Add KMS encryption context support

Fixes #93

cmd/sops/main.go

@@ -150,6 +150,10 @@ func main() {
 			Name:  "config",
 			Usage: "path to sops' config file. If set, sops will not search for the config file recursively.",
 		},
+		cli.StringFlag{
+			Name:  "encryption-context",
+			Usage: "comma separated list of KMS encryption context key:value pairs",
+		},
 	}
 	app.Action = func(c *cli.Context) error {
 		if c.NArg() < 1 {
@@ -304,9 +308,9 @@ func decrypt(c *cli.Context, file string, fileBytes []byte, output io.Writer) er
 func getKeysources(c *cli.Context, file string) ([]sops.KeySource, error) {
 	var kmsKeys []sops.MasterKey
 	var pgpKeys []sops.MasterKey
-
+	kmsEncryptionContext := kms.ParseKMSContext(c.String("encryption-context"))
 	if c.String("kms") != "" {
-		for _, k := range kms.MasterKeysFromArnString(c.String("kms")) {
+		for _, k := range kms.MasterKeysFromArnString(c.String("kms"), kmsEncryptionContext) {
 			kmsKeys = append(kmsKeys, k)
 		}
 	}
@@ -329,7 +333,7 @@ func getKeysources(c *cli.Context, file string) ([]sops.KeySource, error) {
 			for _, k := range pgp.MasterKeysFromFingerprintString(pgpString) {
 				pgpKeys = append(pgpKeys, k)
 			}
-			for _, k := range kms.MasterKeysFromArnString(kmsString) {
+			for _, k := range kms.MasterKeysFromArnString(kmsString, kmsEncryptionContext) {
 				kmsKeys = append(kmsKeys, k)
 			}
 		}
@@ -387,7 +391,8 @@ func rotate(c *cli.Context, file string, fileBytes []byte, output io.Writer) err
 	if err != nil {
 		return cli.NewExitError(fmt.Sprintf("Error encrypting tree: %s", err), exitErrorEncryptingTree)
 	}
-	tree.Metadata.AddKMSMasterKeys(c.String("add-kms"))
+	kmsEncryptionContext := kms.ParseKMSContext(c.String("encryption-context"))
+	tree.Metadata.AddKMSMasterKeys(c.String("add-kms"), kmsEncryptionContext)
 	tree.Metadata.AddPGPMasterKeys(c.String("add-pgp"))
 	tree.Metadata.RemoveKMSMasterKeys(c.String("rm-kms"))
 	tree.Metadata.RemovePGPMasterKeys(c.String("rm-pgp"))

json/store.go

@@ -274,6 +274,7 @@ func (store Store) kmsEntries(in []interface{}) (sops.KeySource, error) {
 		if err != nil {
 			return keysource, fmt.Errorf("Could not parse creation date: %s", err)
 		}
+		key.EncryptionContext = kms.ParseKMSContext(entry["context"].(string))
 		key.CreationDate = creationDate
 		keysource.Keys = append(keysource.Keys, key)
 	}

kms/keysource.go

@@ -24,6 +24,7 @@ type MasterKey struct {
 	Role              string
 	EncryptedKey      string
 	CreationDate      time.Time
+	EncryptionContext map[string]*string
 }
 
 // Encrypt takes a sops data key, encrypts it with KMS and stores the result in the EncryptedKey field
@@ -36,7 +37,7 @@ func (key *MasterKey) Encrypt(dataKey []byte) error {
 		}
 		kmsSvc = kms.New(sess)
 	}
-	out, err := kmsSvc.Encrypt(&kms.EncryptInput{Plaintext: dataKey, KeyId: &key.Arn})
+	out, err := kmsSvc.Encrypt(&kms.EncryptInput{Plaintext: dataKey, KeyId: &key.Arn, EncryptionContext: key.EncryptionContext})
 	if err != nil {
 		return err
 	}
@@ -44,7 +45,7 @@ func (key *MasterKey) Encrypt(dataKey []byte) error {
 	return nil
 }
 
-// EncryptIfNeeded encrypts the provided sops' data ket and encrypts it if it hasn't been encrypted yet
+// EncryptIfNeeded encrypts the provided sops' data key and encrypts it if it hasn't been encrypted yet
 func (key *MasterKey) EncryptIfNeeded(dataKey []byte) error {
 	if key.EncryptedKey == "" {
 		return key.Encrypt(dataKey)
@@ -65,7 +66,7 @@ func (key *MasterKey) Decrypt() ([]byte, error) {
 		}
 		kmsSvc = kms.New(sess)
 	}
-	decrypted, err := kmsSvc.Decrypt(&kms.DecryptInput{CiphertextBlob: k})
+	decrypted, err := kmsSvc.Decrypt(&kms.DecryptInput{CiphertextBlob: k, EncryptionContext: key.EncryptionContext})
 	if err != nil {
 		return nil, fmt.Errorf("Error decrypting key: %v", err)
 	}
@@ -83,7 +84,7 @@ func (key *MasterKey) ToString() string {
 }
 
 // NewMasterKeyFromArn takes an ARN string and returns a new MasterKey for that ARN
-func NewMasterKeyFromArn(arn string) *MasterKey {
+func NewMasterKeyFromArn(arn string, context map[string]*string) *MasterKey {
 	k := &MasterKey{}
 	arn = strings.Replace(arn, " ", "", -1)
 	roleIndex := strings.Index(arn, "+arn:aws:iam::")
@@ -93,18 +94,19 @@ func NewMasterKeyFromArn(arn string) *MasterKey {
 	} else {
 		k.Arn = arn
 	}
+	k.EncryptionContext = context
 	k.CreationDate = time.Now().UTC()
 	return k
 }
 
 // MasterKeysFromArnString takes a comma separated list of AWS KMS ARNs and returns a slice of new MasterKeys for those ARNs
-func MasterKeysFromArnString(arn string) []*MasterKey {
+func MasterKeysFromArnString(arn string, context map[string]*string) []*MasterKey {
 	var keys []*MasterKey
 	if arn == "" {
 		return keys
 	}
 	for _, s := range strings.Split(arn, ",") {
-		keys = append(keys, NewMasterKeyFromArn(s))
+		keys = append(keys, NewMasterKeyFromArn(s, context))
 	}
 	return keys
 }
@@ -156,5 +158,22 @@ func (key MasterKey) ToMap() map[string]string {
 	}
 	out["created_at"] = key.CreationDate.UTC().Format(time.RFC3339)
 	out["enc"] = key.EncryptedKey
+	if key.EncryptionContext != nil {
+		var outContexts []string
+		for k, v := range key.EncryptionContext {
+			outContexts = append(outContexts, k+":"+*v)
+		}
+		out["context"] = strings.Join(outContexts, ",")
+	}
+	return out
+}
+
+// ParseKMSContext takes a comma-separated list of KMS context key:value pairs and returns a map
+func ParseKMSContext(in string) map[string]*string {
+	out := make(map[string]*string)
+	for _, kv := range strings.Split(in, ",") {
+		kv := strings.Split(kv, ":")
+		out[kv[0]] = &kv[1]
+	}
 	return out
 }

kms/keysource_test.go

@@ -49,7 +49,7 @@ func TestKMS(t *testing.T) {
 
 func TestKMSKeySourceFromString(t *testing.T) {
 	s := "arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e+arn:aws:iam::927034868273:role/sops-dev, arn:aws:kms:ap-southeast-1:656532927350:key/9006a8aa-0fa6-4c14-930e-a2dfb916de1d"
-	ks := MasterKeysFromArnString(s)
+	ks := MasterKeysFromArnString(s, nil)
 	k1 := ks[0]
 	k2 := ks[1]
 	expectedArn1 := "arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e"

sops.go

@@ -308,11 +308,11 @@ func (m *Metadata) AddPGPMasterKeys(pgpFps string) {
 }
 
 // AddKMSMasterKeys parses the input comma separated string of AWS KMS ARNs, generates a KMS MasterKey for each ARN, and then adds the keys to the KMS KeySource
-func (m *Metadata) AddKMSMasterKeys(kmsArns string) {
+func (m *Metadata) AddKMSMasterKeys(kmsArns string, context map[string]*string) {
 	for i, ks := range m.KeySources {
 		if ks.Name == "kms" {
 			var keys []MasterKey
-			for _, k := range kms.MasterKeysFromArnString(kmsArns) {
+			for _, k := range kms.MasterKeysFromArnString(kmsArns, context) {
 				keys = append(keys, k)
 			}
 			ks.Keys = append(ks.Keys, keys...)
@@ -333,7 +333,7 @@ func (m *Metadata) RemovePGPMasterKeys(pgpFps string) {
 // RemoveKMSMasterKeys takes a comma separated string of AWS KMS ARNs and removes the keys corresponding to those ARNs from the metadata's KeySources
 func (m *Metadata) RemoveKMSMasterKeys(arns string) {
 	var keys []MasterKey
-	for _, k := range kms.MasterKeysFromArnString(arns) {
+	for _, k := range kms.MasterKeysFromArnString(arns, nil) {
 		keys = append(keys, k)
 	}
 	m.RemoveMasterKeys(keys)

yaml/store.go

@@ -200,6 +200,7 @@ func (store *Store) kmsEntries(in []interface{}) (sops.KeySource, error) {
 			return keysource, fmt.Errorf("Could not parse creation date: %s", err)
 		}
 		key.CreationDate = creationDate
+		key.EncryptionContext = kms.ParseKMSContext(entry["context"].(string))
 		keysource.Keys = append(keysource.Keys, key)
 	}
 	return keysource, nil