diff --git a/src/backup.rs b/src/backup.rs
index 394091f6..e8947917 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -20,6 +20,9 @@ pub use chunker::*;
 mod chunk_store;
 pub use chunk_store::*;
 
+mod index;
+pub use index::*;
+
 mod fixed_index;
 pub use fixed_index::*;
 
diff --git a/src/backup/dynamic_index.rs b/src/backup/dynamic_index.rs
index 3a9b8beb..01e9d16f 100644
--- a/src/backup/dynamic_index.rs
+++ b/src/backup/dynamic_index.rs
@@ -1,6 +1,7 @@
 use failure::*;
 
 use crate::tools;
+use super::IndexFile;
 use super::chunk_stat::*;
 use super::chunk_store::*;
 use super::chunker::*;
@@ -196,6 +197,22 @@ impl DynamicIndexReader {
     }
 }
 
+impl IndexFile for DynamicIndexReader {
+    fn index_count(&self) -> usize {
+        self.index_entries
+    }
+
+    fn index_digest(&self, pos: usize) -> Option<&[u8; 32]> {
+        if pos >= self.index_entries {
+            None
+        } else {
+            Some(unsafe {
+                std::mem::transmute(self.chunk_digest(pos).as_ptr())
+            })
+        }
+    }
+}
+
 pub struct BufferedDynamicReader {
     index: DynamicIndexReader,
     archive_size: u64,
diff --git a/src/backup/fixed_index.rs b/src/backup/fixed_index.rs
index d41601db..bb3197ba 100644
--- a/src/backup/fixed_index.rs
+++ b/src/backup/fixed_index.rs
@@ -1,6 +1,7 @@
 use failure::*;
 
 use crate::tools;
+use super::IndexFile;
 use super::chunk_stat::*;
 use super::chunk_store::*;
 
@@ -132,14 +133,14 @@ impl FixedIndexReader {
 
         if self.index == std::ptr::null_mut() { bail!("detected closed index file."); }
 
-        let index_count = (self.size + self.chunk_size - 1)/self.chunk_size;
+        let index_count = self.index_count();
 
         status.used_bytes += index_count * self.chunk_size;
         status.used_chunks += index_count;
 
         for pos in 0..index_count {
 
-            let digest = unsafe { std::slice::from_raw_parts_mut(self.index.add(pos*32), 32) };
+            let digest = self.index_digest(pos).unwrap();
             if let Err(err) = self.store.touch_chunk(digest) {
                 bail!("unable to access chunk {}, required by {:?} - {}",
                       tools::digest_to_hex(digest), self.filename, err);
@@ -158,6 +159,20 @@ impl FixedIndexReader {
     }
 }
 
+impl IndexFile for FixedIndexReader {
+    fn index_count(&self) -> usize {
+        (self.size + self.chunk_size - 1)/self.chunk_size
+    }
+
+    fn index_digest(&self, pos: usize) -> Option<&[u8; 32]> {
+        if pos >= self.index_count() {
+            None
+        } else {
+            Some(unsafe { std::mem::transmute(self.index.add(pos*32)) })
+        }
+    }
+}
+
 pub struct FixedIndexWriter {
     store: Arc<ChunkStore>,
     filename: PathBuf,
diff --git a/src/backup/index.rs b/src/backup/index.rs
new file mode 100644
index 00000000..1cad4e69
--- /dev/null
+++ b/src/backup/index.rs
@@ -0,0 +1,44 @@
+pub trait IndexFile {
+    fn index_count(&self) -> usize;
+    fn index_digest(&self, pos: usize) -> Option<&[u8; 32]>;
+}
+
+pub struct IndexIterator {
+    pos: usize,
+    count: usize,
+    reader: Box<dyn IndexFile + Send>,
+}
+
+impl Iterator for IndexIterator {
+    type Item = [u8; 32];
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.pos == self.count {
+            return None;
+        }
+
+        let digest = self.reader.index_digest(self.pos).unwrap();
+        self.pos += 1;
+        Some(*digest)
+    }
+}
+
+impl From<Box<dyn IndexFile + Send>> for IndexIterator {
+    fn from(file: Box<dyn IndexFile + Send>) -> Self {
+        Self {
+            pos: 0,
+            count: file.index_count(),
+            reader: file,
+        }
+    }
+}
+
+impl<T: IndexFile + Send + 'static> From<Box<T>> for IndexIterator {
+    fn from(file: Box<T>) -> Self {
+        Self {
+            pos: 0,
+            count: file.index_count(),
+            reader: file,
+        }
+    }
+}