Re: [Proposal] Table-level Transparent Data Encryption (TDE) and Key Management Service (KMS)

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Joe Conway <mail(at)joeconway(dot)com>
Cc: Ryan Lambert <ryan(at)rustprooflabs(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Antonin Houska <ah(at)cybertec(dot)at>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, "Moon, Insung" <Moon_Insung_i3(at)lab(dot)ntt(dot)co(dot)jp>, Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [Proposal] Table-level Transparent Data Encryption (TDE) and Key Management Service (KMS)
Date: 2019-07-09 15:11:32
Message-ID: 20190709151132.njhzizqkw5i45z5z@momjian.us
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On Tue, Jul 9, 2019 at 09:16:17AM -0400, Joe Conway wrote:
> On 7/9/19 8:39 AM, Ryan Lambert wrote:
> > Hi Thomas,
> >
> >> CBC mode does require
> >> random nonces, other modes may be fine with even sequences as long as
> >> the values are not reused.   
> >
> > I disagree that CBC mode requires random nonces, at least based on what
> > NIST has published.  They only require that the IV (not the nonce) must
> > be unpredictable per [1]:
> >
> > " For the CBC and CFB modes, the IVs must be unpredictable."
> >
> > The unpredictable IV can be generated from a non-random nonce including
> > a counter:
> >
> > "There are two recommended methods for generating unpredictable IVs. The
> > first method is to apply the forward cipher function, under the same key
> > that is used for the encryption of the plaintext, to a nonce. The nonce
> > must be a data block that is unique to each execution of the encryption
> > operation. For example, the nonce may be a counter, as described in
> > Appendix B, or a message number."
> >
> > [1] https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf
>
>
> The terms nonce and IV are often used more-or-less interchangeably, and
> it is important to be clear when we are talking about an IV specifically
> - an IV is a specific type of nonce. Nonce means "number used once".
> i.e. unique, whereas an IV (for CBC use anyway) should be unique and
> random but not necessarily kept secret. The NIST requirements that
> Stephen referenced elsewhere on this thread are as I understand it
> intended to ensure the random but unique property with high probability.

Good point about nonce and IV. I wonder if running the nonce through
the cipher with the key makes it random enough to use as an IV.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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