Identifiable parent property (IPP) code[1] 

A code that is embedded in copyrighted content in order to detect unauthorized redistribution of said content by pirates. IPP codes are designed to detect pirates even when segments content are mixed together so as to conceal the pirates' identities.

A unique codeword of an IPP code is hidden into each copy of the content (say, a movie or videogame) such that reselling a copy would expose the seller as a pirate.

To overcome this, a coalition of \(t\) pirates can mix their copies together so as to obfuscate their identities. The descendant bit-string corresponding to the new mixed copy therefore contains subsets of codeword coordinates of the copies that were used in the mixing.

More technically, let \(B=\{c_1 \cdots c_t\}\) be a subset of \(t\) IPP codewords, corresponding to the copies of the pirate coalition. Then, \(a\) is called a descendant of \(B\) if every coordinate of \(a\) also exists as a coordinate (in the same position) of at least one of the codewords in \(B\). In other words, for all coordinates \(i\), we require that \(a_i = c_i\) and some \(c \in B\).

A \(t\)-IPP code has the ability that, given any descendent, a parent codeword can always be identified by examining all possible \(t\)-subsets of the code [2].