A short and sweet implementation of RSA in 64 lines of Erlang
(as counted by the "cloc" utility, which excludes blank lines
and comments).

After getting acquainted with Erlang in my programming languages
course and learning how RSA encryption works in an algorithms
course, I wanted to see how difficult it would be to combine the
two (simply as a fun exercise).

The program features concurrency, as it must generate two very
large prime numbers and does so in two separate threads.

As it uses modular arithmetic to check for primality, there is a
(very small) chance that it will instead generate a pseudo-prime
number instead of a prime number. This underscores the fact that
this is a "for fun" implementation, not meant for in-the-wild
security of any sort.

The particular primality test implemented is known as "Lagrange's
Little Theorem".

Compiling:

	$ erl -compile rsa

Running:

	$ erl -noshell -s rsa main -s init stop

The program will ask for a string message to be entered; the
message will be encrypted, decrypted and then printed on the
console. It will then exit.

Combined with a Base64 codec and a better primality test (such as
Agrawal, Kayal and Saxena's algorithm) this could be made to work
with professional RSA implementations, such as that used by
OpenSSH's connection negotiation RSA and others.

Written by Randy Sorensen in Spring of 2015.