1 files changed, 38 insertions, 0 deletions
diff --git a/third_party/git/sha1dc_git.c b/third_party/git/sha1dc_git.c
new file mode 100644
index 000000000000..5c300e812e0a
--- /dev/null
+++ b/third_party/git/sha1dc_git.c
@@ -0,0 +1,38 @@
+#include "cache.h"
+
+#ifdef DC_SHA1_EXTERNAL
+/*
+ * Same as SHA1DCInit, but with default save_hash=0
+ */
+void git_SHA1DCInit(SHA1_CTX *ctx)
+{
+	SHA1DCInit(ctx);
+	SHA1DCSetSafeHash(ctx, 0);
+}
+#endif
+
+/*
+ * Same as SHA1DCFinal, but convert collision attack case into a verbose die().
+ */
+void git_SHA1DCFinal(unsigned char hash[20], SHA1_CTX *ctx)
+{
+	if (!SHA1DCFinal(hash, ctx))
+		return;
+	die("SHA-1 appears to be part of a collision attack: %s",
+	    hash_to_hex_algop(hash, &hash_algos[GIT_HASH_SHA1]));
+}
+
+/*
+ * Same as SHA1DCUpdate, but adjust types to match git's usual interface.
+ */
+void git_SHA1DCUpdate(SHA1_CTX *ctx, const void *vdata, unsigned long len)
+{
+	const char *data = vdata;
+	/* We expect an unsigned long, but sha1dc only takes an int */
+	while (len > INT_MAX) {
+		SHA1DCUpdate(ctx, data, INT_MAX);
+		data += INT_MAX;
+		len -= INT_MAX;
+	}
+	SHA1DCUpdate(ctx, data, len);
+}