ASCII

The American Standard Code for Information Interchange, or ASCII/US-ASCII, is a way for computers to encode symbols and characters via number codes. The standard version of ASCII includes 128 characters, including all letters of the English alphabet in both upper- and lower-case, the digits 0-9, and 33 'control codes' that are mostly obsolete holdovers from teletype machines. Each character is represented by a number from 0-127 (in decimal, although the system was commonly represented in binary, octal, or hexadecimal as well).

Background

See also: ASCII

ASCII was originally developed as a series of 7-bit teleprinter codes for Bell data services, with development taking place from May 1961 until its publication in 1963. From then, several updates to the standard were implemented, with the most significant updates (at least in terms of character list) occurring in 1965 and 1967.

In 1965, a change was proposed and approved, but not published, leading it to only be used by a select few IBM machines. The 1965 update would have primarily affected the standard's command codes, changing 22 out of the 33 codes' abbreviations to more suitable/descriptive ones. It also would have introduced several printable characters, including all lowercase English letters, and a few lesser-used punctuation marks, such as the tilde (~).

In 1967, a new update was actually published, following through on many of the changes proposed in the 1965 update. This meant that across all devices using ASCII, most command codes would have new abbreviations, and while the new characters were not all introduced with the same codes as the 1965 proposal, all but the Not Symbol (¬) did make it in.

In 1968, then president Lyndon B. Johnson issued a mandate that all computers used by the federal government had to be ASCII-compatible. Since there are many characters beyond the ASCII character set, there were many different code pages developed to define the upper 128 characters (with the lower 128 characters forming ASCII), known as Extended ASCII. The most popular of these was ISO 8859, which defined different codepages, such as Latin-1 (including diacritics for most Western European languages), Latin-2 (Central and Eastern European languages), Cyrillic, Greek, Arabic, and others. Alternative encodings were required to handle ideographs from East Asian languages like Chinese and Japanese kanji, as there are simply too many characters to fit a codepage with only 256 characters. This led to the development of UTF-8 and Unicode, a unified standard that aims to encode characters from every language, with UTF-8 being flexible enough to allow characters to be represented by anywhere between 1 and 4 bytes. Unicode overtook Windows-1252 (an extended ASCII codepage based on Latin-1) as the dominant character encoding by 2007.

The other major competitor for 8-bit character encodings at the time was EBCDIC, developed by IBM and used throughout the 1950's and 1960's on IBM machines.

Printable Character List

The following table contains all printable characters contained within the original, 7-bit ASCII model. It also shows the primary changes in character compositions between the three major updates in the 1960s.

Binary	Oct	Dec	Hex	Character
				1963	1965	1967
010 0000	040	32	20	space
010 0001	041	33	21	!
010 0010	042	34	22	"
010 0011	043	35	23	#
010 0100	044	36	24	$
010 0101	045	37	25	%
010 0110	046	38	26	&
010 0111	047	39	27	'
010 1000	050	40	28	(
010 1001	051	41	29	)
010 1010	052	42	2A	*
010 1011	053	43	2B	+
010 1100	054	44	2C	,
010 1101	055	45	2D	-
010 1110	056	46	2E	.
010 1111	057	47	2F	/
011 0000	060	48	30	0
011 0001	061	49	31	1
011 0010	062	50	32	2
011 0011	063	51	33	3
011 0100	064	52	34	4
011 0101	065	53	35	5
011 0110	066	54	36	6
011 0111	067	55	37	7
011 1000	070	56	38	8
011 1001	071	57	39	9
011 1010	072	58	3A	:
011 1011	073	59	3B	;
011 1100	074	60	3C	<
011 1101	075	61	3D	=
011 1110	076	62	3E	>
011 1111	077	63	3F	?
100 0000	100	64	40	@	`	@
100 0001	101	65	41	A
100 0010	102	66	42	B
100 0011	103	67	43	C
100 0100	104	68	44	D
100 0101	105	69	45	E
100 0110	106	70	46	F
100 0111	107	71	47	G
100 1000	110	72	48	H
100 1001	111	73	49	I
100 1010	112	74	4A	J
100 1011	113	75	4B	K
100 1100	114	76	4C	L
100 1101	115	77	4D	M
100 1110	116	78	4E	N
100 1111	117	79	4F	O
101 0000	120	80	50	P
101 0001	121	81	51	Q
101 0010	122	82	52	R
101 0011	123	83	53	S
101 0100	124	84	54	T
101 0101	125	85	55	U
101 0110	126	86	56	V
101 0111	127	87	57	W
101 1000	130	88	58	X
101 1001	131	89	59	Y
101 1010	132	90	5A	Z
101 1011	133	91	5B	[
101 1100	134	92	5C	\	~	\
101 1101	135	93	5D	]
101 1110	136	94	5E	↑	^
101 1111	137	95	5F	←	_
110 0000	140	96	60		@	`
110 0001	141	97	61		a
110 0010	142	98	62		b
110 0011	143	99	63		c
110 0100	144	100	64		d
110 0101	145	101	65		e
110 0110	146	102	66		f
110 0111	147	103	67		g
110 1000	150	104	68		h
110 1001	151	105	69		i
110 1010	152	106	6A		j
110 1011	153	107	6B		k
110 1100	154	108	6C		l
110 1101	155	109	6D		m
110 1110	156	110	6E		n
110 1111	157	111	6F		o
111 0000	160	112	70		p
111 0001	161	113	71		q
111 0010	162	114	72		r
111 0011	163	115	73		s
111 0100	164	116	74		t
111 0101	165	117	75		u
111 0110	166	118	76		v
111 0111	167	119	77		w
111 1000	170	120	78		x
111 1001	171	121	79		y
111 1010	172	122	7A		z
111 1011	173	123	7B		{
111 1100	174	124	7C	ACK	¬
111 1101	175	125	7D		}
111 1110	176	126	7E	ESC	|	~

Puzzle Application

ASCII art of a bird perched on a branch.

As an encryption method, ASCII is most commonly used just for its alphabet. However, unlike other codes, it has a much larger number range, both literally due to being represented by numbers 65 and over, and by virtue of of having two sets of letters to use, giving a total size of 52 values. This can be very helpful for puzzles that want to use an alphanumeric code but both can't get their numbers down to a 1-26 range and don't want to force solvers to modulo their results. Writers should still be careful, as unlike other alphanumeric codes, there are other characters surrounding both sets of letters, so any errors resulting in numbers outside of the 65-90 or 97-122 may still be interpreted as valid, even if they don't produce letters.

A less common use for ASCII is in ASCII Art, in which characters are types in a fixed-width font and arranged to form images on a larger scale. While this can be used as an actual solving element (see the Notable Examples below), it's more likely to appear as an artistic choice within a puzzle, or as a clue towards a general ASCII or computer-y theme/topic.

Strategy

Identification

A table of ASCII character and their code values (minus the unprintable command codes)

ASCII (as used to represent letters) is ultimately very similar to A1Z26, in that it only uses a series of increasing numbers in order to represent the alphabet. What makes it slightly more difficult is that there are two different sets of numbers that can stand for English letters, and therefore two ranges to remember as important. Most puzzles use the capital letters exclusively, meaning the numbers 65-90 are the most important to remember. Puzzles will rarely use just the lowercase letters, and are more likely to form full sentences using a mix of upper- and lower-case letters. In these cases, solvers will need to watch out for both 65-90 and 97-122, along with any punctuation that may be used like periods (46), commas (44), space (32), and possibly numbers (48-57).

Since ASCII is also an acronym, puzzles may clue it through that as well. Keep an eye out for phrases that could acronym to ASCII, or any sets of five words (titles, categories, etc.) that start with those letters.

Decryption

ASCII is a relatively easy code to decipher, as there are many sites available to translate all common code forms into the characters themselves. This makes the process much easier, and one of these sites should be a mainstay of any puzzle-solvers bookmarks. In case the internet is unavailable, the code can also be printed out in table format, or reduced to a simple pair of numbers to remember where the upper-case and lower-case letters begin. Keeping 65 and 97 in mind as A and a respectively can help vastly reduce the amount of memory dedicated to ASCII needed to solve most puzzles. It's also possible that binary or hexadecimal may be used to represent ASCII; in the common 8-bit representation (or 2 hexadecimal digits), it suffices to look at the last five bits and to then use A1Z26 to convert, as 65 and 97 are 01000001 and 01100001, respectively, with the other letters counting up from A/a.

Notable Examples

Played Straight

• Blather (MITMH 2007) (web) - A puzzle that showed a way to do things the long way with ASCII. Consisting entirely of strings of the word 'blather', this puzzle involved Click to revealcounting the number of letters in each string, converting that number to an ASCII character, and running the entire thing as a Java program.
• ASCII Characters (MITMH 2016) (web) - A rare case of ASCII art being a functional part of a puzzle. In this one, solvers are given a string of characters that Click to revealmust be converted to even-width font and arranged to the correct width in order to form images. Notably, each image can have part deleted and the rest arranged into another image, with this process happening multiple times for each.

Notable Twists

• Whoa -- I have a Migraine! (MITMH 2003) (web) - Uses ASCII characters...but not for art, or for any kind of encryption. Instead, it presents a set of text that Click to revealfunctions as a stereogram or Magic Eye image.
• Lost (MITMH 2004) (web) - Click to revealUsed Extended ASCII characters (specifically DOS line-drawing characters) to create a solvable maze. Doing so correctly lets solvers get their final answer from numbers hidden in the path.
• The Sun Will Come Out (MITMH 2015) (web) - This puzzle plays extensively with the binary values of ASCII characters, Click to revealusing an OR function to combine them into new characters (which is fitting as the puzzle also deals with words that contain the substring OR, like TOM[OR]ROW).

See Also

• Puzzles involving ASCII
• ASCII to Hex, an ASCII translator that includes Hexadecimal, Decimal, Binary, and Base 64 translations of ASCII characters, as well as a ROT13 translator.