Subject: [smime] [Errata Held for Document Update] RFC2631 (5954)

From: RFC Errata System <[email-masked]>
Date: Sun, 12 Jan 2020 20:44:09 -0800 (PST)

The following errata report has been held for document update 
for RFC2631, "Diffie-Hellman Key Agreement Method". 

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You may review the report below and at:
https://www.rfc-editor.org/errata/eid5954

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Status: Held for Document Update
Type: Technical

Reported by: Paul Janson <[email-masked]>
Date Reported: 2020-01-02
Held by: Benjamin Kaduk (IESG)

Section: 2.1.5.

Original Text
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     1. Verify that y lies within the interval [2,p-1]. If it does not,
        the key is invalid.
     2. Compute y^q mod p. If the result == 1, the key is valid.
        Otherwise the key is invalid.

Corrected Text
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     1. Verify that y lies within the interval [2,p-1]. If it does not,
        the key is invalid.
     2. Compute y^q mod p. If the result == 1, the key is valid.
        Otherwise the key is invalid.
     3. Verify that y does not match g.

Notes
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Validating that (g == received y) needs to be an additional exclusion to the valid range [2,p-1]. If party 'a' accepts received public key 'yb' matching 'g', then ZZ matches  public key 'ya'. i.e. if yb = 2, then xb = 1, therefore ZZ = ya^1 = ya

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RFC2631 (draft-ietf-smime-x942-07)
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Title               : Diffie-Hellman Key Agreement Method
Publication Date    : June 1999
Author(s)           : E. Rescorla
Category            : PROPOSED STANDARD
Source              : S/MIME Mail Security
Area                : Security
Stream              : IETF
Verifying Party     : IESG