Subject: Re: [PATCH v2] sha256: add support for Nettle

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Sun, 10 Jul 2022 16:41:23 +0200

On Sun, Jul 10 2022, brian m. carlson wrote:

> @@ -182,6 +182,8 @@ include shared.mak
>  #
>  # Define BLK_SHA256 to use the built-in SHA-256 routines.
>  #
> +# Define NETTLE_SHA256 to use the SHA-256 routines in libnettle.
> +#
>  # Define GCRYPT_SHA256 to use the SHA-256 routines in libgcrypt.
>  #
>  # Define OPENSSL_SHA256 to use the SHA-256 routines in OpenSSL.
> @@ -1842,6 +1844,10 @@ ifdef OPENSSL_SHA256
>  	EXTLIBS += $(LIB_4_CRYPTO)
>  	BASIC_CFLAGS += -DSHA256_OPENSSL
>  else
> +ifdef NETTLE_SHA256
> +	BASIC_CFLAGS += -DSHA256_NETTLE
> +	EXTLIBS += -lnettle
> +else
>  ifdef GCRYPT_SHA256
>  	BASIC_CFLAGS += -DSHA256_GCRYPT
>  	EXTLIBS += -lgcrypt
> @@ -1850,6 +1856,7 @@ else
>  	BASIC_CFLAGS += -DSHA256_BLK
>  endif
>  endif
> +endif

This just carries forward existing technical debt, but it's unfortunate
that we don't catch OPENSSL_SHA256 overridding NETTLE_SHA256, and error
if both are defined.

>  ifdef SHA1_MAX_BLOCK_SIZE
>  	LIB_OBJS += compat/sha1-chunked.o
> @@ -3091,6 +3098,9 @@ $(SP_OBJ): %.sp: %.c %.o
>  sparse: $(SP_OBJ)
>  
>  EXCEPT_HDRS := $(GENERATED_H) unicode-width.h compat/% xdiff/%
> +ifndef NETTLE_SHA256
> +	EXCEPT_HDRS += sha256/nettle.h
> +endif
>  ifndef GCRYPT_SHA256
>  	EXCEPT_HDRS += sha256/gcrypt.h
>  endif
> diff --git a/hash.h b/hash.h
> index 5d40368f18..ea87ae9d92 100644
> --- a/hash.h
> +++ b/hash.h
> @@ -16,7 +16,9 @@
>  #include "block-sha1/sha1.h"
>  #endif
>  
> -#if defined(SHA256_GCRYPT)
> +#if defined(SHA256_NETTLE)
> +#include "sha256/nettle.h"
> +#elif defined(SHA256_GCRYPT)
>  #define SHA256_NEEDS_CLONE_HELPER
>  #include "sha256/gcrypt.h"
>  #elif defined(SHA256_OPENSSL)
> diff --git a/sha256/nettle.h b/sha256/nettle.h
> new file mode 100644
> index 0000000000..b63e1c8190
> --- /dev/null
> +++ b/sha256/nettle.h
> @@ -0,0 +1,31 @@
> +#ifndef SHA256_NETTLE_H
> +#define SHA256_NETTLE_H
> +
> +#include <nettle/sha2.h>
> +
> +typedef struct sha256_ctx nettle_SHA256_CTX;
> +
> +static inline void nettle_SHA256_Init(nettle_SHA256_CTX *ctx)
> +{
> +	sha256_init(ctx);
> +}
> +
> +static inline void nettle_SHA256_Update(nettle_SHA256_CTX *ctx,
> +					const void *data,
> +					size_t len)
> +{
> +	sha256_update(ctx, len, data);
> +}
> +
> +static inline void nettle_SHA256_Final(unsigned char *digest,
> +				       nettle_SHA256_CTX *ctx)
> +{
> +	sha256_digest(ctx, SHA256_DIGEST_SIZE, digest);
> +}
> +
> +#define platform_SHA256_CTX nettle_SHA256_CTX
> +#define platform_SHA256_Init nettle_SHA256_Init
> +#define platform_SHA256_Update nettle_SHA256_Update
> +#define platform_SHA256_Final nettle_SHA256_Final
> +
> +#endif

This looks good to me, except for the small nit that I think this should
be squashed in. For the others we need this inline wrappers, but not for
"init":

diff --git a/sha256/nettle.h b/sha256/nettle.h
index b63e1c81903..5c9811c309a 100644
--- a/sha256/nettle.h
+++ b/sha256/nettle.h
@@ -5,11 +5,6 @@
 
 typedef struct sha256_ctx nettle_SHA256_CTX;
 
-static inline void nettle_SHA256_Init(nettle_SHA256_CTX *ctx)
-{
-	sha256_init(ctx);
-}
-
 static inline void nettle_SHA256_Update(nettle_SHA256_CTX *ctx,
 					const void *data,
 					size_t len)
@@ -24,7 +19,7 @@ static inline void nettle_SHA256_Final(unsigned char *digest,
 }
 
 #define platform_SHA256_CTX nettle_SHA256_CTX
-#define platform_SHA256_Init nettle_SHA256_Init
+#define platform_SHA256_Init sha256_init
 #define platform_SHA256_Update nettle_SHA256_Update
 #define platform_SHA256_Final nettle_SHA256_Final