Question

Erlang has a crypto function which generates public private keys (documentation copied below). However the documentation seems vague and I can’t find any example code that describes how to generate the shared prime number or the generator. Can someone post an example that generates a public/private key pair? Thanks in advance for any help!

dh_generate_key(DHParams) -> {PublicKey,PrivateKey} 
dh_generate_key(PrivateKey, DHParams) -> {PublicKey,PrivateKey} 

Types:
DHParameters = [P, G]
P, G = Mpint
Where P is the shared prime number and G is the shared generator.
PublicKey, PrivateKey = Mpint()
Generates a Diffie-Hellman PublicKey and PrivateKey (if not given).

Answer 1

You don’t generate the shared prime number or the generator for Diffie-Hellman. See:

http://en.wikipedia.org/wiki/Diffie-Hellman_key_exchange

The parameters P and G are agreed to ahead of time by both sides. Using the notation of the Wikipedia article, crypto:dh_generate_key is used for steps 2 & 3 to generate a/A & b/B, and then crypto:dh_compute_key is used for steps 4 & 5 to compute the shared secret s.

For RSA, I don’t know of a standard library function that generates a public/private key pair. Generating primes is a fairly involved algorithm from what I remember; I would strongly recommend you not try to code it yourself. Diffie-Hellman key pairs are not suitable for use with RSA; they are different algorithms intended for different purposes.

Generally you don’t need to generate these at runtime since you can reuse the key pair. You can use any number of other sources to actually generate it. (Maybe ssh-keygen would work? And there’s always OpenSSL.) To use the key pair you’ve created, you’d use the crypto:rsa_ public/private _ encrypt/decrypt functions.