armouring : Java Glossary

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armouring
Converting binary data into printable gibberish so that data transport systems will not corrupt it. You see it used often in certificates, email and HTTP (Hypertext Transfer Protocol) communications.

There are many data transport systems that either ignore, act on or otherwise meddle with control characters embedded in the data. They may trim trailing blanks, change line end characters, convert tabs to spaces etc. etc. Any of these actions would totally corrupt binary data. To pass binary data through such a meddlesome channel, e.g. the email system, it must first be armoured, converted to use only safe printable characters that will not be meddled with, e.g. a-z A-Z 0-9 and the vanilla punctuation. I sometimes refer to character than need special processing to pass through a channel as awkward.

MIME (Multipurpose Internet Mail Extensions) email and email attachments have a configurable encoding scheme, controlled via the Transfer-Content-Encoding mime header, often base64 or Quoted-Printable.

Unfortunately this bulks the message up by 30 to 300% depending on the technique you use. The other end has to recognise the armouring technique and do the reverse to get the binary back.

When 8-bit data are encoded in printable characters, the more printable characters used in the representation, generally the more efficient the protocol. However, the more characters used, the greater the odds one of the characters used will be interfered with by your communication channel.

Armouring Schemes

Unfortunately, there are a plethora of techniques. It is not always obvious just from looking which was used to encode the data:

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