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From: Eric Biggers <ebiggers@kernel.org>
To: linux-crypto@vger.kernel.org
Cc: linux-fscrypt@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Paul Crowley <paulcrowley@google.com>,
	Greg Kaiser <gkaiser@google.com>,
	Michael Halcrow <mhalcrow@google.com>,
	"Jason A . Donenfeld" <Jason@zx2c4.com>,
	Samuel Neves <samuel.c.p.neves@gmail.com>,
	Tomer Ashur <tomer.ashur@esat.kuleuven.be>
Subject: [RFC PATCH v2 01/12] crypto: chacha20-generic - add HChaCha20 library function
Date: Mon, 15 Oct 2018 10:54:13 -0700	[thread overview]
Message-ID: <20181015175424.97147-2-ebiggers@kernel.org> (raw)
In-Reply-To: <20181015175424.97147-1-ebiggers@kernel.org>

From: Eric Biggers <ebiggers@google.com>

Refactor the unkeyed permutation part of chacha20_block() into its own
function, then add hchacha20_block() which is the ChaCha equivalent of
HSalsa20 and is an intermediate step towards XChaCha20 (see
https://cr.yp.to/snuffle/xsalsa-20081128.pdf).  HChaCha20 skips the
final addition of the initial state, and outputs only certain words of
the state.  It should not be used for streaming directly.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 include/crypto/chacha20.h |  2 ++
 lib/chacha20.c            | 50 ++++++++++++++++++++++++++++++++++-----
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/include/crypto/chacha20.h b/include/crypto/chacha20.h
index f76302d99e2be..fbec4e6a87890 100644
--- a/include/crypto/chacha20.h
+++ b/include/crypto/chacha20.h
@@ -19,6 +19,8 @@ struct chacha20_ctx {
 };
 
 void chacha20_block(u32 *state, u8 *stream);
+void hchacha20_block(const u32 *in, u32 *out);
+
 void crypto_chacha20_init(u32 *state, struct chacha20_ctx *ctx, u8 *iv);
 int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key,
 			   unsigned int keysize);
diff --git a/lib/chacha20.c b/lib/chacha20.c
index d907fec6a9ed1..6a484e16171d1 100644
--- a/lib/chacha20.c
+++ b/lib/chacha20.c
@@ -1,5 +1,5 @@
 /*
- * ChaCha20 256-bit cipher algorithm, RFC7539
+ * The "hash function" used as the core of the ChaCha20 stream cipher (RFC7539)
  *
  * Copyright (C) 2015 Martin Willi
  *
@@ -16,14 +16,10 @@
 #include <asm/unaligned.h>
 #include <crypto/chacha20.h>
 
-void chacha20_block(u32 *state, u8 *stream)
+static void chacha20_permute(u32 *x)
 {
-	u32 x[16];
 	int i;
 
-	for (i = 0; i < ARRAY_SIZE(x); i++)
-		x[i] = state[i];
-
 	for (i = 0; i < 20; i += 2) {
 		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],  16);
 		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],  16);
@@ -65,6 +61,25 @@ void chacha20_block(u32 *state, u8 *stream)
 		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],   7);
 		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],   7);
 	}
+}
+
+/**
+ * chacha20_block - generate one keystream block and increment block counter
+ * @state: input state matrix (16 32-bit words)
+ * @stream: output keystream block (64 bytes)
+ *
+ * This is the ChaCha20 core, a function from 64-byte strings to 64-byte
+ * strings.  The caller has already converted the endianness of the input.  This
+ * function also handles incrementing the block counter in the input matrix.
+ */
+void chacha20_block(u32 *state, u8 *stream)
+{
+	u32 x[16];
+	int i;
+
+	memcpy(x, state, 64);
+
+	chacha20_permute(x);
 
 	for (i = 0; i < ARRAY_SIZE(x); i++)
 		put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
@@ -72,3 +87,26 @@ void chacha20_block(u32 *state, u8 *stream)
 	state[12]++;
 }
 EXPORT_SYMBOL(chacha20_block);
+
+/**
+ * hchacha20_block - abbreviated ChaCha20 core, for XChaCha20
+ * @in: input state matrix (16 32-bit words)
+ * @out: output (8 32-bit words)
+ *
+ * HChaCha20 is the ChaCha equivalent of HSalsa20 and is an intermediate step
+ * towards XChaCha20 (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf).
+ * HChaCha20 skips the final addition of the initial state, and outputs only
+ * certain words of the state.  It should not be used for streaming directly.
+ */
+void hchacha20_block(const u32 *in, u32 *out)
+{
+	u32 x[16];
+
+	memcpy(x, in, 64);
+
+	chacha20_permute(x);
+
+	memcpy(&out[0], &x[0], 16);
+	memcpy(&out[4], &x[12], 16);
+}
+EXPORT_SYMBOL(hchacha20_block);
-- 
2.19.1.331.ge82ca0e54c-goog


  reply	other threads:[~2018-10-15 17:56 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-15 17:54 [RFC PATCH v2 00/12] crypto: Adiantum support Eric Biggers
2018-10-15 17:54 ` Eric Biggers [this message]
2018-10-19 14:13   ` [RFC PATCH v2 01/12] crypto: chacha20-generic - add HChaCha20 library function Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 02/12] crypto: chacha20-generic - add XChaCha20 support Eric Biggers
2018-10-19 14:24   ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 03/12] crypto: chacha20-generic - refactor to allow varying number of rounds Eric Biggers
2018-10-19 14:25   ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 04/12] crypto: chacha - add XChaCha12 support Eric Biggers
2018-10-19 14:34   ` Ard Biesheuvel
2018-10-19 18:28     ` Eric Biggers
2018-10-15 17:54 ` [RFC PATCH v2 05/12] crypto: arm/chacha20 - add XChaCha20 support Eric Biggers
2018-10-20  2:29   ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 06/12] crypto: arm/chacha20 - refactor to allow varying number of rounds Eric Biggers
2018-10-20  3:35   ` Ard Biesheuvel
2018-10-20  5:26     ` Eric Biggers
2018-10-15 17:54 ` [RFC PATCH v2 07/12] crypto: arm/chacha - add XChaCha12 support Eric Biggers
2018-10-20  3:36   ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 08/12] crypto: poly1305 - add Poly1305 core API Eric Biggers
2018-10-20  3:45   ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 09/12] crypto: nhpoly1305 - add NHPoly1305 support Eric Biggers
2018-10-20  4:00   ` Ard Biesheuvel
2018-10-20  5:38     ` Eric Biggers
2018-10-20 15:06       ` Ard Biesheuvel
2018-10-22 18:42         ` Eric Biggers
2018-10-22 22:25           ` Ard Biesheuvel
2018-10-22 22:40             ` Eric Biggers
2018-10-22 22:43               ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 10/12] crypto: arm/nhpoly1305 - add NEON-accelerated NHPoly1305 Eric Biggers
2018-10-20  4:12   ` Ard Biesheuvel
2018-10-20  5:51     ` Eric Biggers
2018-10-20 15:00       ` Ard Biesheuvel
2018-10-15 17:54 ` [RFC PATCH v2 11/12] crypto: adiantum - add Adiantum support Eric Biggers
2018-10-20  4:17   ` Ard Biesheuvel
2018-10-20  7:12     ` Eric Biggers
2018-10-23 10:40       ` Ard Biesheuvel
2018-10-24 22:06         ` Eric Biggers
2018-10-30  8:17           ` Herbert Xu
2018-10-15 17:54 ` [RFC PATCH v2 12/12] fscrypt: " Eric Biggers
2018-10-19 15:58 ` [RFC PATCH v2 00/12] crypto: " Jason A. Donenfeld
2018-10-19 18:19   ` Paul Crowley
2018-10-20  3:24     ` Ard Biesheuvel
2018-10-20  5:22       ` Eric Biggers
     [not found]     ` <2395454e-a0dc-408f-4138-9d15ab5f20b8@esat.kuleuven.be>
2018-10-22 11:20       ` Tomer Ashur
2018-10-19 19:04   ` Eric Biggers
2018-10-20 10:26     ` Milan Broz
2018-10-20 13:47       ` Jason A. Donenfeld
2018-11-16 21:52       ` Eric Biggers
2018-11-17 10:29         ` Milan Broz
2018-11-19 19:28           ` Eric Biggers
2018-11-19 20:05             ` Milan Broz
2018-11-19 20:30               ` Jason A. Donenfeld
2018-10-21 22:23     ` Eric Biggers
2018-10-21 22:51       ` Jason A. Donenfeld
2018-10-22 17:17         ` Paul Crowley

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