RSA key format is not supported for python

Question

from Crypto.PublicKey import RSA

pub_key = """
-----BEGIN PGP PUBLIC KEY BLOCK-----
mykeyhere
-----END PGP PUBLIC KEY BLOCK-----
"""

public_key_object = RSA.importKey(pub_key)

This throws the following error - RSA key format is not supported

This is a public PGP key generated with RSA-4096 encryption. I am curious why this library could be throwing errors. Could there be invalid characters in the key? Doesn't look like there are any , no forward slashes or whatnot.

@AKX pycryptodome.readthedocs.io/en/latest/src/public_key/rsa.html — asojidaiod
– asojidaiod, Commented Sep 14, 2020 at 14:30
Well, have you tried .strip() on the key data? As it is, it will now contain a leading and trailing newline. — AKX
– AKX, Commented Sep 14, 2020 at 14:37
Well, if it helps, you can see the heuristics over here: github.com/Legrandin/pycryptodome/blob/master/lib/Crypto/… It doesn't look like PGP PUBLIC KEYs are explicitly supported; the key.export_key('PEM') call linked in the docs you paste generates a -----BEGIN RSA PRIVATE KEY----- key. — AKX
– AKX, Commented Sep 14, 2020 at 14:43

Maarten Bodewes · Accepted Answer · 2020-09-14 21:17:32Z

1

For PGP you need a PGP specific library. PGP, at least for the public keys, uses it's own defined format. If you look at your cryptographic library then you will find this nugget:

The following formats are supported for an RSA public key:

X.509 certificate (binary or PEM format)
X.509 subjectPublicKeyInfo DER SEQUENCE (binary or PEM encoding)
PKCS#1 RSAPublicKey DER SEQUENCE (binary or PEM encoding)
An OpenSSH line (e.g. the content of ~/.ssh/id_ecdsa, ASCII)

So the PGP key format is not supported, only X.509 keys (the certificate contains the subject public key which contains a PKCS#1 public key if RSA is used, like a Matrushka doll) and OpenSSH keys.

Here is the first library that I found: py-pgp, which includes:

from pgp import read_key
key = read_key(data)

for "transferable" keys, which I presume are public keys.

answered Sep 14, 2020 at 21:17

Maarten Bodewes

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President James K. Polk Over a year ago

Also a PGP public key is not necessarily an RSA key at all.

Zach · Accepted Answer · 2023-02-02 17:41:13Z

0

try python-gnupg. it takes care of everything for you

pycryptodome is a low level library. we are free to pick and choose the type of key and cipher over there but we use it only if we know what we are doing ^_^

answered Feb 2, 2023 at 17:41

Zach

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