PostX: http://www.postx.com/docs/PostX_Product_Summary_and_Corp_Overview_v2.pdf
Jon Udell: How to forge an S/MIME signature: http://weblog.infoworld.com/udell/2004/03/23.html
http://crypto.stanford.edu/~dabo/courses/cs255_winter00/RSA.pdf
http://crypto.stanford.edu/~dabo/abstracts/ElGamalattack.html