For all practical purposes, data has Redundancy. From redundancy, you can figure out which data record you are looking at. The attacking program would search for file headers, magic strings and the like to find the target data structure it is looking for.
For an attack against cipher keys it would also be highly useful to simply have a full dump of the target process image. Then simply use every 16/32 octet sequence in the image as a key candidate. This reduces an "impossible" (key space search) problem to a "20 minute problem".