Subject: [TLS] [Technical Errata Reported] RFC5705 (4395)

From: RFC Errata System <[email-masked]>
Date: Tue, 16 Jun 2015 13:04:07 -0700 (PDT)

The following errata report has been submitted for RFC5705,
"Keying Material Exporters for Transport Layer Security (TLS)".

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=5705&eid=4395

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Type: Technical
Reported by: Rick van Rein <[email-masked]>

Section: 4

Original Text
-------------
   If no context is provided, it then computes:

           PRF(SecurityParameters.master_secret, label,
               SecurityParameters.client_random +
               SecurityParameters.server_random
               )[length]

   If context is provided, it computes:

           PRF(SecurityParameters.master_secret, label,
               SecurityParameters.client_random +
               SecurityParameters.server_random +
               context_value_length + context_value
               )[length]

Corrected Text
--------------
   If no context is provided, it then computes:

           PRF(SecurityParameters.master_secret, label,
               SecurityParameters.client_random +
               SecurityParameters.server_random
               )[0..length-1]

   If context is provided, it computes:

           PRF(SecurityParameters.master_secret, label,
               SecurityParameters.client_random +
               SecurityParameters.server_random +
               context_value_length + context_value
               )[0..length-1]

Notes
-----
The current notation is not in line with that of RFC 5246, where the [0..N-1] notation is used on a PRF outcome in Sections 7.4.9 and 8.1 and similar [A..B] notation is also used elsewhere.  This makes me believe that the current text is technically wrong, and not in line with the intentions stated informally below it,

   The output is a pseudorandom bit string of length bytes generated
   from the master_secret.

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-------------
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RFC5705 (draft-ietf-tls-extractor-07)
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Title               : Keying Material Exporters for Transport Layer Security (TLS)
Publication Date    : March 2010
Author(s)           : E. Rescorla
Category            : PROPOSED STANDARD
Source              : Transport Layer Security
Area                : Security
Stream              : IETF
Verifying Party     : IESG