From cc042aaa962b6415f958de426cf44798ce0cd137 Mon Sep 17 00:00:00 2001
From: Adrian Utrilla <adrianutrilla@gmail.com>
Date: Fri, 26 May 2017 11:17:43 +0200
Subject: [PATCH] Make shamir quorum configurable by the user

---
 cmd/sops/main.go | 10 ++++++++++
 sops.go          | 23 ++++++++++++++---------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/cmd/sops/main.go b/cmd/sops/main.go
index 3227fed10..a585dfeb4 100644
--- a/cmd/sops/main.go
+++ b/cmd/sops/main.go
@@ -69,6 +69,9 @@ func loadPlainFile(c *cli.Context, store sops.Store, fileName string, fileBytes
 	if c.Bool("shamir") {
 		tree.Metadata.Shamir = true
 	}
+	if quorum := c.Int("shamir-quorum"); quorum != 0 {
+		tree.Metadata.ShamirQuorum = quorum
+	}
 	tree.GenerateDataKey()
 	return
 }
@@ -207,6 +210,10 @@ func main() {
 			Name: "shamir",
 			Usage: "use Shamir's secret sharing to split the data key among all the master keys",
 		},
+		cli.IntFlag{
+			Name: "shamir-quorum",
+			Usage: "the number of master keys required to retrieve the data key with shamir",
+		},
 	}
 
 	app.Action = func(c *cli.Context) error {
@@ -556,6 +563,9 @@ func loadExample(c *cli.Context, file string) (sops.Tree, error) {
 	if c.Bool("shamir") {
 		tree.Metadata.Shamir = true
 	}
+	if quorum := c.Int("shamir-quorum"); quorum != 0 {
+		tree.Metadata.ShamirQuorum = quorum
+	}
 	key, errs := tree.GenerateDataKey()
 	if len(errs) > 0 {
 		return tree, cli.NewExitError(fmt.Sprintf("Error encrypting the data key with one or more master keys: %s", errs), exitCouldNotRetrieveKey)
diff --git a/sops.go b/sops.go
index 01c3d53dc..c3b798a86 100644
--- a/sops.go
+++ b/sops.go
@@ -53,7 +53,9 @@ const DefaultUnencryptedSuffix = "_unencrypted"
 
 type sopsError string
 
-func (e sopsError) Error() string { return string(e) }
+func (e sopsError) Error() string {
+	return string(e)
+}
 
 // MacMismatch occurs when the computed MAC does not match the expected ones
 const MacMismatch = sopsError("MAC mismatch")
@@ -106,10 +108,10 @@ type Tree struct {
 
 // TrimTreePathComponent trimps a tree path component so that it's a valid tree key
 func TrimTreePathComponent(component string) (string, error) {
-	if component[len(component)-1] != ']' {
+	if component[len(component) - 1] != ']' {
 		return "", fmt.Errorf("Invalid component")
 	}
-	component = component[:len(component)-1]
+	component = component[:len(component) - 1]
 	component = strings.Replace(component, `"`, "", 2)
 	component = strings.Replace(component, `'`, "", 2)
 	return component, nil
@@ -185,7 +187,7 @@ func (tree TreeBranch) walkBranch(in TreeBranch, path []string, onLeaves func(in
 		}
 		key, ok := item.Key.(string)
 		if !ok {
-			return nil, fmt.Errorf("Tree contains a non-string key (type %T): %s. Only string keys are"+
+			return nil, fmt.Errorf("Tree contains a non-string key (type %T): %s. Only string keys are" +
 				"supported", item.Key, item.Key)
 		}
 		newV, err := tree.walkValue(item.Value, append(path, key), onLeaves)
@@ -291,10 +293,10 @@ type Metadata struct {
 	KeySources                []KeySource
 	// Shamir specifies if the data key this file is encrypted with was
 	// split between all key sources using Shamir's Secret Sharing.
-	Shamir bool
+	Shamir                    bool
 	// ShamirQuorum is the number of parts required to recover the original
 	// data key
-	ShamirQuorum int
+	ShamirQuorum              int
 }
 
 // KeySource is a collection of MasterKeys with a Name.
@@ -378,9 +380,12 @@ func (m *Metadata) updateMasterKeysShamir(dataKey []byte) (errs []error) {
 			keyCount++
 		}
 	}
-	quorum := (keyCount / 2) + 1
-	m.ShamirQuorum = quorum
-	parts, err := shamir.Split(dataKey, keyCount, quorum)
+	defaultQuorum := (keyCount / 2) + 1
+	// If the quorum wasn't set, default to half the keys plus one
+	if m.ShamirQuorum == 0 {
+		m.ShamirQuorum = defaultQuorum
+	}
+	parts, err := shamir.Split(dataKey, keyCount, m.ShamirQuorum)
 	if err != nil {
 		errs = append(errs, fmt.Errorf("Could not split data key into parts for Shamir: %s", err))
 		return