1 files changed, 40 insertions, 1 deletions

diff --git a/worktree_commit.go b/worktree_commit.go
index 3145c8a..673eb16 100644
--- a/worktree_commit.go
+++ b/worktree_commit.go
@@ -1,9 +1,12 @@
 package git
 
 import (
+	"bytes"
 	"path"
+	"sort"
 	"strings"
 
+	"golang.org/x/crypto/openpgp"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/filemode"
 	"gopkg.in/src-d/go-git.v4/plumbing/format/index"
@@ -63,7 +66,6 @@ func (w *Worktree) autoAddModifiedAndDeleted() error {
 		if _, err := w.Add(path); err != nil {
 			return err
 		}
-
 	}
 
 	return nil
@@ -93,6 +95,14 @@ func (w *Worktree) buildCommitObject(msg string, opts *CommitOptions, tree plumb
 		ParentHashes: opts.Parents,
 	}
 
+	if opts.SignKey != nil {
+		sig, err := w.buildCommitSignature(commit, opts.SignKey)
+		if err != nil {
+			return plumbing.ZeroHash, err
+		}
+		commit.PGPSignature = sig
+	}
+
 	obj := w.r.Storer.NewEncodedObject()
 	if err := commit.Encode(obj); err != nil {
 		return plumbing.ZeroHash, err
@@ -100,6 +110,22 @@ func (w *Worktree) buildCommitObject(msg string, opts *CommitOptions, tree plumb
 	return w.r.Storer.SetEncodedObject(obj)
 }
 
+func (w *Worktree) buildCommitSignature(commit *object.Commit, signKey *openpgp.Entity) (string, error) {
+	encoded := &plumbing.MemoryObject{}
+	if err := commit.Encode(encoded); err != nil {
+		return "", err
+	}
+	r, err := encoded.Reader()
+	if err != nil {
+		return "", err
+	}
+	var b bytes.Buffer
+	if err := openpgp.ArmoredDetachSign(&b, signKey, r, nil); err != nil {
+		return "", err
+	}
+	return b.String(), nil
+}
+
 // buildTreeHelper converts a given index.Index file into multiple git objects
 // reading the blobs from the given filesystem and creating the trees from the
 // index structure. The created objects are pushed to a given Storer.
@@ -163,7 +189,20 @@ func (h *buildTreeHelper) doBuildTree(e *index.Entry, parent, fullpath string) {
 	h.trees[parent].Entries = append(h.trees[parent].Entries, te)
 }
 
+type sortableEntries []object.TreeEntry
+
+func (sortableEntries) sortName(te object.TreeEntry) string {
+	if te.Mode == filemode.Dir {
+		return te.Name + "/"
+	}
+	return te.Name
+}
+func (se sortableEntries) Len() int               { return len(se) }
+func (se sortableEntries) Less(i int, j int) bool { return se.sortName(se[i]) < se.sortName(se[j]) }
+func (se sortableEntries) Swap(i int, j int)      { se[i], se[j] = se[j], se[i] }
+
 func (h *buildTreeHelper) copyTreeToStorageRecursive(parent string, t *object.Tree) (plumbing.Hash, error) {
+	sort.Sort(sortableEntries(t.Entries))
 	for i, e := range t.Entries {
 		if e.Mode != filemode.Dir && !e.Hash.IsZero() {
 			continue