path: root/acmens.py

# -*- coding: utf-8 -*-
#
# SPDX-License-Identifier: AGPL-3.0-only
#
# Copyright © 2015-2018 Daniel Roesler <diafygi@gmail.com>
# Copyright © 2021 siddharth <s@ricketyspace.net>
#

import argparse
import subprocess
import json
import os
import urllib.request
import sys
import base64
import binascii
import time
import hashlib
import tempfile
import re
import copy
import textwrap

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


__version__ = "0.1.5-dev2"

CA_PRD = "https://acme-v02.api.letsencrypt.org"
CA_STG = "https://acme-staging-v02.api.letsencrypt.org"
CA_DIR = None


def _directory(ca_url):
    global CA_DIR
    if CA_DIR is None:
        CA_DIR = json.loads(urlopen(ca_url + "/directory").read().decode("utf8"))
    return CA_DIR


def _b64(b):
    "Convert bytes to JWT base64 string"
    if type(b) is str:
        b = b.encode()
    return base64.urlsafe_b64encode(b).decode().replace("=", "")


def _cmd(cmd_list, stdin=None, cmd_input=None, err_msg="Command Line Error"):
    "Runs external commands"
    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


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": "acmens",
                },
            )
        )
        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


def _send_signed_request(url, payload, nonce_url, auth, account_key, err_msg, depth=0):
    """Make signed request to ACME endpoint"""
    payload64 = "" if payload is None else _b64(json.dumps(payload).encode("utf8"))
    new_nonce = _do_request(nonce_url)[2]["Replay-Nonce"]
    protected = {"url": url, "alg": "RS256", "nonce": new_nonce}
    protected.update(auth)
    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, auth, account_key, err_msg, depth=(depth + 1)
        )


def _poll_until_not(url, pending_statuses, nonce_url, auth, account_key, err_msg):
    """Poll until status is not in pending_statuses"""
    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, nonce_url, auth, account_key, err_msg
        )
    return result


def _do_challenge(challenge_type, authz_url, nonce_url, auth, account_key, thumbprint):
    """Do ACME challenge"""
    # Request challenges
    sys.stderr.write("Requesting challenges...\n")
    chl_result, chl_code, chl_headers = _send_signed_request(
        authz_url, None, nonce_url, auth, account_key, "Error getting challenges"
    )
    domain = chl_result["identifier"]["value"]

    # Choose challenge.
    preferred_type = "dns-01" if challenge_type == "dns" else "http-01"
    challenge = None
    http_challenge = None
    for c in chl_result["challenges"]:
        if c["type"] == preferred_type:
            challenge = c
        if c["type"] == "http-01":
            http_challenge = c
    if challenge is None:
        if http_challenge is None:
            sys.stderr.write("Error: Unable to find challenges!")
            sys.exit(1)
        challenge = http_challenge  # Fallback to http challenge.
    keyauthorization = "{0}.{1}".format(challenge["token"], thumbprint)
    dns_payload = _b64(hashlib.sha256(keyauthorization.encode()).digest())

    # Ask the user to host the token on their server
    if challenge_type == "dns":
        sys.stderr.write(
            """\
Please update your DNS for '{domain}' to have the following TXT record:

--------------
_acme-challenge    IN    TXT ( \"{keyauth}\" )
--------------

""".format(
                domain=domain, keyauth=dns_payload
            )
        )
    else:
        # Challenge response for http server.
        response_uri = ".well-known/acme-challenge/{0}".format(challenge["token"])

        sys.stderr.write(
            """\
Please update your server to serve the following file at this URL:

--------------
URL: http://{domain}/{uri}
File contents: \"{token}\"
--------------

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

""".format(
                domain=domain, uri=response_uri, token=keyauthorization
            )
        )

    stdout = sys.stdout
    sys.stdout = sys.stderr
    if challenge_type == "dns":
        input("Press Enter when the TXT record is updated on the DNS...")
    else:
        input("Press Enter when you've got the file hosted on your server...")
    sys.stdout = stdout

    # 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"],
        {},
        nonce_url,
        auth,
        account_key,
        "Error requesting challenge verfication: {0}".format(domain),
    )
    chl_verification = _poll_until_not(
        challenge["url"],
        ["pending"],
        nonce_url,
        auth,
        account_key,
        "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))


def _agree_to(terms):
    """Asks user whether they agree to the Let's Encrypt Subscriber
    Agreement. It will immediately exit if user does not agree."""
    ans = input(
        "\nDo you agree to the Let's Encrypt Subscriber Agreement\n({})? ".format(terms)
    )
    if re.search(r"^[Yy]", ans) is None:
        sys.stderr.write("Error: Cannot continue. Exiting.\n")
        sys.exit(1)


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

    :param string ca_url: Let's Encrypt endpoint.
    :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>)
    :param string challenge_type: The challenge type to use.
                         (defaults to http)

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

    """

    # 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([])
    cn = None
    common_name = re.search("Subject:.*? CN *= *([^\s,;/]+)", out.decode("utf8"))
    if common_name is not None:
        domains.add(common_name.group(1))
        cn = common_name.group(1)
    subj_alt_names = re.search(
        "X509v3 Subject Alternative Name: \n +([^\n]+)\n",
        out.decode("utf8"),
        re.MULTILINE | re.DOTALL,
    )
    if subj_alt_names is not None:
        for san in subj_alt_names.group(1).split(", "):
            if san.startswith("DNS:"):
                dm = san[4:]
                if cn is None and dm.find("*") == -1:
                    cn = dm
                domains.add(dm)
    sys.stderr.write("Found domains {}\n".format(", ".join(domains)))

    # Step 3: Ask user for contact email
    if not email:
        default_email = "webmaster@{0}".format(cn)
        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))
    _agree_to(_directory(ca_url)["meta"]["termsOfService"])
    reg = {"termsOfServiceAgreed": True}
    nonce_url = _directory(ca_url)["newNonce"]
    auth = {"jwk": jwk}
    acct_headers = None
    result, code, acct_headers = _send_signed_request(
        _directory(ca_url)["newAccount"],
        reg,
        nonce_url,
        auth,
        account_key,
        "Error registering",
    )
    if code == 201:
        sys.stderr.write("Registered!\n")
    else:
        sys.stderr.write("Already registered!\n")
    auth = {"kid": acct_headers["Location"]}

    sys.stderr.write("Updating account...")
    ua_result, ua_code, ua_headers = _send_signed_request(
        acct_headers["Location"],
        {"contact": ["mailto:{}".format(email)]},
        nonce_url,
        auth,
        account_key,
        "Error updating account",
    )
    sys.stderr.write("Done\n")

    # Step 5: Request challenges for domains
    sys.stderr.write("Making new order for {0}...\n".format(", ".join(domains)))
    id = {"identifiers": []}
    for domain in domains:
        id["identifiers"].append({"type": "dns", "value": domain})
    order, order_code, order_headers = _send_signed_request(
        _directory(ca_url)["newOrder"],
        id,
        nonce_url,
        auth,
        account_key,
        "Error creating new order",
    )
    for authz in order["authorizations"]:
        _do_challenge(challenge_type, authz, nonce_url, auth, account_key, thumbprint)

    # 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)},
        nonce_url,
        auth,
        account_key,
        "Error finalizing order",
    )

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

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

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


def revoke_crt(ca_url, account_key, crt):
    """Use the ACME protocol to revoke an ssl certificate signed by a
    certificate authority.

    :param string ca_url: Let's Encrypt endpoint.
    :param string account_key: Path to your Let's Encrypt account private key.
    :param string crt: Path to the signed certificate.
    """

    def _a64(a):
        "Shortcut function to go from jwt base64 string to bytes"
        return base64.urlsafe_b64decode(str(a + ("=" * (len(a) % 4))))

    # 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,
    }
    sys.stderr.write("Found public key!\n")

    # Step 2: Get account info.
    sys.stderr.write("Getting account info...\n")
    reg = {"onlyReturnExistiing": True}
    nonce_url = _directory(ca_url)["newNonce"]
    auth = {"jwk": jwk}
    acct_headers = None
    result, code, acct_headers = _send_signed_request(
        _directory(ca_url)["newAccount"],
        reg,
        nonce_url,
        auth,
        account_key,
        "Error getting account info",
    )
    auth = {"kid": acct_headers["Location"]}

    # Step 3: Generate the payload.
    crt_der = _cmd(
        ["openssl", "x509", "-in", crt, "-outform", "DER"], err_msg="DER export error"
    )
    crt_der64 = _b64(crt_der)
    rvk_payload = {
        "certificate": crt_der64,
    }
    _send_signed_request(
        _directory(ca_url)["revokeCert"],
        rvk_payload,
        nonce_url,
        auth,
        account_key,
        "Error revoking certificate",
    )
    sys.stderr.write("Certificate revoked!\n")


def 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.

You may also revoke a signed Let's Encrypt (ACME) certificate.


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
$ acmens --account-key user.key --email user@example.com --csr domain.csr > signed.crt
--------------

Example: Revoking a signed certificate:
--------------
$ acmens --revoke --account-key user.key --crt domain.crt
--------------
""",
    )
    parser.add_argument("--version", action="store_true", help="Show version and exit")
    parser.add_argument(
        "--revoke", action="store_true", help="Revoke a signed certificate"
    )
    parser.add_argument(
        "--stage", action="store_true", help="Use Let's Encrypt's staging endpoint"
    )
    parser.add_argument(
        "-k",
        "--account-key",
        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(
        "-c",
        "--challenge",
        default="http",
        help="Challenge type (http or dns), default is http",
    )
    parser.add_argument("--csr", help="path to your certificate signing request")
    parser.add_argument("--crt", help="path to your signed certificate")

    args = parser.parse_args()
    if args.version:
        print("acmens v{}".format(__version__))
        sys.exit(0)
    if args.account_key is None:
        sys.stderr.write("Error: Path account key is required\n")
        sys.exit(1)
    if (not args.revoke) and (args.csr is None):
        sys.stderr.write("Error: Path to CSR required\n")
        sys.exit(1)
    if args.revoke and args.crt is None:
        sys.stderr.write("Error: Path to signed cert required\n")
        sys.exit(1)

    ca_url = CA_PRD
    if args.stage:
        ca_url = CA_STG

    if args.revoke:
        revoke_crt(ca_url, args.account_key, args.crt)
    else:
        signed_crt = sign_csr(
            ca_url,
            args.account_key,
            args.csr,
            email=args.email,
            challenge_type=args.challenge,
        )
        sys.stdout.write(signed_crt)


if __name__ == "__main__":
    main()