diff --git a/src/backup/archive_index.rs b/src/backup/archive_index.rs
index f06a83e5..8252559a 100644
--- a/src/backup/archive_index.rs
+++ b/src/backup/archive_index.rs
@@ -1,5 +1,6 @@
 use failure::*;
 
+use crate::tools;
 use super::chunk_store::*;
 use super::chunker::*;
 
@@ -142,7 +143,7 @@ impl ArchiveIndexReader {
             let digest = self.chunk_digest(pos);
             if let Err(err) = self.store.touch_chunk(digest) {
                 bail!("unable to access chunk {}, required by {:?} - {}",
-                      digest_to_hex(digest), self.filename, err);
+                      tools::digest_to_hex(digest), self.filename, err);
             }
         }
         Ok(())
@@ -430,7 +431,7 @@ impl ArchiveIndexWriter {
 
         match self.store.insert_chunk(&self.chunk_buffer) {
             Ok((is_duplicate, digest)) => {
-                println!("ADD CHUNK {:016x} {} {} {}", self.chunk_offset, chunk_size, is_duplicate,  digest_to_hex(&digest));
+                println!("ADD CHUNK {:016x} {} {} {}", self.chunk_offset, chunk_size, is_duplicate,  tools::digest_to_hex(&digest));
                 self.writer.write(unsafe { &std::mem::transmute::<u64, [u8;8]>(self.chunk_offset as u64) })?;
                 self.writer.write(&digest)?;
                 self.chunk_buffer.truncate(0);
diff --git a/src/backup/chunk_store.rs b/src/backup/chunk_store.rs
index eed6b82f..d0cdebe4 100644
--- a/src/backup/chunk_store.rs
+++ b/src/backup/chunk_store.rs
@@ -37,26 +37,14 @@ pub struct ChunkStore {
     _lockfile: File,
 }
 
-const HEX_CHARS: &'static [u8; 16] = b"0123456789abcdef";
-
 // TODO: what about sysctl setting vm.vfs_cache_pressure (0 - 100) ?
 
-pub fn digest_to_hex(digest: &[u8]) -> String {
-
-    let mut buf = Vec::<u8>::with_capacity(digest.len()*2);
-
-    for i in 0..digest.len() {
-        buf.push(HEX_CHARS[(digest[i] >> 4) as usize]);
-        buf.push(HEX_CHARS[(digest[i] & 0xf) as usize]);
-    }
-
-    unsafe { String::from_utf8_unchecked(buf) }
-}
-
 fn digest_to_prefix(digest: &[u8]) -> PathBuf {
 
     let mut buf = Vec::<u8>::with_capacity(2+1+2+1);
 
+    const HEX_CHARS: &'static [u8; 16] = b"0123456789abcdef";
+
     buf.push(HEX_CHARS[(digest[0] as usize) >> 4]);
     buf.push(HEX_CHARS[(digest[0] as usize) &0xf]);
     buf.push(HEX_CHARS[(digest[1] as usize) >> 4]);
@@ -151,7 +139,7 @@ impl ChunkStore {
         let mut chunk_path = self.chunk_dir.clone();
         let prefix = digest_to_prefix(&digest);
         chunk_path.push(&prefix);
-        let digest_str = digest_to_hex(&digest);
+        let digest_str = tools::digest_to_hex(&digest);
         chunk_path.push(&digest_str);
 
         const UTIME_NOW: i64 = ((1 << 30) - 1);
@@ -180,7 +168,7 @@ impl ChunkStore {
         let mut chunk_path = self.chunk_dir.clone();
         let prefix = digest_to_prefix(&digest);
         chunk_path.push(&prefix);
-        let digest_str = digest_to_hex(&digest);
+        let digest_str = tools::digest_to_hex(&digest);
         chunk_path.push(&digest_str);
 
         let mut f = std::fs::File::open(&chunk_path)?;
@@ -287,12 +275,12 @@ impl ChunkStore {
 
         let digest = hasher.finish();
 
-        //println!("DIGEST {}", digest_to_hex(&digest));
+        //println!("DIGEST {}", tools::digest_to_hex(&digest));
 
         let mut chunk_path = self.chunk_dir.clone();
         let prefix = digest_to_prefix(&digest);
         chunk_path.push(&prefix);
-        let digest_str = digest_to_hex(&digest);
+        let digest_str = tools::digest_to_hex(&digest);
         chunk_path.push(&digest_str);
 
         let lock = self.mutex.lock();
diff --git a/src/backup/image_index.rs b/src/backup/image_index.rs
index 1d1c290d..4d882890 100644
--- a/src/backup/image_index.rs
+++ b/src/backup/image_index.rs
@@ -1,5 +1,6 @@
 use failure::*;
 
+use crate::tools;
 use super::chunk_store::*;
 
 use std::sync::Arc;
@@ -135,7 +136,7 @@ impl ImageIndexReader {
             let digest = unsafe { std::slice::from_raw_parts_mut(self.index.add(pos*32), 32) };
             if let Err(err) = self.store.touch_chunk(digest) {
                 bail!("unable to access chunk {}, required by {:?} - {}",
-                      digest_to_hex(digest), self.filename, err);
+                      tools::digest_to_hex(digest), self.filename, err);
             }
         }
 
@@ -289,7 +290,7 @@ impl ImageIndexWriter {
 
         let (is_duplicate, digest) = self.store.insert_chunk(chunk)?;
 
-        println!("ADD CHUNK {} {} {} {}", pos, chunk.len(), is_duplicate,  digest_to_hex(&digest));
+        println!("ADD CHUNK {} {} {} {}", pos, chunk.len(), is_duplicate, tools::digest_to_hex(&digest));
 
         if is_duplicate { self.duplicate_chunks += 1; }
         
diff --git a/src/tools.rs b/src/tools.rs
index 5d842377..39b3fada 100644
--- a/src/tools.rs
+++ b/src/tools.rs
@@ -397,3 +397,18 @@ pub fn get_hardware_address() -> Result<String, Error> {
 
     Ok(format!("{:0x}", digest))
 }
+
+pub fn digest_to_hex(digest: &[u8]) -> String {
+
+    const HEX_CHARS: &'static [u8; 16] = b"0123456789abcdef";
+
+    let mut buf = Vec::<u8>::with_capacity(digest.len()*2);
+
+    for i in 0..digest.len() {
+        buf.push(HEX_CHARS[(digest[i] >> 4) as usize]);
+        buf.push(HEX_CHARS[(digest[i] & 0xf) as usize]);
+    }
+
+    unsafe { String::from_utf8_unchecked(buf) }
+}
+