From: Martin Willi <martin@strongswan.org>
To: Eric Biggers <ebiggers3@gmail.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au,
Eric Biggers <ebiggers@google.com>,
linux-fscrypt@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org,
Jaegeuk Kim <jaegeuk@kernel.org>,
Michael Halcrow <mhalcrow@google.com>,
Paul Crowley <paulcrowley@google.com>,
David Gstir <david@sigma-star.at>,
"Jason A . Donenfeld" <Jason@zx2c4.com>,
Stephan Mueller <smueller@chronox.de>
Subject: Re: [RFC PATCH] crypto: chacha20 - add implementation using 96-bit nonce
Date: Mon, 11 Dec 2017 08:38:45 +0100 [thread overview]
Message-ID: <1512977925.28078.12.camel@strongswan.org> (raw)
In-Reply-To: <20171208221716.GB104193@gmail.com>
Hi,
> Anyway, I actually thought it was intentional that the ChaCha
> implementations in the Linux kernel allowed specifying the block
> counter, and therefore allowed seeking to any point in the keystream,
> exposing the full functionality of the cipher.
If I remember correctly, it was indeed intentional. When building the
chacha20poly1305 AEAD both in [1] and [2], a block counter of 0 is used
to generate the Poly1305 key. For the ChaCha20 encryption, an explicit
initial block counter of 1 is used to avoid reusing the same counter.
Maybe it would be possible to implement this with implicit counters,
but doing this explicitly looked much clearer to me. So I guess there
are use cases for explicit block counters in ChaCha20.
Best regards
Martin
[1] https://tools.ietf.org/html/rfc7539#section-2.8
[2] https://tools.ietf.org/html/rfc7634#section-2
next prev parent reply other threads:[~2017-12-11 7:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-08 11:55 [RFC PATCH] crypto: chacha20 - add implementation using 96-bit nonce Ard Biesheuvel
2017-12-08 22:17 ` Eric Biggers
2017-12-08 22:42 ` Ard Biesheuvel
2017-12-08 22:54 ` Ard Biesheuvel
2017-12-08 23:11 ` Eric Biggers
2017-12-08 23:27 ` Ard Biesheuvel
2017-12-11 7:38 ` Martin Willi [this message]
2017-12-11 6:55 ` Herbert Xu
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