Implement challenge 15 pkcs7 validation.

src/bytes.rs

@@ -101,6 +101,22 @@ impl Bytes {
         }
     }
 
+    pub fn has_valid_pkcs7(&mut self, block_size: usize) -> bool {
+        if self.len() > 0 && self.len() % block_size != 0 {
+            return false;
+        }
+        let last_block_index = self.len() / block_size - 1;
+        let last_block = self.get_block(last_block_index, block_size).0;
+        let pad_byte_count = last_block[block_size - 1];
+        for i in 0..(pad_byte_count as usize) {
+            let byte = last_block[block_size - 1 - i];
+            if byte != pad_byte_count {
+                return false;
+            }
+        }
+        return true;
+    }
+
     pub fn xor(Bytes(a): &Bytes, Bytes(b): &Bytes) -> Bytes {
         Bytes(
             Iterator::zip(a.iter(), b.iter())

src/main.rs

@@ -21,4 +21,6 @@ fn main() {
     set2::challenge12();
     set2::challenge13();
     set2::challenge14();
+    set2::challenge15();
+    set2::challenge16();
 }

src/set2.rs

@@ -390,3 +390,26 @@ pub fn challenge14() {
         roundtrip_text.to_utf8()[..17].to_string()
     );
 }
+
+pub fn challenge15() {
+    assert_eq!(
+        Bytes::from_utf8("ICE ICE BABY\u{4}\u{4}\u{4}").has_valid_pkcs7(16),
+        false
+    );
+    assert_eq!(
+        Bytes::from_utf8("ICE ICE BABY\u{4}\u{4}\u{4}\u{4}").has_valid_pkcs7(16),
+        true
+    );
+    assert_eq!(
+        Bytes::from_utf8("ICE ICE BABY\u{3}\u{3}\u{4}\u{4}").has_valid_pkcs7(16),
+        false
+    );
+    let mut bytes = Bytes::from_utf8("ICE ICE BABY\u{3}\u{3}\u{4}\u{4}");
+    bytes.pad_pkcs7(16);
+    assert_eq!(bytes.has_valid_pkcs7(16), true);
+    println!("[okay] Challenge 15: PKCS7 works");
+}
+
+pub fn challenge16() {
+    println!("[xxxx] Challenge 16: TBD");
+}