A few suggested changes "That is, SSP permits potential DKIM signers to publish statements about how they use DKIM, and also to publish directions for DKIM validators (receivers) on how they are to handle a class of received messages."
Revised That is, SSP permits potential DKIM signers to publish statements about how they use DKIM, and also to publish a policy guideline for the DKIM validators to assist in further message processing ***************************************** "By associating an organization's verifiable identity to a message, the reputation of that organization can then be used by a message-receiving engine, for determining message handling, such as whether to deliver the message to the designated recipient. This is what DKIM Base permits." Revised By associating an organization's verifiable identity to a message, the reputation of that organization can then be used by a message-receiving engine, for determining message handling. ***************************************** Delete the following section as SSP doesn't detect anything, just advises receivers about sender policy By contrast, SSP seeks to detect misbehaviors, specifically related to unauthorized use of the email address in a message's RFC2822.From field <addr-spec>. SSP does not seek to deal with other identity fraud, such as in the human-readable RFC2822.From <display-name>, the Subject field, or in the message body, or any use of "cousin" domains that can be confused with a target domain ******************************************* Bill Oxley Messaging Engineer Cox Communications 404-847-6397 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Dave Crocker Sent: Tuesday, December 11, 2007 12:36 AM To: [email protected] Subject: [ietf-dkim] Draft summary of SSP functionality -v2 Folks, Here is a revised version of the SSP Summary Description, based on comments received: The IETF's DKIM working group has followed its specification of a base method for associating a responsible identity to an email, via cryptographic signing. The new specification is for Sender Signing Practices (SSP). The SSP specification describes itself as defining a mechanism "senders may use to advertise how they sign their outgoing mail, and how verifiers should access and interpret those results." That is, SSP permits potential DKIM signers to publish statements about how they use DKIM, and also to publish directions for DKIM validators (receivers) on how they are to handle a class of received messages. The SSP mechanism permits a potential signer -- that is, the owner of a domain name -- to publish an SSP-specific DNS record -- a TXT record in an SSP-specific branch under the domain name. On the receive-side, the domain name under which the DNS query is made is taken from the author's mailbox address -- the rfc2822.From <addr-spec> portion of an address -- in a received message. By associating an organization's verifiable identity to a message, the reputation of that organization can then be used by a message-receiving engine, for determining message handling, such as whether to deliver the message to the designated recipient. This is what DKIM Base permits. By contrast, SSP seeks to detect misbehaviors, specifically related to unauthorized use of the email address in a message's RFC2822.From field <addr-spec>. SSP does not seek to deal with other identity fraud, such as in the human-readable RFC2822.From <display-name>, the Subject field, or in the message body, or any use of "cousin" domains that can be confused with a target domain. SSP is motivated by a desire on the part of message senders, to inform message recipients about constraints on the senders' practices. The premise is that receivers with this additional information will be able to detect, and possibly reject, a class of mail that is not legitimate. At best, the mechanism is approximate, in that a legitimate message might begin with a legitimate signature that becomes broken during transit. When SSP is used, such messages will be treated by the recipient as exceptions. The current SSP draft provides for two basic conditions which will trigger a query: 1. Unsigned message. When a receiver gets a message that has no DKIM signature, they can query the DNS for an SSP record that is associated with the domain name in the (first) rfc2822.From field header mailbox address. 2. Signed message. When a receiver gets a message that is signed, and lists one identity in the signature's i= parameter -- the identity on behalf of which the message is signed -- but another in the (first) address in the From field, then perform the SSP query, described in step 1. The publisher of an SSP record can say that: 1. All mail that they send is signed by them 2. All mail that they send is signed by them and they do not send mail via intermediaries -- called "third parties" -- such as mailing lists that may modify and re-sign the message. Messages that fail an SSP analysis are handled as exceptions. The publisher of an SSP record may request that such mail be treated to: 1. Further consideration, where the exceptional status is only one factor in determining handling. 2. Rejected. SSP also permits the publisher to declare that the record applies to all of its sub-domains, although there is a DNS limitation on reconciling deeply nested sub-domains with this record. The SSP specification defines a 10-step "check procedure" that is a decision tree for performing SSP analysis. As an example of implications, the SSP rejection semantics would mean that a SSP-conformant receiving site would reject a message that has a broken author signature,even if it still had a valid signature by an operator with a good reputation. SSP is likely to have a number of other interactions with email handling practice. Given that adoption of a new mechanism like DKIM's base signing takes many years, adoption by any arbitrary sender/receiver pair is unlikely for many years, absent prior arrangement. So most publishers of SSP records will be sending to sites that are not checking them. Equally it should be assumed that receivers will almost always obtain a failed SSP DNS query, for every message with a new (un-cached) domain name in the From field. d/ -- Dave Crocker Brandenburg InternetWorking bbiw.net _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html
