diff --git a/cryptography_s_des_exploring/sdes/decrypt.py b/cryptography_s_des_exploring/sdes/decrypt.py
new file mode 100644
index 0000000..3dbed72
--- /dev/null
+++ b/cryptography_s_des_exploring/sdes/decrypt.py
@@ -0,0 +1,38 @@
+from cryptography_s_des_exploring.sdes.keys import generate_subkeys
+from cryptography_s_des_exploring.sdes.sdes import apply_table, function, IP, s0, expansion, s1, IP_inv
+from cryptography_s_des_exploring.sdes.blocks import decode, decode_bytes
+
+
+def decrypt_block(key: str, block: str):
+    """
+    Encrypt the 8-bit block with 10-bit key.
+
+    key is a binary which represented with a 10 character string.
+    block is a binary which represented with 8 character string.
+    """
+
+    key1, key2 = generate_subkeys(key)
+
+    temp = apply_table(block, IP)
+    temp = function(expansion, s0, s1, key2, temp)
+    temp = temp[4:] + temp[:4]
+    temp = function(expansion, s0, s1, key1, temp)
+    plaintext = apply_table(temp, IP_inv)
+
+    return plaintext
+
+
+def decrypt(key: str, message: str):
+    """
+    Encrypt the message with the 10-bit key.
+    The message is split into 8-bit blocks.
+
+    key is a binary which represented with a 10 character string.
+    """
+
+    decoded = decode_bytes(message)
+
+    decrypted = list(map(lambda b: decrypt_block(key, b), decoded))
+
+    return decode(decrypted)
+
diff --git a/cryptography_s_des_exploring/sdes/encrypt.py b/cryptography_s_des_exploring/sdes/encrypt.py
new file mode 100644
index 0000000..73368fe
--- /dev/null
+++ b/cryptography_s_des_exploring/sdes/encrypt.py
@@ -0,0 +1,38 @@
+from cryptography_s_des_exploring.sdes.keys import generate_subkeys
+from cryptography_s_des_exploring.sdes.sdes import apply_table, function, IP, s0, expansion, s1, IP_inv
+from cryptography_s_des_exploring.sdes.blocks import encode, encode_bytes
+
+
+def encrypt_block(key: str, block: str):
+    """
+    Encrypt the 8-bit block with 10-bit key.
+
+    key is a binary which represented with a 10 character string.
+    block is a binary which represented with 8 character string.
+    """
+
+    key1, key2 = generate_subkeys(key)
+
+    temp = apply_table(block, IP)
+    temp = function(expansion, s0, s1, key1, temp)
+    temp = temp[4:] + temp[:4]
+    temp = function(expansion, s0, s1, key2, temp)
+    ciphertext = apply_table(temp, IP_inv)
+
+    return ciphertext
+
+
+def encrypt(key: str, message: str):
+    """
+    Encrypt the message with the 10-bit key.
+    The message is split into 8-bit blocks.
+
+    key is a binary which represented with a 10 character string.
+    """
+
+    encoded = encode(message)
+
+    encrypted = list(map(lambda b: encrypt_block(key, b), encoded))
+
+    return encode_bytes(encrypted)
+
diff --git a/tests/sdes/test_decrypt.py b/tests/sdes/test_decrypt.py
new file mode 100644
index 0000000..3a94ce0
--- /dev/null
+++ b/tests/sdes/test_decrypt.py
@@ -0,0 +1,29 @@
+import pytest
+from cryptography_s_des_exploring.sdes.decrypt import decrypt, decrypt_block
+
+
+@pytest.mark.parametrize("key, message, expected_ciphertext", [
+    ('1111001110', '00100001', '11110011'),
+    ('1111001111', '11110111', '00010011'),
+    # 0b1101000 = 104 ('h')
+    ('1111001110', '10100011', '01101000'),
+    # 0b1100101 = 101 ('e')
+    ('1111001110', '10000111', '01100101'),
+    # 0b1101100 = 108 ('l')
+    ('1111001110', '11100110', '01101100'),
+    # 0b1101111 = 111 ('o')
+    ('1111001110', '11001110', '01101111'),
+])
+def test_encrypt_block(key, message, expected_ciphertext):
+    result = decrypt_block(key, message)
+    assert expected_ciphertext == result
+
+
+@pytest.mark.parametrize("key, message, expected_ciphertext", [
+    ('1111001110', 'wkwaR1xMpoE=', 'hello'),
+    ('1111001110', 'nEp+f+C3CRmcSkp/5s1MCQ==', 'привіт'),
+])
+def test_encrypt(key, message, expected_ciphertext):
+    result = decrypt(key, message)
+    assert expected_ciphertext == result
+
diff --git a/tests/sdes/test_encrypt.py b/tests/sdes/test_encrypt.py
new file mode 100644
index 0000000..35ab37e
--- /dev/null
+++ b/tests/sdes/test_encrypt.py
@@ -0,0 +1,29 @@
+import pytest
+from cryptography_s_des_exploring.sdes.encrypt import encrypt, encrypt_block
+
+
+@pytest.mark.parametrize("key, message, expected_ciphertext", [
+    ('1111001110', '11110011', '00100001'),
+    ('1111001111', '00010011', '11110111'),
+    # 0b1101000 = 104 ('h')
+    ('1111001110', '01101000', '10100011'),
+    # 0b1100101 = 101 ('e')
+    ('1111001110', '01100101', '10000111'),
+    # 0b1101100 = 108 ('l')
+    ('1111001110', '01101100', '11100110'),
+    # 0b1101111 = 111 ('o')
+    ('1111001110', '01101111', '11001110'),
+])
+def test_encrypt_block(key, message, expected_ciphertext):
+    result = encrypt_block(key, message)
+    assert expected_ciphertext == result
+
+
+@pytest.mark.parametrize("key, message, expected_ciphertext", [
+    ('1111001110', 'hello', b'wkwaR1xMpoE='),
+    ('1111001110', 'привіт', b'nEp+f+C3CRmcSkp/5s1MCQ=='),
+])
+def test_encrypt(key, message, expected_ciphertext):
+    result = encrypt(key, message)
+    assert expected_ciphertext == result
+