What is Base64? (Cryptography Cipher)


Base64 is a cipher (without key and reversible) that converts (encode) a data (message) in 64 characters of the ASCII string.

Decoder / Encoder

See also the Google encoder/decoder


  • for datastore that accepts only ASCII string format
  • to have a portable version of the data between systems. ie get rid of:
  • having data encoded on only 64 characters (ie without the point for instance)

Example: base64 is used in the basic authentication scheme to encode the value.



A text message with only string

  • Transform the text into binary data by applying the character set table conversion
  • Transform the binary into a succession of characters with the alphabet conversion table
  • add the optional trailing character =
  • and you get the base64 cipher


The decode steps are the same as the encode steps but in reverse. You need to use the encoded character as input.


A base64 value has the following format:



  • base64Conversion is the conversion when the alphabet conversion is applied
  • = is one or several optional trailing character


The alphabet is the conversion table between binary data (base 2) and its equivalent:

base64url (base64 for URL) replaces:

  • the + with -
  • and / with _

because + and / are reserved characters in a URL

Binary Number Base 64 Number Character Base64 Character Base64Url
0000 0 A A
0001 1 B B
0010 2 C C
0011 3 D D
0100 4 E E
0101 5 F F
0110 6 G G
0111 7 H H
1000 8 I I
1001 9 J J
1010 10 K K
11 L L
12 M M
13 N N
14 O O
15 P P
16 Q Q
17 R R
18 S S
19 T T
20 U U
21 V V
22 W W
23 X X
24 Y Y
25 Z Z
26 a a
27 b b
28 c c
29 d d
30 e e
31 f f
32 g g
33 h h
34 i i
35 j j
36 k k
37 l l
38 m m
39 n n
40 o o
41 p p
42 q q
43 r r
44 s s
45 t t
46 u u
47 v v
48 w w
49 x x
50 y y
51 z z
52 0 0
53 1 1
54 2 2
55 3 3
56 4 4
57 5 5
58 6 6
59 7 7
60 8 8
61 9 9
62 + -
0011 1111 63 / _


Javascript Node

const base64 =  Buffer.from('Hello Base 64').toString('base64');

atob / btoa javascript function are deprecated.


const base64 = window.btoa("Hello World");
console.log(`Base64: ${base64}`);
const plainText = window.atob(base64);
console.log(`Plain Text: ${plainText}`);

To decode a base64 URL encoding:

function base64Decode(s){
  // from base64 url to base 64
  s = s
       .replace(/-/g, '+')
       .replace(/_/g, '/');
  return window.atob(s);

See the decoder/encoder script above.


base64 command utility

cat my-file | base64

Open Ssl


echo Hello World ! | openssl base64


String encode = Base64.getEncoder().encodeToString("Foo".getBytes());
byte[] decode = Base64.getDecoder().decode(encode);
System.out.println(new String(decode,StandardCharsets.UTF_8));

Documentation / Reference

  • rfc4648 - The Base16, Base32, and Base64 Data Encodings

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