How to convert a PEM public key to a JWK and back in Python

1import json
2 
3from cryptography.hazmat.primitives.asymmetric import ec, ed25519, rsa
4from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat, load_pem_public_key
5from jwt.algorithms import ECAlgorithm, OKPAlgorithm, RSAAlgorithm  # PyJWT, with "pyjwt[crypto]"
6 
7 
8def pem_to_jwk(pem: bytes) -> dict:
9    key = load_pem_public_key(pem)
10    if isinstance(key, ec.EllipticCurvePublicKey):
11        return ECAlgorithm.to_jwk(key, as_dict=True)
12    if isinstance(key, rsa.RSAPublicKey):
13        return RSAAlgorithm.to_jwk(key, as_dict=True)
14    if isinstance(key, ed25519.Ed25519PublicKey):
15        return OKPAlgorithm.to_jwk(key, as_dict=True)
16    raise TypeError(f"unsupported key type {type(key).__name__}")
17 
18 
19def jwk_to_pem(jwk: dict) -> bytes:
20    algorithm = {"EC": ECAlgorithm, "RSA": RSAAlgorithm, "OKP": OKPAlgorithm}[jwk["kty"]]
21    key = algorithm.from_jwk(jwk)  # rejects points that are not on the curve
22    return key.public_bytes(Encoding.PEM, PublicFormat.SubjectPublicKeyInfo)

1with open("pub.pem", "rb") as f:
2    jwk = pem_to_jwk(f.read())
3print(json.dumps(jwk))
4with open("out.jwk.json", "w") as f:
5    json.dump(jwk, f)
6 
7with open("pub.jwk.json") as f:
8    pem = jwk_to_pem(json.load(f))
9print(pem.decode(), end="")
10with open("out.pem", "wb") as f:
11    f.write(pem)
12 
13with open("ed25519.pem", "rb") as f:
14    print(json.dumps(pem_to_jwk(f.read())))