How to read python RSA Pem key correctly?

Question

I want to read a RSA public key from database. I am using rsa python lib. public key is stored as a text.

when i print type of key and it value i get (var name is pk) ( print(type(pk), pk) ):

<class 'bytes'> b'-----BEGIN RSA PUBLIC KEY-----\\nMIIBCgKCAQEAmXSSnzrY2/z7zLZuF7KZZFP7mbmYEeRhpQsQfpEv4t/Fvz6/g5QO\\n79ZcGBd6wOxshGFSLYPAl1oB3GPNkwr+mdjqtSIXzhhvW9Xjjx4dIUVn7JrtsBXi\\nr7aG85HEYyk3LLBoWus9X+XJ/tiHlQzqY2o8+dO31X4HBeWzflczrNXN3ntGGf4S\\noAaqJKlkUSxdGexvJUhmli9x+CKQoojFHxHfq1IZldRMPb8O8N6RSZIA5t2n6vpw\\nGPx8tBm7Eub5nVi+sACHS6rLdAHcd+D4tBCjp9wp2dGu77/oRUI7aomRFRMmBf7/\\nZkHHzor2kGIZ3fYHEL7g+WkVsxqGXblG8QIDAQAB\\n-----END RSA PUBLIC KEY-----\\n'

but when i use

 pubkey = rsa.PublicKey.load_pkcs1(pk)

i get

File "/usr/local/lib/python3.11/site-packages/rsa/pem.py", line 77, in _pem_lines raise ValueError('No PEM start marker "%r" found' % pem_start) ValueError: No PEM start marker "b'-----BEGIN RSA PUBLIC KEY-----'" found

error all the time. Why is that? How to fix it?

I tried to make it work but no luck yet.

Answer 1

There are two issues with your code:

1. the PEM seems to be badly encoded, or it is altered during the encoding / decoding process. Due to this the newline character has gone from \n to \\n in the above binary string;
2. you're handling the string as a binary string input, where the escape is not turned into an actual newline.

To fix this directly in code you can insert the following line before your load_pkcs1 statement:

pk = pk.replace(b'\\n', b'\n').decode('ascii')

which should fix the encoding and unescape the newline characters.

Not sure if and why the PEM is stored as a binary string; the whole point of a PEM structure is that it is text instead of binary.