Re: [pkix] Question about Curve P-192

Dan Brown <danibrown@blackberry.com> Thu, 10 May 2018 18:51 UTC

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From: Dan Brown <danibrown@blackberry.com>
To: Russ Housley <housley@vigilsec.com>, Ernst G Giessmann <giessman@informatik.hu-berlin.de>
CC: IETF PKIX <pkix@ietf.org>
Thread-Topic: [pkix] Question about Curve P-192
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Date: Thu, 10 May 2018 18:51:00 +0000
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Subject: Re: [pkix] Question about Curve P-192
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Hi Denis,

 

Please, do not use P-192, unless there are some severe constraints.

 

Even if you credit EC with a very generous 16 extra bits in security
(compared to hashes & ciphers), P-192 would only reach 96+16=112-bit
security, which does not meet the current best practice of 128 bit security.

 

History as I understand it: NIST P-192 was meant for the 80-bit level
(though it looks like 96-bit). This low security level has been widely
deprecated since 2010, at least informally - to what extent it is formally
deprecated, I don't recall off-hand. I recall added text to ANSI X9.62/63
deprecating this security level.

Anyway, originally, the idea was to use P-192 with SHA-1, P-224 with
SHA-224, etc.

I think that there were also OIDs for P-192, e.g. secp192k1, and OIDs for
ECDSA-with-SHA1, which could be combined in some ways.  I do not recall how
far these OIDs made into IETF, i.e. as algorithm identifiers.

Using 160-bit hash in ECDSA with P-192 renders the EU-CMA security to 80
bits, which is waste considering that P-192 potentially provides 96-bit
security.  As noted in the thread below, the standards have options to
truncate a longer hash, which should correct this.

 

Arguably, the security of P-192 has fared far better than SHA-1 in some
ways, yet SHA-1 is probably much more widely used than P-192, though
admittedly hashes are considered a general purpose tool.

 

Best regards,

Dan

 

 

From: pkix [mailto:pkix-bounces@ietf.org] On Behalf Of Russ Housley
Sent: Thursday, May 10, 2018 1:30 PM
To: Ernst G Giessmann <giessman@informatik.hu-berlin.de>;
Cc: IETF PKIX <pkix@ietf.org>;
Subject: Re: [pkix] Question about Curve P-192

 

Ernst:

 

Of course, this technique works.  That said, I am not aware of any algorithm
identifiers that make use of the P-192 curve for digital signature or key
agreement.

 

Russ

 

 

On May 10, 2018, at 1:24 PM, Ernst G Giessmann
<giessman@informatik.hu-berlin.de <mailto:giessman@informatik.hu-berlin.de>
> wrote:

 

Yes, there is a standardized way: 
Pick up a corresponding hash function, in case of P-192 it should be SHA-224
and take the 192 left most bits of the hash value as the input to the EC
sign primitive.
The correspondig signature suite can be defined with ISO 14888-3, which
allows the specification of the algo (e.g. EC-DSA, EC-KCDSA or whatsoever),
the curve and the hash function.
Kind regards,
/Ernst.

Am 2018-05-10 um 19:07 schrieb Denis:

Hello everybody,

Curve P-192 is specified in FIPS PUB 186-4 (Digital Signature Standard
(DSS)).

There is no "SHA-192" hash function defined in FIPS PUB 180-4 (Secure Hash
Standard (SHS)).

Is there any standardized way to use a hash function with Curve P-192 ? 

Is there any RFC or any another document that specifies a cryptographic
suite for Curve P-192 ?

Denis

 







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