diff --git a/Cargo.lock b/Cargo.lock
index 5e4f78c..e16a0af 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -90,6 +90,12 @@ dependencies = [
 [[package]]
 name = "p12"
 version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "base64",
+ "common",
+ "rand",
+]
 
 [[package]]
 name = "p13"
@@ -214,9 +220,9 @@ checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
 
 [[package]]
 name = "rand"
-version = "0.9.1"
+version = "0.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9fbfd9d094a40bf3ae768db9361049ace4c0e04a4fd6b359518bd7b73a73dd97"
+checksum = "6db2770f06117d490610c7488547d543617b21bfa07796d7a12f6f1bd53850d1"
 dependencies = [
  "rand_chacha",
  "rand_core",
diff --git a/Cargo.toml b/Cargo.toml
index 5343f5a..bf4fef7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,3 +5,9 @@ edition = "2024"
 
 [workspace]
 members = ["problems/*", "common"]
+
+[workspace.dependencies]
+hex = "0.4.3"
+base64 = "0.22.1"
+anyhow = "1.0.98"
+rand = "0.9.2"
diff --git a/cryptopal_book/.gitignore b/cryptopal_book/.gitignore
new file mode 100644
index 0000000..7585238
--- /dev/null
+++ b/cryptopal_book/.gitignore
@@ -0,0 +1 @@
+book
diff --git a/problems/p1/Cargo.toml b/problems/p1/Cargo.toml
index 36de262..d5055a0 100644
--- a/problems/p1/Cargo.toml
+++ b/problems/p1/Cargo.toml
@@ -4,5 +4,5 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-hex = "0.4.3"
-base64 = "0.22.1"
+hex = { workspace = true }
+base64 = { workspace = true }
diff --git a/problems/p10/Cargo.toml b/problems/p10/Cargo.toml
index 06ef0c3..99d1931 100644
--- a/problems/p10/Cargo.toml
+++ b/problems/p10/Cargo.toml
@@ -4,7 +4,7 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-anyhow = "1.0"
-hex = "0.4"
-base64 = "0.22"
+anyhow = { workspace = true }
+hex = { workspace = true }
+base64 = { workspace = true }
 common = { path = "../../common" }
diff --git a/problems/p11/Cargo.toml b/problems/p11/Cargo.toml
index 7111df7..6182a9a 100644
--- a/problems/p11/Cargo.toml
+++ b/problems/p11/Cargo.toml
@@ -5,4 +5,4 @@ edition = "2024"
 
 [dependencies]
 common = { path = "../../common" }
-rand = "0.9.1"
+rand = { workspace = true }
diff --git a/problems/p12/Cargo.toml b/problems/p12/Cargo.toml
index eb7d2e7..3690b2a 100644
--- a/problems/p12/Cargo.toml
+++ b/problems/p12/Cargo.toml
@@ -4,3 +4,7 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+common = { path = "../../common" }
+rand = { workspace = true }
+base64 = { workspace = true }
+anyhow = { workspace = true }
diff --git a/problems/p12/src/main.rs b/problems/p12/src/main.rs
index e7a11a9..bde7810 100644
--- a/problems/p12/src/main.rs
+++ b/problems/p12/src/main.rs
@@ -1,3 +1,82 @@
-fn main() {
-    println!("Hello, world!");
+use std::process::exit;
+
+use anyhow::Result;
+use base64::{Engine, engine::general_purpose::STANDARD};
+use common::{aes_ecb_enc, pkcs7_padding};
+use rand::{prelude::*, rand_core::block};
+
+fn gen_random_key() -> [u8; 16] {
+    let mut rng = rand::rng();
+    let mut key = [0u8; 16];
+    rng.fill(&mut key);
+    key
+}
+
+fn oracle(controlled_input: &[u8], key: &[u8; 16], unknown_string: &[u8]) -> Vec<u8> {
+    let mut data = Vec::new();
+    data.extend_from_slice(controlled_input);
+    data.extend_from_slice(unknown_string);
+
+    pkcs7_padding(&mut data, 16);
+
+    aes_ecb_enc(&data, key).unwrap()
+}
+
+fn main() -> Result<()> {
+    let b64_unknown_string = "Um9sbGluJyBpbiBteSA1LjAKV2l0aCBteSByYWctdG9wIGRvd24gc28gbXkgaGFpciBjYW4gYmxvdwpUaGUgZ2lybGllcyBvbiBzdGFuZGJ5IHdhdmluZyBqdXN0IHRvIHNheSBoaQpEaWQgeW91IHN0b3A/IE5vLCBJIGp1c3QgZHJvdmUgYnkK";
+    let unknown_string = STANDARD.decode(b64_unknown_string)?;
+    let key = gen_random_key();
+
+    // let plaintext = Vec::new();
+
+    // step1. find padding length and unknown_string length.
+    let mut padding_len = 0;
+
+    let prev_cipher = oracle(&vec![0; padding_len], &key, &unknown_string);
+    while prev_cipher.len() + 16 != oracle(&vec![0; padding_len], &key, &unknown_string).len() {
+        padding_len += 1;
+    }
+    println!("padding_len: {padding_len}"); // 6
+    let unknown_str_len = prev_cipher.len() - padding_len;
+    println!("unknown_str_len: {unknown_str_len}");
+
+    assert_eq!(unknown_str_len, unknown_string.len()); // debug use
+
+    let mut cracked: Vec<u8> = Vec::new();
+
+    let mut flag = false;
+
+    while cracked.len() != unknown_str_len {
+        padding_len += 1;
+        for i in 0..=255u8 {
+            let mut block = Vec::new();
+            block.push(i);
+            block.extend_from_slice(&cracked[..cracked.len().min(15)]);
+
+            pkcs7_padding(&mut block, 16);
+            block.extend(b"1".repeat(padding_len));
+            let cipher = oracle(&block, &key, &unknown_string);
+
+            let chunks: Vec<&[u8]> = cipher.chunks(16).collect();
+            let first_16 = chunks[0];
+            let need_crack_16 = chunks[chunks.len() - 1 - ((cracked.len() + 1) / 16)];
+            if first_16 == need_crack_16 {
+                cracked.insert(0, i);
+                flag = true;
+                break;
+            }
+        }
+        if flag {
+            flag = false;
+        } else {
+            println!("Error. Some byte not found.");
+            println!("Cerrent length: {}", cracked.len());
+            exit(0)
+        }
+    }
+    println!("{}", String::from_utf8_lossy(&cracked));
+    // println!("{}", String::from_utf8_lossy(&plaintext));
+    assert_eq!(cracked, unknown_string);
+
+    Ok(())
 }
diff --git a/problems/p15/Cargo.toml b/problems/p15/Cargo.toml
index 9ad3a39..88bd750 100644
--- a/problems/p15/Cargo.toml
+++ b/problems/p15/Cargo.toml
@@ -4,4 +4,4 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-anyhow = "1.0.98"
+anyhow = { workspace = true }
diff --git a/problems/p2/Cargo.toml b/problems/p2/Cargo.toml
index dc22998..a384a03 100644
--- a/problems/p2/Cargo.toml
+++ b/problems/p2/Cargo.toml
@@ -4,4 +4,4 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-hex = "0.4.3"
+hex = { workspace = true }
diff --git a/problems/p3/Cargo.toml b/problems/p3/Cargo.toml
index 8fe35a6..cd5a38c 100644
--- a/problems/p3/Cargo.toml
+++ b/problems/p3/Cargo.toml
@@ -5,4 +5,4 @@ edition = "2024"
 
 [dependencies]
 common = { path = "../../common/" }
-hex = "0.4.3"
+hex = { workspace = true }
diff --git a/problems/p4/Cargo.toml b/problems/p4/Cargo.toml
index f6b82cf..f84ac06 100644
--- a/problems/p4/Cargo.toml
+++ b/problems/p4/Cargo.toml
@@ -4,5 +4,5 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-hex = "0.4.3"
+hex = { workspace = true }
 common = { path = "../../common/" }
diff --git a/problems/p5/Cargo.toml b/problems/p5/Cargo.toml
index 75dbd0f..0a77a7b 100644
--- a/problems/p5/Cargo.toml
+++ b/problems/p5/Cargo.toml
@@ -5,5 +5,5 @@ edition = "2024"
 
 [dependencies]
 common = { path = "../../common/" }
-hex = "0.4.3"
-anyhow = "1.0.98"
+hex = { workspace = true }
+anyhow = { workspace = true }
diff --git a/problems/p6/Cargo.toml b/problems/p6/Cargo.toml
index 1a64dfe..90eeab4 100644
--- a/problems/p6/Cargo.toml
+++ b/problems/p6/Cargo.toml
@@ -4,6 +4,6 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-base64 = "0.22.1"
-anyhow = "1.0.98"
+base64 = { workspace = true }
+anyhow = { workspace = true }
 common = { path = "../../common/" }
diff --git a/problems/p7/Cargo.toml b/problems/p7/Cargo.toml
index 62de4f3..6392ba6 100644
--- a/problems/p7/Cargo.toml
+++ b/problems/p7/Cargo.toml
@@ -4,6 +4,6 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-anyhow = "1.0.98"
-hex = "0.4.3"
-base64 = "0.22.1"
+anyhow = { workspace = true }
+hex = { workspace = true }
+base64 = { workspace = true }
diff --git a/problems/p8/Cargo.toml b/problems/p8/Cargo.toml
index 24397e3..5f82952 100644
--- a/problems/p8/Cargo.toml
+++ b/problems/p8/Cargo.toml
@@ -4,4 +4,4 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-hex = "0.4.3"
+hex = { workspace = true }