How do bcprov and bcprov-ext differ?

Question

I noticed that there are two bouncycastle provider libraries for Java; bcprov and bcprov-ext. How do they differ? How do I choose which to use?

Answer 1

bcprov is typically the library you want.

bcprov-ext includes some obscure crypto algorithms that haven't been part of the main release since v1.4.0.

This is briefly explained on the latest releases page:

From release 1.40 some implementations of encryption algorithms were removed from the regular jar files at the request of a number of users. Jars with names of the form *-ext-* still include these (at the moment the list is: NTRU).

NTRU seems to be this algorithm. Personally I'd never heard of it before...