I have been given some Python code from the backend that decrypts some data. On my side, the Android app, I need to also decrypt it.
Here are some snippets of the Python code which I believe are the most relevant.
cipher = PKCS1_OAEP.new(privkey)
And this is the module that it comes from
from Crypto.Cipher import PKCS1_v1_5
from Crypto.Cipher import PKCS1_OAEP
Looking at the documentation for PKCS1_OAEP.new
https://www.dlitz.net/software/pycrypto/api/2.6/Crypto.Cipher.PKCS1_OAEP-module.html
And then comparing with the JavaDoc for Cipher https://docs.oracle.com/javase/6/docs/technotes/guides/security/StandardNames.html#Cipher
I deduced that this Python algorithm can be expressed as follows using the Java Cipher class (Note the code is in Kotlin)
val cipher = Cipher.getInstance("RSA/NONE/OAEPWithSHA1AndMGF1Padding", "BC")
Note that BC is the provider. I found out that BouncyCastle is popular and is included in the Android framework
So what is the error?
The backend returns me a 404 when the answer to the challenge is wrong. When I execute the Python code (which hits the same endpoints) it works. In terms of the POST request, I compared both and I am sending it in the correct way.
What would I like to know
Am I using the correct algorithm? I am trying to systematically cross out potential issues before moving onto another
Note that I also tried
val cipher = Cipher.getInstance("RSA/NONE/OAEPPadding", "BC")
