[TLS] [Technical Errata Reported] RFC8446 (5874)

RFC Errata System <rfc-editor@rfc-editor.org> Sat, 12 October 2019 04:22 UTC

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Subject: [TLS] [Technical Errata Reported] RFC8446 (5874)
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The following errata report has been submitted for RFC8446,
"The Transport Layer Security (TLS) Protocol Version 1.3".

--------------------------------------
You may review the report below and at:
https://www.rfc-editor.org/errata/eid5874

--------------------------------------
Type: Technical
Reported by: Mr Laurie Perrin <lperrin@bellaliant.net>;

Section: 5.1

Original Text
-------------
...

   Application Data messages contain data that is opaque to TLS.
   Application Data messages are always protected.  Zero-length
   fragments of Application Data MAY be sent, as they are potentially
   useful as a traffic analysis countermeasure.  Application Data
   fragments MAY be split across multiple records or coalesced into a
   single record.

Corrected Text
--------------
...

   Application Data messages contain data that is opaque to TLS.
   Application Data messages are always protected.  Zero-length
   fragments of Application Data (i.e. those encapsulating an
   TLSInnerPlaintext record having a content field of length zero)
   MAY be sent, as they are potentially useful as a traffic analysis
   countermeasure. Application Data fragments MAY be split across
   multiple records or coalesced into a single record.

Notes
-----
In the interest of clarity, it may be prudent to specify the type of record for
which a fragment of length zero is being considered - it cannot be that of the
TLSCiphertext itself, for "Application Data messages are always protected,"
therefore I infer this relates to the TLSInnerPlaintext content field (of
length "TLSPlaintext.length") - i.e. to the TLSPlaintext fragment.

Note: This comment also applies to previous versions of the TLS specification,
in particular with the introduction of the respective text concerning zero-length
fragments in RFC 5246. In TLS 1.2, this would be the GenericXXCipher content
field of length "TLSCompressed.length" - i.e. to the TLSCompressed fragment.

Note: The implications of zero-length records must be considered with respect to
potential vectors for denial of service.

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--------------------------------------
RFC8446 (draft-ietf-tls-tls13-28)
--------------------------------------
Title               : The Transport Layer Security (TLS) Protocol Version 1.3
Publication Date    : August 2018
Author(s)           : E. Rescorla
Category            : PROPOSED STANDARD
Source              : Transport Layer Security
Area                : Security
Stream              : IETF
Verifying Party     : IESG