2.4 MIME and Transfer encoding

MIME and Transfer Encoding

MIME

1

3

Message Format: Multimedia Extensions

? MIME: Multimedia Internet Mail Extension, RFC 2045-49, 2056 ~ an extension of RFC 822 for resolving prob. in SMTP/822 scheme

? additional lines in msg header declare MIME content type

(generated by user agent)

(header lines)

MIME version

From: kwk@csie.ntut.edu.tw To: kwk@en.ntut.edu.tw

method used to encode data

multimedia data type, subtype, parameter declaration

blank line

Subject: Test of E-Mail. MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Type: image/jpeg

base64 encoded data ..... .........................

encoded data

......base64 encoded data

MIME

(RFC 2045/46 for more on headers) 3

3

E-Mail Message Format

? SMTP: protocol for exchanging email messages

? RFC 822: standard for text message format:

? header lines, e.g.,

? To: ? From: ? Subject: ? Message ID ? Date ? Received ? X-priority ? body ? the "message", 7-bit ASCII

characters only

MIME

header body

blank line

(details on next page)

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3

MIME (Multipurpose Internet Mail Extensions) Types

Content-Type: type/subtype; parameters

Content-Transfer-Encoding: base 64

Audio

1. Rxer convert msg's body to ? exampe subtypes: basic (8-bit

its original non-ASCII first

mu-law encoded), 32k ADPCM

(32 kbps coding)

2. Then, uses type to determine Video

what actions it should take

? example subtypes: mpeg,

Type/subtype : Text

? example subtypes: plain, html

Image

quicktime

Application

? other data that must be processed by reader before "viewable"

? example subtypes: jpeg, gif

? example subtypes: msword,

octet-stream, pdf, ps

MIME(To register Types to IANA: see RFC 2048)

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MIME References

? RFC 2045 ? MIME (Multipurpose Internet Mail Extensions) Part One: Format of Internet Message Bodies

? RFC 2046 ? MIME (Multipurpose Internet Mail Extensions) Part Two: Media Types

? RFC 2047 ? MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text

? RFC 2048 ? MIME (Multipurpose Internet Mail Extensions) Part Four: Registration Procedures

? RFC 2049 ? MIME (Multipurpose Internet Mail Extensions) Part Five: Conformance Criteria and Examples

? RFC 2156 ? MIXER (MIME Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME

? RFC 2159 ? A MIME Body Part for FAX

? RFC 2183 ? Communicating Presentation Information in Internet Messages

? RFC 2231 ? MIME Parameter Value and Encoded Word Extensions

MIME

5

3

MIME Content - Transfer Encoding

? Transfer encodings for message bodies to provide reliable delivery across the largest networking environment ? provide human readable and reasonable compact

Encoding Schemes

No encoding

3

Example - Multipart Type

From: kwke@ntut.edu.tw To: kwk@en.ntut.edu.tw Subject: test of multipart type

(containing many objects) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary=98766789

Part I

--98766789 ? Separation begin with " - - " Content-Transfer-Encoding: quoted-printable

Content-Type: text/plain

Dear ALL, Please study

hard

on

end with " CR LF Networking course.

?"

--98766789

Content-Transfer-Encoding: base64

Content-Type: image/jpeg

Part II base64 encoded data .....

.........................

......base64 encoded data

MIME --98766789-- ? End of the last part

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Transfer Encoding Selection

Example - Outlook Express

Choose here

(x ~ vender/application specific)

MIME

7

MIME

8

3

Quoted-Printable Encoding

? Encoding data consisting largely of printable ASCII characters

~ represents non-mail safe characters by hexadecimal representation of their code and introduce reversible (soft) line breaks to limit message lines to 76 characters (or less).

? Q.P. encoding rules:

? General 8-bit representation

~ used when none of following rules apply Explained

? Literal representation

next page

? White space

? Line breaks

~ use " CR LF " combination (i.e., 0D0AH)

? Soft line breaks

"="

~ for lines > 76 char., (excluding CR,LF), inserts " 3D0D0A " at

or before character position 75 (called soft line break).

MIME

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3

Quoted-Printable Encoding (cont'd)

? General 8-bit representation

? any character ? "=" + " two-digit hexadecimal representation of the octet's value "

? Ex: 8-bit value "12" ? "=0C"

? Literal representation

? any character in the decimal range 33 ("!", 21H) to 126("~", 7EH) ? represented as that ASCII character

? Exception: 61 ("=", 3DH)

? White space

? "tab" ? octet value : 9 ()

? "blank" ? octet value : 32 ()

IRA

? Exception: "tab" and "blank" at the end of a line ? (encoding) using Gen. 8-bit repre.

example

(decoding) delete any trailing white space (HT and BS)

MIME

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"Quoted" means . . .

? Using the equal sign (" = ") as a quote character to indicate both the non-mail safe characters and soft line break

? Quoted-printable is an encoding using ASCII characters for non-ASCII text. It is defined as a MIME content transfer encoding for use in Internet e-mail.

MIME

10

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Base64/Radix-64 Encoding

? Encoding arbitrary binary data to be invulnerable to the processing by mail transport programs : that does not consist mainly of text characters - Process in a 3-octet (24-bit) basis - every 6-bit mapped to 8-bit codeword/character

No "-" ;

No ctrl char.

RFC 1421, 2045

MIME

(26 + 1)'s

printable characters

Ex.

12

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Base-64 Example

6-bit 6-bit 6-bit 6-bit

base64 base64 base64 base64

Char. 1 Char. 2 Char. 3 Char. 4

? Example

IRA

00100011 01011100 10010001

001000 110101 110010 010001

I

1 y

R

A block of 24-bit raw data

* no control characters in the set for traversing mail-handling systems that

4 characters for transferring scan the data for control characters.

MIME

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E-mail Example ? 1 (7-bit ASCII)

From: "kai-wei ke" To: Cc: "Elton John" Subject: Mail test Date: Sun, 17 Mar 2002 22:09:43 +0800 MIME-Version: 1.0 Content-Type: multipart/mixed;

boundary="---=_NextPart_000_0009_01C1CE00.713E1360" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000

This is a multi-part message in MIME format.

------=_NextPart_000_0009_01C1CE00.713E1360 Content-Type: text/plain;

charset="big5" Content-Transfer-Encoding: 7bit

This is a test of MIME encoding stuff. You must look at the encoded form for details.

(cont'd on next page) Kai-Wei

MIME

= NextPart 000 0009 01C1CE00 713E1360

15

E-mail in Details

If Double clicking

Press Right botton

MIME

(next pages) 14

Example ? 2 (base64)

Content-Type: text/plain; name="test.txt"

Ex-1(cont'd)

Content-Transfer-Encoding: 7bit

From: "kai-wei ke"

Content-Disposition: attachment;

To:

filename="test.txt"

Cc: "Elton John"

Subject: Mail test

This is a test of MIME attachment.

Date: Sun, 17 Mar 2002 22:49:15 +0800

MIME-Version: 1.0 Content-Type: multipart/mixed;

------=_NextPart_000_0009_01C1CE00.713E1360--

boundary="----=_NextPart_000_0075_01C1CE05.F702D1C0"

X-Priority: 3

X-MSMail-Priority: Normal

X-Mailer: Microsoft Outlook Express 6.00.2600.0000

X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000

This is a multi-part message in MIME format.

------=_NextPart_000_0075_01C1CE05.F702D1C0 Content-Type: text/plain;

charset="Windows-1252" Content-Transfer-Encoding: base64

Exercise

VGhpcyBpcyBhIHRlc3Qgb2YgTUlNRSBlbmNvZGluZyBzdHVmZi4NCllvdSBtdXN0IGxvb2sgYXQg dGhlIGVuY29kZWQgZm9ybSBmb3IgZGV0YWlscy4NCg0KS2FpLVdlaQ==

------=_NextPart_000_0075_01C1CE05.F702D1C0

MIME

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QP Example

= 4 blank 7 blank follows

MIME

IRA Control Characters

Format Control

International Reference Alphabet (or IAC)

Vertical Formatting

Control characters

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MIME

For 8-bit ASCII, b8 ?even/odd parity bit or just zero

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IRA Control Characters

Information Separator

Transmission Control

MIME

19

MIME

Miscellaneous

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