The RSA and Diffie-Hellman protocols are part of asymmetric cryptography. But is there a word to distinguish between cryptosystem like RSA (i.e. there are two keys, one for encryption and another for decryption) and Diffie-Hellman (i.e. two parties have a public and private component that they share together to achieve shared key but finding private component will be useless if there is no one to share key with).

Essentially, I am trying to differentiate between key-exchange specific protocol vs. public-key cryptosystem.

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    If I understand you correctly (though, may be not) key exchange with RSA encryption is called key encryption and DH key exchange is called key agreement.
    – Crypt32
    Apr 18, 2017 at 6:48

2 Answers 2


RSA - is a way to encrypt/sign data. The protocol has data as input on the one end of the channel and the same data as output on the other end.

DH - is a way to generate keys. It takes no user data as input on any end of the channel. And it has a big random (not uniformly distributed) number as an output, the same on both ends.

Yes, RSA is often used to encrypt symmetric session keys, but it's only one way to use it. In that case keys are generated outside of RSA protocol, and are only transmitted via RSA.


I apologize if I am wrong, but I think, DH is only a key exchange protocol and has nothing to do with encryption. I think the public and private components are confusing you. Please understand that the public and private pairs, give rise to the same pair of keys at both end, hence, the encryption that follows, is symmetric and not asymmetric since, both the parties have same keys.

On the other hand RSA is an asymmetric encryption technique, where both the keys are mathematical inverse of each other.

I hope I was able to differentiate both the techniques clearly.

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