mc root source folder cleanup

mc/crypto/offline.go

@@ -0,0 +1,26 @@
+package crypto
+
+import (
+	"crypto/md5"
+
+	"github.com/google/uuid"
+)
+
+// UUIDv3 Variation of google.uuid.NewHash
+// We need this because we want a 14-byte namespace and Google forces 16
+func UUIDv3(space []byte, data []byte) uuid.UUID {
+	h := md5.New()
+	h.Reset()
+	h.Write(space) //nolint:errcheck
+	h.Write(data)  //nolint:errcheck
+	s := h.Sum(nil)
+	var u uuid.UUID
+	copy(u[:], s)
+	u[6] = (u[6] & 0x0f) | uint8((3&0xf)<<4) // Version 3
+	u[8] = (u[8] & 0x3f) | 0x80              // RFC 4122 variant
+	return u
+}
+
+func FromOfflinePlayer(displayName string) uuid.UUID {
+	return UUIDv3([]byte("OfflinePlayer:"), []byte(displayName))
+}