extern void * read_sha1_file(const unsigned char *sha1, char *type, unsigned long *size);
extern int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned char *return_sha1);
-extern int check_sha1_signature(unsigned char *sha1, void *buf, unsigned long size, const char *type);
+extern int check_sha1_signature(const unsigned char *sha1, void *buf, unsigned long size, const char *type);
/* Read a tree into the cache */
extern int read_tree(void *buffer, unsigned long size, int stage);