Base64 and base64url

Base64 Code Introduction

First ,Base64 It's a way of encoding , Instead of real encryption . Even if ,Base64 It is only used as a simple “ encryption ” To protect some data , Real encryption is usually cumbersome .

Base64 Use 64 A common printable character to store and represent binary word data , At the same time, simple encryption can also be carried out , Generate unreadable text .Base64 The character set includes large 、 Small letters , Arabic numerals 0-9, as well as "+“ and ”/“, And suffixed ”=“ total 65 Characters , Among them, only the former 64 individual . How to use this 64 Characters to represent binary data ？ This needs to be in decimal 0 To 63 And the use of 64 Establish a one-to-one correspondence between characters . The specific mapping is decimal 0 To 63 And, in turn, "A-Z”, “a-z”, “0-9”, “+”, "/" One-to-one correspondence . In the computer 64 One possibility only needs 6bits Can express （26=64）, therefore Base64 The expression is essentially based on 6bits In units of , Use the specified general character set to represent and store binary data .

Base64 Encoding table

Code value	character	Code value	character	Code value	character	Code value	character
0	A	16	Q	32	g	48	w
1	B	17	R	33	h	49	x
2	C	18	S	34	i	50	y
3	D	19	T	35	j	51	z
4	E	20	U	36	k	52	0
5	F	21	V	37	l	53	1
6	G	22	W	38	m	54	2
7	H	23	X	39	n	55	3
8	I	24	Y	40	o	56	4
9	J	25	Z	41	p	57	5
10	K	26	a	42	q	58	6
11	L	27	b	43	r	59	7
12	M	28	c	44	s	60	8
13	N	29	d	45	t	61	9
14	O	30	e	46	u	62	+
15	P	31	f	47	v	63	/

Using tools http://www.lzltool.com/base64 It can be parsed online Base64, take Base64 Convert to string or hexadecimal 、 or Base64Url Format

Base64URL Code Introduction

Due to the standard Base64 Characters... May appear after encoding + and /, stay URL Can't be used as a parameter directly , So there is another kind of "url safe" Of base64 code , In fact, it is to put characters + and / Become respectively - and _
because = Characters can also appear in Base64 In the encoding , but = Use in URL、Cookie There's ambiguity in it , therefore ,Base64URL After coding, it will put = Get rid of
Get rid of = How to decode after ？ because Base64 It's a 3 Bytes become 4 Bytes , therefore ,Base64 The length of the code is always 4 Multiple , therefore , Need to add = hold Base64 The length of the string becomes 4 Multiple , It can be decoded normally .

Using tools http://www.lzltool.com/base64url It can be parsed online Base64URL, take Base64URL Convert to string or hexadecimal 、 or Base64 Format