sha256: add support for Nettle

For SHA-256, we currently have support for OpenSSL and libgcrypt because
these two libraries contain optimized implementations that can take
advantage of native processor instructions.  However, OpenSSL is not
suitable for linking against for Linux distros due to licensing
incompatibilities with the GPLv2, and libgcrypt has been less favored by
cryptographers due to some security-related implementation issues,
which, while not affecting our use of hash algorithms, has affected its
reputation.

Let's add another option that's compatible with the GPLv2, which is
Nettle.  This is an option which is generally better than libgcrypt
because on many distros GnuTLS (which uses Nettle) is used for HTTPS and
therefore as a practical matter it will be available on most systems.
As a result, prefer it over libgcrypt and our built-in implementation.

Nettle also has recently gained support for Intel's SHA-NI instructions,
which compare very favorably to other implementations, as well as
assembly implementations for when SHA-NI is not available.

A git gc on git.git sees a 12% performance improvement with Nettle over
our block SHA-256 implementation due to general assembly improvements.
With SHA-NI, the performance of raw SHA-256 on a 2 GiB file goes from
7.296 seconds with block SHA-256 to 1.523 seconds with Nettle.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Makefile b/Makefile
index 04d0fd1fe60702c2040f3658301ce7e322761ceb..52a9f9799786c60fcd5535d60ba5f5a40b36901a 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -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
 
 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 5d40368f18a4d38ef3a62ae3ff378b0167e35a74..ea87ae9d92f7931b376b337e721059060d037eb8 100644 (file)
--- 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 (file)
index 0000000..b63e1c8
--- /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