MIME and Transfer Encoding

Transcription

1 Message Format MIME and Transfer Encoding MIME 1 Message Format: Multimedia Extensions MIME: Multimedia Internet Mail Extension, RFC , 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) MIME version method used to encode data multimedia data type, subtype, parameter declaration blank line encoded data From: kwk@csie.ntut.edu.tw To: kwk@en.ntut.edu.tw Subject: Test of . Content-Transfer-Encoding: base64 Content-Type: image/jpeg base64 encoded data base64 encoded data (RFC 2045/46 for more on headers) MIME 3 (header lines) SMTP: protocol for exchanging 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 header body (details on next page) blank line MIME 2 MIME (Multipurpose Internet Mail Extensions) Types Content-Type: type/subtype; parameters Content-Transfer-Encoding: base Rxer convert msg s body to its original non-ascii first 2. Then, uses type to determine what actions it should take Type/subtype : Text example subtypes: plain, html Image example subtypes: jpeg, gif (To register Types to IANA: see RFC 2048) Audio exampe subtypes: basic (8-bit mu-law encoded), 32k ADPCM (32 kbps coding) Video example subtypes: mpeg, quicktime Application other data that must be processed by reader before viewable example subtypes: msword, octet-stream, pdf, ps MIME 4

2 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 Part I Part II Example - Multipart Type From: kwke@ntut.edu.tw To: kwk@en.ntut.edu.tw Subject: test of multipart type (containing many objects) Content-Type: multipart/mixed; boundary= Separation begin with -- Content-Transfer-Encoding: quoted-printable Content-Type: text/plain Dear ALL, end with CR LF Please study hard on Networking course Content-Transfer-Encoding: base64 Content-Type: image/jpeg base64 encoded data base64 encoded data End of the last part MIME 6 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 Transfer Encoding Selection Example - Outlook Express No encoding Choose here (x ~ vender/application specific) MIME 7 MIME 8

3 Quoted-Printable Encoding Quoted means... 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 Literal representation White space Line breaks ~ use CR LF combination (i.e., 0D0AH) Soft line breaks Explained next page = ~ for lines > 76 char., (excluding CR,LF), inserts 3D0D0A at or before character position 75 (called soft line break). MIME 9 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 (<tab>) blank octet value : 32 (<sp>) Exception: tab and blank at the end of a line (encoding) using Gen. 8-bit repre. IRA example (decoding) delete any trailing white space (HT and BS) MIME 11 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 . MIME 10 Base64/Radix-64 Encoding Encoding arbitrary binary data to be invulnerable to the processing by mail transport programs : - Process in a 3-octet (24-bit) basis - every mapped to 8-bit codeword/character No - ; No ctrl char. RFC 1421, 2045 that does not consist mainly of text characters ( ) s printable characters MIME 12 Ex.

4 Base-64 Example in Details Example IRA If Double clicking Press Right botton base64 base64 base64 base64 Char. 1 Char. 2 Char. 3 Char I 1 y R A block of 24-bit raw data 4 characters for transferring * no control characters in the set for traversing mail-handling systems that scan the data for control characters. MIME 13 Example 1 (7-bit ASCII) (cont d on next page) From: "kai-wei ke" <kwk@en.ntut.edu.tw> To: <kwk@csie.ntut.edu.tw> Cc: "Elton John" <s @ntut.edu.tw> Subject: Mail test Date: Sun, 17 Mar :09: Content-Type: multipart/mixed; boundary="---- =_NextPart_000_0009_01C1CE00.713E1360" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express X-MimeOLE: Produced By Microsoft MimeOLE V 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. Kai-Wei MIME 15 = NextPart C1CE00 713E1360 MIME (next pages) 14 Example 2 (base64) Content-Type: text/plain; name="test.txt" Content-Transfer-Encoding: 7bit From: "kai-wei ke" <kwk@en.ntut.edu.tw> Content-Disposition: attachment; To: <kwk@csie.ntut.edu.tw> filename="test.txt" Cc: "Elton John" <s @ntut.edu.tw> Subject: Mail test This is a test of MIME attachment. Date: Sun, 17 Mar :49: =_NextPart_000_0009_01C1CE00.713E Content-Type: multipart/mixed; boundary="----=_nextpart_000_0075_01c1ce05.f702d1c0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express X-MimeOLE: Produced By Microsoft MimeOLE V 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 Ex-1(cont d) VGhpcyBpcyBhIHRlc3Qgb2YgTUlNRSBlbmNvZGluZyBzdHVmZi4NCllvdSBtdXN0IGxvb2sgYXQg dghligvuy29kzwqgzm9ybsbmb3igzgv0ywlscy4ncg0ks2fplvdlaq== =_NextPart_000_0075_01C1CE05.F702D1C0 MIME 16

5 QP Example International Reference Alphabet (or IAC) = 4 blank 7 blank follows Vertical Formatting Control characters MIME 17 For 8-bit ASCII, b 8 even/odd parity bit or just zero MIME 18 IRA Control Characters IRA Control Characters Information Separator Format Control Transmission Control Miscellaneous MIME 19 MIME 20

6 American Standard Code for Information Interchange (ASCII) ASCII control characters MIME 21 MIME 22