Difference between revisions of "RFC6047"
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Interoperability Protocol (iTIP) to Internet email-based transports. | Interoperability Protocol (iTIP) to Internet email-based transports. | ||
Calendaring entries defined by the iCalendar Object Model (iCalendar) | Calendaring entries defined by the iCalendar Object Model (iCalendar) | ||
− | are wrapped using constructs from RFC 5322 and MIME (RFC 2045, RFC | + | are wrapped using constructs from [[RFC5322|RFC 5322]] and MIME ([[RFC2045|RFC 2045]], RFC |
− | 2046, RFC 2047, and RFC 2049), and then transported over SMTP. | + | 2046, [[RFC2047|RFC 2047]], and [[RFC2049|RFC 2049]]), and then transported over SMTP. |
'''Status of This Memo''' | '''Status of This Memo''' | ||
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received public review and has been approved for publication by the | received public review and has been approved for publication by the | ||
Internet Engineering Steering Group (IESG). Further information on | Internet Engineering Steering Group (IESG). Further information on | ||
− | Internet Standards is available in Section 2 of RFC 5741. | + | Internet Standards is available in Section 2 of [[RFC5741|RFC 5741]]. |
Information about the current status of this document, any errata, | Information about the current status of this document, any errata, | ||
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document authors. All rights reserved. | document authors. All rights reserved. | ||
− | This document is subject to BCP 78 and the IETF Trust's Legal | + | This document is subject to [[BCP78|BCP 78]] and the IETF Trust's Legal |
Provisions Relating to IETF Documents | Provisions Relating to IETF Documents | ||
(http://trustee.ietf.org/license-info) in effect on the date of | (http://trustee.ietf.org/license-info) in effect on the date of | ||
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necessary to convey iCalendar Transport-independent Interoperability | necessary to convey iCalendar Transport-independent Interoperability | ||
Protocol (iTIP) [iTIP] over Internet email (using MIME) as defined in | Protocol (iTIP) [iTIP] over Internet email (using MIME) as defined in | ||
− | + | [[RFC5322]] and [[RFC2045]]. Therefore, this document defines the | |
iCalendar Message-Based Interoperability Protocol (iMIP). | iCalendar Message-Based Interoperability Protocol (iMIP). | ||
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | ||
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | ||
− | document are to be interpreted as described in RFC 2119 | + | document are to be interpreted as described in [[RFC2119|RFC 2119]] [[RFC2119]]. |
Calendaring and scheduling roles are referred to in quoted strings of | Calendaring and scheduling roles are referred to in quoted strings of | ||
Line 127: | Line 127: | ||
=== Terminology === | === Terminology === | ||
− | The email terms used in this memo are defined in | + | The email terms used in this memo are defined in [[RFC5322]] and |
− | + | [[RFC2045]]. The calendaring and scheduling terms used in this memo | |
are defined in [iCAL] and [iTIP]. | are defined in [iCAL] and [iTIP]. | ||
Line 142: | Line 142: | ||
and the recipient is the "Organizer" of the event. | and the recipient is the "Organizer" of the event. | ||
− | The | + | The [[RFC5322]] "Reply-To" header field typically contains the email |
address of the originator of the scheduling message. However, this | address of the originator of the scheduling message. However, this | ||
cannot be guaranteed because the sender of the iMIP message might not | cannot be guaranteed because the sender of the iMIP message might not | ||
Line 161: | Line 161: | ||
authentication, authorization, and confidentiality. Authentication | authentication, authorization, and confidentiality. Authentication | ||
and confidentiality can be achieved using Secure/MIME (S/MIME) | and confidentiality can be achieved using Secure/MIME (S/MIME) | ||
− | + | [[RFC5750]] [[RFC5751]], which uses the Security Multiparts framework for | |
− | MIME | + | MIME [[RFC1847]]. |
==== Authorization ==== | ==== Authorization ==== | ||
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this are presented later in this document. | this are presented later in this document. | ||
− | + | [[RFC1847]] message flow in iTIP supports someone working on behalf of | |
a "Calendar User" through use of the "sent-by" parameter that is | a "Calendar User" through use of the "sent-by" parameter that is | ||
associated with the "ATTENDEE" and "ORGANIZER" properties. However, | associated with the "ATTENDEE" and "ORGANIZER" properties. However, | ||
Line 189: | Line 189: | ||
==== Authentication ==== | ==== Authentication ==== | ||
− | Authentication MUST be performed using S/MIME | + | Authentication MUST be performed using S/MIME [[RFC5750]] [[RFC5751]]. |
Authentication is possible only on messages that have been signed. | Authentication is possible only on messages that have been signed. | ||
Unauthenticated messages (i.e., unsigned messages) may not be | Unauthenticated messages (i.e., unsigned messages) may not be | ||
Line 197: | Line 197: | ||
To ensure confidentiality using iMIP, implementations SHOULD utilize | To ensure confidentiality using iMIP, implementations SHOULD utilize | ||
− | encryption specified in S/MIME | + | encryption specified in S/MIME [[RFC5750]] [[RFC5751]]. iMIP does not |
restrict a "Calendar User Agent" (CUA) from forwarding iCalendar | restrict a "Calendar User Agent" (CUA) from forwarding iCalendar | ||
objects to other users or agents. | objects to other users or agents. | ||
Line 209: | Line 209: | ||
Because [iTIP] does not preclude "Attendees" from forwarding | Because [iTIP] does not preclude "Attendees" from forwarding | ||
− | "VEVENT"s or "VTODO"s to others, the | + | "VEVENT"s or "VTODO"s to others, the [[RFC5322]] "Sender" value may not |
equal that of the "Organizer". Additionally, the "Organizer" or | equal that of the "Organizer". Additionally, the "Organizer" or | ||
− | "Attendee" cannot be reliably inferred by the | + | "Attendee" cannot be reliably inferred by the [[RFC5322]] "Sender" or |
"Reply-To" header field values of an iMIP message. The relevant | "Reply-To" header field values of an iMIP message. The relevant | ||
address MUST be ascertained by opening the "text/calendar" MIME body | address MUST be ascertained by opening the "text/calendar" MIME body | ||
Line 219: | Line 219: | ||
A MIME body part containing content information that conforms to this | A MIME body part containing content information that conforms to this | ||
− | document MUST have an | + | document MUST have an [[RFC2045]] "Content-Type" value of |
− | "text/calendar". The | + | "text/calendar". The [[RFC2045]] "Content-Type" header field MUST also |
include the MIME parameter "method". The value MUST be the same | include the MIME parameter "method". The value MUST be the same | ||
(ignoring case) as the value of the "METHOD" property within the | (ignoring case) as the value of the "METHOD" property within the | ||
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Note 1: A MIME message containing multiple iCalendar objects with | Note 1: A MIME message containing multiple iCalendar objects with | ||
different "method" values MUST be further encapsulated with a | different "method" values MUST be further encapsulated with a | ||
− | "multipart/mixed" MIME entity | + | "multipart/mixed" MIME entity [[RFC2046]]. This will allow each of |
the iCalendar objects to be encapsulated within their own | the iCalendar objects to be encapsulated within their own | ||
"text/calendar" MIME entity. | "text/calendar" MIME entity. | ||
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Note that according to [iCAL] the default character set for iCalendar | Note that according to [iCAL] the default character set for iCalendar | ||
objects is UTF-8 [UTF-8]. However, the default character set for a | objects is UTF-8 [UTF-8]. However, the default character set for a | ||
− | "text/*" MIME entity according to | + | "text/*" MIME entity according to [[RFC2046]] is US-ASCII. Thus, a |
"charset" MIME parameter MUST be present if the iCalendar object | "charset" MIME parameter MUST be present if the iCalendar object | ||
contains characters that can't be represented in the US-ASCII | contains characters that can't be represented in the US-ASCII | ||
Line 257: | Line 257: | ||
(i.e., "multipart/mixed") or included in a MIME message with a clear- | (i.e., "multipart/mixed") or included in a MIME message with a clear- | ||
text, human-readable form of the scheduling message (i.e., | text, human-readable form of the scheduling message (i.e., | ||
− | "multipart/alternative" | + | "multipart/alternative" [[RFC2046]]). |
In order to permit the information in the scheduling message to be | In order to permit the information in the scheduling message to be | ||
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CUAs can use other MIME parameters of the "Content-Type" header | CUAs can use other MIME parameters of the "Content-Type" header | ||
field, as well as a language specified in the Content-Language header | field, as well as a language specified in the Content-Language header | ||
− | field | + | field [[RFC3282]], to pick a "text/calendar" part for processing if a |
"multipart/alternative" MIME message contains more than one | "multipart/alternative" MIME message contains more than one | ||
"text/calendar" part. | "text/calendar" part. | ||
Line 284: | Line 284: | ||
Unless an iMIP message is transported over 8-bit clean transport | Unless an iMIP message is transported over 8-bit clean transport | ||
(such as SMTP [8BITMIME]), a transfer encoding such as quoted- | (such as SMTP [8BITMIME]), a transfer encoding such as quoted- | ||
− | printable or base64 | + | printable or base64 [[RFC2045]] MUST be used for iCalendar objects |
containing any characters that can't be represented in the US-ASCII | containing any characters that can't be represented in the US-ASCII | ||
character set. For example: | character set. For example: | ||
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Implementations MAY include a "Content-Disposition" header field to | Implementations MAY include a "Content-Disposition" header field to | ||
define a file name for an iCalendar object. However, the handling of | define a file name for an iCalendar object. However, the handling of | ||
− | a MIME part MUST be based on its | + | a MIME part MUST be based on its [[RFC2045]] "Content-Type" and not on |
the extension specified in the "Content-Disposition", as different | the extension specified in the "Content-Disposition", as different | ||
email malware is known to trick User Agents into misinterpreting | email malware is known to trick User Agents into misinterpreting | ||
Line 341: | Line 341: | ||
Compliant applications MUST support signing and encrypting | Compliant applications MUST support signing and encrypting | ||
"text/calendar" body parts using a mechanism based on S/MIME | "text/calendar" body parts using a mechanism based on S/MIME | ||
− | + | [[RFC5750]] [[RFC5751]] in order to facilitate the authentication of the | |
originator of the iCalendar object (see Sections 2.2.2 and 2.2.3). | originator of the iCalendar object (see Sections 2.2.2 and 2.2.3). | ||
The steps for processing a signed iMIP message are described below: | The steps for processing a signed iMIP message are described below: | ||
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that the email address of the signer MUST be specified in the | that the email address of the signer MUST be specified in the | ||
rfc822Name field of the "subject alternative name" extension of | rfc822Name field of the "subject alternative name" extension of | ||
− | the signer certificate, as specified in | + | the signer certificate, as specified in [[RFC5280]], |
Section 4.1.2.6.) Note that the signer is not necessarily the | Section 4.1.2.6.) Note that the signer is not necessarily the | ||
person sending an e-mail message, since an e-mail message can be | person sending an e-mail message, since an e-mail message can be | ||
Line 377: | Line 377: | ||
If calendar confidentiality is required by the sender, signed iMIP | If calendar confidentiality is required by the sender, signed iMIP | ||
− | messages SHOULD be encrypted by a mechanism based on S/MIME | + | messages SHOULD be encrypted by a mechanism based on S/MIME [[RFC5750]] |
− | + | [[RFC5751]]. If iMIP is used within a single ADministrative Management | |
− | Domain (ADMD) | + | Domain (ADMD) [[RFC5598]], SMTP STARTTLS [SMTP-TLS] (together with |
STARTTLS in IMAP/POP [IMAP-POP-TLS]) MAY alternatively be used to | STARTTLS in IMAP/POP [IMAP-POP-TLS]) MAY alternatively be used to | ||
provide calendar confidentiality. | provide calendar confidentiality. | ||
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Use of S/MIME makes the security considerations discussed in | Use of S/MIME makes the security considerations discussed in | ||
− | + | [[RFC5750]] [[RFC5751]] relevant to this document. For additional | |
security considerations regarding certificate and Certificate | security considerations regarding certificate and Certificate | ||
− | Revocation List (CRL) verification, please see | + | Revocation List (CRL) verification, please see [[RFC5280]]. |
== Examples == | == Examples == | ||
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in properties such as "DESCRIPTION", "ATTACH", "CONTACT", and others. | in properties such as "DESCRIPTION", "ATTACH", "CONTACT", and others. | ||
Two forms of URIs are the Message ID (MID) and the Content-ID (CID). | Two forms of URIs are the Message ID (MID) and the Content-ID (CID). | ||
− | These are defined in | + | These are defined in [[RFC2392]]. Although [[RFC2392]] allows |
referencing messages or MIME body parts in other MIME entities or | referencing messages or MIME body parts in other MIME entities or | ||
stores, it is strongly RECOMMENDED that iMIP implementations include | stores, it is strongly RECOMMENDED that iMIP implementations include | ||
Line 757: | Line 757: | ||
[iCAL] Desruisseaux, B., Ed., "Internet Calendaring and | [iCAL] Desruisseaux, B., Ed., "Internet Calendaring and | ||
Scheduling Core Object Specification (iCalendar)", | Scheduling Core Object Specification (iCalendar)", | ||
− | RFC 5545, September 2009. | + | [[RFC5545|RFC 5545]], September 2009. |
[iTIP] Daboo, C., Ed., "iCalendar Transport-Independent | [iTIP] Daboo, C., Ed., "iCalendar Transport-Independent | ||
− | Interoperability Protocol (iTIP)", RFC 5546, December | + | Interoperability Protocol (iTIP)", [[RFC5546|RFC 5546]], December |
2009. | 2009. | ||
− | + | [[RFC5322]] Resnick, P., Ed., "Internet Message Format", [[RFC5322|RFC 5322]], | |
October 2008. | October 2008. | ||
[MAILTO] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' | [MAILTO] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' | ||
− | URI Scheme", RFC 6068, October 2010. | + | URI Scheme", [[RFC6068|RFC 6068]], October 2010. |
− | + | [[RFC1847]] Galvin, J., Murphy, S., Crocker, S., and N. Freed, | |
"Security Multiparts for MIME: Multipart/Signed and | "Security Multiparts for MIME: Multipart/Signed and | ||
− | Multipart/Encrypted", RFC 1847, October 1995. | + | Multipart/Encrypted", [[RFC1847|RFC 1847]], October 1995. |
− | + | [[RFC2045]] Freed, N. and N. Borenstein, "Multipurpose Internet Mail | |
Extensions (MIME) Part One: Format of Internet Message | Extensions (MIME) Part One: Format of Internet Message | ||
− | Bodies", RFC 2045, November 1996. | + | Bodies", [[RFC2045|RFC 2045]], November 1996. |
− | + | [[RFC2046]] Freed, N. and N. Borenstein, "Multipurpose Internet Mail | |
− | Extensions (MIME) Part Two: Media Types", RFC 2046, | + | Extensions (MIME) Part Two: Media Types", [[RFC2046|RFC 2046]], |
November 1996. | November 1996. | ||
− | + | [[RFC2392]] Levinson, E., "Content-ID and Message-ID Uniform Resource | |
− | Locators", RFC 2392, August 1998. | + | Locators", [[RFC2392|RFC 2392]], August 1998. |
− | + | [[RFC2119]] Bradner, S., "Key words for use in RFCs to Indicate | |
− | Requirement Levels", BCP 14, RFC 2119, March 1997. | + | Requirement Levels", [[BCP14|BCP 14]], [[RFC2119|RFC 2119]], March 1997. |
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO | [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO | ||
− | 10646", STD 63, RFC 3629, November 2003. | + | 10646", [[STD63|STD 63]], [[RFC3629|RFC 3629]], November 2003. |
[SMTP-TLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over | [SMTP-TLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over | ||
− | Transport Layer Security", RFC 3207, February 2002. | + | Transport Layer Security", [[RFC3207|RFC 3207]], February 2002. |
[IMAP-POP-TLS] | [IMAP-POP-TLS] | ||
Newman, C., "Using TLS with IMAP, POP3 and ACAP", | Newman, C., "Using TLS with IMAP, POP3 and ACAP", | ||
− | RFC 2595, June 1999. | + | [[RFC2595|RFC 2595]], June 1999. |
− | + | [[RFC5750]] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet | |
Mail Extensions (S/MIME) Version 3.2 Certificate | Mail Extensions (S/MIME) Version 3.2 Certificate | ||
− | Handling", RFC 5750, January 2010. | + | Handling", [[RFC5750|RFC 5750]], January 2010. |
− | + | [[RFC5751]] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet | |
Mail Extensions (S/MIME) Version 3.2 Message | Mail Extensions (S/MIME) Version 3.2 Message | ||
− | Specification", RFC 5751, January 2010. | + | Specification", [[RFC5751|RFC 5751]], January 2010. |
− | + | [[RFC5280]] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., | |
Housley, R., and W. Polk, "Internet X.509 Public Key | Housley, R., and W. Polk, "Internet X.509 Public Key | ||
Infrastructure Certificate and Certificate Revocation | Infrastructure Certificate and Certificate Revocation | ||
− | List (CRL) Profile", RFC 5280, May 2008. | + | List (CRL) Profile", [[RFC5280|RFC 5280]], May 2008. |
=== Informative References === | === Informative References === | ||
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[8BITMIME] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. | [8BITMIME] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. | ||
Crocker, "SMTP Service Extension for 8bit-MIMEtransport", | Crocker, "SMTP Service Extension for 8bit-MIMEtransport", | ||
− | RFC 1652, July 1994. | + | [[RFC1652|RFC 1652]], July 1994. |
− | + | [[RFC5598]] Crocker, D., "Internet Mail Architecture", [[RFC5598|RFC 5598]], July | |
2009. | 2009. | ||
− | + | [[RFC3282]] Alvestrand, H., "Content Language Headers", [[RFC3282|RFC 3282]], May | |
2002. | 2002. | ||
− | Appendix A. Changes since RFC 2447 | + | Appendix A. Changes since [[RFC2447|RFC 2447]] |
Updated references. Split them into Normative and Informative. | Updated references. Split them into Normative and Informative. | ||
Line 828: | Line 828: | ||
Updated examples to use example.com/example.net domains. | Updated examples to use example.com/example.net domains. | ||
− | Corrected usage of RFC 2119 language. | + | Corrected usage of [[RFC2119|RFC 2119]] language. |
Clarified that charset=UTF-8 is required, unless the calendar can be | Clarified that charset=UTF-8 is required, unless the calendar can be | ||
Line 866: | Line 866: | ||
The editor of this document wishes to thank Frank Dawson, Steve | The editor of this document wishes to thank Frank Dawson, Steve | ||
− | Mansour, and Steve Silverberg, the original authors of RFC 2447, as | + | Mansour, and Steve Silverberg, the original authors of [[RFC2447|RFC 2447]], as |
well as the following individuals who have participated in the | well as the following individuals who have participated in the | ||
drafting, review, and discussion of this memo: | drafting, review, and discussion of this memo: |
Latest revision as of 02:21, 22 October 2020
Internet Engineering Task Force (IETF) A. Melnikov, Ed. Request for Comments: 6047 Isode Ltd Obsoletes: 2447 December 2010 Category: Standards Track ISSN: 2070-1721
iCalendar Message-Based Interoperability Protocol (iMIP)
Abstract
This document, "iCalendar Message-Based Interoperability Protocol (iMIP)", specifies a binding from the iCalendar Transport-independent Interoperability Protocol (iTIP) to Internet email-based transports. Calendaring entries defined by the iCalendar Object Model (iCalendar) are wrapped using constructs from RFC 5322 and MIME (RFC 2045, RFC 2046, RFC 2047, and RFC 2049), and then transported over SMTP.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6047.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.
4.3. Single Component with an ATTACH Property and
Contents
Introduction
This document provides the transport-specific information ("binding") necessary to convey iCalendar Transport-independent Interoperability Protocol (iTIP) [iTIP] over Internet email (using MIME) as defined in RFC5322 and RFC2045. Therefore, this document defines the iCalendar Message-Based Interoperability Protocol (iMIP).
Related Memos
Implementers will need to be familiar with several other memos that, along with this memo, form a framework for Internet calendaring and scheduling standards.
This document specifies an Internet email binding for iTIP.
[iCAL] specifies a core specification of objects, data types, properties, and property parameters.
[iTIP] specifies an interoperability protocol for scheduling between different implementations.
This memo does not attempt to repeat the specification of concepts or definitions from these other memos. Where possible, references are made to the memo that provides for the specification of these concepts or definitions.
Formatting Conventions
The mechanisms defined in this memo are defined in prose. In order to refer to elements of the calendaring and scheduling model, core object, or interoperability protocol defined in [iCAL] and [iTIP], some formatting conventions have been used.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 RFC2119.
Calendaring and scheduling roles are referred to in quoted strings of text with the first character of each word in uppercase. For example, "Organizer" refers to a role of a "Calendar User" within the scheduling protocol defined by [iTIP].
Calendar components defined by [iCAL] are referred to with capitalized, quoted strings of text. All calendar components start with the letter "V". For example, "VEVENT" refers to the event calendar component, "VTODO" refers to the to-do calendar component, and "VJOURNAL" refers to the daily journal calendar component.
Scheduling methods defined by [iTIP] are referred to with capitalized, quoted strings of text. For example, "REQUEST" refers to the method for requesting a scheduling calendar component be created or modified; "REPLY" refers to the method a recipient of a request uses to update their status with the "Organizer" of the calendar component.
Properties defined by [iCAL] are referred to with capitalized, quoted strings of text, followed by the word "property". For example, "ATTENDEE" property refers to the iCalendar property used to convey the calendar address of a "Calendar User".
Property parameters defined by [iCAL] are referred to with lowercase, quoted strings of text, followed by the word "parameter". For example, "value" parameter refers to the iCalendar property parameter used to override the default data type for a property value.
Terminology
The email terms used in this memo are defined in RFC5322 and RFC2045. The calendaring and scheduling terms used in this memo are defined in [iCAL] and [iTIP].
MIME Message Format Binding
This section defines the message binding to the MIME electronic mail transport.
The sections below refer to the "originator" and the "recipient" of an iMIP message. In the case of a "request" method, the originator is the "Organizer" and the recipient is an "Attendee" of the event. In the case of a "response" method, the originator is an "Attendee" and the recipient is the "Organizer" of the event.
The RFC5322 "Reply-To" header field typically contains the email address of the originator of the scheduling message. However, this cannot be guaranteed because the sender of the iMIP message might not be the originator of the scheduling message and the sender's "Mail User Agent" (MUA) might not enforce iMIP semantics by translating the originator's address into the "Reply-To" email header field.
MIME Media Type
A MIME entity containing content information formatted according to this document will be referenced as a "text/calendar" content type [iCAL]. It is assumed that this content type will be transported through a MIME electronic mail transport.
Security
This section addresses several aspects of security including authentication, authorization, and confidentiality. Authentication and confidentiality can be achieved using Secure/MIME (S/MIME) RFC5750 RFC5751, which uses the Security Multiparts framework for MIME RFC1847.
Authorization
In iTIP messages [iTIP], only the "Organizer" is authorized to modify or cancel calendar entries she organizes. That is, [email protected] is not allowed to modify or cancel a meeting that was organized by [email protected]. Furthermore, only the respondent has the authorization to indicate their status to the "Organizer". That is, the "Organizer" MUST ignore an iTIP message from [email protected] that declines a meeting invitation for [email protected].
Implementations of iMIP SHOULD verify the authenticity of the creator of an iCalendar object before taking any action. Methods for doing this are presented later in this document.
RFC1847 message flow in iTIP supports someone working on behalf of a "Calendar User" through use of the "sent-by" parameter that is associated with the "ATTENDEE" and "ORGANIZER" properties. However, there is no mechanism to verify whether or not a "Calendar User" has authorized someone to work on their behalf. It is left to implementations to provide mechanisms for the "Calendar Users" to make that decision.
Authentication
Authentication MUST be performed using S/MIME RFC5750 RFC5751. Authentication is possible only on messages that have been signed. Unauthenticated messages (i.e., unsigned messages) may not be trusted.
Confidentiality
To ensure confidentiality using iMIP, implementations SHOULD utilize encryption specified in S/MIME RFC5750 RFC5751. iMIP does not restrict a "Calendar User Agent" (CUA) from forwarding iCalendar objects to other users or agents.
Email Addresses
The calendar address specified within the "ORGANIZER" and "ATTENDEE" properties in an iCalendar object sent using iMIP MUST be a proper "mailto:" [MAILTO] URI specification for the corresponding "Organizer" or "Attendee" of the "VEVENT" or "VTODO".
Because [iTIP] does not preclude "Attendees" from forwarding "VEVENT"s or "VTODO"s to others, the RFC5322 "Sender" value may not equal that of the "Organizer". Additionally, the "Organizer" or "Attendee" cannot be reliably inferred by the RFC5322 "Sender" or "Reply-To" header field values of an iMIP message. The relevant address MUST be ascertained by opening the "text/calendar" MIME body part and examining the "ATTENDEE" and "ORGANIZER" properties.
Content-Type Header Field
A MIME body part containing content information that conforms to this document MUST have an RFC2045 "Content-Type" value of "text/calendar". The RFC2045 "Content-Type" header field MUST also include the MIME parameter "method". The value MUST be the same (ignoring case) as the value of the "METHOD" property within the iCalendar object.
Note 1: A MIME message containing multiple iCalendar objects with different "method" values MUST be further encapsulated with a "multipart/mixed" MIME entity RFC2046. This will allow each of the iCalendar objects to be encapsulated within their own "text/calendar" MIME entity.
Note 2: A MIME body part with a "Content-Type" value of "text/calendar" that lacks the "method" parameter is not considered to be an iMIP body part and thus is not subject to the requirements specified in this document.
Note that according to [iCAL] the default character set for iCalendar objects is UTF-8 [UTF-8]. However, the default character set for a "text/*" MIME entity according to RFC2046 is US-ASCII. Thus, a "charset" MIME parameter MUST be present if the iCalendar object contains characters that can't be represented in the US-ASCII character set and, as specified in [iCAL], it MUST have the value "UTF-8".
The optional "component" MIME parameter defines the iCalendar component type contained within the iCalendar object.
The following is an example of this header field with a value that indicates an event message.
Content-Type: text/calendar; method=REQUEST; charset=UTF-8; component=vevent
The "text/calendar" content type allows for the scheduling message type to be included in a MIME message with other content information (i.e., "multipart/mixed") or included in a MIME message with a clear- text, human-readable form of the scheduling message (i.e., "multipart/alternative" RFC2046).
In order to permit the information in the scheduling message to be understood by MIME User Agents (UAs) that do not support the "text/calendar" content type, scheduling messages SHOULD be sent with an alternative, human-readable form of the information.
Note that "multipart/alternative" MUST NOT be used to represent two slightly different iCalendar objects, for example, two "VEVENT"s with alternative starting times.
CUAs can use other MIME parameters of the "Content-Type" header field, as well as a language specified in the Content-Language header field RFC3282, to pick a "text/calendar" part for processing if a "multipart/alternative" MIME message contains more than one "text/calendar" part.
Any receiving UA compliant with this specification MUST be able to process "text/calendar" body parts enclosed within "multipart/*". Note that a "multipart/mixed" MIME message can include multiple "text/calendar" components. The receiving UA MUST be able to process all of them.
Content-Transfer-Encoding Header Field
Unless an iMIP message is transported over 8-bit clean transport (such as SMTP [8BITMIME]), a transfer encoding such as quoted- printable or base64 RFC2045 MUST be used for iCalendar objects containing any characters that can't be represented in the US-ASCII character set. For example:
From: [email protected] To: [email protected] Subject: Phone Conference Mime-Version: 1.0 Date: Wed, 07 May 2008 21:30:25 +0400 Message-ID: <[email protected]> Content-Type: text/calendar; method=REQUEST; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:[email protected] ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:[email protected] DTSTAMP:20080507T170000Z DTSTART:20080701T160000Z DTEND:20080701T163000Z SUMMARY:Phone call to discuss your last visit DESCRIPTION:=D1=82=D1=8B =D0=BA=D0=B0=D0=BA - =D0=B4=D0=BE=D0=
=B2=D0=BE=D0=BB=D0=B5=D0=BD =D0=BF=D0=BE=D0=B5=D0=B7=D0=B4=D0=BA=D0 =BE=D0=B9?
UID:calsvr.example.com-8739701987387998 SEQUENCE:0 STATUS:TENTATIVE END:VEVENT END:VCALENDAR
Content-Disposition Header Field
Implementations MAY include a "Content-Disposition" header field to define a file name for an iCalendar object. However, the handling of a MIME part MUST be based on its RFC2045 "Content-Type" and not on the extension specified in the "Content-Disposition", as different email malware is known to trick User Agents into misinterpreting content of messages by specifying a file extension in the Content- Disposition header field that doesn't correspond to the value of the "Content-Type" header field.
Security Considerations
The security threats that applications must address when implementing iTIP are detailed in [iTIP]. In particular, two spoofing threats are identified in Section 6.1 of [iTIP]: spoofing the "Organizer", and spoofing an "Attendee". To address these threats, the originator of an iCalendar object must be authenticated by a recipient. Once
authenticated, a determination can be made as to whether or not the originator is authorized to perform the requested operation. Compliant applications MUST support signing and encrypting "text/calendar" body parts using a mechanism based on S/MIME RFC5750 RFC5751 in order to facilitate the authentication of the originator of the iCalendar object (see Sections 2.2.2 and 2.2.3). The steps for processing a signed iMIP message are described below:
1. Using S/MIME, determine who signed the "text/calendar" body part
containing the iCalendar object. This is the "signer". (Note that the email address of the signer MUST be specified in the rfc822Name field of the "subject alternative name" extension of the signer certificate, as specified in RFC5280, Section 4.1.2.6.) Note that the signer is not necessarily the person sending an e-mail message, since an e-mail message can be forwarded.
2. Correlate the signer to either an "ATTENDEE" property or to the
"ORGANIZER" property in the iCalendar object, based on the method and the calendar component specified in the iCalendar object, as defined in Section 1.4 of [iTIP]. If the signer cannot be correlated to an "ATTENDEE"/"ORGANIZER" property, then actively warn the user controlling the "Calendar User Agent" that the iCalendar object is untrusted, and encourage the user to ignore the message, but give advanced users the option to (a) view the certificate of the signer and the entire certificate chain (if any) in order to help decide if the signer should be trusted to send the message, and then (b) allow the CUA to accept and process the iCalendar object.
3. Determine whether or not the "ATTENDEE"/"ORGANIZER" is authorized
to perform the operation as defined by [iTIP]. If the conditions are not met, ignore the message.
4. If all the above conditions are met, the message can be processed.
S/MIME signing also protects against malicious changes to messages in transit.
If calendar confidentiality is required by the sender, signed iMIP messages SHOULD be encrypted by a mechanism based on S/MIME RFC5750 RFC5751. If iMIP is used within a single ADministrative Management Domain (ADMD) RFC5598, SMTP STARTTLS [SMTP-TLS] (together with STARTTLS in IMAP/POP [IMAP-POP-TLS]) MAY alternatively be used to provide calendar confidentiality.
Once a signed and/or encrypted iMIP message is received and successfully verified (as detailed above) by a CUA, the CUA SHOULD remember whether the sender of the message is using signing and/or encrypting. If an unsigned iMIP message is received from the same sender later on, the receiving CUA SHOULD warn the receiving user about a possible man-in-the-middle attack and SHOULD ignore the message, unless explicitly overridden by the user.
Implementations MAY provide means for users to disable signing and encrypting.
It is possible to receive iMIP messages sent by someone working on behalf of another "Calendar User". This is determined by examining the "sent-by" parameter in the relevant "ORGANIZER" or "ATTENDEE" property. [iCAL] and [iTIP] provide no mechanism to verify that a "Calendar User" has authorized someone else to work on their behalf. To address this security issue, implementations MUST provide mechanisms for the "Calendar Users" to make that decision before applying changes from someone working on behalf of a "Calendar User". One way to achieve this is to reject iMIP messages sent by users other than the "ORGANIZER" or the "ATTENDEE"s. Alternatively, the receiver could have a list of trusted <sent-by, organizer> proxies in its local security policy. And yet another way is to prompt the user for confirmation.
iMIP-based calendaring is frequently deployed within a single ADMD, with boundary filtering employed to restrict email calendaring flows to be inside the ADMD. This can help in minimizing malicious changes to calendaring messages in transit, as well as in making authorization decisions less risky.
A security consideration associated with the use of the Content- Disposition header field is described in Section 2.6.
Use of S/MIME makes the security considerations discussed in RFC5750 RFC5751 relevant to this document. For additional security considerations regarding certificate and Certificate Revocation List (CRL) verification, please see RFC5280.
Examples
Single Component with an ATTACH Property
This minimal message shows how an iCalendar object references an attachment. The attachment is accessible via its URL.
From: [email protected] To: [email protected] Subject: Phone Conference Mime-Version: 1.0 Content-Type: text/calendar; method=REQUEST; charset=US-ASCII Content-Transfer-Encoding: 7bit
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:[email protected] ATTENDEE;RSVP=YES:mailto:[email protected] DTSTAMP:19970611T190000Z DTSTART:19970701T210000Z DTEND:19970701T230000Z SUMMARY:Phone Conference DESCRIPTION:Please review the attached document. UID:calsvr.example.com-873970198738777 ATTACH:ftp://ftp.bar.example.com/pub/docs/foo.doc STATUS:CONFIRMED END:VEVENT END:VCALENDAR
Using multipart/alternative for Low-Fidelity Clients
This example shows how a client can emit a multipart message that includes both a plain text version and the full iCalendar object. Clients that do not support "text/calendar" will still be capable of rendering the plain text representation.
From: [email protected] To: [email protected] Subject: Phone Conference Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="01BD3665.3AF0D360"
--01BD3665.3AF0D360 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit
This is an alternative representation of a "text/calendar" MIME object.
When: 7/1/1997 10:00AM PDT - 7/1/97 10:30AM PDT Where: Organizer: [email protected] Summary: Phone Conference
--01BD3665.3AF0D360 Content-Type: text/calendar; method=REQUEST; charset=US-ASCII Content-Transfer-Encoding: 7bit
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:[email protected] ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:[email protected] DTSTAMP:19970611T190000Z DTSTART:19970701T170000Z DTEND:19970701T173000Z SUMMARY:Phone Conference UID:calsvr.example.com-8739701987387771 SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR
--01BD3665.3AF0D360
Single Component with an ATTACH Property and Inline Attachment
This example shows how a message containing an iCalendar object references an attached document. The reference is made using a Content-ID (CID). Thus, the iCalendar object and the document are packaged in a "multipart/related" encapsulation.
From: [email protected] To: [email protected] Subject: Phone Conference Mime-Version: 1.0 Content-Type: multipart/related; boundary="boundary-example-1"
--boundary-example-1
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="event.ics"
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:[email protected] ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:[email protected] DTSTAMP:19970611T190000Z DTSTART:19970701T180000Z DTEND:19970701T183000Z SUMMARY:Phone Conference UID:calsvr.example.com-8739701987387771 ATTACH:cid:[email protected] SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR
--boundary-example-1 Content-Type: application/msword; name="FieldReport.doc" Content-Transfer-Encoding: base64 Content-Disposition: inline; filename="FieldReport.doc" Content-ID: <[email protected]>
0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAABAAAARAAAAAAA AAAAEAAAQAAAAAEAAAD+////AAAAAEUAAAD/////////////////////////////////
...
--boundary-example-1--
Multiple Similar Components
Multiple iCalendar components of the same type can be included in the iCalendar object when the "METHOD" is the same for each component.
From: [email protected] To: [email protected] Subject: Summer Company Holidays Mime-Version: 1.0 Content-Type: text/calendar; method=PUBLISH; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="event.ics"
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:PUBLISH VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:[email protected] DTSTAMP:19970611T150000Z DTSTART:19970701T150000Z DTEND:19970701T230000Z SUMMARY:Company Picnic DESCRIPTION:Food and drink will be provided UID:calsvr.example.com-873970198738777-1 SEQUENCE:0 STATUS:CONFIRMED END:VEVENT BEGIN:VEVENT ORGANIZER:mailto:[email protected] DTSTAMP:19970611T190000Z DTSTART:19970715T150000Z DTEND:19970715T230000Z SUMMARY:Company Bowling Tournament DESCRIPTION:We have 10 lanes reserved UID:calsvr.example.com-873970198738777-2 SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR
Multiple Mixed Components
Different component types must be encapsulated in separate iCalendar objects.
From: [email protected] To: [email protected] Subject: Phone Conference Mime-Version: 1.0 Content-Type: multipart/mixed;
boundary="--FEE3790DC7E35189CA67CE2C"
This is a multi-part message in MIME format.
FEE3790DC7E35189CA67CE2C
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="event1.ics"
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:[email protected] ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:[email protected] DTSTAMP:19970611T190000Z DTSTART:19970701T210000Z DTEND:19970701T230000Z SUMMARY:Phone Conference DESCRIPTION:Discuss what happened at the last meeting UID:calsvr.example.com-8739701987387772 SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR
FEE3790DC7E35189CA67CE2C
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="todo1.ics"
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VTODO DUE:19970701T160000Z ORGANIZER:mailto:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:[email protected] ATTENDEE;RSVP=YES:mailto:[email protected] SUMMARY:Phone Conference DESCRIPTION:Discuss a new location for the company picnic UID:calsvr.example.com-td-8739701987387773 SEQUENCE:0 STATUS:NEEDS-ACTION END:VEVENT END:VCALENDAR
FEE3790DC7E35189CA67CE2C
Detailed Components with an ATTACH Property
This example shows the format of a message containing a group meeting between three individuals. The "multipart/related" encapsulation is used because the iCalendar object contains an ATTACH property that uses a CID to reference the attachment.
From: [email protected] MIME-Version: 1.0 To: [email protected],[email protected] Subject: REQUEST - Phone Conference Content-Type: multipart/related;
boundary="--FEE3790DC7E35189CA67CE2C"
FEE3790DC7E35189CA67CE2C
Content-Type: multipart/alternative;
boundary="--00FEE3790DC7E35189CA67CE2C00"
00FEE3790DC7E35189CA67CE2C00
Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit
When: 7/1/1997 10:00PM PDT - 7/1/97 10:30 PM PDT Where: Organizer: [email protected] Summary: Let's discuss the attached document
00FEE3790DC7E35189CA67CE2C00
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII;
Component=vevent
Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="event.ics"
BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:[email protected] ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:[email protected] ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:[email protected] ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:[email protected] DTSTAMP:19970611T190000Z DTSTART:19970621T170000Z DTEND:199706211T173000Z SUMMARY:Let's discuss the attached document UID:calsvr.example.com-873970198738777-8aa ATTACH:cid:calsvr.example.com-12345aaa SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR
00FEE3790DC7E35189CA67CE2C00
FEE3790DC7E35189CA67CE2C
Content-Type: application/msword; name="FieldReport.doc" Content-Transfer-Encoding: base64 Content-Disposition: inline; filename="FieldReport.doc" Content-ID: <calsvr.example.com-12345aaa>
R0lGODdhTAQZAJEAAFVVVd3d3e4AAP///ywAAAAATAQZAAAC/5yPOSLhD6OctNqLs94Xq AG4kiW5omm6sq27gvH8kzX9o1y+s73/g8MCofEovGITCoxKMbyCR16cNSq9YrNarfcrvd riIH5LL5jE6rxc3G+v2cguf0uv2Oz+v38L7/DxgoOKjURnjIIbe3yNjo+AgZWYVIWWl5i ZnJY6J
...
FEE3790DC7E35189CA67CE2C
Recommended Practices
This section outlines a series of recommended practices when using a messaging transport to exchange iCalendar objects.
Use of Content and Message IDs
The [iCAL] specification makes frequent use of the URI for data types in properties such as "DESCRIPTION", "ATTACH", "CONTACT", and others. Two forms of URIs are the Message ID (MID) and the Content-ID (CID). These are defined in RFC2392. Although RFC2392 allows referencing messages or MIME body parts in other MIME entities or stores, it is strongly RECOMMENDED that iMIP implementations include all referenced messages and body parts in a single MIME entity. Simply put, if an iCalendar object contains CID or MID references to other messages or body parts, implementations should ensure that these messages and/or body parts are transmitted with the iCalendar object. If they are not, there is no guarantee that the receiving CUA will have the access or the authorization to view those objects.
IANA Considerations
The "text/calendar" MIME media type was registered in [iCAL].
References
Normative References
[iCAL] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)", RFC 5545, September 2009.
[iTIP] Daboo, C., Ed., "iCalendar Transport-Independent
Interoperability Protocol (iTIP)", RFC 5546, December 2009.
RFC5322 Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[MAILTO] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, October 2010.
RFC1847 Galvin, J., Murphy, S., Crocker, S., and N. Freed,
"Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, October 1995.
RFC2045 Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996.
RFC2046 Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.
RFC2392 Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998.
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[SMTP-TLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[IMAP-POP-TLS]
Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, June 1999.
RFC5750 Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Certificate Handling", RFC 5750, January 2010.
RFC5751 Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010.
RFC5280 Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008.
Informative References
[8BITMIME] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport", RFC 1652, July 1994.
RFC5598 Crocker, D., "Internet Mail Architecture", RFC 5598, July
2009.
RFC3282 Alvestrand, H., "Content Language Headers", RFC 3282, May
2002.
Appendix A. Changes since RFC 2447
Updated references. Split them into Normative and Informative.
Updated examples to use example.com/example.net domains.
Corrected usage of RFC 2119 language.
Clarified that charset=UTF-8 is required, unless the calendar can be entirely represented in US-ASCII.
Clarified that 7-bit content transfer encodings should be used unless the calendar object is known to be transferred over 8-bit clean transport.
Clarified that file extension specified in the Content-Disposition header field is not to be used to override the "Content-Type" MIME type.
Disallowed use of "multipart/alternative" for slightly different representations of the same calendar.
Clarified handling of the "method" MIME parameter of the "Content- Type" header field.
Clarified that in an iMIP message an ORGANIZER/ATTENDEE property contains a mailto: URI.
Fixed examples with ATTENDEE property to use "CUTYPE=" instead of "TYPE=".
Clarified that message integrity/confidentiality should be achieved using S/MIME.
Provided additional examples.
Improved the Security Considerations section.
Made multiple editorial changes to different sections of the document.
Appendix B. Acknowledgements
The editor of this document wishes to thank Frank Dawson, Steve Mansour, and Steve Silverberg, the original authors of RFC 2447, as well as the following individuals who have participated in the drafting, review, and discussion of this memo:
Reinhold Kainhofer, Cyrus Daboo, Bernard Desruisseaux, Eliot Lear, and Peter Saint-Andre.
Author's Address
Alexey Melnikov (editor) Isode Ltd 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK
EMail: [email protected]