Generate JWT token signed with RSA key in python

Question

I am trying to convert this java code for generating JWT token in python.

String privateKeyContent = privateKey
    .replaceAll(Definitions.ApiGeneral.LINE_BREAKER, "")
    .replace(Definitions.AuthProperty.PRIVATE_KEY_START, "")
    .replace(Definitions.AuthProperty.PRIVATE_KEY_END, "");

PKCS8EncodedKeySpec keySpecPKCS8 = new PKCS8EncodedKeySpec(Base64.getDecoder().decode(privateKeyContent));

KeyFactory kf = KeyFactory.getInstance(Definitions.AuthProperty.RSA_KEY_FACTORY);
PrivateKey privKey = kf.generatePrivate(keySpecPKCS8);

String jwtAudUrl = System.getenv(Definitions.IamProperty.IAM_URL_KEY) + System.getenv(Definitions.IamProperty.JWT_AUD_URI_KEY);
String jwtToken = Jwts.builder()
    .setAudience(jwtAudUrl)
    .setSubject(serviceId)
    .setIssuer(serviceId)
    .setExpiration(new Date(new Date().getTime() + TimeUnit.MINUTES.toMillis(Definitions.AuthProperty.JWT_TOKEN_EXPIRY_IN_MINUTES)))
    .signWith(privKey)
    .compact();

Python:

import jwt

serviceID = "abc"
secret = '-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----'

due_date = datetime.now() + timedelta(minutes=10)
header = {"alg": "RS256"}
expiry = int(due_date.timestamp())
payload = {"iss": serviceID, "sub": serviceID, "exp": expiry, "aud": iam_url + "/oauth2/access_token"}

priv_rsakey = serialization.load_pem_private_key(secret.encode('utf8'), password=None, backend=default_backend())
token=jwt.encode(payload, priv_rsakey, algorithm='RS256')

However, I keep on getting this error :

ValueError: ('Could not deserialize key data. The data may be in an incorrect format, it may be encrypted with an unsupported algorithm, or it may be an unsupported key type (e.g. EC curves with explicit parameters).', [_OpenSSLErrorWithText(code=503841036, lib=60, reason=524556, reason_text=b'error:1E08010C:DECODER routines::unsupported')])

Can someone please help me with this ?

Topaco · Accepted Answer · 2022-05-05T08:12:43.080

The issue is precisely identified in the error message: Your private key is incorrectly formatted. A PEM encoded key consists of the Base64 encoded body, which contains a line break after every 64 characters, and a header and footer on separate lines. Your key is missing the line breaks.

load_pem_private_key() expects at least header and footer on separate lines, but is tolerant about line breaks in the body, i.e. they are optional. So you have to pass your key e.g. like this:

secret = '-----BEGIN RSA PRIVATE KEY-----\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\n-----END RSA PRIVATE KEY-----'

or

secret = '''-----BEGIN RSA PRIVATE KEY-----
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
-----END RSA PRIVATE KEY-----'''

With this change the code works (after adding the missing iam_url and the missing import statements).

Note that PKCS8EncodedKeySpec in the Java code expects a DER encoded private key in PKCS#8 format, while in the Python code a PEM encoded private key in PKCS#1 format is applied.

A DER encoded key results from a PEM encoded key by removing header, footer and all line breaks, and Base64 decoding the rest. The Cryptography library supports the import of a DER encoded private key with load_der_private_key():

import base64
secret = base64.b64decode('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') 
priv_rsakey = serialization.load_der_private_key(secret, password=None, backend=default_backend())

load_pem_private_key() and load_der_private_key() support both PKCS#8 and PKCS#1 format.

Thanks so much! This worked. But still, when I am trying to generate an access token from JWT token, I am getting this error - "Jwt token is not in the proper format or contains invalid characters" — student, May 05 '22 at 16:21
@student - The Python and Java code produce *fully equivalent* tokens, assuming the *same* data for *aud*, *sub*, *iss*, and *exp* and the *same* private key. So if a JWT generated with the Java code works, but one generated with the Python code does not, it is due to different data or different keys. Currently, your question is missing the information to answer this. Therefore, for further analysis, please edit your question and post two JWTs, one created with the Java code and one created with the Python code, so that both can be compared. — Topaco, May 05 '22 at 18:01
I have made the edits. The error I am getting with python JWT is : JWT has expired or is not valid — student, May 05 '22 at 19:08
This is possibly due to the `exp` value. Check this value and adjust the time offset if necessary. — Topaco, May 06 '22 at 05:18

Generate JWT token signed with RSA key in python

1 Answers1