What does base-64 mean?

General Information ID:    INFO992
Version:    1.0
Published:    10/21/2008

Description

Base64 is a method of encoding binary data as ASCII text. This is necessary for sending files via Internet email, which can only handle 7-bit ASCII text.

Base64 is the industry standard format for SSL certificate content. The most common web servers will generate a certificate signing requests as well as accept SSL certificates in base-64 format.

The size of the certificate content will depend on the encryption strength of the certificate (512bit, 1024bit, 2048bit).

Here is an example of a base64-encoded certificate.

-----BEGIN CERTIFICATE-----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==
-----END CERTIFICATE-----

The base64 alphabet

The base64 alphabet is shown in the below table.  Whenever the value of a six-bit group matches one of the values in the Value columns, that value is replaced by the seven-bit ASCII value of the corresponding character shown in the Char column to the right of the Value column.

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


15
P
32
g
49
x


16
Q
33
h
50
y


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