diff --git a/Cargo.toml b/Cargo.toml
index 9c3c86a..9234cdc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,6 +11,7 @@ des = { path = "des" }
 rand = "0.9"
 rstest = "0.26"
 thiserror = "2"
+zeroize = { version = "1.8", features = ["derive"] }
 
 [workspace.lints.clippy]
 pedantic = "warn"
diff --git a/cipher-core/src/traits.rs b/cipher-core/src/traits.rs
index 0f91a5d..6def9c3 100644
--- a/cipher-core/src/traits.rs
+++ b/cipher-core/src/traits.rs
@@ -28,7 +28,7 @@ pub trait BlockLike: Sized + Copy + Clone {
 /// Minimal trait describing a fixed-size key-like value.
 ///
 /// Concrete key types (e.g. `Secret<const N: usize>`) should implement this.
-pub trait KeyLike: Sized + Copy + Clone {
+pub trait KeyLike: Sized {
     /// Size of the key in bytes.
     const SIZE: usize;
 
diff --git a/des/Cargo.toml b/des/Cargo.toml
index c9cd878..ac6ab25 100644
--- a/des/Cargo.toml
+++ b/des/Cargo.toml
@@ -5,6 +5,8 @@ authors = ["Kristofers Solo <dev@kristofers.xyz>"]
 edition = "2024"
 
 [dependencies]
+cipher-core.workspace = true
+zeroize.workspace = true
 
 [dev-dependencies]
 claims.workspace = true
diff --git a/des/src/constants.rs b/des/src/constants.rs
new file mode 100644
index 0000000..add1c88
--- /dev/null
+++ b/des/src/constants.rs
@@ -0,0 +1,86 @@
+// DES Constants (from FIPS 46-3 spec)
+/// Initial Permutation (IP) table.
+pub const IP: [u8; 64] = [
+    58, 50, 42, 34, 26, 18, 10, 2, 60, 52, 44, 36, 28, 20, 12, 4, 62, 54, 46, 38, 30, 22, 14, 6,
+    64, 56, 48, 40, 32, 24, 16, 8, 57, 49, 41, 33, 25, 17, 9, 1, 59, 51, 43, 35, 27, 19, 11, 3, 61,
+    53, 45, 37, 29, 21, 13, 5, 63, 55, 47, 39, 31, 23, 15, 7,
+];
+
+/// Inverse Initial Permutation (FP) table.
+pub const FP: [u8; 64] = [
+    40, 8, 48, 16, 56, 24, 64, 32, 39, 7, 47, 15, 55, 23, 63, 31, 38, 6, 46, 14, 54, 22, 62, 30,
+    37, 5, 45, 13, 53, 21, 61, 29, 36, 4, 44, 12, 52, 20, 60, 28, 35, 3, 43, 11, 51, 19, 59, 27,
+    34, 2, 42, 10, 50, 18, 58, 26, 33, 1, 41, 9, 49, 17, 57, 25,
+];
+
+/// Expansion permutation (32 to 48 bits).
+pub const E_BOX: [u8; 48] = [
+    32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17, 16, 17, 18,
+    19, 20, 21, 20, 21, 22, 23, 24, 25, 24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1,
+];
+
+/// P-box permutation (32 bits).
+pub const P_BOX: [u8; 32] = [
+    16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10, 2, 8, 24, 14, 32, 27, 3, 9, 19,
+    13, 30, 6, 22, 11, 4, 25,
+];
+
+/// S-boxes: 8 boxes, each 4x16 (row x col) -> 0-15.
+pub const S_BOXES: [[[u8; 16]; 4]; 8] = [
+    // S1
+    [
+        [14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7],
+        [0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8],
+        [4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0],
+        [15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13],
+    ],
+    // S2
+    [
+        [15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10],
+        [3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5],
+        [0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15],
+        [13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9],
+    ],
+    // S3
+    [
+        [10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8],
+        [13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1],
+        [13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7],
+        [1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12],
+    ],
+    // S4
+    [
+        [7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15],
+        [13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9],
+        [10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4],
+        [3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14],
+    ],
+    // S5
+    [
+        [2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9],
+        [14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6],
+        [4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14],
+        [11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3],
+    ],
+    // S6
+    [
+        [12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11],
+        [10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8],
+        [9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6],
+        [4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13],
+    ],
+    // S7
+    [
+        [4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1],
+        [13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6],
+        [1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2],
+        [6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12],
+    ],
+    // S8
+    [
+        [13, 2, 8, 4, 6, 15, 11, 1, 19, 9, 3, 14, 5, 0, 12, 7],
+        [1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2],
+        [7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8],
+        [2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11],
+    ],
+];
diff --git a/des/src/des.rs b/des/src/des.rs
new file mode 100644
index 0000000..c74f61e
--- /dev/null
+++ b/des/src/des.rs
@@ -0,0 +1,14 @@
+use crate::key::subkeys::Subkeys;
+use cipher_core::KeyLike;
+
+#[derive(Debug)]
+pub struct Des {
+    subkeys: Subkeys,
+}
+
+impl Des {
+    #[must_use]
+    pub fn new(_key: impl KeyLike) -> Self {
+        todo!()
+    }
+}
diff --git a/des/src/key/mod.rs b/des/src/key/mod.rs
new file mode 100644
index 0000000..951536e
--- /dev/null
+++ b/des/src/key/mod.rs
@@ -0,0 +1,19 @@
+mod secret_int;
+pub mod subkeys;
+
+use crate::secret_int;
+
+secret_int! {
+    /// A single DES round subkey (48 bits stored in lower bits of u64).
+    pub struct Subkey(u64, 48, 0x0000_FFFF_FFFF_FFFF);
+}
+
+secret_int! {
+    /// 56-bit key after PC-1 (lower 56 bits used).
+    pub struct Key56(u64, 56, 0x00FF_FFFF_FFFF_FFFF);
+}
+
+secret_int! {
+    /// 28-bit half (C or D), stored in lower 28 bits of u32.
+    pub struct Half28(u32, 28, 0x0FFF_FFFF);
+}
diff --git a/des/src/key/secret_int.rs b/des/src/key/secret_int.rs
new file mode 100644
index 0000000..b358ae6
--- /dev/null
+++ b/des/src/key/secret_int.rs
@@ -0,0 +1,84 @@
+/// Macro to generate a masked, zeroizable integer wrapper type.
+///
+/// Usage:
+/// ```
+/// secret_int! {
+///     /// docs...
+///     pub struct Subkey(u64, 48, 0x0000_FFFF_FFFF_FFFFu64);
+/// }
+/// ```
+///
+/// Optional `clone` token enables an explicit Clone impl:
+/// ```
+/// secret_int! { pub struct Foo(u32, 28, 0x0FFF_FFFFu32, clone); }
+/// ```
+#[macro_export]
+macro_rules! secret_int {
+    (
+    $(#[$meta:meta])*
+    $vis:vis struct $name:ident ( $int:ty, $bits:expr, $mask:expr $(, $opt:ident )? );
+) => {
+        $(#[$meta])*
+        #[derive(::zeroize::ZeroizeOnDrop, Default, Eq)]
+        #[zeroize(drop)]
+        $vis struct $name($int);
+
+        impl $name {
+            /// Number of meaningful bits.
+            pub const BITS: usize = $bits;
+            /// Mask to restrict the underlying integer to valid bits.
+            pub const MASK: $int = $mask;
+
+            /// Create from the given integer.
+            #[inline]
+            #[must_use]
+            pub const fn from_int(key: $int) -> Self {
+                Self(key & Self::MASK)
+            }
+
+            /// Return as masked integer value;
+            #[inline]
+            #[must_use]
+            pub const fn as_int(&self) -> $int {
+                self.0 & Self::MASK
+            }
+
+            /// Zero value.
+            pub const fn zero() -> Self {
+                Self(0)
+            }
+        }
+
+        // Optionally add Clone if requested explicitly (discouraged for secrets)
+        secret_int!(@maybe_add_clone $( $opt )? ; $name, $int);
+
+        impl ::std::fmt::Debug for $name {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
+                f.write_str(concat!(stringify!($name), "[REDACTED]"))
+            }
+        }
+
+        impl From<$int> for $name {
+            fn from(v: $int) -> Self {
+                Self::from_int(v)
+            }
+        }
+
+        impl PartialEq for $name {
+            fn eq(&self, other: &Self) -> bool {
+                self.as_int() == other.as_int()
+            }
+        }
+    };
+
+    // helper arm: create Clone impl only when "clone" token present
+    (@maybe_add_clone clone ; $name:ident, $int:ty) => {
+        impl Clone for $name {
+            fn clone(&self) -> Self {
+                // explicit clone - intentionally duplicating secret
+                Self::from_int(self.as_int())
+            }
+        }
+    };
+    (@maybe_add_clone ; $name:ident, $int:ty) => {};
+}
diff --git a/des/src/key/subkeys.rs b/des/src/key/subkeys.rs
new file mode 100644
index 0000000..d3bcc70
--- /dev/null
+++ b/des/src/key/subkeys.rs
@@ -0,0 +1,154 @@
+use crate::key::Subkey;
+use cipher_core::{CryptoError, CryptoResult, KeyLike};
+use std::fmt::Debug;
+
+/// Key Permutation table (64 to 56 bits).
+const PC1: [u8; 56] = [
+    57, 49, 41, 33, 25, 17, 9, 1, 58, 50, 42, 34, 26, 18, 10, 2, 59, 51, 43, 35, 27, 19, 11, 3, 60,
+    52, 44, 36, 63, 55, 47, 39, 31, 23, 15, 7, 62, 54, 46, 38, 30, 22, 14, 6, 61, 53, 45, 37, 29,
+    21, 13, 5, 28, 20, 12, 4,
+];
+
+/// Compression Permutation table (56 to 48 bits).
+const PC2: [u8; 48] = [
+    14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10, 23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2, 41, 52,
+    31, 37, 47, 55, 30, 40, 51, 45, 33, 48, 44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32,
+];
+
+/// Number of Key Bits Shifted per Round
+const ROUND_ROTATIONS: [u8; 16] = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1];
+
+/// Container for all 16 round subkeys; zeroized on drop.
+pub struct Subkeys([Subkey; 16]);
+
+impl Subkeys {
+    #[inline]
+    #[must_use]
+    pub const fn new_empty() -> Self {
+        Self([const { Subkey::zero() }; 16])
+    }
+
+    #[inline]
+    #[must_use]
+    pub const fn as_array(&self) -> &[Subkey; 16] {
+        &self.0
+    }
+
+    #[inline]
+    pub fn set(&mut self, idx: usize, sk: Subkey) {
+        self.0[idx] = sk;
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn get(&self, idx: usize) -> Option<&Subkey> {
+        self.0.get(idx)
+    }
+
+    pub fn from_key(key: &impl KeyLike) -> CryptoResult<Self> {
+        let key_bytes = key.as_bytes();
+        let key_len = key_bytes.len();
+
+        if key_len != 8 {
+            return Err(CryptoError::invalid_key_size(8, key_len));
+        }
+
+        // Produce 56 bits after PC-1 as two 28-bit halves C0 and D0 (MSB-first bit order)
+        let (c_bits, d_bits) = PC1.iter().enumerate().fold(
+            ([0; 28], [0; 28]),
+            |(mut c_bits, mut d_bits), (idx, &pos)| {
+                let bit = get_bit_be(key_bytes, pos);
+                if idx < 28 {
+                    c_bits[idx] = bit;
+                } else {
+                    d_bits[idx - 28] = bit;
+                }
+                (c_bits, d_bits)
+            },
+        );
+
+        let mut c = bits_to_u28(&c_bits);
+        let mut d = bits_to_u28(&d_bits);
+
+        let out = ROUND_ROTATIONS.iter().enumerate().fold(
+            [const { Subkey::zero() }; 16],
+            |mut acc, (round, &shifts)| {
+                c = rotate_left_28(c, shifts.into());
+                d = rotate_left_28(d, shifts.into());
+                let sub48 = pc2_from_cd(c, d);
+                acc[round] = Subkey::from(sub48);
+                acc
+            },
+        );
+
+        Ok(Self(out))
+    }
+
+    pub(crate) fn as_u64_array(&self) -> [u64; 16] {
+        self.0
+            .iter()
+            .enumerate()
+            .fold([0; 16], |mut out, (idx, sk)| {
+                out[idx] = sk.as_int();
+                out
+            })
+    }
+}
+
+fn pc2_from_cd(c: u32, d: u32) -> u64 {
+    let combined: [u8; 56] = (0..28)
+        .flat_map(|idx| {
+            let bit_idx = 27 - idx;
+            [((c >> bit_idx) & 1) as u8, ((d >> bit_idx) & 1) as u8]
+        })
+        .collect::<Vec<_>>()
+        .try_into()
+        .expect("");
+
+    let out = PC2.iter().fold(0, |acc, &pos| {
+        let bit = u64::from(combined[(pos as usize).saturating_sub(1)]);
+        (acc << 1) | bit
+    });
+
+    out & 0xFFFF_FFFF_FFFF
+}
+
+const U28_MASK: u32 = 0x0FFF_FFFF;
+
+#[inline]
+#[must_use]
+const fn get_bit_be(bytes: &[u8], pos: u8) -> u8 {
+    let p = (pos as usize).saturating_sub(1);
+    let byte_idx = p / 8;
+    let bit_idx = 7 - (p % 8);
+    (bytes[byte_idx] >> bit_idx) & 1
+}
+
+#[inline]
+#[must_use]
+fn bits_to_u28(bits: &[u8; 28]) -> u32 {
+    let mut v = 0;
+    for &b in bits {
+        v = (v << 1) | (u32::from(b));
+    }
+    v & U28_MASK
+}
+
+#[inline]
+#[must_use]
+const fn rotate_left_28(v: u32, n: u32) -> u32 {
+    let v = v & U28_MASK;
+    ((v << n) | (v >> (28 - n))) & U28_MASK
+}
+
+impl Debug for Subkeys {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("Subkeys[REDACTED]")
+    }
+}
+
+impl Default for Subkeys {
+    fn default() -> Self {
+        Self::new_empty()
+    }
+}
diff --git a/des/src/lib.rs b/des/src/lib.rs
index e69de29..f2d37c8 100644
--- a/des/src/lib.rs
+++ b/des/src/lib.rs
@@ -0,0 +1,5 @@
+pub(crate) mod constants;
+mod des;
+mod key;
+
+pub use des::Des;