etymologyexpressionsidioms
The phrase "on the up-and-up" means "legitimate" or "legal" or "reputable" or, to use another idiom, "above-board". For instance:
Although Pete didn't look like a city official, Joe assumed his offer to sell the Brooklyn Bridge was totally on the up-and-up.
Where does this expression come from?
Related: What does “We don’t do anything that’s not completely up and up” mean?
Citing Picturesque Expressions by Laurence Urdang, Facts on File Dictionary of Clichés (p.317), and the OED, Ken Greenwald had this comprehensive explanation of the phrase at Wordwizard:
PART AND PARCEL means essential portion or element, integral part, a vital part of a larger entity. <“Traveling was part and parcel of his sales position.”>. In this reduplicative phrase (repetition of an element), which has been common since the 14th century, the nouns ‘part’ and ‘parcel’ are synonyms and have been since the 14th century, ‘part’ being the older word (11th century) and ‘parcel’ (14th century) the newer. The alliteration and tautology/redundancy in the expression serve to emphasize the importance of a constituent to the whole. The expression has been used as a legal term from the mid-16th century on, principally for clauses of a law and for parts of a landholding. It didn’t start to be used in its present figurative sense until about 1800. ‘Part or parcel’ and ‘part nor parcel’ have also been used since the 16th century.
Earliest reference from OED:
1535-6 ‘Act 27 Henry VIII,’ c. 11 “This present Act, and euery PART AND PARCEL therof, shall extend [etc.]. Ibid. c. 26 The. . . . Lordships . . . to be PART AND PARCELL of the same hundred [of Wesebery].”
Earliest I can find via Google Books (from A Christian Directorie Guiding Men to Their Salvation, 1585):
The standard expression is cut and dried, though usages such as That's pretty cut and dry have started to appear more in recent decades, as this NGram shows.
It's a metaphoric reference to grass/hay/herbs/etc. being cut, dried, and thus ready for sale/use (nothing more needs to be done). By extension it comes to mean no more discussion needs to take place. By further extension, no decision or thought is required at all (the ordinary default suffices).
OP's example isn't a very appropriate one. Most people would say the rule was clear-cut (overt, explicit, unambiguous), not cut and dried (fully decided upon, finalised, settled).
Best Answer
Apparently its origin isn't clear. Grammarist.com reports:
The article then provides three citations for the first meaning, dated 1929, 1937, 1938, and one 1949 citation for the latter meaning. Merriam-webster.com says “First Known Use of UP-AND-UP 1863” for the meaning “an honest or respectable course”, but gives no citations. Languagehat.com has numerous comments on the two different meanings, but nothing about etymology; and Geoffrey Nunberg uses “on the up and up” as an example of a phrase that many people use one way, and many another, with people in either group not knowing of the other.