diff --git a/Cargo.toml b/Cargo.toml
index d74816a..47f5564 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 
 [dependencies]
 hex = "^0.3"
-openssl = "^0.10"
 base64 = "^0.2"
 typenum = "^1.0"
+openssl = "^0.10"
+rand = "^0.7"
\ No newline at end of file
diff --git a/src/bytes.rs b/src/bytes.rs
index d6db992..b907f4c 100644
--- a/src/bytes.rs
+++ b/src/bytes.rs
@@ -149,6 +149,20 @@ impl Bytes {
         self
     }
 
+    pub fn unpad(mut self) -> Option<Self> {
+        let len = self.len();
+
+        let last_byte = self.data[len-1];
+        let end_start = len - (last_byte as usize);
+        match self.data.iter().skip(end_start).all(|x| *x == last_byte) {
+            true => {
+                self.data.resize(end_start, 0u8);
+                Some(self)
+            },
+            false => None,
+        }
+    }
+
     pub fn pad_to_multiple(self, num: usize) -> Self {
         let num = (num - (self.len() % num)) as u8;
         self.pad(num)
diff --git a/src/crypto.rs b/src/crypto.rs
index f8c2e31..3632c82 100644
--- a/src/crypto.rs
+++ b/src/crypto.rs
@@ -1,51 +1,121 @@
 use crate::bytes::Bytes;
 
-pub use openssl::symm::Mode;
+pub use openssl::symm::{Cipher, Crypter, Mode};
 
 pub struct Aes {
     key: Vec<u8>,
+    pad: bool,
 }
 
 impl Aes {
     const BLOCK_SIZE: usize = 16;
 
-    pub fn new(key: &[u8]) -> Option<Aes> {
+    pub fn new(key: &[u8], pad: bool) -> Option<Aes> {
         let len = key.len();
         if len == 16 || len == 24 || len == 32 {
-            return Some(Aes { key: key.to_vec() });
+            return Some(Aes {
+                key: key.to_vec(),
+                pad,
+            });
         };
         None
     }
 
-    fn cipher(&self) -> openssl::symm::Cipher {
-        match self.key.len() {
-            16 => Some(openssl::symm::Cipher::aes_128_ecb()),
-            24 => Some(openssl::symm::Cipher::aes_192_ecb()),
-            32 => Some(openssl::symm::Cipher::aes_256_ecb()),
-            _ => None,
+    pub fn cbc(&self, data: Vec<u8>, iv: &[u8], mode: Mode) -> Option<Vec<u8>> {
+        if (!self.pad) && (data.len() % Self::BLOCK_SIZE != 0) {
+            return None;
         }
-        .unwrap()
-    }
+        let mut data = self.maybe_pad(data, mode);
+        let mut iv_ = [0u8; Self::BLOCK_SIZE];
+        let mut output_buffer = [0u8; 2 * Self::BLOCK_SIZE];
 
-    fn crypter(&self, mode: openssl::symm::Mode) -> openssl::symm::Crypter {
-        let cipher = self.cipher();
-        openssl::symm::Crypter::new(cipher, mode, &self.key, None).unwrap()
+        iv_.clone_from_slice(iv);
+        let mut iv = iv_;
+
+        let mut crypter = self.crypter(mode);
+        for chunk in data.chunks_exact_mut(Self::BLOCK_SIZE) {
+            match mode {
+                Mode::Decrypt => {
+                    let mut old_chunk = [0u8; Self::BLOCK_SIZE];
+                    old_chunk.copy_from_slice(chunk);
+
+                    Self::update(&mut crypter, chunk, &mut output_buffer);
+                    Self::xor_into(&output_buffer, &iv, chunk);
+
+                    iv.clone_from_slice(&old_chunk);
+                }
+                Mode::Encrypt => {
+                    Self::xor(chunk, &iv);
+
+                    Self::update(&mut crypter, chunk, &mut output_buffer);
+                    chunk.copy_from_slice(&output_buffer[0..Self::BLOCK_SIZE]);
+
+                    iv.copy_from_slice(chunk);
+                }
+            }
+        }
+        let data = self.maybe_unpad(data, mode);
+        Some(data.clone())
     }
 
     pub fn ecb(&self, mut data: Vec<u8>, mode: Mode) -> Option<Vec<u8>> {
-        if data.len() % Self::BLOCK_SIZE != 0 {
+        if (!self.pad) && (data.len() % Self::BLOCK_SIZE != 0) {
             return None;
         }
 
         let mut crypter = self.crypter(mode);
         let mut output_buffer = [0u8; 2 * Self::BLOCK_SIZE];
+        let mut data = self.maybe_pad(data, mode);
         for chunk in data.chunks_exact_mut(Self::BLOCK_SIZE) {
-            crypter.update(chunk, &mut output_buffer);
+            Self::update(&mut crypter, chunk, &mut output_buffer);
             chunk.copy_from_slice(&output_buffer[0..Self::BLOCK_SIZE]);
         }
+
+        let data = self.maybe_unpad(data, mode);
         Some(data)
     }
 
+    fn cipher(&self) -> Cipher {
+        match self.key.len() {
+            16 => Some(Cipher::aes_128_ecb()),
+            24 => Some(Cipher::aes_192_ecb()),
+            32 => Some(Cipher::aes_256_ecb()),
+            _ => None,
+        }
+        .unwrap()
+    }
+
+    fn crypter(&self, mode: Mode) -> Crypter {
+        let cipher = self.cipher();
+        let mut crypter = Crypter::new(cipher, mode, &self.key, None).unwrap();
+        crypter.pad(false);
+        crypter
+    }
+
+    fn maybe_pad(&self, data: Vec<u8>, mode: Mode) -> Vec<u8> {
+        match (self.pad, mode) {
+            (true, Mode::Encrypt) => Bytes { data }.pad_to_multiple(Self::BLOCK_SIZE).into(),
+            _ => data,
+        }
+    }
+
+    fn maybe_unpad(&self, data: Vec<u8>, mode: Mode) -> Vec<u8> {
+        match (self.pad, mode) {
+            (true, Mode::Decrypt) => Bytes { data }.unpad().unwrap().into(),
+            _ => data,
+        }
+    }
+
+
+    fn update(crypter: &mut Crypter, chunk: &[u8], output: &mut [u8]) {
+        assert!(
+            Self::BLOCK_SIZE
+                == crypter
+                    .update(chunk, output)
+                    .expect("Error while updating crypter")
+        );
+    }
+
     fn xor(a: &mut [u8], b: &[u8]) {
         for (l, r) in a.iter_mut().zip(b.iter()) {
             *l = *l ^ r;
@@ -57,40 +127,4 @@ impl Aes {
             *t = l ^ r;
         }
     }
-
-    pub fn cbc(&self, data: Vec<u8>, iv: &[u8], mode: Mode) -> Option<Vec<u8>> {
-        let data = crate::bytes::Bytes::from(data);
-        let mut data = data.pad_to_multiple(Self::BLOCK_SIZE);
-        let mut crypter = self.crypter(mode);
-        let mut iv_ = [0u8; Self::BLOCK_SIZE];
-        let mut output_buffer = [0u8; 2 * Self::BLOCK_SIZE];
-
-        iv_.clone_from_slice(iv);
-        let mut iv = iv_;
-        for chunk in data.chunks_exact_mut(Self::BLOCK_SIZE) {
-            match mode {
-                Mode::Decrypt => {
-                    let mut old_chunk = [0u8; Self::BLOCK_SIZE];
-                    old_chunk.copy_from_slice(chunk);
-
-                    let len = crypter.update(chunk, &mut output_buffer);
-                    Self::xor_into(&output_buffer, &iv, chunk);
-
-                    println!("IV: {:?}\nIB: {:?}\nOB: {:?} ({:?})\n\n", iv, old_chunk, chunk, len);
-
-                    iv.clone_from_slice(&old_chunk);
-                }
-                Mode::Encrypt => {
-                    Self::xor(chunk, &iv);
-
-                    crypter.update(chunk, &mut output_buffer);
-                    chunk.copy_from_slice(&output_buffer[0..Self::BLOCK_SIZE]);
-
-                    iv.copy_from_slice(chunk);
-                }
-            }
-        }
-        println!("{:?}", data);
-        Some(data.data.clone())
-    }
 }
diff --git a/src/main.rs b/src/main.rs
index 8264ef9..5003f2c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,8 +2,9 @@ mod bytes;
 mod crypto;
 mod io;
 
-use bytes::Bytes;
+use crate::bytes::Bytes;
 use openssl::symm::Mode;
+use rand::Rng;
 
 fn q01() {
     println!("Running q01");
@@ -90,7 +91,7 @@ fn q06() {
 
     let key = input.find_best_xor_cipher();
     let _output = input.xor_repeating(&key).to_string().unwrap();
-    // println!("  {}", output);
+    // println!("  {}", _output.replace("\n", "\n  "));
 }
 
 fn q07() {
@@ -100,11 +101,12 @@ fn q07() {
     let input = Bytes::from_base64(&input);
     let key = Bytes::from_string("YELLOW SUBMARINE");
     let _output = Bytes {
-        data: crypto::Aes::new(&key).unwrap()
+        data: crypto::Aes::new(&key, false)
+            .unwrap()
             .ecb(input.into(), Mode::Decrypt)
             .unwrap(),
     };
-    // println!("  {}", _output.to_string().unwrap());
+    // println!("  {}", _output.to_string().unwrap().replace("\n", "\n  "));
 }
 
 fn q08() {
@@ -152,8 +154,89 @@ fn q10() {
     let key = b"YELLOW SUBMARINE";
     let iv = [0u8; 16];
 
-    let output = crypto::Aes::new(key).unwrap().cbc(input.into(), &iv, Mode::Decrypt);
-    println!("{}", Bytes::from(output.unwrap()).to_string().unwrap());
+    let _output = crypto::Aes::new(key, false)
+        .unwrap()
+        .cbc(input.into(), &iv, Mode::Decrypt);
+    // println!("{}", Bytes::from(_output.unwrap()).to_string().unwrap().replace("\n", "\n  "));
+}
+
+fn q11() {
+    println!("Running q11");
+    let black_box = |mut data: Vec<u8>| -> (bool, Vec<u8>) {
+        let mut rng = rand::thread_rng();
+        let dist = rand::distributions::Standard;
+        let key: Vec<u8> = rng.sample_iter(&dist).take(16).collect();
+        let iv: Vec<u8> = rng.sample_iter(&dist).take(16).collect();
+        let aes = crypto::Aes::new(&key, true).unwrap();
+        let mut start: Vec<u8> = rng.sample_iter(&dist).take(rng.gen_range(5,11)).collect();
+        let mut end: Vec<u8> = rng.sample_iter(&dist).take(rng.gen_range(5,11)).collect();
+
+        start.append(&mut data);
+        start.append(&mut end);
+
+        match rand::random() {
+            false => (false, aes.cbc(start, &iv, Mode::Encrypt).unwrap()),
+            true => (true, aes.ecb(start, Mode::Encrypt).unwrap()),
+        }
+    };
+
+    let oracle = |data: &Vec<u8>| -> bool {
+        data[16..32] == data[32..48]
+    };
+
+    for i in 0..128 {
+        let data = [0u8;64];
+        let (ecb, data) = black_box(data.to_vec());
+        assert!(ecb == oracle(&data));
+    }
+}
+
+fn q12()
+{
+    println!("Running q12");
+    let key: Vec<u8> = rand::thread_rng().sample_iter(rand::distributions::Standard).take(16).collect();
+    let plaintext: Vec<u8> = Bytes::from_base64("Um9sbGluJyBpbiBteSA1LjAKV2l0aCBteSByYWctdG9wIGRvd24gc28gbXkgaGFpciBjYW4gYmxvdwpUaGUgZ2lybGllcyBvbiBzdGFuZGJ5IHdhdmluZyBqdXN0IHRvIHNheSBoaQpEaWQgeW91IHN0b3A/IE5vLCBJIGp1c3QgZHJvdmUgYnkK").into();
+    let aes = crate::crypto::Aes::new(&key, true).unwrap();
+
+    let blackbox = |mut data: Vec<u8>| -> Vec<u8> {
+        data.append(&mut plaintext.clone());
+        aes.ecb(data, Mode::Encrypt).unwrap()
+    };
+
+    let starting_size = blackbox(Vec::new()).len();
+    let (first_increment, next_size) = (0..).map(|x:usize| (x, blackbox(std::iter::repeat(0u8).take(x).collect()).len())).find(|(i,x)| *x != starting_size).unwrap();
+    let block_size = next_size - starting_size;
+    println!("  Block size is {}", block_size);
+    assert!(block_size == 16);
+
+    let long_block = blackbox(std::iter::repeat(0u8).take(128).collect());
+    let using_ecb = long_block[48..64] == long_block[64..80];
+    println!("  Using ECB: {}", using_ecb);
+    assert!(using_ecb);
+
+    println!("  First size increment at {}", first_increment);
+
+    let data_length = starting_size - first_increment;
+    let mut known: Vec<u8> = Vec::with_capacity(data_length);
+    println!("  Data length: {}", data_length);
+
+    for byte_index in 0..data_length
+    {
+        let nulls: Vec<u8> = std::iter::repeat(0u8).take(starting_size - known.len() - 1).collect();
+        let target_block = &blackbox(nulls.clone())[0..starting_size];
+        let mut found = false;
+        'byteiter: for b in 0u8..=255u8 {
+            let this_block = &blackbox(nulls.iter().chain(known.iter()).chain(std::iter::once(&b)).cloned().take(starting_size).collect())[0..starting_size];
+            if this_block == target_block
+            {
+                known.push(b);
+                found = true;
+                break 'byteiter;
+            }
+        }
+        assert!(found);
+    }
+    // println!("  {}", String::from_utf8(known).unwrap().replace("\n", "\n  "));
 }
 
 fn main() {
@@ -167,4 +250,6 @@ fn main() {
     q08();
     q09();
     q10();
+    q11();
+    q12();
 }