sign_csr.py

#!/usr/bin/env python
import argparse, subprocess, json, os, urllib2, sys, base64, binascii, time, \
    hashlib, tempfile, re, copy, textwrap
try:
    from urllib.request import urlopen # Python 3
except ImportError:
    from urllib2 import urlopen # Python 2


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

    :param string pubkey: Path to the user account public 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 bool file_based: An optional flag indicating that the
                            hosting should be file-based rather
                            than providing a simple python HTTP
                            server.

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

    """
    #CA = "https://acme-staging.api.letsencrypt.org"
    CA = "https://acme-v01.api.letsencrypt.org"
    DIRECTORY = json.loads(urlopen(CA + "/directory").read().decode('utf8'))
    nonce_req = urllib2.Request("{0}/directory".format(CA))
    nonce_req.get_method = lambda : 'HEAD'

    def _b64(b):
        "Shortcut function to go from bytes to jwt base64 string"
        return base64.urlsafe_b64encode(b).replace("=", "")

    # Step 1: Get account public key
    sys.stderr.write("Reading pubkey file...\n")
    proc = subprocess.Popen(["openssl", "rsa", "-pubin", "-in", pubkey, "-noout", "-text"],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    out, err = proc.communicate()
    if proc.returncode != 0:
        raise IOError("Error loading {0}".format(pubkey))
    pub_hex, pub_exp = re.search(
        "Modulus(?: \((?:2048|4096) bit\)|)\:\s+00:([a-f0-9\:\s]+?)Exponent\: ([0-9]+)",
        out, 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)
    header = {
        "alg": "RS256",
        "jwk": {
            "e": pub_exp64,
            "kty": "RSA",
            "n": pub_mod64,
        },
    }
    accountkey_json = json.dumps(header['jwk'], sort_keys=True, separators=(',', ':'))
    thumbprint = _b64(hashlib.sha256(accountkey_json).digest())
    sys.stderr.write("Found public key!\n")

    # Step 2: Get the domain names to be certified
    sys.stderr.write("Reading csr file...\n")
    proc = subprocess.Popen(["openssl", "req", "-in", csr, "-noout", "-text"],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    out, err = proc.communicate()
    if proc.returncode != 0:
        raise IOError("Error loading {0}".format(csr))
    domains = set([])
    common_name = re.search("Subject:.*? CN *= *([^\s,;/]+)", out)
    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, 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 = raw_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 payloads that need to be signed
    # registration
    sys.stderr.write("Building request payloads...\n")
    reg_nonce = urllib2.urlopen(nonce_req).headers['Replay-Nonce']
    reg_raw = json.dumps({
        "resource": "new-reg",
        "contact": ["mailto:{0}".format(email)],
        "agreement": DIRECTORY['meta']['terms-of-service'],
    }, sort_keys=True, indent=4)
    reg_b64 = _b64(reg_raw)
    reg_protected = copy.deepcopy(header)
    reg_protected.update({"nonce": reg_nonce})
    reg_protected64 = _b64(json.dumps(reg_protected, sort_keys=True, indent=4))
    reg_file = tempfile.NamedTemporaryFile(dir=".", prefix="register_", suffix=".json")
    reg_file.write("{0}.{1}".format(reg_protected64, reg_b64))
    reg_file.flush()
    reg_file_name = os.path.basename(reg_file.name)
    reg_file_sig = tempfile.NamedTemporaryFile(dir=".", prefix="register_", suffix=".sig")
    reg_file_sig_name = os.path.basename(reg_file_sig.name)

    # need signature for each domain identifiers
    ids = []
    for domain in domains:
        sys.stderr.write("Building request for {0}...\n".format(domain))
        id_nonce = urllib2.urlopen(nonce_req).headers['Replay-Nonce']
        id_raw = json.dumps({
            "resource": "new-authz",
            "identifier": {
                "type": "dns",
                "value": domain,
            },
        }, sort_keys=True)
        id_b64 = _b64(id_raw)
        id_protected = copy.deepcopy(header)
        id_protected.update({"nonce": id_nonce})
        id_protected64 = _b64(json.dumps(id_protected, sort_keys=True, indent=4))
        id_file = tempfile.NamedTemporaryFile(dir=".", prefix="domain_", suffix=".json")
        id_file.write("{0}.{1}".format(id_protected64, id_b64))
        id_file.flush()
        id_file_name = os.path.basename(id_file.name)
        id_file_sig = tempfile.NamedTemporaryFile(dir=".", prefix="domain_", suffix=".sig")
        id_file_sig_name = os.path.basename(id_file_sig.name)
        ids.append({
            "domain": domain,
            "protected64": id_protected64,
            "data64": id_b64,
            "file": id_file,
            "file_name": id_file_name,
            "sig": id_file_sig,
            "sig_name": id_file_sig_name,
        })

    # need signature for the final certificate issuance
    sys.stderr.write("Building request for CSR...\n")
    proc = subprocess.Popen(["openssl", "req", "-in", csr, "-outform", "DER"],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    csr_der, err = proc.communicate()
    csr_der64 = _b64(csr_der)
    csr_nonce = urllib2.urlopen(nonce_req).headers['Replay-Nonce']
    csr_raw = json.dumps({
        "resource": "new-cert",
        "csr": csr_der64,
    }, sort_keys=True, indent=4)
    csr_b64 = _b64(csr_raw)
    csr_protected = copy.deepcopy(header)
    csr_protected.update({"nonce": csr_nonce})
    csr_protected64 = _b64(json.dumps(csr_protected, sort_keys=True, indent=4))
    csr_file = tempfile.NamedTemporaryFile(dir=".", prefix="cert_", suffix=".json")
    csr_file.write("{0}.{1}".format(csr_protected64, csr_b64))
    csr_file.flush()
    csr_file_name = os.path.basename(csr_file.name)
    csr_file_sig = tempfile.NamedTemporaryFile(dir=".", prefix="cert_", suffix=".sig")
    csr_file_sig_name = os.path.basename(csr_file_sig.name)

    # Step 5: Ask the user to sign the registration and requests
    sys.stderr.write("""\
STEP 2: You need to sign some files (replace 'user.key' with your user private key).

openssl dgst -sha256 -sign user.key -out {0} {1}
{2}
openssl dgst -sha256 -sign user.key -out {3} {4}

""".format(
    reg_file_sig_name, reg_file_name,
    "\n".join("openssl dgst -sha256 -sign user.key -out {0} {1}".format(i['sig_name'], i['file_name']) for i in ids),
    csr_file_sig_name, csr_file_name))

    stdout = sys.stdout
    sys.stdout = sys.stderr
    raw_input("Press Enter when you've run the above commands in a new terminal window...")
    sys.stdout = stdout

    # Step 6: Load the signatures
    reg_file_sig.seek(0)
    reg_sig64 = _b64(reg_file_sig.read())
    for n, i in enumerate(ids):
        i['sig'].seek(0)
        i['sig64'] = _b64(i['sig'].read())

    # Step 7: Register the user
    sys.stderr.write("Registering {0}...\n".format(email))
    reg_data = json.dumps({
        "header": header,
        "protected": reg_protected64,
        "payload": reg_b64,
        "signature": reg_sig64,
    }, sort_keys=True, indent=4)
    reg_url = "{0}/acme/new-reg".format(CA)
    try:
        resp = urllib2.urlopen(reg_url, reg_data)
        result = json.loads(resp.read())
    except urllib2.HTTPError as e:
        err = e.read()
        # skip already registered accounts
        if "Registration key is already in use" in err:
            sys.stderr.write("Already registered. Skipping...\n")
        else:
            sys.stderr.write("Error: reg_data:\n")
            sys.stderr.write("POST {0}\n".format(reg_url))
            sys.stderr.write(reg_data)
            sys.stderr.write("\n")
            sys.stderr.write(err)
            sys.stderr.write("\n")
            raise

    # Step 8: Request challenges for each domain
    responses = []
    tests = []
    for n, i in enumerate(ids):
        sys.stderr.write("Requesting challenges for {0}...\n".format(i['domain']))
        id_data = json.dumps({
            "header": header,
            "protected": i['protected64'],
            "payload": i['data64'],
            "signature": i['sig64'],
        }, sort_keys=True, indent=4)
        id_url = "{0}/acme/new-authz".format(CA)
        try:
            resp = urllib2.urlopen(id_url, id_data)
            result = json.loads(resp.read())
        except urllib2.HTTPError as e:
            sys.stderr.write("Error: id_data:\n")
            sys.stderr.write("POST {0}\n".format(id_url))
            sys.stderr.write(id_data)
            sys.stderr.write("\n")
            sys.stderr.write(e.read())
            sys.stderr.write("\n")
            raise
        challenge = [c for c in result['challenges'] if c['type'] == "http-01"][0]
        keyauthorization = "{0}.{1}".format(challenge['token'], thumbprint)

        # challenge request
        sys.stderr.write("Building challenge responses for {0}...\n".format(i['domain']))
        test_nonce = urllib2.urlopen(nonce_req).headers['Replay-Nonce']
        test_raw = json.dumps({
            "resource": "challenge",
            "keyAuthorization": keyauthorization,
        }, sort_keys=True, indent=4)
        test_b64 = _b64(test_raw)
        test_protected = copy.deepcopy(header)
        test_protected.update({"nonce": test_nonce})
        test_protected64 = _b64(json.dumps(test_protected, sort_keys=True, indent=4))
        test_file = tempfile.NamedTemporaryFile(dir=".", prefix="challenge_", suffix=".json")
        test_file.write("{0}.{1}".format(test_protected64, test_b64))
        test_file.flush()
        test_file_name = os.path.basename(test_file.name)
        test_file_sig = tempfile.NamedTemporaryFile(dir=".", prefix="challenge_", suffix=".sig")
        test_file_sig_name = os.path.basename(test_file_sig.name)
        tests.append({
            "uri": challenge['uri'],
            "protected64": test_protected64,
            "data64": test_b64,
            "file": test_file,
            "file_name": test_file_name,
            "sig": test_file_sig,
            "sig_name": test_file_sig_name,
        })

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

    # Step 9: Ask the user to sign the challenge responses
    sys.stderr.write("""\
STEP 3: You need to sign some more files (replace 'user.key' with your user private key).

{0}

""".format(
    "\n".join("openssl dgst -sha256 -sign user.key -out {0} {1}".format(
        i['sig_name'], i['file_name']) for i in tests)))

    stdout = sys.stdout
    sys.stdout = sys.stderr
    raw_input("Press Enter when you've run the above commands in a new terminal window...")
    sys.stdout = stdout

    # Step 10: Load the response signatures
    for n, i in enumerate(ids):
        tests[n]['sig'].seek(0)
        tests[n]['sig64'] = _b64(tests[n]['sig'].read())

    # Step 11: Ask the user to host the token on their server
    for n, i in enumerate(ids):
        if file_based:
            sys.stderr.write("""\
STEP {0}: Please update your server to serve the following file at this URL:

--------------
URL: http://{1}/{2}
File contents: \"{3}\"
--------------

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

""".format(n + 4, i['domain'], responses[n]['uri'], responses[n]['data']))

            stdout = sys.stdout
            sys.stdout = sys.stderr
            raw_input("Press Enter when you've got the file hosted on your server...")
            sys.stdout = stdout
        else:
            sys.stderr.write("""\
STEP {0}: You need to run this command on {1} (don't stop the python command until the next step).

sudo python -c "import BaseHTTPServer; \\
    h = BaseHTTPServer.BaseHTTPRequestHandler; \\
    h.do_GET = lambda r: r.send_response(200) or r.end_headers() or r.wfile.write('{2}'); \\
    s = BaseHTTPServer.HTTPServer(('0.0.0.0', 80), h); \\
    s.serve_forever()"

""".format(n + 4, i['domain'], responses[n]['data']))

            stdout = sys.stdout
            sys.stdout = sys.stderr
            raw_input("Press Enter when you've got the python command running on your server...")
            sys.stdout = stdout

        # Step 12: Let the CA know you're ready for the challenge
        sys.stderr.write("Requesting verification for {0}...\n".format(i['domain']))
        test_data = json.dumps({
            "header": header,
            "protected": tests[n]['protected64'],
            "payload": tests[n]['data64'],
            "signature": tests[n]['sig64'],
        }, sort_keys=True, indent=4)
        test_url = tests[n]['uri']
        try:
            resp = urllib2.urlopen(test_url, test_data)
            test_result = json.loads(resp.read())
        except urllib2.HTTPError as e:
            sys.stderr.write("Error: test_data:\n")
            sys.stderr.write("POST {0}\n".format(test_url))
            sys.stderr.write(test_data)
            sys.stderr.write("\n")
            sys.stderr.write(e.read())
            sys.stderr.write("\n")
            raise

        # Step 13: Wait for CA to mark test as valid
        sys.stderr.write("Waiting for {0} challenge to pass...\n".format(i['domain']))
        while True:
            try:
                resp = urllib2.urlopen(test_url)
                challenge_status = json.loads(resp.read())
            except urllib2.HTTPError as e:
                sys.stderr.write("Error: test_data:\n")
                sys.stderr.write("GET {0}\n".format(test_url))
                sys.stderr.write(test_data)
                sys.stderr.write("\n")
                sys.stderr.write(e.read())
                sys.stderr.write("\n")
                raise
            if challenge_status['status'] == "pending":
                time.sleep(2)
            elif challenge_status['status'] == "valid":
                sys.stderr.write("Passed {0} challenge!\n".format(i['domain']))
                break
            else:
                raise KeyError("'{0}' challenge did not pass: {1}".format(i['domain'], challenge_status))

    # Step 14: Get the certificate signed
    sys.stderr.write("Requesting signature...\n")
    csr_file_sig.seek(0)
    csr_sig64 = _b64(csr_file_sig.read())
    csr_data = json.dumps({
        "header": header,
        "protected": csr_protected64,
        "payload": csr_b64,
        "signature": csr_sig64,
    }, sort_keys=True, indent=4)
    csr_url = "{0}/acme/new-cert".format(CA)
    try:
        resp = urllib2.urlopen(csr_url, csr_data)
        signed_der = resp.read()
    except urllib2.HTTPError as e:
        sys.stderr.write("Error: csr_data:\n")
        sys.stderr.write("POST {0}\n".format(csr_url))
        sys.stderr.write(csr_data)
        sys.stderr.write("\n")
        sys.stderr.write(e.read())
        sys.stderr.write("\n")
        raise

    # Step 15: Convert the signed cert from DER to PEM
    sys.stderr.write("Certificate signed!\n")

    if file_based:
        sys.stderr.write("You can remove the acme-challenge file from your webserver now.\n")
    else:
        sys.stderr.write("You can stop running the python command on your server (Ctrl+C works).\n")

    signed_der64 = base64.b64encode(signed_der)
    signed_pem = """\
-----BEGIN CERTIFICATE-----
{0}
-----END CERTIFICATE-----
""".format("\n".join(textwrap.wrap(signed_der64, 64)))

    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 and this script does not ask for your private keys. It will print out
commands that you need to run with your private key or on your server as root,
which gives you a chance to review the commands instead of trusting this script.

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

Prerequisites:
* openssl
* python

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

""")
    parser.add_argument("-p", "--public-key", required=True, help="path to your account public key")
    parser.add_argument("-e", "--email", default=None, help="contact email, default is webmaster@<shortest_domain>")
    parser.add_argument("-f", "--file-based", action='store_true', help="if set, a file-based response is used")
    parser.add_argument("csr_path", help="path to your certificate signing request")

    args = parser.parse_args()
    signed_crt = sign_csr(args.public_key, args.csr_path, email=args.email, file_based=args.file_based)
    sys.stdout.write(signed_crt)