diff --git a/aes/tests/aes_cbc.rs b/aes/tests/aes_cbc.rs
new file mode 100644
index 0000000..0f4c147
--- /dev/null
+++ b/aes/tests/aes_cbc.rs
@@ -0,0 +1,115 @@
+//! NIST SP 800-38A AES-128-CBC test vectors.
+
+use aes::{AesCbc, Iv};
+use claims::assert_ok;
+
+// NIST SP 800-38A test vectors for AES-128-CBC
+const NIST_KEY: u128 = 0x2b7e1516_28aed2a6_abf71588_09cf4f3c;
+const NIST_IV: u128 = 0x00010203_04050607_08090a0b_0c0d0e0f;
+
+// Test vector blocks (plaintext -> ciphertext)
+const NIST_BLOCKS: [(u128, u128); 4] = [
+    (
+        0x6bc1bee2_2e409f96_e93d7e11_7393172a,
+        0x7649abac_8119b246_cee98e9b_12e9197d,
+    ),
+    (
+        0xae2d8a57_1e03ac9c_9eb76fac_45af8e51,
+        0x5086cb9b_507219ee_95db113a_917678b2,
+    ),
+    (
+        0x30c81c46_a35ce411_e5fbc119_1a0a52ef,
+        0x73bed6b8_e3c1743b_7116e69e_22229516,
+    ),
+    (
+        0xf69f2445_df4f9b17_ad2b417b_e66c3710,
+        0x3ff1caa1_681fac09_120eca30_7586e1a1,
+    ),
+];
+
+#[test]
+fn nist_single_block_encrypt() {
+    let cipher = AesCbc::new(NIST_KEY, Iv::new(NIST_IV));
+    let plaintext = NIST_BLOCKS[0].0.to_be_bytes();
+    let expected = NIST_BLOCKS[0].1.to_be_bytes();
+
+    let ciphertext = assert_ok!(cipher.encrypt(&plaintext));
+
+    // Result includes PKCS#7 padding (16 bytes padding for aligned input)
+    assert_eq!(ciphertext.len(), 32);
+    assert_eq!(&ciphertext[..16], &expected);
+}
+
+#[test]
+fn nist_single_block_decrypt() {
+    let cipher = AesCbc::new(NIST_KEY, Iv::new(NIST_IV));
+    let plaintext = NIST_BLOCKS[0].0.to_be_bytes();
+
+    // First encrypt to get valid padded ciphertext
+    let ciphertext = assert_ok!(cipher.encrypt(&plaintext));
+    let decrypted = assert_ok!(cipher.decrypt(&ciphertext));
+
+    assert_eq!(decrypted, plaintext);
+}
+
+#[test]
+fn nist_multi_block_encrypt() {
+    let cipher = AesCbc::new(NIST_KEY, Iv::new(NIST_IV));
+
+    // Concatenate all 4 plaintext blocks (64 bytes)
+    let mut plaintext = Vec::with_capacity(64);
+    for (pt, _) in &NIST_BLOCKS {
+        plaintext.extend_from_slice(&pt.to_be_bytes());
+    }
+
+    // Concatenate expected ciphertext blocks
+    let mut expected = Vec::with_capacity(64);
+    for (_, ct) in &NIST_BLOCKS {
+        expected.extend_from_slice(&ct.to_be_bytes());
+    }
+
+    let ciphertext = assert_ok!(cipher.encrypt(&plaintext));
+
+    // Result includes padding (64 + 16 = 80 bytes)
+    assert_eq!(ciphertext.len(), 80);
+    // First 3 blocks should match NIST vectors exactly
+    assert_eq!(&ciphertext[..48], &expected[..48]);
+}
+
+#[test]
+fn nist_multi_block_roundtrip() {
+    let cipher = AesCbc::new(NIST_KEY, Iv::new(NIST_IV));
+
+    let mut plaintext = Vec::with_capacity(64);
+    for (pt, _) in &NIST_BLOCKS {
+        plaintext.extend_from_slice(&pt.to_be_bytes());
+    }
+
+    let ciphertext = assert_ok!(cipher.encrypt(&plaintext));
+    let decrypted = assert_ok!(cipher.decrypt(&ciphertext));
+
+    assert_eq!(decrypted, plaintext);
+}
+
+#[test]
+fn empty_plaintext() {
+    let cipher = AesCbc::new(NIST_KEY, Iv::new(NIST_IV));
+
+    let ciphertext = assert_ok!(cipher.encrypt(&[]));
+    // Empty input gets full block of padding
+    assert_eq!(ciphertext.len(), 16);
+
+    let decrypted = assert_ok!(cipher.decrypt(&ciphertext));
+    assert!(decrypted.is_empty());
+}
+
+#[test]
+fn arbitrary_length_plaintext() {
+    let cipher = AesCbc::new(NIST_KEY, Iv::new(NIST_IV));
+
+    let plaintext = b"This is a test message with arbitrary length!";
+    let ciphertext = assert_ok!(cipher.encrypt(plaintext));
+    let decrypted = assert_ok!(cipher.decrypt(&ciphertext));
+
+    assert_eq!(decrypted, plaintext);
+}
diff --git a/cipher-factory/src/context.rs b/cipher-factory/src/context.rs
index b71ebb4..e44bdc5 100644
--- a/cipher-factory/src/context.rs
+++ b/cipher-factory/src/context.rs
@@ -55,9 +55,10 @@ impl CipherContext {
     }
 
     fn process_cbc(&self) -> CipherResult<String> {
-        let iv = self.iv.as_ref().ok_or_else(|| {
-            CipherError::InvalidPadding("CBC mode requires an IV".into())
-        })?;
+        let iv = self
+            .iv
+            .as_ref()
+            .ok_or_else(|| CipherError::InvalidPadding("CBC mode requires an IV".into()))?;
 
         let cipher = self.algorithm.new_cbc_cipher(&self.key, iv)?;