Merge pull request #80 from aerostitch/hmac_always_byte_array

Migrate hmac to []byte and handle transition

decode.go

@@ -5,7 +5,18 @@ import (
 	"github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
 )
 
+// adjustHmac will force the hmac to be a byte array if present as string
+func adjustHmac(record map[string]*dynamodb.AttributeValue) {
+	if val, ok := record["hmac"]; ok {
+		if len(val.B) == 0 && val.S != nil {
+			val.B = []byte(*val.S)
+			val.S = nil
+		}
+	}
+}
+
 // Decode decode the supplied struct from the dynamodb result map
 func Decode(data map[string]*dynamodb.AttributeValue, rawVal interface{}) error {
+	adjustHmac(data)
 	return dynamodbattribute.UnmarshalMap(data, rawVal)
 }

ds.go

@@ -1,6 +1,7 @@
 package unicreds
 
 import (
+	"bytes"
 	"encoding/base64"
 	"errors"
 	"io/ioutil"
@@ -62,7 +63,7 @@ type Credential struct {
 	Version   string `dynamodbav:"version"`
 	Key       string `dynamodbav:"key"`
 	Contents  string `dynamodbav:"contents"`
-	Hmac      string `dynamodbav:"hmac"`
+	Hmac      []byte `dynamodbav:"hmac"`
 	CreatedAt int64  `dynamodbav:"created_at"`
 }
 
@@ -168,7 +169,7 @@ func GetHighestVersionSecret(tableName *string, name string, encContext *Encrypt
 			"#N": aws.String("name"),
 		},
 		ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
-			":name": &dynamodb.AttributeValue{
+			":name": {
 				S: aws.String(name),
 			},
 		},
@@ -235,7 +236,7 @@ func GetHighestVersion(tableName *string, name string) (string, error) {
 			"#N": aws.String("name"),
 		},
 		ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
-			":name": &dynamodb.AttributeValue{
+			":name": {
 				S: aws.String(name),
 			},
 		},
@@ -548,7 +549,7 @@ func decryptCredential(cred *Credential, encContext *EncryptionContextValue) (*D
 
 	hexhmac := ComputeHmac256(contents, hmacKey)
 
-	if hexhmac != cred.Hmac {
+	if !bytes.Equal(hexhmac, cred.Hmac) {
 		return nil, ErrHmacValidationFailed
 	}
 

encryptor.go

@@ -28,10 +28,13 @@ func Encrypt(key, plaintext []byte) ([]byte, error) {
 
 // ComputeHmac256 compute a hmac256 signature of the supplied message and return
 // the value hex encoded
-func ComputeHmac256(message, secret []byte) string {
+func ComputeHmac256(message, secret []byte) []byte {
 	h := hmac.New(sha256.New, secret)
 	h.Write(message)
-	return hex.EncodeToString(h.Sum(nil))
+	src := h.Sum(nil)
+	dst := make([]byte, hex.EncodedLen(len(src)))
+	hex.Encode(dst, src)
+	return dst
 }
 
 // Decrypt AES encryption method which matches the pycrypto package