The crypto application
The purpose of the Crypto application is to provide an Erlang API to cryptographic functions, see crypto(3erl). Note that the API is on a fairly low level and there are some corresponding API functions available in public_key(3erl), on a higher abstraction level, that uses the crypto application in its implementation.
The current crypto implementation uses nifs to interface OpenSSLs crypto library and requires OpenSSL package version 0.9.8 or higher.
Source releases of OpenSSL can be downloaded from the OpenSSL project home page, or mirror sites listed there.