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From: Eric Biggers <ebiggers@kernel.org>
To: "Stephan Müller" <smueller@chronox.de>
Cc: herbert@gondor.apana.org.au, mathew.j.martineau@linux.intel.com,
	dhowells@redhat.com, linux-crypto@vger.kernel.org,
	linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org,
	keyrings@vger.kernel.org
Subject: Re: [PATCH 3/5] crypto: add RFC5869 HKDF
Date: Wed, 6 Jan 2021 23:30:50 -0800	[thread overview]
Message-ID: <X/a4qt9Oiw4WgoRY@sol.localdomain> (raw)
In-Reply-To: <12679948.uLZWGnKmhe@positron.chronox.de>

On Mon, Jan 04, 2021 at 10:49:13PM +0100, Stephan Müller wrote:
> RFC5869 specifies an extract and expand two-step key derivation
> function. The HKDF implementation is provided as a service function that
> operates on a caller-provided HMAC cipher handle.

HMAC isn't a "cipher".

> The extract function is invoked via the crypto_hkdf_setkey call.

Any reason not to call this crypto_hkdf_extract(), to match the specification?

> RFC5869
> allows two optional parameters to be provided to the extract operation:
> the salt and additional information. Both are to be provided with the
> seed parameter where the salt is the first entry of the seed parameter
> and all subsequent entries are handled as additional information. If
> the caller intends to invoke the HKDF without salt, it has to provide a
> NULL/0 entry as first entry in seed.

Where does "additional information" for extract come from?  RFC 5869 has:

	HKDF-Extract(salt, IKM) -> PRK

	Inputs:
	      salt     optional salt value (a non-secret random value);
		       if not provided, it is set to a string of HashLen zeros.
	      IKM      input keying material

There's no "additional information".

> 
> The expand function is invoked via the crypto_hkdf_generate and can be
> invoked multiple times. This function allows the caller to provide a
> context for the key derivation operation. As specified in RFC5869, it is
> optional. In case such context is not provided, the caller must provide
> NULL / 0 for the info / info_nvec parameters.

Any reason not to call this crypto_hkdf_expand() to match the specification?

- Eric

  reply	other threads:[~2021-01-07  7:31 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-04 21:45 [PATCH 0/5] Add KDF implementations to crypto API Stephan Müller
2021-01-04 21:47 ` [PATCH 1/5] crypto: Add key derivation self-test support code Stephan Müller
2021-01-04 21:47 ` [PATCH 2/5] crypto: add SP800-108 counter key derivation function Stephan Müller
2021-01-04 21:49 ` [PATCH 3/5] crypto: add RFC5869 HKDF Stephan Müller
2021-01-07  7:30   ` Eric Biggers [this message]
2021-01-07  7:53     ` Stephan Mueller
2021-01-07 18:53       ` Eric Biggers
2021-01-04 21:49 ` [PATCH 4/5] security: DH - use KDF implementation from crypto API Stephan Müller
2021-01-12  1:34   ` Jarkko Sakkinen
2021-01-04 21:50 ` [PATCH 5/5] fs: use HKDF implementation from kernel " Stephan Müller
2021-01-07  7:19   ` Eric Biggers
2021-01-07  7:49     ` Stephan Mueller
2021-01-07 18:47       ` Eric Biggers
2021-01-04 22:20 ` [PATCH 0/5] Add KDF implementations to " Eric Biggers
2021-01-07  6:37   ` Stephan Mueller
2021-01-07  6:59     ` Eric Biggers
2021-01-07  7:12       ` Eric Biggers

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