Definition of "plaintext"

There are weak keys in the sense that their use by foisting chosen plaintexts can be proved, which could be interesting for chip cards with a ‘burnt-in key’.

2007, Reinhard Wobst, “Life After DES: New Methods, New Attacks”, in Angelika Shafir, transl., Cryptology Unlocked, John Wiley & Sons, Ltd, section 3 (IDEA: A Special-Class Algoritmh), subsection 5 (Cryptanalyzing IDEA), page 239