Cryptography Reference
In-Depth Information
Diagram D.1 Radix-
64
Encoding Illustration
24
−
bit
Binary input
→
6
-bit
6
-bit
6
-bit
6
-bit
f
64
*
f
64
*
f
64
*
f
64
*
Encoding
←
8
-bit
8
-bit
8
-bit
8
-bit
32
−
bit
Example D.4
For instance, suppose that the text for encoding consists of the
three bytes
01010000
,
00100001
, and
10000000
, which are put into four
6
-bit in-
put values:
010100
,
000010
,
000110
, and
000000
, whose decimal representations
are:
20
,
2
,
5
, and
0
. Looking at Table D.1, we get the radix-
64
encodings as:
UCFA.
The radix-64 conversion also appends a CRC for the purpose of detecting
transmission errors. Essentially this is a
checksum
, meaning a value computed
to check the validity of a data transmission, usually by detecting transmission
errors. In the case of the armor checksum, a 24-bit CRC is converted to four
bytes of radix-64 encoding that is prepended by an = sign to the four-byte code.
For the actual mechanism by which this is done, the reader may consult [213].
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