Support reading from snapshots encrypted with different keys

src/util/str_util.h

@@ -38,5 +38,6 @@ bool is_zero(void *buf, size_t size);
 bool memcheck(uint8_t *buf, uint8_t byte, size_t len);
 std::string urldecode(const std::string & orig);
 size_t fromhexstr(const std::string & from, size_t bytes, uint8_t *to);
+std::string tohexstr(const uint8_t *from, size_t bytes);
 
 #pragma GCC visibility pop