synta-python 0.1.4

//! Python bindings for PKINIT types (RFC 4556 + RFC 6112 + RFC 8636).
//!
//! Exposes the ASN.1 structures used in PKINIT AS exchanges as frozen
//! Python classes under the ``synta.krb5`` namespace.
//!
//! # Classes
//!
//! | Rust type                       | Python name                   | RFC / section   |
//! |---------------------------------|-------------------------------|-----------------|
//! | [`PyEncryptionKey`]             | `EncryptionKey`               | RFC 3961 §2     |
//! | [`PyChecksum`]                  | `Checksum`                    | RFC 3961 §4     |
//! | [`PyKDFAlgorithmId`]            | `KDFAlgorithmId`              | RFC 8636 §3.1   |
//! | [`PyIssuerAndSerialNumber`]     | `IssuerAndSerialNumber`       | RFC 4556 §3.2.2 |
//! | [`PyExternalPrincipalIdentifier`]| `ExternalPrincipalIdentifier`| RFC 4556 §3.2.2 |
//! | [`PyPKAuthenticator`]           | `PKAuthenticator`             | RFC 4556 §3.2.1 |
//! | [`PyAuthPack`]                  | `AuthPack`                    | RFC 4556 §3.2.1 |
//! | [`PyPaPkAsReq`]                 | `PaPkAsReq`                   | RFC 4556 §3.2.2 |
//! | [`PyDHRepInfo`]                 | `DHRepInfo`                   | RFC 4556 §3.2.4 |
//! | [`PyKDCDHKeyInfo`]              | `KDCDHKeyInfo`                | RFC 4556 §3.2.4 |
//! | [`PyReplyKeyPack`]              | `ReplyKeyPack`                | RFC 4556 §3.2.3 |
//! | [`PyPaPkAsRep`]                 | `PaPkAsRep`                   | RFC 4556 §3.2.4 |
//!
//! Call [`register_pkinit_classes`] from
//! ``synta_python::krb5::register_krb5_module`` to install the classes.

use pyo3::exceptions::PyOverflowError;
use pyo3::prelude::*;
use pyo3::types::{PyBytes, PyList};

use crate::error::SyntaErr;
use crate::types::PyObjectIdentifier;
use synta::traits::Encode;
use synta::{Decoder, Encoding, ObjectIdentifier};

// ── helpers ───────────────────────────────────────────────────────────────────

/// Re-encode a synta `Element<'_>` to owned DER bytes.
fn encode_element_to_vec(elem: &synta::Element<'_>) -> PyResult<Vec<u8>> {
    let mut encoder = synta::Encoder::new(Encoding::Der);
    elem.encode(&mut encoder).map_err(SyntaErr)?;
    Ok(encoder.finish().map_err(SyntaErr)?)
}

// ── Leaf classes (no nested pyclass fields) ───────────────────────────────────

/// Kerberos EncryptionKey — RFC 3961 §2 / RFC 4556
///
/// Contains the encryption algorithm type identifier and the raw key material.
///
/// ```python
/// key = synta.krb5.EncryptionKey.from_der(der_bytes)
/// print(key.keytype, key.keyvalue.hex())
/// ```
#[pyclass(frozen, name = "EncryptionKey")]
pub struct PyEncryptionKey {
    keytype: i64,
    keyvalue: Vec<u8>,
}

#[pymethods]
impl PyEncryptionKey {
    /// Parse a DER-encoded EncryptionKey SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::EncryptionKey<'_> = dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            keytype: parsed
                .keytype
                .as_i64()
                .map_err(|_| PyOverflowError::new_err("keytype out of i64 range"))?,
            keyvalue: parsed.keyvalue.as_bytes().to_vec(),
        })
    }

    /// Kerberos encryption type number (RFC 3961 Table 1).
    #[getter]
    fn keytype(&self) -> i64 {
        self.keytype
    }

    /// Raw key material bytes.
    #[getter]
    fn keyvalue<'py>(&self, py: Python<'py>) -> Bound<'py, PyBytes> {
        PyBytes::new(py, &self.keyvalue)
    }

    fn __repr__(&self) -> String {
        format!(
            "EncryptionKey(keytype={}, keyvalue=<{} bytes>)",
            self.keytype,
            self.keyvalue.len()
        )
    }
}

/// Kerberos Checksum — RFC 3961 §4 / RFC 4556
///
/// Contains the checksum algorithm type identifier and the raw checksum value.
///
/// ```python
/// ck = synta.krb5.Checksum.from_der(der_bytes)
/// print(ck.cksumtype, ck.checksum.hex())
/// ```
#[pyclass(frozen, name = "Checksum")]
pub struct PyChecksum {
    cksumtype: i64,
    checksum: Vec<u8>,
}

#[pymethods]
impl PyChecksum {
    /// Parse a DER-encoded Checksum SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::Checksum<'_> = dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            cksumtype: parsed
                .cksumtype
                .as_i64()
                .map_err(|_| PyOverflowError::new_err("cksumtype out of i64 range"))?,
            checksum: parsed.checksum.as_bytes().to_vec(),
        })
    }

    /// Kerberos checksum type number.
    #[getter]
    fn cksumtype(&self) -> i64 {
        self.cksumtype
    }

    /// Raw checksum bytes.
    #[getter]
    fn checksum<'py>(&self, py: Python<'py>) -> Bound<'py, PyBytes> {
        PyBytes::new(py, &self.checksum)
    }

    fn __repr__(&self) -> String {
        format!(
            "Checksum(cksumtype={}, checksum=<{} bytes>)",
            self.cksumtype,
            self.checksum.len()
        )
    }
}

/// PKINIT KDF algorithm identifier — RFC 8636 §3.1
///
/// Identifies the key-derivation function used in a PKINIT exchange.
///
/// ```python
/// kdf = synta.krb5.KDFAlgorithmId.from_der(der_bytes)
/// print(kdf.kdf_id)   # ObjectIdentifier("1.3.6.1.5.2.3.6.2")
/// ```
#[pyclass(frozen, name = "KDFAlgorithmId")]
pub struct PyKDFAlgorithmId {
    kdf_id: ObjectIdentifier,
}

#[pymethods]
impl PyKDFAlgorithmId {
    /// Parse a DER-encoded KDFAlgorithmId SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::KDFAlgorithmId = dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            kdf_id: parsed.kdf_id,
        })
    }

    /// Key-derivation function OID.
    #[getter]
    fn kdf_id(&self, py: Python<'_>) -> PyResult<Py<PyObjectIdentifier>> {
        Py::new(py, PyObjectIdentifier::from_oid(self.kdf_id.clone()))
    }

    fn __repr__(&self) -> String {
        format!("KDFAlgorithmId(kdf_id='{}')", self.kdf_id)
    }
}

/// PKINIT IssuerAndSerialNumber — RFC 4556 §3.2.2
///
/// Identifies a certificate by its issuer Name and serial number.
///
/// ```python
/// isn = synta.krb5.IssuerAndSerialNumber.from_der(der_bytes)
/// print(isn.serial_number)
/// ```
#[pyclass(frozen, name = "IssuerAndSerialNumber")]
pub struct PyIssuerAndSerialNumber {
    issuer: Vec<u8>,
    serial_number_bytes: Vec<u8>,
}

#[pymethods]
impl PyIssuerAndSerialNumber {
    /// Parse a DER-encoded IssuerAndSerialNumber SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::IssuerAndSerialNumber<'_> =
            dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            issuer: parsed.issuer.as_bytes().to_vec(),
            serial_number_bytes: parsed.serial_number.as_bytes().to_vec(),
        })
    }

    /// DER-encoded issuer Name bytes (raw Name SEQUENCE).
    #[getter]
    fn issuer<'py>(&self, py: Python<'py>) -> Bound<'py, PyBytes> {
        PyBytes::new(py, &self.issuer)
    }

    /// Certificate serial number as a Python :class:`int`.
    #[getter]
    fn serial_number<'py>(&self, py: Python<'py>) -> PyResult<Bound<'py, PyAny>> {
        let bytes_obj = PyBytes::new(py, &self.serial_number_bytes);
        let kwargs = pyo3::types::PyDict::new(py);
        kwargs.set_item(pyo3::intern!(py, "signed"), true)?;
        py.get_type::<pyo3::types::PyInt>().call_method(
            "from_bytes",
            (bytes_obj, "big"),
            Some(&kwargs),
        )
    }

    fn __repr__(&self) -> String {
        format!(
            "IssuerAndSerialNumber(issuer=<{} bytes>, serial=<{} bytes>)",
            self.issuer.len(),
            self.serial_number_bytes.len(),
        )
    }
}

/// PKINIT PKAuthenticator — RFC 4556 §3.2.1
///
/// The client's proof of liveness in a PKINIT AS-REQ.
///
/// ```python
/// auth = synta.krb5.PKAuthenticator.from_der(der_bytes)
/// print(auth.ctime, auth.nonce)
/// ```
#[pyclass(frozen, name = "PKAuthenticator")]
pub struct PyPKAuthenticator {
    cusec: i64,
    ctime: String,
    nonce: i64,
    pa_checksum: Option<Vec<u8>>,
    freshness_token: Option<Vec<u8>>,
}

#[pymethods]
impl PyPKAuthenticator {
    /// Parse a DER-encoded PKAuthenticator SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::PKAuthenticator<'_> = dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            cusec: parsed
                .cusec
                .as_i64()
                .map_err(|_| PyOverflowError::new_err("cusec out of i64 range"))?,
            ctime: parsed.ctime.to_string(),
            nonce: parsed
                .nonce
                .as_i64()
                .map_err(|_| PyOverflowError::new_err("nonce out of i64 range"))?,
            pa_checksum: parsed.pa_checksum.map(|s| s.as_bytes().to_vec()),
            freshness_token: parsed.freshness_token.map(|s| s.as_bytes().to_vec()),
        })
    }

    /// Microsecond component of the client's current time (0–999 999).
    #[getter]
    fn cusec(&self) -> i64 {
        self.cusec
    }

    /// Client's current time as a string (``YYYYMMDDHHMMSSz``).
    #[getter]
    fn ctime(&self) -> &str {
        &self.ctime
    }

    /// Nonce preventing replay attacks.
    #[getter]
    fn nonce(&self) -> i64 {
        self.nonce
    }

    /// Optional SHA-1 checksum of the DER-encoded AS-REQ body, or ``None``.
    #[getter]
    fn pa_checksum<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.pa_checksum.as_deref().map(|b| PyBytes::new(py, b))
    }

    /// Optional freshness token from the KDC (RFC 8070), or ``None``.
    #[getter]
    fn freshness_token<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.freshness_token.as_deref().map(|b| PyBytes::new(py, b))
    }

    fn __repr__(&self) -> String {
        format!(
            "PKAuthenticator(ctime='{}', nonce={})",
            self.ctime, self.nonce
        )
    }
}

/// PKINIT DHRepInfo — RFC 4556 §3.2.4
///
/// Carries the KDC's Diffie-Hellman reply inside a PA-PK-AS-REP.
///
/// ```python
/// rep = synta.krb5.DHRepInfo.from_der(der_bytes)
/// print(len(rep.dh_signed_data))
/// ```
#[pyclass(frozen, name = "DHRepInfo")]
pub struct PyDHRepInfo {
    dh_signed_data: Vec<u8>,
    server_dhnonce: Option<Vec<u8>>,
}

#[pymethods]
impl PyDHRepInfo {
    /// Parse a DER-encoded DHRepInfo SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::DHRepInfo<'_> = dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            dh_signed_data: parsed.dh_signed_data.as_bytes().to_vec(),
            server_dhnonce: parsed.server_dhnonce.map(|s| s.as_bytes().to_vec()),
        })
    }

    /// CMS SignedData containing the KDC's DH public key.
    #[getter]
    fn dh_signed_data<'py>(&self, py: Python<'py>) -> Bound<'py, PyBytes> {
        PyBytes::new(py, &self.dh_signed_data)
    }

    /// Optional server DH nonce, or ``None``.
    #[getter]
    fn server_dhnonce<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.server_dhnonce.as_deref().map(|b| PyBytes::new(py, b))
    }

    fn __repr__(&self) -> String {
        format!(
            "DHRepInfo(dh_signed_data=<{} bytes>)",
            self.dh_signed_data.len()
        )
    }
}

/// PKINIT KDCDHKeyInfo — RFC 4556 §3.2.4
///
/// The KDC's DH public key and associated PKINIT parameters.
///
/// ```python
/// info = synta.krb5.KDCDHKeyInfo.from_der(der_bytes)
/// print(info.nonce, info.subject_public_key.hex())
/// ```
#[pyclass(frozen, name = "KDCDHKeyInfo")]
pub struct PyKDCDHKeyInfo {
    subject_public_key: Vec<u8>,
    nonce: i64,
    dh_key_expiration: Option<String>,
}

#[pymethods]
impl PyKDCDHKeyInfo {
    /// Parse a DER-encoded KDCDHKeyInfo SEQUENCE.
    #[staticmethod]
    fn from_der(data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::KDCDHKeyInfo<'_> = dec.decode().map_err(SyntaErr)?;
        Ok(Self {
            subject_public_key: parsed.subject_public_key.as_bytes().to_vec(),
            nonce: parsed
                .nonce
                .as_i64()
                .map_err(|_| PyOverflowError::new_err("nonce out of i64 range"))?,
            dh_key_expiration: parsed.dh_key_expiration.map(|t| t.to_string()),
        })
    }

    /// KDC's DH public key as raw BIT STRING payload bytes.
    #[getter]
    fn subject_public_key<'py>(&self, py: Python<'py>) -> Bound<'py, PyBytes> {
        PyBytes::new(py, &self.subject_public_key)
    }

    /// Nonce echoed from the client's PA-PK-AS-REQ.
    #[getter]
    fn nonce(&self) -> i64 {
        self.nonce
    }

    /// Optional DH key expiration time as a string (``YYYYMMDDHHMMSSz``), or ``None``.
    #[getter]
    fn dh_key_expiration(&self) -> Option<&str> {
        self.dh_key_expiration.as_deref()
    }

    fn __repr__(&self) -> String {
        format!(
            "KDCDHKeyInfo(nonce={}, subject_public_key=<{} bytes>)",
            self.nonce,
            self.subject_public_key.len()
        )
    }
}

// ── Composite classes (contain nested pyclass fields) ─────────────────────────

/// PKINIT ExternalPrincipalIdentifier — RFC 4556 §3.2.2
///
/// Identifies a certificate by subject name, issuer/serial pair, or SKI.
/// All three fields are OPTIONAL; at least one SHOULD be present.
///
/// ```python
/// epi = synta.krb5.ExternalPrincipalIdentifier.from_der(der_bytes)
/// if epi.subject_key_identifier:
///     print(epi.subject_key_identifier.hex())
/// ```
#[pyclass(frozen, name = "ExternalPrincipalIdentifier")]
pub struct PyExternalPrincipalIdentifier {
    subject_name: Option<Vec<u8>>,
    issuer_and_serial_number: Option<Py<PyIssuerAndSerialNumber>>,
    subject_key_identifier: Option<Vec<u8>>,
}

#[pymethods]
impl PyExternalPrincipalIdentifier {
    /// Parse a DER-encoded ExternalPrincipalIdentifier SEQUENCE.
    #[staticmethod]
    fn from_der(py: Python<'_>, data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::ExternalPrincipalIdentifier<'_> =
            dec.decode().map_err(SyntaErr)?;
        let issuer_and_serial_number = parsed
            .issuer_and_serial_number
            .map(|isn| {
                Py::new(
                    py,
                    PyIssuerAndSerialNumber {
                        issuer: isn.issuer.as_bytes().to_vec(),
                        serial_number_bytes: isn.serial_number.as_bytes().to_vec(),
                    },
                )
            })
            .transpose()?;
        Ok(Self {
            subject_name: parsed.subject_name.map(|s| s.as_bytes().to_vec()),
            issuer_and_serial_number,
            subject_key_identifier: parsed.subject_key_identifier.map(|s| s.as_bytes().to_vec()),
        })
    }

    /// DER-encoded subject Name, or ``None``.
    #[getter]
    fn subject_name<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.subject_name.as_deref().map(|b| PyBytes::new(py, b))
    }

    /// :class:`IssuerAndSerialNumber` identifying the certificate, or ``None``.
    #[getter]
    fn issuer_and_serial_number<'py>(
        &self,
        py: Python<'py>,
    ) -> Option<Bound<'py, PyIssuerAndSerialNumber>> {
        self.issuer_and_serial_number
            .as_ref()
            .map(|x| x.clone_ref(py).into_bound(py))
    }

    /// Subject key identifier bytes, or ``None``.
    #[getter]
    fn subject_key_identifier<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.subject_key_identifier
            .as_deref()
            .map(|b| PyBytes::new(py, b))
    }
}

/// PKINIT ReplyKeyPack — RFC 4556 §3.2.3
///
/// The session key and checksum sent by the KDC to an authenticated client.
///
/// ```python
/// pack = synta.krb5.ReplyKeyPack.from_der(der_bytes)
/// print(pack.reply_key.keytype)
/// ```
#[pyclass(frozen, name = "ReplyKeyPack")]
pub struct PyReplyKeyPack {
    reply_key: Py<PyEncryptionKey>,
    as_checksum: Py<PyChecksum>,
}

#[pymethods]
impl PyReplyKeyPack {
    /// Parse a DER-encoded ReplyKeyPack SEQUENCE.
    #[staticmethod]
    fn from_der(py: Python<'_>, data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::ReplyKeyPack<'_> = dec.decode().map_err(SyntaErr)?;
        let reply_key = Py::new(
            py,
            PyEncryptionKey {
                keytype: parsed
                    .reply_key
                    .keytype
                    .as_i64()
                    .map_err(|_| PyOverflowError::new_err("keytype out of i64 range"))?,
                keyvalue: parsed.reply_key.keyvalue.as_bytes().to_vec(),
            },
        )?;
        let as_checksum = Py::new(
            py,
            PyChecksum {
                cksumtype: parsed
                    .as_checksum
                    .cksumtype
                    .as_i64()
                    .map_err(|_| PyOverflowError::new_err("cksumtype out of i64 range"))?,
                checksum: parsed.as_checksum.checksum.as_bytes().to_vec(),
            },
        )?;
        Ok(Self {
            reply_key,
            as_checksum,
        })
    }

    /// The session key returned by the KDC.
    #[getter]
    fn reply_key<'py>(&self, py: Python<'py>) -> Bound<'py, PyEncryptionKey> {
        self.reply_key.clone_ref(py).into_bound(py)
    }

    /// The AS-REQ checksum authenticating the exchange.
    #[getter]
    fn as_checksum<'py>(&self, py: Python<'py>) -> Bound<'py, PyChecksum> {
        self.as_checksum.clone_ref(py).into_bound(py)
    }

    fn __repr__(&self) -> String {
        String::from("ReplyKeyPack(...)")
    }
}

/// PKINIT PA-PK-AS-REP — RFC 4556 §3.2.4
///
/// CHOICE: DH-based reply (``DhInfo``) or RSA-encrypted reply (``EncKeyPack``).
///
/// ```python
/// rep = synta.krb5.PaPkAsRep.from_der(der_bytes)
/// if rep.variant == "DhInfo":
///     print(len(rep.dh_info.dh_signed_data))
/// else:
///     print(rep.enc_key_pack.hex())
/// ```
#[pyclass(frozen, name = "PaPkAsRep")]
pub struct PyPaPkAsRep {
    variant: &'static str,
    dh_info: Option<Py<PyDHRepInfo>>,
    enc_key_pack: Option<Vec<u8>>,
}

#[pymethods]
impl PyPaPkAsRep {
    /// Parse a DER-encoded PA-PK-AS-REP CHOICE.
    #[staticmethod]
    fn from_der(py: Python<'_>, data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::PaPkAsRep<'_> = dec.decode().map_err(SyntaErr)?;
        match parsed {
            synta_krb5::pkinit::PaPkAsRep::DhInfo(dh) => {
                let dh_info = Py::new(
                    py,
                    PyDHRepInfo {
                        dh_signed_data: dh.dh_signed_data.as_bytes().to_vec(),
                        server_dhnonce: dh.server_dhnonce.map(|s| s.as_bytes().to_vec()),
                    },
                )?;
                Ok(Self {
                    variant: "DhInfo",
                    dh_info: Some(dh_info),
                    enc_key_pack: None,
                })
            }
            synta_krb5::pkinit::PaPkAsRep::EncKeyPack(pack) => Ok(Self {
                variant: "EncKeyPack",
                dh_info: None,
                enc_key_pack: Some(pack.as_bytes().to_vec()),
            }),
        }
    }

    /// Active CHOICE variant: ``"DhInfo"`` or ``"EncKeyPack"``.
    #[getter]
    fn variant(&self) -> &'static str {
        self.variant
    }

    /// :class:`DHRepInfo` when the variant is ``"DhInfo"``, else ``None``.
    #[getter]
    fn dh_info<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyDHRepInfo>> {
        self.dh_info
            .as_ref()
            .map(|x| x.clone_ref(py).into_bound(py))
    }

    /// CMS EnvelopedData bytes when the variant is ``"EncKeyPack"``, else ``None``.
    #[getter]
    fn enc_key_pack<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.enc_key_pack.as_deref().map(|b| PyBytes::new(py, b))
    }

    fn __repr__(&self) -> String {
        format!("PaPkAsRep(variant='{}')", self.variant)
    }
}

/// PKINIT AuthPack — RFC 4556 §3.2.1
///
/// The client's signed authentication package, embedded in a PA-PK-AS-REQ.
///
/// ```python
/// pack = synta.krb5.AuthPack.from_der(der_bytes)
/// print(pack.pk_authenticator.nonce)
/// ```
#[pyclass(frozen, name = "AuthPack")]
pub struct PyAuthPack {
    pk_authenticator: Py<PyPKAuthenticator>,
    client_public_value: Option<Vec<u8>>,
    supported_cmstypes: Option<Vec<u8>>,
    client_dhnonce: Option<Vec<u8>>,
    supported_kdfs: Option<Vec<Py<PyKDFAlgorithmId>>>,
}

#[pymethods]
impl PyAuthPack {
    /// Parse a DER-encoded AuthPack SEQUENCE.
    #[staticmethod]
    fn from_der(py: Python<'_>, data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::AuthPack<'_> = dec.decode().map_err(SyntaErr)?;
        let pka = parsed.pk_authenticator;
        let pk_authenticator = Py::new(
            py,
            PyPKAuthenticator {
                cusec: pka
                    .cusec
                    .as_i64()
                    .map_err(|_| PyOverflowError::new_err("cusec out of i64 range"))?,
                ctime: pka.ctime.to_string(),
                nonce: pka
                    .nonce
                    .as_i64()
                    .map_err(|_| PyOverflowError::new_err("nonce out of i64 range"))?,
                pa_checksum: pka.pa_checksum.map(|s| s.as_bytes().to_vec()),
                freshness_token: pka.freshness_token.map(|s| s.as_bytes().to_vec()),
            },
        )?;
        let client_public_value = parsed
            .client_public_value
            .as_ref()
            .map(encode_element_to_vec)
            .transpose()?;
        let supported_cmstypes = parsed
            .supported_cmstypes
            .as_ref()
            .map(encode_element_to_vec)
            .transpose()?;
        let client_dhnonce = parsed.client_dhnonce.map(|s| s.as_bytes().to_vec());
        let supported_kdfs = parsed
            .supported_kdfs
            .map(|kdfs| {
                kdfs.into_iter()
                    .map(|kdf| Py::new(py, PyKDFAlgorithmId { kdf_id: kdf.kdf_id }))
                    .collect::<PyResult<Vec<_>>>()
            })
            .transpose()?;
        Ok(Self {
            pk_authenticator,
            client_public_value,
            supported_cmstypes,
            client_dhnonce,
            supported_kdfs,
        })
    }

    /// :class:`PKAuthenticator` proving client liveness.
    #[getter]
    fn pk_authenticator<'py>(&self, py: Python<'py>) -> Bound<'py, PyPKAuthenticator> {
        self.pk_authenticator.clone_ref(py).into_bound(py)
    }

    /// DER-encoded client DH SubjectPublicKeyInfo, or ``None``.
    #[getter]
    fn client_public_value<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.client_public_value
            .as_deref()
            .map(|b| PyBytes::new(py, b))
    }

    /// DER-encoded supported CMS algorithm list, or ``None``.
    #[getter]
    fn supported_cmstypes<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.supported_cmstypes
            .as_deref()
            .map(|b| PyBytes::new(py, b))
    }

    /// Client DH nonce bytes, or ``None``.
    #[getter]
    fn client_dhnonce<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.client_dhnonce.as_deref().map(|b| PyBytes::new(py, b))
    }

    /// List of supported :class:`KDFAlgorithmId` entries, or ``None``.
    #[getter]
    fn supported_kdfs<'py>(&self, py: Python<'py>) -> PyResult<Option<Bound<'py, PyList>>> {
        self.supported_kdfs
            .as_ref()
            .map(|kdfs| {
                let list = PyList::empty(py);
                for kdf in kdfs {
                    list.append(kdf.clone_ref(py).into_bound(py))?;
                }
                Ok(list)
            })
            .transpose()
    }

    fn __repr__(&self) -> String {
        String::from("AuthPack(...)")
    }
}

/// PKINIT PA-PK-AS-REQ — RFC 4556 §3.2.2
///
/// Pre-authentication data sent by the client in the initial AS-REQ.
///
/// ```python
/// req = synta.krb5.PaPkAsReq.from_der(der_bytes)
/// print(len(req.signed_auth_pack))
/// ```
#[pyclass(frozen, name = "PaPkAsReq")]
pub struct PyPaPkAsReq {
    signed_auth_pack: Vec<u8>,
    trusted_certifiers: Option<Vec<Py<PyExternalPrincipalIdentifier>>>,
    kdc_pk_id: Option<Vec<u8>>,
}

#[pymethods]
impl PyPaPkAsReq {
    /// Parse a DER-encoded PA-PK-AS-REQ SEQUENCE.
    #[staticmethod]
    fn from_der(py: Python<'_>, data: &[u8]) -> PyResult<Self> {
        let mut dec = Decoder::new(data, Encoding::Der);
        let parsed: synta_krb5::pkinit::PaPkAsReq<'_> = dec.decode().map_err(SyntaErr)?;
        let signed_auth_pack = parsed.signed_auth_pack.as_bytes().to_vec();
        let trusted_certifiers = parsed
            .trusted_certifiers
            .map(|certs| {
                certs
                    .into_iter()
                    .map(|epi| {
                        let isn = epi
                            .issuer_and_serial_number
                            .map(|isn| {
                                Py::new(
                                    py,
                                    PyIssuerAndSerialNumber {
                                        issuer: isn.issuer.as_bytes().to_vec(),
                                        serial_number_bytes: isn.serial_number.as_bytes().to_vec(),
                                    },
                                )
                            })
                            .transpose()?;
                        Py::new(
                            py,
                            PyExternalPrincipalIdentifier {
                                subject_name: epi.subject_name.map(|s| s.as_bytes().to_vec()),
                                issuer_and_serial_number: isn,
                                subject_key_identifier: epi
                                    .subject_key_identifier
                                    .map(|s| s.as_bytes().to_vec()),
                            },
                        )
                    })
                    .collect::<PyResult<Vec<_>>>()
            })
            .transpose()?;
        let kdc_pk_id = parsed.kdc_pk_id.map(|s| s.as_bytes().to_vec());
        Ok(Self {
            signed_auth_pack,
            trusted_certifiers,
            kdc_pk_id,
        })
    }

    /// CMS SignedData wrapping the client's AuthPack.
    #[getter]
    fn signed_auth_pack<'py>(&self, py: Python<'py>) -> Bound<'py, PyBytes> {
        PyBytes::new(py, &self.signed_auth_pack)
    }

    /// List of :class:`ExternalPrincipalIdentifier` for acceptable KDC certs, or ``None``.
    #[getter]
    fn trusted_certifiers<'py>(&self, py: Python<'py>) -> PyResult<Option<Bound<'py, PyList>>> {
        self.trusted_certifiers
            .as_ref()
            .map(|certs| {
                let list = PyList::empty(py);
                for cert in certs {
                    list.append(cert.clone_ref(py).into_bound(py))?;
                }
                Ok(list)
            })
            .transpose()
    }

    /// Subject key identifier of the preferred KDC certificate, or ``None``.
    #[getter]
    fn kdc_pk_id<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyBytes>> {
        self.kdc_pk_id.as_deref().map(|b| PyBytes::new(py, b))
    }

    fn __repr__(&self) -> String {
        format!(
            "PaPkAsReq(signed_auth_pack=<{} bytes>)",
            self.signed_auth_pack.len()
        )
    }
}

// ── Module registration ───────────────────────────────────────────────────────

/// Register all PKINIT Python classes into `m` (the ``synta.krb5`` submodule).
///
/// Called from ``synta_python::krb5::register_krb5_module``.
pub fn register_pkinit_classes(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_class::<PyEncryptionKey>()?;
    m.add_class::<PyChecksum>()?;
    m.add_class::<PyKDFAlgorithmId>()?;
    m.add_class::<PyIssuerAndSerialNumber>()?;
    m.add_class::<PyPKAuthenticator>()?;
    m.add_class::<PyDHRepInfo>()?;
    m.add_class::<PyKDCDHKeyInfo>()?;
    m.add_class::<PyExternalPrincipalIdentifier>()?;
    m.add_class::<PyReplyKeyPack>()?;
    m.add_class::<PyPaPkAsRep>()?;
    m.add_class::<PyAuthPack>()?;
    m.add_class::<PyPaPkAsReq>()?;
    Ok(())
}