diff --git a/src/primitive/blockcipher/aes.zig b/src/primitive/blockcipher/aes.zig
index dd9ab1f..8c69d40 100644
--- a/src/primitive/blockcipher/aes.zig
+++ b/src/primitive/blockcipher/aes.zig
@@ -122,7 +122,8 @@ pub fn aes_decrypt_block(n_rounds: comptime_int, block_in: *const [AES_BLOCK_SIZ
 
 pub fn aes_128_encrypt_block(key: *const [Aes128Parameters.KEY_SIZE]u8, block_in: *const [AES_BLOCK_SIZE]u8, block_out: *[AES_BLOCK_SIZE]u8) void {
     // Prepare the subkeys for AddRoundKey.
-    const expanded_key = aes_128_expand_key(key);
+    var expanded_key = aes_128_expand_key(key);
+    defer @memset(&expanded_key, 0);
 
     // Call the generic encryption procedure.
     aes_encrypt_block(Aes128Parameters.N_ROUNDS, block_in, block_out, &expanded_key);
@@ -130,7 +131,8 @@ pub fn aes_128_encrypt_block(key: *const [Aes128Parameters.KEY_SIZE]u8, block_in
 
 pub fn aes_128_decrypt_block(key: *const [Aes128Parameters.KEY_SIZE]u8, block_in: *const [AES_BLOCK_SIZE]u8, block_out: *[AES_BLOCK_SIZE]u8) void {
     // Prepare the subkeys for AddRoundKey.
-    const expanded_key = aes_128_expand_key(key);
+    var expanded_key = aes_128_expand_key(key);
+    defer @memset(&expanded_key, 0);
 
     // Call the generic decryption procedure.
     aes_decrypt_block(Aes128Parameters.N_ROUNDS, block_in, block_out, &expanded_key);
@@ -138,7 +140,8 @@ pub fn aes_128_decrypt_block(key: *const [Aes128Parameters.KEY_SIZE]u8, block_in
 
 pub fn aes_192_encrypt_block(key: *const [Aes192Parameters.KEY_SIZE]u8, block_in: *const [AES_BLOCK_SIZE]u8, block_out: *[AES_BLOCK_SIZE]u8) void {
     // Prepare the subkeys for AddRoundKey.
-    const expanded_key = aes_192_expand_key(key);
+    var expanded_key = aes_192_expand_key(key);
+    defer @memset(&expanded_key, 0);
 
     // Call the generic encryption procedure.
     aes_encrypt_block(Aes192Parameters.N_ROUNDS, block_in, block_out, &expanded_key);
@@ -146,7 +149,8 @@ pub fn aes_192_encrypt_block(key: *const [Aes192Parameters.KEY_SIZE]u8, block_in
 
 pub fn aes_192_decrypt_block(key: *const [Aes192Parameters.KEY_SIZE]u8, block_in: *const [AES_BLOCK_SIZE]u8, block_out: *[AES_BLOCK_SIZE]u8) void {
     // Prepare the subkeys for AddRoundKey.
-    const expanded_key = aes_192_expand_key(key);
+    var expanded_key = aes_192_expand_key(key);
+    defer @memset(&expanded_key, 0);
 
     // Call the generic decryption procedure.
     aes_decrypt_block(Aes192Parameters.N_ROUNDS, block_in, block_out, &expanded_key);
@@ -154,7 +158,8 @@ pub fn aes_192_decrypt_block(key: *const [Aes192Parameters.KEY_SIZE]u8, block_in
 
 pub fn aes_256_encrypt_block(key: *const [Aes256Parameters.KEY_SIZE]u8, block_in: *const [AES_BLOCK_SIZE]u8, block_out: *[AES_BLOCK_SIZE]u8) void {
     // Prepare the subkeys for AddRoundKey.
-    const expanded_key = aes_256_expand_key(key);
+    var expanded_key = aes_256_expand_key(key);
+    defer @memset(&expanded_key, 0);
 
     // Call the generic encryption procedure.
     aes_encrypt_block(Aes256Parameters.N_ROUNDS, block_in, block_out, &expanded_key);
@@ -162,7 +167,8 @@ pub fn aes_256_encrypt_block(key: *const [Aes256Parameters.KEY_SIZE]u8, block_in
 
 pub fn aes_256_decrypt_block(key: *const [Aes256Parameters.KEY_SIZE]u8, block_in: *const [AES_BLOCK_SIZE]u8, block_out: *[AES_BLOCK_SIZE]u8) void {
     // Prepare the subkeys for AddRoundKey.
-    const expanded_key = aes_256_expand_key(key);
+    var expanded_key = aes_256_expand_key(key);
+    defer @memset(&expanded_key, 0);
 
     // Call the generic decryption procedure.
     aes_decrypt_block(Aes256Parameters.N_ROUNDS, block_in, block_out, &expanded_key);
diff --git a/src/primitive/blockcipher/des.zig b/src/primitive/blockcipher/des.zig
new file mode 100644
index 0000000..256b27b
--- /dev/null
+++ b/src/primitive/blockcipher/des.zig
@@ -0,0 +1,180 @@
+const std = @import("std");
+const testing = std.testing;
+
+// ----------------------------------- DES CONSTANTS -----------------------------------  //
+
+pub const DES_BLOCK_SIZE = 64 / 8;
+
+pub const DES_TRUE_KEY_SIZE = 56 / 8;
+pub const DES_ENCODED_KEY_SIZE = 64 / 8;
+
+pub const DES_SUBKEY_SIZE = 48 / 8;
+
+pub const DES_N_ROUNDS = 16;
+
+pub const DES_INITIAL_PERMUTATION = [_]u6{
+    58, 50, 42, 35, 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,
+};
+
+pub const DES_INV_INITIAL_PERMUTATION = [_]u6{
+    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,
+};
+
+pub const DES_BIT_SELECTION_TABLE_E = [_]u5{
+    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,
+};
+
+pub const DES_KS_SHIFT_SCHEDULE = .{ 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };
+
+// ----------------------------------- ENCRYPTION/DECRYPTION -----------------------------------  //
+
+pub fn des_encrypt_block(
+    block_in: *const [DES_BLOCK_SIZE]u8,
+    block_out: *[DES_BLOCK_SIZE]u8,
+    key: *const [DES_ENCODED_KEY_SIZE]u8,
+) void {
+    var state: [DES_BLOCK_SIZE]u8 = undefined;
+    des_initial_permutation(block_in, &state);
+
+    var expanded_key = des_expand_key(key);
+    defer @memset(&expanded_key, 0);
+
+    for (0..DES_N_ROUNDS) |round|
+        des_perform_round(&state, expanded_key[round]);
+
+    des_inv_initial_permutation(&state, block_out);
+}
+
+pub fn des_decrypt_block(
+    block_in: *const [DES_BLOCK_SIZE]u8,
+    block_out: *[DES_BLOCK_SIZE]u8,
+    key: *const [DES_ENCODED_KEY_SIZE]u8,
+) void {
+    var state: [DES_BLOCK_SIZE]u8 = undefined;
+    des_inv_initial_permutation(block_in, &state);
+
+    var expanded_key = des_expand_key(key);
+    defer @memset(&expanded_key, 0);
+
+    for (0..DES_N_ROUNDS) |round|
+        des_perform_round(&state, expanded_key[DES_N_ROUNDS - round - 1]);
+
+    des_initial_permutation(&state, block_out);
+}
+
+pub fn des_expand_key(key: *const [DES_ENCODED_KEY_SIZE]u8) [DES_N_ROUNDS][DES_SUBKEY_SIZE]u8 {
+    var cd = des_permuted_choice_1(key);
+    var subkeys: [DES_N_ROUNDS][DES_SUBKEY_SIZE]u8 = undefined;
+
+    for (0..DES_N_ROUNDS) |i| {
+        rol(cd[0 .. DES_TRUE_KEY_SIZE / 2], DES_KS_SHIFT_SCHEDULE[i]);
+        rol(cd[DES_TRUE_KEY_SIZE / 2 ..], DES_KS_SHIFT_SCHEDULE[i]);
+        des_permuted_choice_2(cd, &subkeys[i]);
+    }
+}
+
+pub fn des_permuted_choice_1(key: *const [DES_ENCODED_KEY_SIZE]u8) [DES_TRUE_KEY_SIZE]u8 {
+    const PC1 = .{
+        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,
+    };
+
+    var result: [DES_TRUE_KEY_SIZE]u8 = undefined;
+    permute_bits(DES_TRUE_KEY_SIZE, key, &result, PC1);
+
+    return result;
+}
+
+pub fn des_permuted_choice_2(cd: *const [DES_TRUE_KEY_SIZE]u8, out: *[DES_SUBKEY_SIZE]u8) void {
+    const PC2 = .{
+        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,
+    };
+
+    permute_bits(DES_SUBKEY_SIZE, cd, out, PC2);
+}
+
+pub fn des_perform_round(state: *[DES_BLOCK_SIZE]u8, subkey: *[DES_SUBKEY_SIZE]u8) void {
+    const f_output = des_cipher_function_f(state[DES_BLOCK_SIZE / 2 ..], subkey);
+    const new_r = xor(DES_BLOCK_SIZE / 2, state[0 .. DES_BLOCK_SIZE / 2], f_output);
+
+    @memcpy(state[0 .. DES_BLOCK_SIZE / 2], state[DES_BLOCK_SIZE / 2 ..]);
+    @memcpy(state[DES_BLOCK_SIZE / 2 ..], new_r[0..]);
+}
+
+pub fn des_cipher_function_f(word: [DES_BLOCK_SIZE / 2]u8, subkey: [DES_SUBKEY_SIZE]u8) [DES_BLOCK_SIZE / 2]u8 {
+    // todo
+    _ = .{ word, subkey };
+}
+
+pub fn des_initial_permutation(in: *const [DES_BLOCK_SIZE]u8, out: *[DES_BLOCK_SIZE]u8) void {
+    permute_bits(DES_BLOCK_SIZE, in, out, DES_INITIAL_PERMUTATION);
+}
+
+pub fn des_inv_initial_permutation(in: *const [DES_BLOCK_SIZE]u8, out: *[DES_BLOCK_SIZE]u8) void {
+    permute_bits(DES_BLOCK_SIZE, in, out, DES_INV_INITIAL_PERMUTATION);
+}
+
+// ----------------------------------- HELPERS -----------------------------------  //
+
+fn permute_bits(L: comptime_int, in: *const [8]u8, out: *[L]u8, key: [8 * L]u6) void {
+    for (0..8 * L) |i| {
+        const pi = key[i];
+        const bit = get_nth_bit(in, pi);
+        set_nth_bit(out, pi, bit);
+    }
+}
+
+fn get_nth_bit(bytes: *const [8]u8, n: u6) u1 {
+    const byte_idx = n / 8;
+    const bit_idx = n % 8;
+
+    return @truncate(bytes[byte_idx] >> (7 - bit_idx));
+}
+
+fn set_nth_bit(bytes: *const [8]u8, n: u6, bit: u1) void {
+    const byte_idx = n / 8;
+    const bit_idx = n % 8;
+
+    if (bit == 1)
+        bytes[byte_idx] |= (1 << (7 - bit_idx))
+    else
+        bytes[byte_idx] &= ~(1 << (7 - bit_idx));
+}
+
+fn xor(L: comptime_int, a: [L]u8, b: [L]u8) [L]u8 {
+    var result: [L]u8 = undefined;
+    for (0..L) |i|
+        result[i] = a[i] ^ b[i];
+    return result;
+}
+
+fn rol(word: *[DES_TRUE_KEY_SIZE / 2]u8, positions: comptime_int) void {
+    // todo
+    _ = .{ word, positions };
+}
+
+// ----------------------------------- TEST VECTORS -----------------------------------  //
+
+//