CODEWITHSUNDEEP
cryptographyrsasecure-coding
sosig
sosig

Reputation: 13

RSA two-way decryption?

I've been experimenting with RSA encryption in python (cryptography.hazmat.primitives.asymmetric). I have the following setup: On one end is the client with the public key sending encrypted data back to the server, which holds the private key. Right now I've got one-directional encryption working, but I'm wondering how you would (or if you should) securely decrypt a message client-side. I thought about just encrypting the private key and storing it, but then the password would appear in the code and expose the key to compromise. Is there a way to securely implement this with a key exchange? Or--the most likely alternative--is this a misuse of the protocol?

EDIT: Wanted to clarify that the possible concerns here would be that using RSA in this way might expose the private key on the file system or between the server and the client.

Upvotes: 1

Views: 1068

Answers (1)

Chris Dodd
Chris Dodd

Reputation: 126110

The normal way is for the server to encrypt the reply with the client's public key and client decrypt with its private key. This requires TWO RSA keypairs -- one for the client and one for the server, and requires each end to know the other's public key.

This need (along with high cost of PKE compared to symmetric encryption) is why PKE is normally only used for authentication and/or key exchange, and a symmetric cipher is used to actually encrypt traffic.

Upvotes: 5

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