How to parse a JKS in Python

parse_jks.py

from pprint import pprint
import dataclasses
import struct
from datetime import datetime
import cryptography.x509
from cryptography.x509 import Certificate


def next_long(f):
    return struct.unpack(">Q", f.read(8))[0]


def next_int(f):
    return struct.unpack(">I", f.read(4))[0]


def next_short(f):
    return struct.unpack(">H", f.read(2))[0]


def next_string(f):
    string_length = next_short(f)
    return f.read(string_length).decode("utf8")


def next_timestamp(f):
    return datetime.fromtimestamp(next_long(f) / 1000.0)


def next_cert(f):
    cert_type = next_string(f)
    cert_length = next_int(f)
    cert_bytes = f.read(cert_length)
    return cryptography.x509.load_der_x509_certificate(cert_bytes)


@dataclasses.dataclass
class CertificateEntry:
    alias: str
    timestamp: datetime
    certificate: Certificate


@dataclasses.dataclass
class KeyAndCertificatesEntry:
    alias: str
    timestamp: datetime
    certificates: list[Certificate]
    key: bytes  # PKCS8


def parse_jks(jks_path: str) -> list[CertificateEntry | KeyAndCertificatesEntry]:
    entries = []
    with open(jks_path, 'rb') as f:
        magic = next_int(f)
        version = next_int(f)
        assert magic == 0xfeedfeed
        assert version == 2

        num_entries = next_int(f)
        for entry in range(num_entries):
            entry_type = next_int(f)
            alias = next_string(f)
            timestamp = next_timestamp(f)
            if entry_type == 2:
                cert = next_cert(f)
                entries.append(CertificateEntry(alias, timestamp, cert))
            else:
                private_key_length = next_int(f)
                private_key = f.read(private_key_length)
                num_certs = next_int(f)
                certs = []
                for i in range(num_certs):
                    certs.append(next_cert(f))
                entries.append(CertificateEntry(alias, timestamp, certs, private_key))

    return entries


jks_entries = parse_jks(r"C:\Tools\java\jdk-17.0.1+12\lib\security\cacerts")
pprint(jks_entries)