diff --git a/2017/04/1passphrases.py b/2017/04/1passphrases.py
new file mode 100755
index 0000000..cfde831
--- /dev/null
+++ b/2017/04/1passphrases.py
@@ -0,0 +1,23 @@
+#!/usr/bin/env python3
+# passphrase validity checker. see file `notes` for details
+# only strings with NO DUPLICATE words are valid
+
+if __name__ == '__main__':
+    total_valid = 0
+
+    def check_for_duplicates(list):
+        has_duplicate = False
+        for i in range(1, len(list)):
+            for j in range(i):
+                if list[i] == list[j]:
+                    has_duplicate = True
+        return has_duplicate
+
+    with open("input", "r", encoding="utf-8") as passphrase_input:
+        for passphrase in passphrase_input:
+            is_valid = False
+            passwords = passphrase.split()
+            is_valid = not check_for_duplicates(passwords)
+            if is_valid:
+                total_valid += 1
+    print(total_valid)
diff --git a/2017/04/notes b/2017/04/notes
new file mode 100644
index 0000000..fe28fa9
--- /dev/null
+++ b/2017/04/notes
@@ -0,0 +1,7 @@
+high-entropy passphrases!
+
+passphrases have all-lowercase space-separated strings of words.
+valid passphrases have NO DUPLICATE words.
+
+how many of the provided passphrases ARE VALID, i.e., have NO DUPLICATE words?
+provided passphrases are in file `input`