1 files changed, 40 insertions, 0 deletions
diff --git a/cmd/userkey/main.go b/cmd/userkey/main.go
new file mode 100644
index 0000000..5ecd5f1
--- /dev/null
+++ b/cmd/userkey/main.go
@@ -0,0 +1,40 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+)
+
+func main() {
+	user := os.Args[1]
+	if len(user) < 3 {
+		log.Fatalf("User name argument expected.")
+	}
+	encoded, err := ioutil.ReadAll(os.Stdin)
+	if err != nil || len(encoded) == 0 {
+		log.Fatalf("Expected exactly 1 secret")
+	}
+	sk, err := hex.DecodeString(string(encoded))
+	if err != nil || len(sk) < 32 {
+		log.Fatalf("hex.DecodeString() = %d, %v", len(sk), err)
+		return
+	}
+	mac := hmac.New(sha256.New, sk)
+	mac.Write([]byte(user))
+	fmt.Println(hex.EncodeToString(mac.Sum(nil)))
+}
+
+// ValidMAC reports whether messageMAC is a valid HMAC tag for message.
+func ValidMAC(message, messageMAC, key []byte) bool {
+	mac := hmac.New(sha256.New, key)
+	mac.Write(message)
+	expectedMAC := mac.Sum(nil)
+	return hmac.Equal(messageMAC, expectedMAC)
+}
+
+var sk []byte