Editing Base64 (section)

==Design==
The particular set of 64 characters chosen to represent the 64-digit values for the base varies between implementations. The general strategy is to choose 64 characters that are common to most encodings and that are also printable. This combination leaves the data unlikely to be modified in transit through information systems, such as email, that were traditionally not [[8-bit clean]].<ref name="autogenerated2006">{{cite IETF |title= The Base16, Base32, and Base64 Data Encodings |rfc= 4648 |date=October 2006 |publisher=[[Internet Engineering Task Force|IETF]] |access-date= March 18, 2010}}</ref> For example, [[MIME]]'s Base64 implementation uses <code>A</code>–<code>Z</code>, <code>a</code>–<code>z</code>, and <code>0</code>–<code>9</code> for the first 62 values. Other variations share this property but differ in the symbols chosen for the last two values; an example is [[UTF-7]].

The earliest instances of this type of encoding were created for dial-up communication between systems running the same [[operating system|OS]] – for example, [[uuencoding|uuencode]] for [[UNIX]] and [[BinHex]] for the [[TRS-80]] (later adapted for the [[Macintosh]]) – and could therefore make more assumptions about what characters were safe to use. For instance, uuencode uses uppercase letters, digits, and many punctuation characters, but no lowercase.<ref name="rfc 1421">{{cite IETF |title= Privacy Enhancement for InternetElectronic Mail: Part I: Message Encryption and Authentication Procedures |rfc= 1421 |date=February 1993 |publisher=[[Internet Engineering Task Force|IETF]] |access-date= March 18, 2010}}</ref><ref name="rfc 2045">{{cite IETF |title= Multipurpose Internet Mail Extensions: (MIME) Part One: Format of Internet Message Bodies |rfc= 2045 |date=November 1996 |publisher=[[Internet Engineering Task Force|IETF]] |access-date= March 18, 2010}}</ref><ref name="rfc 3548">{{cite IETF |title= The Base16, Base32, and Base64 Data Encodings |rfc= 3548 |date=July 2003 |publisher=[[Internet Engineering Task Force|IETF]] |access-date= March 18, 2010}}</ref><ref name="autogenerated2006"/>