Perform elliptic-curve Diffie-Hellmann key exchange over Curve25519 on the commandline.

go get -u github.com/ansemjo/curvekey

Generate a new key:

$ curvekey new -k my.sec -p my.pub

Obtain a peer's public key and obtain a shared secret:

$ curvekey dh -p peer.pub -k my.sec
shared secret:
  edSr8Lko65qj4wk62S8/31iex4FFGDJyD5AAB9pjnq4=

Your partner can obtain the same secret with his secret key:

$ curvekey dh -p my.pub -k peer.sec
shared secret:
  edSr8Lko65qj4wk62S8/31iex4FFGDJyD5AAB9pjnq4=

For an ephemeral key omit the secret key:

$ curvekey dh -p peer.pub
shared secret:
  MblUjj06Rh8Q/V0HoPl6nrFavXmCEuHChG5HM0hdnJ4=
ephemeral public key:
  Emqq9yeFdhhspTW6aldqWWXSOpLxHDL4kVZUqMlKYAE=

Transmit the ephemeral public key to your peer:

$ curvekey dh -k peer.sec -p Emqq9yeFdhhspTW6aldqWWXSOpLxHDL4kVZUqMlKYAE=
shared secret:
  MblUjj06Rh8Q/V0HoPl6nrFavXmCEuHChG5HM0hdnJ4=

Consult the command help at any time:

$ curvekey --help
$ curvekey help shared
...

Other usage examples and scenarios can be found in examples:

• password-based keys generated with ansemjo/stdkdf

This is unauthenticated Diffie-Hellmann. You should

• transmit your public keys over secure channels
• post them at a public place controlled by you
• verify their integrity over a second channel
• sign them by other means, e.g. GnuPG

Otherwise you may be susceptible to a man-in-the-middle attack.

And anyway: this was mainly intended as a thought experiment and another fun commandline tool to go with ansemjo/stdkdf and ansemjo/aenker. Do not rely on this.

Copyright (c) 2018 Anton Semjonov Licensed under the MIT License