[RFC,v2,01/12] crypto: chacha20-generic - add HChaCha20 library function
diff mbox series

Message ID 20181015175424.97147-2-ebiggers@kernel.org
State Superseded
Headers show
Series
  • crypto: Adiantum support
Related show

Commit Message

Eric Biggers Oct. 15, 2018, 5:54 p.m. UTC
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(-)

Comments

Ard Biesheuvel Oct. 19, 2018, 2:13 p.m. UTC | #1
On 16 October 2018 at 01:54, Eric Biggers <ebiggers@kernel.org> wrote:
> 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>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

> ---
>  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
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Patch
diff mbox series

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);