Base91 Encoding

Question 1

What is Base91 encoding? (Definition)

Answer

Base91 (or BasE91) is a method of encoding binary data into printable characters developed to facilitate transmission via text channels (email, messaging, etc.).

Base91 is an alternative to Base64, using an expanded alphabet of 91 printable ASCII characters ranging from 0x21 to 0x7E, excluding the dash - (0x2D), the backslash \ (0x5C), and the apostrophe ' (0x27).

Question 2

How to encode using Base91?

Answer

Base91 encoding consists of grouping the bits of binary data into 13-bit blocks (i.e., 2^13 = 8192 possible values).

Each block is encoded as two symbols from the 91-character alphabet (91² = 8281 possible combinations).

Example: The string dCode is encoded as xJ,Jc,A in Base91.

The standard encoding table is:

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 decode Base91?

Answer

Base91 decoding involves performing the inverse operation of encoding.

Each pair of symbols is converted into a 13-bit integer value.

The bits are then reassembled to reconstruct the original bytes, which can be read according to the original text's encoding (ASCII, UTF-8, etc.).

Example: The message encoded in Base 91 RJ}G%wA 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

Why use Base91 instead of Base64?

Answer

Base91 provides a more compact representation of data than Base64 while remaining compatible with text communication channels.

It is therefore useful for optimizing the size of encoded messages in contexts where every byte counts (SMS transmission, text storage, etc.).

Question 6

When was Base91 invented?

Answer

Joachim Henke claims it was invented in 2005, see here

Base91 Encoding

Base 91 Decoder

Base 91 Encoder

Answers to Questions (FAQ)

What is Base91 encoding? (Definition)

How to encode using Base91?

How to decode Base91?

How to recognize BasE91 ciphertext?

Why use Base91 instead of Base64?

When was Base91 invented?

Source code

Cite dCode

Need Help ?

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	"