I'm taking a class in coding theory right now, and I've been surprised by how naturally it can be described using abstract algebra. There are also many deep relationships to important results in group theory. For example, the automorphism group of the binary Golay code (which was used during the Voyager missions to transmit pictures back to earth) is the Mathieu group M24, one of the sporadic groups from the classification of finite simple groups!<p><a href="https://en.wikipedia.org/wiki/Binary_Golay_code" rel="nofollow">https://en.wikipedia.org/wiki/Binary_Golay_code</a>