[PATCH v3 2/3] sha1dc: optionally use sha1collisiondetection as a submodule

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Add an option to use the sha1collisiondetection library from the
submodule in sha1collisiondetection/ instead of in the copy in the
sha1dc/ directory.

This allows us to try out the submodule in sha1collisiondetection
without breaking the build for anyone who's not expecting them as we
work out any kinks.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 .gitmodules            |  4 ++++
 Makefile               | 12 ++++++++++++
 hash.h                 |  4 ++++
 sha1collisiondetection |  1 +
 4 files changed, 21 insertions(+)
 create mode 100644 .gitmodules
 create mode 160000 sha1collisiondetection

diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000000..cbeebdab7a
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,4 @@
+[submodule "sha1collisiondetection"]
+	path = sha1collisiondetection
+	url = https://github.com/cr-marcstevens/sha1collisiondetection.git
+	branch = master
diff --git a/Makefile b/Makefile
index b94cd5633c..f0cac1f246 100644
--- a/Makefile
+++ b/Makefile
@@ -162,6 +162,12 @@ all::
 # algorithm. This is slower, but may detect attempted collision attacks.
 # Takes priority over other *_SHA1 knobs.
 #
+# Define DC_SHA1_SUBMODULE in addition to DC_SHA1 to use the
+# sha1collisiondetection shipped as a submodule instead of the
+# non-submodule copy in sha1dc/. This is an experimental option used
+# by the git project to migrate to using sha1collisiondetection as a
+# submodule.
+#
 # Define OPENSSL_SHA1 environment variable when running make to link
 # with the SHA1 routine from openssl library.
 #
@@ -1448,8 +1454,14 @@ ifdef APPLE_COMMON_CRYPTO
 	BASIC_CFLAGS += -DSHA1_APPLE
 else
 	DC_SHA1 := YesPlease
+ifdef DC_SHA1_SUBMODULE
+	LIB_OBJS += sha1collisiondetection/lib/sha1.o
+	LIB_OBJS += sha1collisiondetection/lib/ubc_check.o
+	BASIC_CFLAGS += -DDC_SHA1_SUBMODULE
+else
 	LIB_OBJS += sha1dc/sha1.o
 	LIB_OBJS += sha1dc/ubc_check.o
+endif
 	BASIC_CFLAGS += \
 		-DSHA1_DC \
 		-DSHA1DC_NO_STANDARD_INCLUDES \
diff --git a/hash.h b/hash.h
index a11fc9233f..bef3e630a0 100644
--- a/hash.h
+++ b/hash.h
@@ -8,7 +8,11 @@
 #elif defined(SHA1_OPENSSL)
 #include <openssl/sha.h>
 #elif defined(SHA1_DC)
+#ifdef DC_SHA1_SUBMODULE
+#include "sha1collisiondetection/lib/sha1.h"
+#else
 #include "sha1dc/sha1.h"
+#endif
 #else /* SHA1_BLK */
 #include "block-sha1/sha1.h"
 #endif
diff --git a/sha1collisiondetection b/sha1collisiondetection
new file mode 160000
index 0000000000..19d97bf5af
--- /dev/null
+++ b/sha1collisiondetection
@@ -0,0 +1 @@
+Subproject commit 19d97bf5af05312267c2e874ee6bcf584d9e9681
-- 
2.13.1.611.g7e3b11ae1