
computer. The script will request you to manually deploy the acme
challenge on your server.

NOTE: YOUR ACCOUNT KEY NEEDS TO BE DIFFERENT FROM YOUR DOMAIN KEY.

Prerequisites:
* openssl
* python version 3

Example: Generate an account keypair, a domain key and csr, and have the domain csr signed.
--------------
$ openssl genrsa -aes256 4096 > user.key
$ openssl rsa -in user.key -pubout > user.pub
$ openssl genrsa -aes256 4096 > domain.key
$ openssl req -new -sha256 -key domain.key -subj "/CN=example.com" > domain.csr
$ python3 acmens.py --account-key user.key --email user@example.com domain.csr > signed.crt
--------------

""")
    parser.add_argument("-k", "--account-key", required=True, help="path to your Let's Encrypt account private key")
    parser.add_argument("-e", "--email", default=None, help="contact email, default is webmaster@<shortest_domain>")
    parser.add_argument("--csr", help="path to your certificate signing request")

    args = parser.parse_args()
    if args.csr is None:
        sys.stderr.write('Error: Path to CSR required\n')
        sys.exit(1)

    signed_crt = sign_csr(args.account_key, args.csr, email=args.email)
    sys.stdout.write(signed_crt)