Added/Blockchain RSA Algorithm

blockchain/rivest_shamir_adleman.py

@@ -0,0 +1,123 @@
+"""
+RSA Encryption and Decryption using the `cryptography` library.
+
+This script demonstrates RSA encryption and decryption using the
+`cryptography` library. The `cryptography` library is a package
+which provides cryptographic recipes and primitives to Python
+developers. It aims to support all currently supported versions
+of Python.
+
+The RSA algorithm is an asymmetric encryption algorithm, meaning
+that it uses two keys: one public and one private. The public key
+can be shared with everyone, while the private key must be kept
+secret. In RSA, this asymmetry is based on the practical difficulty
+of the factorization of the product of two large prime numbers, the
+"factoring problem". The public key consists of the modulus n and
+the public (or encryption) exponent e. The private key consists of
+the modulus n and the private (or decryption) exponent d, which must
+be kept secret. RSA is often used to encrypt session keys, which are
+symmetric keys used to encrypt data in a symmetric encryption scheme.
+This avoids the need to distribute a symmetric key to each party
+wanting to encrypt data.
+
+References:
+- RSA Algorithm: https://en.wikipedia.org/wiki/RSA_(cryptosystem)
+- cryptography library: https://cryptography.io/
+
+"""
+
+from doctest import testmod
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.asymmetric import padding, rsa
+
+
+def generate_key_pair():
+    """
+    Generate RSA key pair.
+
+    Returns:
+        private_key: Private key for decryption.
+        public_key: Public key for encryption.
+
+    >>> private_key, public_key = generate_key_pair()
+    >>> isinstance(private_key, rsa.RSAPrivateKey)
+    True
+    >>> isinstance(public_key, rsa.RSAPublicKey)
+    True
+    """
+
+    private_key = rsa.generate_private_key(
+        public_exponent=65537, key_size=2048, backend=default_backend()
+    )
+
+    public_key = private_key.public_key()
+
+    return private_key, public_key
+
+
+def encrypt(message, public_key):
+    """
+    Encrypt a message using RSA.
+
+    Args:
+        message (str): Message to be encrypted.
+        public_key: Public key for encryption.
+
+    Returns:
+        bytes: Encrypted ciphertext.
+
+    >>> private_key, public_key = generate_key_pair()
+    >>> message = "Hello, this is a message to be encrypted!"
+    >>> ciphertext = encrypt(message, public_key)
+    >>> decrypted_message = decrypt(ciphertext, private_key)
+    >>> decrypted_message == message
+    True
+    """
+
+    ciphertext = public_key.encrypt(
+        message.encode(),
+        padding.OAEP(
+            mgf=padding.MGF1(algorithm=hashes.SHA256()),
+            algorithm=hashes.SHA256(),
+            label=None,
+        ),
+    )
+    return ciphertext
+
+
+def decrypt(ciphertext, private_key):
+    """
+    Decrypt a ciphertext using RSA.
+
+    Args:
+        ciphertext (bytes): Encrypted ciphertext.
+        private_key: Private key for decryption.
+
+    Returns:
+        str: Decrypted plaintext.
+
+    >>> private_key, public_key = generate_key_pair()
+    >>> message = "Hello, this is a message to be encrypted!"
+    >>> ciphertext = encrypt(message, public_key)
+    >>> decrypted_message = decrypt(ciphertext, private_key)
+    >>> decrypted_message == message
+    True
+    """
+
+    plaintext = private_key.decrypt(
+        ciphertext,
+        padding.OAEP(
+            mgf=padding.MGF1(algorithm=hashes.SHA256()),
+            algorithm=hashes.SHA256(),
+            label=None,
+        ),
+    )
+    return plaintext.decode()
+
+
+if __name__ == "__main__":
+    testmod(name="generate_key_pair", verbose=True)
+    testmod(name="encrypt", verbose=True)
+    testmod(name="decrypt", verbose=True)