diff --git a/samples/test_osnma.py b/samples/test_osnma.py
index 5ddc629..8e304fa 100644
--- a/samples/test_osnma.py
+++ b/samples/test_osnma.py
@@ -1,6 +1,16 @@
 """
 test script for Galileo OSNMA
 
+[1] Galileo Open Service Navigation Message Authentication (OSNMA)
+    Signal-in-Space Interface Control Document (SIS ICD), October, 2023.
+
+[2] Galileo Open Service Navigation Message Authentication (OSNMA)
+    Receiver Guidelines Issue 1.3, January, 2024.
+
+Note:
+    to use the package for OSNMA, the user needs to
+    install the public keys provided by EUSPA.
+
 @author Rui Hirokawa
 
 """
diff --git a/samples/test_osnma_tv.py b/samples/test_osnma_tv.py
index 47b30de..d8c94bc 100644
--- a/samples/test_osnma_tv.py
+++ b/samples/test_osnma_tv.py
@@ -1,7 +1,10 @@
 """
-test script for Galileo OSNMA based on [1]
+test script for Galileo OSNMA based on [2]
 
 [1] Galileo Open Service Navigation Message Authentication (OSNMA)
+    Signal-in-Space Interface Control Document (SIS ICD), October, 2023.
+
+[2] Galileo Open Service Navigation Message Authentication (OSNMA)
     Receiver Guidelines Issue 1.3, January, 2024.
 
 @author Rui Hirokawa
diff --git a/samples/test_qznma.py b/samples/test_qznma.py
index 1ba96aa..8da41b3 100644
--- a/samples/test_qznma.py
+++ b/samples/test_qznma.py
@@ -1,16 +1,28 @@
 """
 sample for QZNMA
 
+[1] Quasi-Zenith Satellite System Interface Specification
+    Satellite Positioning, Navigation and Timing Service (IS-QZSS-PNT-006),
+    July, 2024
+
+Note:
+    to use the package for QZSNMA, the user needs to
+    install the public keys provided by QSS.
+
 @author Rui Hirokawa
 
 """
 
+import os
 from binascii import unhexlify
 import numpy as np
 from cssrlib.gnss import prn2sat, uGNSS
 from cssrlib.qznma import qznma, uNavId
 import matplotlib.pyplot as plt
 
+if not os.path.exists('../data/pubkey/qznma/002.der'):
+    print('please install public key file from QSS.')
+
 dtype = [('wn', 'int'), ('tow', 'float'), ('prn', 'int'),
          ('type', 'int'), ('len', 'int'), ('nav', 'S512')]
 msg_nav_t = {uNavId.GPS_LNAV: 'LNAV', uNavId.GPS_CNAV: 'CNAV',