Difference between revisions of "Base64"

From OpenSSLWiki
Jump to navigationJump to search
(openssl base64 specificities)
(2 intermediate revisions by one other user not shown)
Line 1: Line 1:
 
Encode binary information 8 bits into ASCII.
 
Encode binary information 8 bits into ASCII.
  
This is PEM base encode, it exists other base64 encoding scheme like this uses by crypt.
+
This is PEM base encode, it exists other base64 encoding scheme like this used by crypt.
  
 
== Algorithm ==
 
== Algorithm ==
Line 27: Line 27:
 
crypto/evp/bio_b64.C
 
crypto/evp/bio_b64.C
  
 +
If you need to encode a block of data, use the '''<tt>EVP_EncodeBlock</tt>''' function, example:
 +
<pre>
 +
unsigned char sourceData[16] = {0x30,0x82,0x07,0x39,0x30,0x82,0x05,0x21,0xA0,0x03,0x02,0x01,0x02,0x02,0x04,0x00};
 +
char encodedData[100];
 +
EVP_EncodeBlock((unsigned char *)encodedData, sourceData, 16);
 +
printf(encodedData);
 +
</pre>
  
 
=== WARNINGS ===
 
=== WARNINGS ===
Line 44: Line 51:
  
 
Base64 itself does not impose a line split, but openssl uses it in PEM context hence enforce that base64 content is splitted by lines with a maximum of 80 characters.
 
Base64 itself does not impose a line split, but openssl uses it in PEM context hence enforce that base64 content is splitted by lines with a maximum of 80 characters.
 +
 +
With C code it is possible to ask to disregard lines breaks : BIO_set_flags(d,BIO_FLAGS_BASE64_NO_NL);
  
  
 
[[Category:Encoding]]
 
[[Category:Encoding]]

Revision as of 15:58, 27 June 2017

Encode binary information 8 bits into ASCII.

This is PEM base encode, it exists other base64 encoding scheme like this used by crypt.

Algorithm

3 x 8 bits binary are concatenated to form a 24bits word that is split in 4 x 6bits each being translating into an ascii value using a character ordered in following list :

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ 
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
0000000000111111111122222222223333333333444444444455555555556666
0123456789012345678901234567890123456789012345678901234567890123

[what makes 26 * 2 + 10 + 2 = 64 values]

Since it encodes by group of 3 bytes, when last group of 3 bytes miss one byte then = is used, when it miss 2 bytes then == is used for padding.

Openssl command

base64 or -enc base64 can be used to decode lines see Command_Line_Utilities

EVP API

crypto/evp/encode.c crypto/evp/bio_b64.C

If you need to encode a block of data, use the EVP_EncodeBlock function, example:

unsigned char sourceData[16] = {0x30,0x82,0x07,0x39,0x30,0x82,0x05,0x21,0xA0,0x03,0x02,0x01,0x02,0x02,0x04,0x00};
char encodedData[100];
EVP_EncodeBlock((unsigned char *)encodedData, sourceData, 16);
printf(encodedData);

WARNINGS

other unsupported base64 scheme

Warning crypt() password encryption function uses another base64 scheme which is not the openssl base64 one. :

./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
0000000000111111111122222222223333333333444444444455555555556666
0123456789012345678901234567890123456789012345678901234567890123

base64 uses PEM 80 characters per line

Base64 itself does not impose a line split, but openssl uses it in PEM context hence enforce that base64 content is splitted by lines with a maximum of 80 characters.

With C code it is possible to ask to disregard lines breaks : BIO_set_flags(d,BIO_FLAGS_BASE64_NO_NL);