kiwi-vpn/api/kiwi_vpn_api/easyrsa.py

"""
Python interface to EasyRSA CA.
"""

from __future__ import annotations

import subprocess
from datetime import datetime
from enum import Enum, auto
from pathlib import Path

from OpenSSL import crypto
from passlib import pwd
from pydantic import BaseModel

from .config import Config, KeyAlgorithm, Settings
from .db import Connection, Device


class DistinguishedName(BaseModel):
    """
    An `X.509 distinguished name` (DN) as specified in RFC 5280
    """

    country: str
    state: str
    city: str
    organization: str
    organizational_unit: str
    email: str
    common_name: str

    @classmethod
    def build(cls, device: Device | None = None) -> DistinguishedName:
        """
        Create a DN from the current config and an optional device
        """

        # extract server DN config
        server_dn = Config._.server_dn
        result = cls(
            country=server_dn.country.value,
            state=server_dn.state.value,
            city=server_dn.city.value,
            organization=server_dn.organization.value,
            organizational_unit=server_dn.organizational_unit.value,
            email=server_dn.email.value,
            common_name=server_dn.common_name,
        )

        # no device specified -> done
        if device is None:
            return result

        # don't override locked or empty fields
        if not (server_dn.country.locked
                or device.owner.country is None):
            result.country = device.owner.country

        if not (server_dn.state.locked
                or device.owner.state is None):
            result.state = device.owner.state

        if not (server_dn.city.locked
                or device.owner.city is None):
            result.city = device.owner.city

        if not (server_dn.organization.locked
                or device.owner.organization is None):
            result.organization = device.owner.organization

        if not (server_dn.organizational_unit.locked
                or device.owner.organizational_unit is None):
            result.organizational_unit = device.owner.organizational_unit

        # definitely use derived email and common_name
        result.email = device.owner.email
        result.common_name = f"{device.owner.name}_{device.name}"

        return result

    @property
    def easyrsa_args(self) -> list[str]:
        """
        Pass this DN as arguments to easyrsa
        """

        return [
            "--dn-mode=org",

            f"--req-c={self.country}",
            f"--req-st={self.state}",
            f"--req-city={self.city}",
            f"--req-org={self.organization}",
            f"--req-ou={self.organizational_unit}",
            f"--req-email={self.email}",
            f"--req-cn={self.common_name}",
        ]


class CertificateType(Enum):
    """
    Possible types of certificates
    """

    ca = auto()
    client = auto()
    server = auto()

    def __str__(self) -> str:
        return self._name_


class EasyRSA:
    """
    Represents an EasyRSA PKI.
    """

    @property
    def output_directory(self) -> Path:
        """
        Where certificates are stored
        """

        return Settings._.data_dir.joinpath("pki")

    @property
    def ca_password(self) -> str:
        """
        Get CA password from config, or generate a new one
        """

        config = Config._

        if (ca_password := config.crypto.ca_password) is None:
            # generate and save new CA password
            ca_password = pwd.genword(
                length=32,
                charset="ascii_62",
            )

            config.crypto.ca_password = ca_password
            config.save()

        return config.crypto.ca_password

    def __easyrsa(
        self,
        *easyrsa_args: str,
    ) -> subprocess.CompletedProcess:
        """
        Call the `easyrsa` executable
        """

        return subprocess.run(
            [
                "easyrsa", "--batch",
                f"--pki-dir={self.output_directory}",
                *easyrsa_args,
            ],
            stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
            check=True,
        )

    def __build_cert(
        self,
        cert_filename: Path,
        expiry_days: int | None,
        *easyrsa_args: str,
    ) -> crypto.X509:
        """
        Create an X.509 certificate
        """

        config = Config._

        # always include password options
        extra_args: list[str] = [
            f"--passout=pass:{self.ca_password}",
            f"--passin=pass:{self.ca_password}",
        ]

        # if given, include expiry option
        if expiry_days is not None:
            extra_args += [f"--days={expiry_days}"]

        # if configured, include algorithm option
        if (algorithm := config.crypto.key_algorithm) is not None:
            args_map = {
                KeyAlgorithm.rsa2048: [
                    "--use-algo=rsa", "--keysize=2048"
                ],
                KeyAlgorithm.rsa2048: [
                    "--use-algo=rsa", "--keysize=2048"
                ],
                KeyAlgorithm.secp256r1: [
                    "--use-algo=ec", "--curve=secp256r1"
                ],
                KeyAlgorithm.secp384r1: [
                    "--use-algo=ec", "--curve=secp384r1"
                ],
                KeyAlgorithm.ed25519: [
                    "--use-algo=ed", "--curve=ed25519"
                ]
            }

            if algorithm not in args_map:
                raise ValueError(f"Unexpected algorithm: {algorithm}")

            extra_args += args_map[algorithm]

        # call easyrsa
        self.__easyrsa(
            *extra_args,
            *easyrsa_args
        )

        # parse the new certificate
        with open(
            self.output_directory.joinpath(cert_filename), "rb"
        ) as cert_file:
            return crypto.load_certificate(
                crypto.FILETYPE_PEM, cert_file.read()
            )

    def init_pki(self) -> None:
        """
        Clean working directory
        """

        self.__easyrsa("init-pki")

    def build_ca(self) -> crypto.X509:
        """
        Build the CA certificate
        """

        cert = self.__build_cert(
            Path("ca.crt"),
            Config._.crypto.ca_expiry_days,

            "--dn-mode=cn_only",
            "--req-cn=kiwi-vpn-ca",

            "build-ca",
        )

        # # this takes long!
        # self.__easyrsa("gen-dh")
        return cert

    def issue(
        self,
        cert_type: CertificateType = CertificateType.client,
        dn: DistinguishedName = DistinguishedName.build(),
    ) -> crypto.X509 | None:
        """
        Issue a client or server certificate
        """

        if not (cert_type is CertificateType.client
                or cert_type is CertificateType.server):
            return None

        return self.__build_cert(
            Path(f"issued/{dn.common_name}.crt"),
            Config._.crypto.cert_expiry_days,

            *dn.easyrsa_args,

            f"build-{cert_type}-full",
            dn.common_name,
            "nopass",
        )


# some basic test

if __name__ == "__main__":
    easy_rsa = EasyRSA()
    easy_rsa.init_pki()

    ca = easy_rsa.build_ca()
    server = easy_rsa.issue(CertificateType.server)
    client = None

    # check if configured
    if (current_config := Config.load()) is not None:
        # connect to database
        Connection.connect(current_config.db.uri)

        if (device := Device.get(1)) is not None:
            with Connection.session as db:
                db.add(device)
                dn = DistinguishedName.build(device)

            client = easy_rsa.issue(dn=dn)

    date_format, encoding = "%Y%m%d%H%M%SZ", "ascii"

    for cert in (ca, server, client):
        if cert is not None:
            print(cert.get_subject().CN)
            print(cert.get_signature_algorithm().decode(encoding))

            assert (na := cert.get_notAfter()) is not None
            print(datetime.strptime(na.decode(encoding), date_format))