Fix: #850. Obsolete parameters.

draft-ietf-httpbis-digest-headers.md

@@ -238,7 +238,7 @@ transformations (eg. transfer codings for HTTP/1.1 see 6.1 of
 A representation digest consists of
 the value of a checksum computed on the entire selected `representation data`
 (see Section 7 of {{SEMANTICS}}) of a resource identified according to Section 5.5.2 of {{SEMANTICS}}
-together with an indication of the algorithm used (and any parameters)
+together with an indication of the algorithm used
 
 ~~~ abnf
    representation-data-digest = digest-algorithm "="
@@ -278,6 +278,8 @@ A recipient MAY ignore any or all of the representation-data-digests in a Digest
 field. This allows the recipient to choose which digest-algorithm(s) to use for
 validation instead of verifying every received representation-data-digest.
 
+A recipient MUST ignore a representation-data-digest containing parameters.
+
 A sender MAY send a representation-data-digest using a digest-algorithm without
 knowing whether the recipient supports the digest-algorithm, or even knowing
 that the recipient will ignore it.
@@ -327,15 +329,13 @@ Two examples of its use are
 
 # Digest Algorithm Values {#algorithms}
 
-Digest-algorithm values are used to indicate a specific digest computation.  For
-some digest-algorithms, one or more parameters can be supplied.
+Digest-algorithm values are used to indicate a specific digest computation.
 
 ~~~
    digest-algorithm = token
 ~~~
 
-The BNF for "parameter" is defined in Section 5.7.6 of
-{{SEMANTICS}}. All digest-algorithm values are case-insensitive
+All digest-algorithm values are case-insensitive
 but the lower case is preferred.
 
 The Internet Assigned Numbers Authority (IANA) acts as a registry for
@@ -464,6 +464,12 @@ This RFC deprecates the negotiation of Content-MD5 as it has been obsoleted by
 [RFC7231].
 The `contentMD5` token defined in Section 5 of [RFC3230] MUST NOT be used as a digest-algorithm.
 
+# Obsolete Digest Header Field Parameters {#obsolete-parameters}
+
+This RFC obsoletes the usage of parameters with `Digest` introduced in
+Section 4.1.1 and 4.2 of [RFC3230] because this feature has not been widely deployed
+and complicates field-value processing.
+
 # Relationship to Subresource Integrity (SRI)
 
 Subresource Integrity [SRI] is an integrity mechanism that shares some
@@ -1059,7 +1065,13 @@ in conjuction with the encrypted content-coding {{?RFC8188}}.
 
 ## Algorithm Agility
 
-...
+Algorithm agility is achieved establishing the IANA Digest Algorithm Values registry,
+and adding it the "Status" field making it possible to deprecate and obsolete insecure algorithms.
+
+The now obsoleted [RFC3230] allowed passing parameters to digest-algorithms:
+if those parameters are used to verify the checksum, there will be enough space for bad or insecure
+implementations. If a digest-algorithm want to support parameters, it can encode them into the
+representation-data-digest.
 
 # IANA Considerations
 
@@ -1483,3 +1495,4 @@ _RFC Editor: Please remove this section before publication._
 * Reference httpbis-semantics #1156
 * Add contentMD5 as an obsoleted digest-algorithm #1249
 * Use lowercase digest-algorithms names in the doc and in the digest-algorithm IANA table.
+* Obsolete parameters #850