What is "chiasmus"

Chiasmus \Chi*as"mus\ (k[-i]*[a^]z"m[u^]s), n. [NL., fr. Gr. chiasmo`s a placing crosswise, fr. chia`zein. See Chiasm.] (Rhet.) An inversion of the order of words or phrases, when repeated or subsequently referred to in a sentence; thus,

If e'er to bless thy sons My voice or hands deny, These hands let useful skill forsake, This voice in silence die.
--Dwight.

in grammar, inversion of word order, 1871, Latinized from Greek khiasmos "a placing crosswise, diagonal arrangement" (see chi).\n\nAdam, first of men,\n
To first of women, Eve.\n
["Paradise Lost"] \n

n. (context rhetoric English) An inversion of the relationship between the elements of phrases.

1. n. inversion in the second of two parallel phrases

2. [also: chiasmi (pl)]

In rhetoric, chiasmus, or less commonly chiasm, (Latin term from Greek χίασμα, "crossing", from the Greek χιάζω, chiázō, "to shape like the letter Χ") is the figure of speech in which two or more clauses are related to each other through a reversal of structures in order to make a larger point; that is, the clauses display inverted parallelism. Chiasmus was particularly popular in the literature of the ancient world, including Hebrew, Greek, and Latin, where it was used to articulate the balance of order within the text. As a popular example, many long and complex chiasmi have been found in Shakespeare and the Greek and Hebrew texts of the Bible. It is also found throughout the Quran and the Book of Mormon.

Today, chiasmus is applied fairly broadly to any "criss-cross" structure, although in classical rhetoric it was distinguished from other similar devices, such as the antimetabole. In its classical application, chiasmus would have been used for structures that do not repeat the same words and phrases, but invert a sentence's grammatical structure or ideas. The concept of chiasmus on a higher level, applied to motifs, turns of phrase, or whole passages, is called chiastic structure.

The elements of simple chiasmus are often labelled in the form A B B A, where the letters correspond to grammar, words, or meaning. For example John F. Kennedy said, "ask not what your country can do for you; ask what you can do for your country".

Chiasmus is a secret German government block cipher that was leaked by reverse engineering. It became notorious for its dilettant use in the BSI's software GSTOOL, which used it in insecure Electronic Codebook (ECB) mode and generated the key with a pseudo random number generator initialized to the current system time, which means an effective key length that can easily be broken by brute force. The BSI tried to prevent the publication of these findings with legal threats.

Chiasmus seems to be resistant against the most common cryptographic attacks (linear and differential cryptanalysis), but a lot slower than the openly available state of the art ciphers such as AES.