JWKS parsing

jwks2asn1.py

#!/usr/bin/env python3
#
# openssl asn1parse -noout -out private_key.der -genconf <(python jwks2asn1.py private_key.json)
# openssl rsa -in private_key.der -inform der > private_key.pem
#
# rfc7517.3 : urlsafe_b64decode
# rfc7517.A.1 : ints are big-indian
#

import base64
import dataclasses
import json
import operator
import pathlib
import sys


@dataclasses.dataclass
class Jwks:
    n: int
    e: int
    d: int
    p: int
    q: int
    dp: int
    dq: int
    qi: int

    def __post_init__(self):
        for field in dataclasses.fields(self):
            name, type_ = field.name, field.type
            value = getattr(self, name)
            if not isinstance(value, type_):
                if isinstance(value, str):
                    value = base64.urlsafe_b64decode(f"{value}==")
                if isinstance(value, bytes):
                    value = int.from_bytes(value, byteorder="big")
                setattr(self, name, type_(value))

    @classmethod
    def from_jwks(cls, jwks_file: pathlib.Path):
        fields = (_.name for _ in dataclasses.fields(cls))
        return cls(*operator.itemgetter(*fields)(json.loads(jwks_file.read_text())))

    def asasn1(self):
        prefix = [
            "asn1=SEQUENCE:private_key",
            "[private_key]",
            "version=INTEGER:0",
        ] + [
            f"{field.name}=INTEGER:0X{getattr(self, field.name):X}"
            for field in dataclasses.fields(self)
        ]
        return "\n".join(prefix)


print(Jwks.from_jwks(pathlib.Path(sys.argv[1])).asasn1())

tiny_jwks2asn1.py

#!/usr/bin/env python3
#
# openssl asn1parse -noout -out private_key.der -genconf <(python tiny_jwks2asn1.py private_key.json)
# openssl rsa -in private_key.der -inform der > private_key.pem
#
# rfc7517.3 : urlsafe_b64decode
# rfc7517.A.1 : ints are big-indian
#

import base64
import json
import pathlib
import sys


asn1_header = ["asn1=SEQUENCE:private_key", "[private_key]", "version=INTEGER:0"]
fields = ("n", "e", "d", "p", "q", "dp", "dq", "qi")


def parse(value: str) -> int:
    data = base64.urlsafe_b64decode(f"{value}==")
    return int.from_bytes(data, byteorder="big")


jwks = json.loads(pathlib.Path(sys.argv[1]).read_text())
print(
    "\n".join(
        asn1_header + [f"{field}=INTEGER:0X{parse(jwks[field]):X}" for field in fields]
    )
)