Base91 Encoding

Question 1

What is Base91 encoding? (Definition)

Answer

Base91 (or BasE91) is an alternative to base64 but with an expanded alphabet to 91 characters: the 94 printable ASCII characters (from 0x21 to 0x7E) omitting -: dash (0x2D), \: backslash (0x5C) and ': apostrophe (0x27). It allows any binary data to be encoded into a character string composed only of printable characters (and therefore transmissible via text messaging, etc.)

Question 2

How to encrypt using Base91 cipher?

Answer

Base91 encoding splits data into 13-bit binary packets (ie 2 ^ 13 = 8192 values) which are then encoded in 2 letters of the alphabet (which contains 91 characters and 91 ^ 2 = 8281).

Example: DCODE string is coded xJ,Jc,A in Base91

The symbols used by the base are :

0	A	1	B	2	C	3	D	4	E	5	F	6	G	7	H	8	I	9	J	10	K	11	L	12	M
13	N	14	O	15	P	16	Q	17	R	18	S	19	T	20	U	21	V	22	W	23	X	24	Y	25	Z
26	a	27	b	28	c	29	d	30	e	31	f	32	g	33	h	34	i	35	j	36	k	37	l	38	m
39	n	40	o	41	p	42	q	43	r	44	s	45	t	46	u	47	v	48	w	49	x	50	y	51	z
52	0	53	1	54	2	55	3	56	4	57	5	58	6	59	7	60	8	61	9	62	!	63	#	64	$
65	%	66	&	67	(	68	)	69	*	70	+	71	,	72	.	73	/	74	:	75	;	76	<	77	=
78	>	79	?	80	@	81	[	82	]	83	^	84	_	85	`	86	{	87	\|	88	}	89	~	90	"

Question 3

How to decrypt Base91 cipher?

Answer

The decryption performs the inverse conversion to base 91.

To simplify, the message is split into groups of 2 letters which are converted into 13-bit data. The message is then read with the original encoding (ASCII or Unicode).

Example: The message encoded in Base 91 xJ,Jc,A is decoded in DCODE.

Question 4

How to recognize BasE91 ciphertext?

Answer

The message is composed only of printable ASCII characters (except dash, backslash and apostrophe) that is 91 characters maximum.

Base91 encoded messages are on average 23% longer than the original message.

The author writes his code basE91 (with a capital E)

Question 5

When Base91 have been invented?

Answer

Joachim Henke claim it was invented in 2005, see here (link)

Base91 Encoding

Base 91 Decoder

Base 91 Encoder

Answers to Questions (FAQ)

What is Base91 encoding? (Definition)

How to encrypt using Base91 cipher?

How to decrypt Base91 cipher?

How to recognize BasE91 ciphertext?

When Base91 have been invented?

Source code

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Questions / Comments

0	A	1	B	2	C	3	D	4	E	5	F	6	G	7	H	8	I	9	J	10	K	11	L	12	M
13	N	14	O	15	P	16	Q	17	R	18	S	19	T	20	U	21	V	22	W	23	X	24	Y	25	Z
26	a	27	b	28	c	29	d	30	e	31	f	32	g	33	h	34	i	35	j	36	k	37	l	38	m
39	n	40	o	41	p	42	q	43	r	44	s	45	t	46	u	47	v	48	w	49	x	50	y	51	z
52	0	53	1	54	2	55	3	56	4	57	5	58	6	59	7	60	8	61	9	62	!	63	#	64	$
65	%	66	&	67	(	68	)	69	*	70	+	71	,	72	.	73	/	74	:	75	;	76	<	77	=
78	>	79	?	80	@	81	[	82	]	83	^	84	_	85	`	86	{	87	\|	88	}	89	~	90	"

0	A	1	B	2	C	3	D	4	E	5	F	6	G	7	H	8	I	9	J	10	K	11	L	12	M
13	N	14	O	15	P	16	Q	17	R	18	S	19	T	20	U	21	V	22	W	23	X	24	Y	25	Z
26	a	27	b	28	c	29	d	30	e	31	f	32	g	33	h	34	i	35	j	36	k	37	l	38	m
39	n	40	o	41	p	42	q	43	r	44	s	45	t	46	u	47	v	48	w	49	x	50	y	51	z
52	0	53	1	54	2	55	3	56	4	57	5	58	6	59	7	60	8	61	9	62	!	63	#	64	$
65	%	66	&	67	(	68	)	69	*	70	+	71	,	72	.	73	/	74	:	75	;	76	<	77	=
78	>	79	?	80	@	81	[	82	]	83	^	84	_	85	`	86	{	87	\|	88	}	89	~	90	"

0	A	1	B	2	C	3	D	4	E	5	F	6	G	7	H	8	I	9	J	10	K	11	L	12	M
13	N	14	O	15	P	16	Q	17	R	18	S	19	T	20	U	21	V	22	W	23	X	24	Y	25	Z
26	a	27	b	28	c	29	d	30	e	31	f	32	g	33	h	34	i	35	j	36	k	37	l	38	m
39	n	40	o	41	p	42	q	43	r	44	s	45	t	46	u	47	v	48	w	49	x	50	y	51	z
52	0	53	1	54	2	55	3	56	4	57	5	58	6	59	7	60	8	61	9	62	!	63	#	64	$
65	%	66	&	67	(	68	)	69	*	70	+	71	,	72	.	73	/	74	:	75	;	76	<	77	=
78	>	79	?	80	@	81	[	82	]	83	^	84	_	85	`	86	{	87	\|	88	}	89	~	90	"