diff --git a/src/day11.rs b/src/day11.rs
new file mode 100644
index 0000000..455eec4
--- /dev/null
+++ b/src/day11.rs
@@ -0,0 +1,76 @@
+use aoc_runner_derive::aoc;
+
+#[aoc(day11, part1)]
+fn part1(input: &str) -> String {
+    PasswordCounter::from(input.to_owned()).find(|p| {
+        let r1 = rule1(&p);
+        let r2 = rule2(&p);
+        let r3 = rule3(&p);
+        r1 && r2 && r3
+    }).unwrap()
+}
+
+fn rule1(pw: &str) -> bool {
+    let pw = pw.as_bytes();
+    for i in 0..pw.len() - 2 {
+        if pw[i + 1] == pw[i] + 1 && pw[i + 2] == pw[i] + 2 {
+            return true;
+        }
+    }
+    false
+}
+
+fn rule2(pw: &str) -> bool {
+    !pw.contains(['i', 'o', 'l'])
+}
+
+fn rule3(pw: &str) -> bool {
+    let mut pair_one = None;
+    let pw = pw.as_bytes();
+    for i in 0..pw.len() - 1 {
+        if pw[i] == pw[i + 1] {
+            if let Some(b) = pair_one {
+                if b != pw[i] {
+                    return true;
+                }
+            } else {
+                pair_one = Some(pw[i]);
+            }
+        }
+    }
+    false
+}
+
+struct PasswordCounter {
+    current: [u8; 8],
+}
+
+impl PasswordCounter {
+    fn from(seed: String) -> Self {
+        let mut current = [0u8; 8];
+        for i in 0..8 {
+            current[i] = seed.as_bytes()[i];
+        }
+        PasswordCounter { current }
+    }
+}
+
+impl Iterator for PasswordCounter {
+    type Item = String;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let pw = &mut self.current;
+        for i in (0..pw.len()).rev() {
+            pw[i] += 1;
+            if pw[i] != b'z' + 1 {
+                break;
+            }
+            pw[i] = b'a';
+        }
+
+        Some(String::from_iter(self.current.iter().map(|b| *b as char)))
+    }
+}
+
+#[cfg(test)]
+mod tests {}
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index a434274..2ceb10c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,5 +3,6 @@ extern crate aoc_runner;
 extern crate aoc_runner_derive;
 
 mod day10;
+mod day11;
 
 aoc_lib! { year = 2015 }