PGP and RSA protocols are the two widely used protocols in a number of servers and email applications for security with public/private key pair.

What is the difference between them? What other popular protocols are available?

  • 1
    GnuPG keypair using which system? GnuPG can use RSA.
    – muru
    Jun 9, 2016 at 21:13
  • For my OpenSSH server I have generated RSA key pair and for my thunderbird mail encryption I have used enigmail to generate PGP key pair, again the whole concept is confusing, difference between RSA key pair and SSH public private key pair, and again PGP public private key pair and GnuPG key pair
    – rancho
    Jun 9, 2016 at 21:20
  • 1
    PGP is a protocol, GPG implements that protocol. It can use RSA or something else, just like SSH can use ECDSA instead of RSA. security.stackexchange.com/questions/1750/…, security.stackexchange.com/questions/37581/… The question doesn't make any sense.
    – muru
    Jun 9, 2016 at 21:21

1 Answer 1


Using a car analogy:

  • PGP is a car
  • OpenPGP is the design for the PGP car
  • GnuPG is another car using the same design
  • RSA is a diesel engine, and other engines are available
  • SSH isn't a car at all. But it uses engines.

RSA is a public-key cryptosystem. That is, it is an algorithm for encrypting, decrypting and signing data using a set of two keys (the public key and private key).

PGP and GnuPG both offer the use of RSA for general purpose encryption and signing of data. They also offer other options, like Elgamal and DSA.

SSH uses RSA for authentication, not encryption. The server has your public key, and you have the private key, and SSH uses this fact to make sure you are, well, you. SSH also supports other keypairs, for example, ECDSA.

Further reading on the Information Security Stack Exchange:

And you should probably read What is the difference between SSL vs SSH? Which is more secure? as well.

  • I also like the analogy. But better compare OpenPGP with regulations for cars or something like this, nobody cares for how the car looks like nor how the requirements are achieved, as long as they match the rules. The same applies to software: the RFC/standards define a set of rules, but not propose any "software design" at all. Different OpenPGP implementations do things in very different ways.
    – Jens Erat
    Jun 11, 2016 at 18:13
  • @muru, So how is GnuPG different from PGP? What's the difference? | When Snowden says that "encrypting works", is he talking about PGP or RSA?
    – Pacerier
    Jan 31, 2018 at 14:54
  • Is OpenPGP a protocol like TLS?
    – Pacerier
    Jan 31, 2018 at 15:00

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