Columnar transposition

The keyword's letters number the columns by alphabetical order, the text fills the grid row by row, and the ciphertext is the columns read in that order. Every character is a cell, spaces too, so decode(encode(x)) is x for any input. Textbook vectors drop the spaces and punctuation before filling the grid, and stripNonAlpha: true does that for you. key is required.

const columnar = create("columnar");
columnar.encode("ATTACK AT DAWN", { key: "ZEBRA" }).text; // "C TAWT AATNAKD"
columnar.decode("C TAWT AATNAKD", { key: "ZEBRA" }).text; // "ATTACK AT DAWN"
columnar.encode("WE ARE DISCOVERED. FLEE AT ONCE", { key: "ZEBRAS", stripNonAlpha: true }).text; // "EVLNACDTESEAROFODEECWIREE"

Repeated letters in the key are ordered left to right. This is also the second step of the historical ADFGVX.

Columnar is the one cipher with state. The instance keeps an LRU cache of its last 128 answers, so asking the same thing twice costs nothing. Nothing caps how often you call it, which matters when a loop tries thousands of candidate keys.