diff --git a/README.md b/README.md
index 0b50f2a..c0cdcdc 100644
--- a/README.md
+++ b/README.md
@@ -103,7 +103,7 @@ As an example, to check if the key `000102030405060708090A0B0C0D0E0F` is used to
 >>> pkt = LoRa(binascii.unhexlify(p))
 >>> pkt
 <LoRa  Preamble=0x0 PHDR=0x0 PHDR_CRC=0x0 MType=Join-request RFU=0 Major=0 Join_Request_Field=[<Join_Request  AppEUI='lovecafe' DevEUI='meeetoo' DevNonce=26985 |>] MIC=0x53024c49 |>
->>> checkMIC(binascii.unhexlify(key), str(pkt))
+>>> checkMIC(binascii.unhexlify(key), bytes(pkt))
 True
 ```
 
diff --git a/lutil/crypto.py b/lutil/crypto.py
index 85f99f1..5f08d40 100644
--- a/lutil/crypto.py
+++ b/lutil/crypto.py
@@ -63,6 +63,7 @@ def checkMIC(key, hexpkt, direction=1):
     except Exception:
         mic = binascii.hexlify(mic)
     cmic = bytes(getPHY_CMAC(key, hexpkt), 'utf-8')
+    print (repr(mic), repr(cmic))
     return (mic == cmic)
 
 # TODO: more helpers
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..92b7a89
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,2 @@
+pycryptodome
+scapy