Re: [auth48] AUTH48: RFC-to-be 9474 <draft-irtf-cfrg-rsa-blind-signatures-14> for your review

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Authors,

While reviewing this document during AUTH48, please resolve (as necessary) the following questions, which are also in the XML file.

1) <!-- [rfced] Please insert any keywords (beyond those that appear in the
title) for use on <https://www.rfc-editor.org/search>. -->


2) <!-- [rfced] Please ensure that the guidelines listed in Section 2.1
of RFC 5743 have been adhered to in this document. -->


3) <!-- [rfced] Section 1:

a) We updated this sentence to clarify that the family of variants is
specified by this document and not computed.  Please let us know any
objections.

Original:
 This document specifies a protocol for computing RSA blind signatures
 using RSA-PSS encoding, and a family of variants for this protocol,
 denoted RSABSSA (RSA Blind Signature with Appendix).

Currently:
 This document specifies (1) a protocol for computing RSA blind
 signatures using RSA-PSS encoding and (2) a family of variants
 (Section 5) for this protocol, denoted RSABSSA (RSA Blind Signature
 with Appendix).

b) We see in other documents and in online searches that "RSABSSA" is
often listed as "RSA-BSSA" and defined as "RSA Blind Signature Scheme
with Appendix".  We also see that "RSA-BSSA" and (lowercased) "RSA
Blind Signature Scheme with Appendix" were used in version -01 of
this document but then changed, and we realize that any changes would
affect such listings as "RSABSSA-SHA384-PSS-Randomized" and
"RSABSSA-SHA384-PSS-Deterministic".

Please let us know if you would like to make any updates as related
to this term.  (We are fine either way but thought that this item was
worth pointing out.) -->


4) <!-- [rfced] Section 4:  Should any of the artwork in this section
be sourcecode?  Please see
<https://www.rfc-editor.org/materials/sourcecode-types.txt>, and let
us know if any changes are needed.  If the sourcecode-types page
does not contain an applicable type, please let us know.
Also, if you use sourcecode, it is acceptable to leave the "type"
attribute unset. -->


5) <!-- [rfced] Sections 4.1 through 4.4:  We changed the artwork to
sourcecode with type="pseudocode" in these sections.

See <https://www.rfc-editor.org/materials/sourcecode-types.txt> for a
list of sourcecode types.

Please review, and let us know any objections. -->


6) <!-- [rfced] Section 4.2:  "If EMSA-PSS-ENCODE raises an error, raise
the error" reads oddly here.  Do two entities raise the same error,
or does one entity forward the error thrown by EMSA-PSS-ENCODE?
If you would like to rephrase, please provide alternative text.

Original:
 2. If EMSA-PSS-ENCODE raises an error, raise the error and stop

Perhaps:
 2. If EMSA-PSS-ENCODE raises an error, stop

Or possibly:
 2. If EMSA-PSS-ENCODE throws an error, raise the error and stop -->


7) <!-- [rfced] Section 5:  We do not see "RSASSA-PSS" mentioned in
Section 9.1.1 of RFC 8017.  Is EMSA-PSS-ENCODE considered an
RSASSA-PSS parameter?  If yes, will this be clear to readers?
Please let us know if any changes are needed.

Original:
 Each
 variant specifies RSASSA-PSS parameters as defined in Section 9.1.1
 of [RFC8017] and the type of message preparation function applied (as
 described in Section 4.1). -->


8) <!--[rfced]  Would it be correct to expand the first mention of “MGF1” as “mask generation function 1 (MGF1)" (per use in RFC 9151, which references RFC 8017), or do you prefer to leave the text as is (to match use in RFC 8017)?

Current:
  Each variant uses the MGF1 mask generation function 
  defined in Appendix B.2.1. of [RFC8017].

Perhaps:
  Each variant uses the mask generation function 1 (MGF1) 
  defined in Appendix B.2.1. of [RFC8017].
-->


9) <!-- [rfced] Section 5:  We had trouble parsing these sentences.
If the suggested text is not correct, please provide clarifying text.

Original:
 1.  RSABSSA-SHA384-PSS-Randomized: This named variant uses SHA-384 as
     the hash function, MGF1 with SHA-384 as the PSS mask generation
     function, a 48-byte salt length, and uses the randomized
     preparation function (PrepareRandomize).

 2.  RSABSSA-SHA384-PSSZERO-Randomized: This named variant uses
     SHA-384 as the hash function, MGF1 with SHA-384 as the PSS mask
     generation function, an empty PSS salt, and uses the randomized
     preparation function (PrepareRandomize).

 3.  RSABSSA-SHA384-PSS-Deterministic: This named variant uses SHA-384
     as the hash function, MGF1 with SHA-384 as the PSS mask
     generation function, 48-byte salt length, and uses the identity
     preparation function (PrepareIdentity).

 4.  RSABSSA-SHA384-PSSZERO-Deterministic: This named variant uses
     SHA-384 as the hash function, MGF1 with SHA-384 as the PSS mask
     generation function, an empty PSS salt, and uses the identity
     preparation function (PrepareIdentity).  This is the only variant
     that produces deterministic signatures over the client's input
     message msg.

Suggested:
 RSABSSA-SHA384-PSS-Randomized:  This named variant uses SHA-384 as
    the hash function, MGF1 with SHA-384 as the PSS mask generation
    function, and a 48-byte salt length; it also uses the randomized
    preparation function (PrepareRandomize).

 RSABSSA-SHA384-PSSZERO-Randomized:  This named variant uses SHA-384
    as the hash function, MGF1 with SHA-384 as the PSS mask generation
    function, and an empty PSS salt; it also uses the randomized
    preparation function (PrepareRandomize).

 RSABSSA-SHA384-PSS-Deterministic:  This named variant uses SHA-384 as
    the hash function, MGF1 with SHA-384 as the PSS mask generation
    function, and a 48-byte salt length; it also uses the identity
    preparation function (PrepareIdentity).

 RSABSSA-SHA384-PSSZERO-Deterministic:  This named variant uses
    SHA-384 as the hash function, MGF1 with SHA-384 as the PSS mask
    generation function, and an empty PSS salt; it also uses the
    identity preparation function (PrepareIdentity).  This is the
    only variant that produces deterministic signatures over the
    client's input message msg. -->


10) <!-- [rfced] Section 6.1:  "errors generated throughout this
specification" reads oddly.  If the suggested text is not
acceptable, please provide alternative text.

Original:
 The explicit errors generated throughout this specification, along
 with the conditions that lead to each error, are listed in the
 definitions for Blind, BlindSign, and Finalize.

Suggested:
 The generation of explicit errors as discussed throughout this
 specification, along with the conditions that lead to each error,
 are listed in the definitions for Blind, BlindSign, and Finalize. -->


11) <!-- [rfced] Section 6.2:  Should "RSASSA-PSS OID" be "id-RSASSA-PSS
OID" per RFC 5756?

Original:
 If the server public key is carried in an X.509 certificate, it MUST
 use the RSASSA-PSS OID [RFC5756]. -->


12) <!-- [rfced] Section 7:

a) We don't see any mention of "PrepareRandomize" or "preparation"
(as in "randomized preparation function (PrepareRandomize)" from
Section 5) in [Lys22].  Will this text and citation be clear to
readers?

Original:
 Lysyanskaya also proved that the RSABSSA variants which use the
 PrepareRandomize function achieve blindness in [Lys22].

b) We don't see any mention of "PrepareIdentity" in Section 7.3.
Will this text and citation be clear to readers?

Original:
 However, additional
 assumptions on the message inputs are required for blindness to hold
 for RSABSSA variants that use the PrepareIdentity function; see
 Section 7.3 for more discussion on those results. -->


13) <!-- [rfced] Section 7.4:  Because this is the first mention of
"message randomizer prefix", we updated this sentence for ease of the
reader.  Please let us know any objections.

Original:
 All random values in the protocol, including the salt, message
 randomizer prefix, and random blind value in Blind, MUST be generated
 from a cryptographically secure random number generator [RFC4086].

Currently:
 All random values in the protocol, including the salt, message
 randomizer prefix (msg_prefix; see Appendix A), and random blind
 value in Blind, MUST be generated from a cryptographically secure
 random number generator [RFC4086]. -->


14) <!-- [rfced] Section 7.6:

a) We do not see any mention of "v3" or "version 3" as related to
X.509 in RFC 4055.  Will this citation be clear to readers?

Original:
 First, it is recommended in recent
 standards, including TLS 1.3 [RFC8446], X.509v3 [RFC4055], and even
 PKCS#1 itself.

b) Because this text is quoted, we updated it to match the text in
RFC 8017.  Please let us know any concerns; for example, if you wish
to keep "recommended for eventual adoption", the quotes will need to
be removed.

Original:
 According to [RFC8017], "Although no attacks are
 known against RSASSA-PKCS#1 v1.5, in the interest of increased
 robustness, RSA-PSS [RFC8017] is recommended for eventual adoption in
 new applications."

Currently:
 According to [RFC8017], "Although no attacks are known
 against RSASSA-PKCS1-v1_5, in the interest of increased robustness,
 RSASSA-PSS is REQUIRED in new applications."

c) We could not find "RSASSA-PKCS#1 v1.5" in any published RFC.
We changed "RSASSA-PKCS#1 v1.5" to "RSASSA-PKCS1-v1_5" per
RFC 8017 and other published RFCs accordingly.  Please let us know
any concerns.

Original:
 While RSA-PSS is more complex than RSASSA-PKCS#1
 v1.5 encoding, ubiquity of RSA-PSS support influenced the design
 decision in this draft, despite PKCS#1 v1.5 having equivalent
 security properties for digital signatures [JKM18].

Currently:
 While RSA-PSS is more
 complex than RSASSA-PKCS1-v1_5 encoding, ubiquity of RSA-PSS support
 influenced the design decision in this document, despite PKCS #1 v1.5
 having equivalent security properties for digital signatures [JKM18].

d) We do not see any mention of "FDH" or the word "full" in [RSA-FDH].
Will this citation be clear to readers?

Original:
 Full Domain Hash (FDH) [RSA-FDH] encoding is also possible, and this
 variant has equivalent security to PSS [KK18]. -->


15) <!-- [rfced] Informative References:  As we have found that some
".edu" pages are not always stable*, may we update the listings
below as follows?

* (although we could not find an alternative to the page provided for
[Chaum83])

Original:
 [RSA-FDH]  Bellare, M. and P. Rogaway, "Random Oracles are Practical:
            A Paradigm for Designing Efficient Protocols", October
            1995, <https://cseweb.ucsd.edu/~mihir/papers/ro.pdf>.

Suggsted:
 [RSA-FDH]  Bellare, M. and P. Rogaway, "Random Oracles are Practical:
            A Paradigm for Designing Efficient Protocols", CCS '93:
            Proceedings of the 1st ACM conference on Computer and
            communications security, pp. 62-73, DOI 10.1145/
            168588.168596, December 1993, <https://dl.acm.org/doi/
            abs/10.1145/168588.168596>.
...
Original:
 [RemoteTimingAttacks]
            Boneh, D. and D. Brumley, "Remote Timing Attacks are
            Practical", 12th Usenix Security Symposium, May 2003,
            <https://crypto.stanford.edu/~dabo/papers/ssl-timing.pdf>.

Suggested:
 [RemoteTimingAttacks]
            Brumley, D. and D. Boneh, "Remote Timing Attacks are
            Practical", Proceedings of the 12th USENIX Security
            Symposium, August 2003,
            <https://www.usenix.org/legacy/events/sec03/tech/brumley/
            brumley.pdf>. -->


16) <!-- [rfced] Informative References:  Per
<https://doi.org/10.6028/nist.fips.186-4>, which steers to
<https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf>, FIPS
186-4 has been superseded by FIPS 186-5.  May we update as suggested?

Original:
 The RECOMMENDED method for generating the server signing key pair is
 as specified in FIPS 186-4 [DSS].
...
 [DSS]      "Digital Signature Standard (DSS)", National Institute of
            Standards and Technology report,
            DOI 10.6028/nist.fips.186-4, July 2013,
            <https://doi.org/10.6028/nist.fips.186-4>.

Suggested:
 The RECOMMENDED method for generating the server signing key pair is
 as specified in FIPS 186-5 [DSS].
...
 [DSS]      "Digital Signature Standard (DSS)", National Institute of
            Standards and Technology report,
            DOI 10.6028/nist.fips.186-5, February 2023,
            <https://doi.org/10.6028/NIST.FIPS.186-5>. -->


17) <!-- [rfced] Informative References:  The following references are
not cited anywhere in this document.  Please let us know where they
should be cited; otherwise, the listings will be removed.

Side note regarding [UProve]:  If this listing is to be kept, please
advise regarding the currently listed date.  We could not find a
February 2012 version.  Is this date correct?

Original:
 [BLS-Proposal]
            Ladd, W., "[Privacy-pass] External verifiability: a
            concrete proposal", July 2020,
            <https://mailarchive.ietf.org/arch/msg/privacy-pass/
            BDOOhSLwB3uUJcfBiss6nUF5sUA/>.
...
 [KLRX20]   Kastner, J., Loss, J., Rosenberg, M., and J. Xu, "On
            Pairing-Free Blind Signature Schemes in the Algebraic
            Group Model", September 2020,
            <https://eprint.iacr.org/2020/1071>.
...
 [PolytimeROS]
            Benhamouda, F., Lepoint, T., Loss, J., Orru, M., and M.
            Raykova, "On the (in)security of ROS", July 2020,
            <https://eprint.iacr.org/2020/945>.
...
 [TZ22]     Tessaro, S. and C. Zhu, "Short Pairing-Free Blind
            Signatures with Exponential Security", January 2022,
            <https://eprint.iacr.org/2022/047>.
...
 [UProve]   Microsoft, "U-Prove", February 2012,
            <https://www.microsoft.com/en-us/research/project/
            u-prove/>. -->


18) <!-- [rfced] Appendices A.1 through A.4:  We changed the artwork to
sourcecode with type="test-vectors".

See <https://www.rfc-editor.org/materials/sourcecode-types.txt> for a
list of sourcecode types.

Please review, and let us know any objections. -->


19) <!-- [rfced] Please review the "Inclusive Language" portion of the
online Style Guide at
<https://www.rfc-editor.org/styleguide/part2/#inclusive_language>,
and let us know if any changes are needed.

Note that our script did not flag any words in particular, but this
should still be reviewed as a best practice. -->


20) <!-- [rfced] Please let us know if any changes are needed for the
following:

a) The following terms were used inconsistently in this document.
We chose to use the latter forms.  Please let us know any objections.

 Random Oracle Model / random oracle model (per RFC 8017)

 zero knowledge proofs / zero-knowledge proofs

b) The following term appears to be used inconsistently in this
document.  Please let us know which form is preferred.

 signature-message pair (1 instance) /
   (message, signature) pair (3 instances in Section 7.5)

c) Should "random prefix" in Section 4.5 be "message randomizer
prefix" or perhaps "msg_prefix"? -->


Thank you.

RFC Editor/lb/ap


On Sep 18, 2023, at 6:18 PM, [e-mail] wrote:

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Updated 2023/09/18

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--------------------------------------
RFC9474 (draft-irtf-cfrg-rsa-blind-signatures-14)

Title            : RSA Blind Signatures
Author(s)        : F. Denis, F. Jacobs, C. A. Wood
WG Chair(s)      : 
Area Director(s) :