Here is a quick summary,

an exerpt of a summary, based on Ayn Rand's essay The Objectivist Ethics, from The Virtue of Selfishness:

...[W]hen one speaks of man's right to exist for his own sake, for his own rational self-interest, most people assume automatically that this means his right to sacrifice others. Such an assumption is a confession of their own belief that to injure, enslave, rob or murder others is in man's self-interest--which he must selflessly renounce. The idea that man's self-interest can be served only by a non-sacrificial relationship with others has never occurred to those humanitarian apostles of unselfishness, who proclaim their desire to achieve the brotherhood of men. And it will not occur to them, or to anyone, so long as the concept "rational" is omitted from the context of "values," "desires," "self-interest" and ethics." (30-31) "The principle of trade is justice." (31) People should earn what they get, not take it undeserved, and not give anything to anyone else who is undeserving. "To love is to value. ... The man who does not value himself cannot value anything or anyone." (32)

Emphasis mine. I'm not sure if the page numbers refer to the paperback or the hardcover, I don't have my copy with me.

Ayn Rand almost makes "selfishness" synonymous with "morality". But only if it is truly rational. And the key to rationality isn't only the ability to use formal propositional logic, though that's very important, but to have the words and concepts that you use refer to aspects of reality (as best you can).