Merge pull request #16 from serengil/feat-task-1212-homomorphic-suppo…

…rt-for-tensors

Feat task 1212 homomorphic support for tensors

README.md

@@ -28,6 +28,8 @@ Even though fully homomorphic encryption (FHE) has become available in recent ti
 - 📏 Generating smaller ciphertexts
 - 🧠 Well-suited for memory-constrained environments
 - ⚖️ Strikes a favorable balance for practical use cases
+- 🔑 Supporting encryption and decryption of vectors
+- 🗝️ Performing homomorphic addition, homomorphic element-wise multiplication and scalar multiplication on encrypted vectors
 
 # Installation [![PyPI](https://img.shields.io/pypi/v/lightphe.svg)](https://pypi.org/project/lightphe/)
 
@@ -157,24 +159,30 @@ with pytest.raises(ValueError, match="Paillier is not homomorphic with respect t
 
 However, if you tried to multiply ciphertexts with RSA, or xor ciphertexts with Goldwasser-Micali, these will be succeeded because those cryptosystems support those homomorphic operations.
 
-# Encrypt & Decrypt Tensors
+# Working with vectors
 
-You can encrypt the output tensors of machine learning models with LightPHE.
+You can encrypt the output vectors of machine learning models with LightPHE. These encrypted tensors come with homomorphic operation support.
 
 ```python
+# build an additively homomorphic cryptosystem
 cs = LightPHE(algorithm_name="Paillier")
 
-# define plain tensor
-tensor = [1.005, 2.005, 3.005, -4.005, 5.005]
+# define plain tensors
+t1 = [1.005, 2.05, -3.5, 4]
+t2 = [5, 6.2, 7.002, 8.02]
 
-# encrypt tensor
-encrypted_tensors = cs.encrypt(tensor)
+# encrypt tensors
+c1 = cs.encrypt(t1)
+c2 = cs.encrypt(t2)
 
-# decrypt tensor
-decrypted_tensors = cs.decrypt(encrypted_tensors)
+# perform homomorphic addition
+c3 = c1 + c2
+
+# decrypt the addition tensor
+t3 = cs.decrypt(c3)
 
-for i, decrypted_tensor in enumerate(decrypted_tensors):
-    assert tensor[i] == decrypted_tensor
+for i, tensor in enumerate(t3):
+   assert abs((t1[i] + t2[i]) - restored_tensor) < 0.5
 ```
 
 # Contributing

lightphe/__init__.py

@@ -4,7 +4,7 @@
 from lightphe.models.Homomorphic import Homomorphic
 from lightphe.models.Ciphertext import Ciphertext
 from lightphe.models.Algorithm import Algorithm
-from lightphe.models.Tensor import EncryptedTensor, EncryptedTensors
+from lightphe.models.Tensor import Fraction, EncryptedTensor
 from lightphe.cryptosystems.RSA import RSA
 from lightphe.cryptosystems.ElGamal import ElGamal
 from lightphe.cryptosystems.Paillier import Paillier
@@ -29,6 +29,7 @@ def __init__(
         keys: Optional[dict] = None,
         key_file: Optional[str] = None,
         key_size: Optional[int] = None,
+        precision: int = 5,
     ):
         """
         Build LightPHE class
@@ -39,8 +40,10 @@ def __init__(
             keys (dict): optional private-public key pair
             key_file (str): if keys are exported, you can load them into cryptosystem
             key_size (int): key size in bits
+            precision (int): precision for homomorphic operations on tensors
         """
         self.algorithm_name = algorithm_name
+        self.precision = precision
 
         if key_file is not None:
             keys = self.restore_keys(target_file=key_file)
@@ -105,7 +108,7 @@ def __build_cryptosystem(
             raise ValueError(f"unimplemented algorithm - {algorithm_name}")
         return cs
 
-    def encrypt(self, plaintext: Union[int, float, list]) -> Union[Ciphertext, EncryptedTensors]:
+    def encrypt(self, plaintext: Union[int, float, list]) -> Union[Ciphertext, EncryptedTensor]:
         """
         Encrypt a plaintext with a built cryptosystem
         Args:
@@ -126,7 +129,7 @@ def encrypt(self, plaintext: Union[int, float, list]) -> Union[Ciphertext, Encry
         return Ciphertext(algorithm_name=self.algorithm_name, keys=self.cs.keys, value=ciphertext)
 
     def decrypt(
-        self, ciphertext: Union[Ciphertext, EncryptedTensors]
+        self, ciphertext: Union[Ciphertext, EncryptedTensor]
     ) -> Union[int, List[int], List[float]]:
         """
         Decrypt a ciphertext with a buit cryptosystem
@@ -138,51 +141,62 @@ def decrypt(
         if self.cs.keys.get("private_key") is None:
             raise ValueError("You must have private key to perform decryption")
 
-        if isinstance(ciphertext, EncryptedTensors):
+        if isinstance(ciphertext, EncryptedTensor):
             # then this is encrypted tensor
             return self.__decrypt_tensors(encrypted_tensor=ciphertext)
 
         return self.cs.decrypt(ciphertext=ciphertext.value)
 
-    def __encrypt_tensors(self, tensor: list) -> EncryptedTensors:
+    def __encrypt_tensors(self, tensor: list) -> EncryptedTensor:
         """
         Encrypt a given tensor
         Args:
             tensor (list of int or float)
         Returns
             encrypted tensor (list of encrypted tensor object)
         """
-        encrypted_tensor: List[EncryptedTensor] = []
+        encrypted_tensor: List[Fraction] = []
         for m in tensor:
-            sign = 1 if m >= 0 else -1
-            # get rid of sign anyway
-            m = m * sign
-            sign_encrypted = self.cs.encrypt(plaintext=sign)
             if isinstance(m, int):
-                dividend_encrypted = self.cs.encrypt(plaintext=m)
-                divisor_encrypted = self.cs.encrypt(plaintext=1)
-                c = EncryptedTensor(
+                dividend_encrypted = self.cs.encrypt(
+                    plaintext=(m % self.cs.plaintext_modulo) * pow(10, self.precision)
+                )
+                abs_dividend_encrypted = self.cs.encrypt(
+                    plaintext=(abs(m) % self.cs.plaintext_modulo) * pow(10, self.precision)
+                )
+                divisor_encrypted = self.cs.encrypt(plaintext=pow(10, self.precision))
+                c = Fraction(
                     dividend=dividend_encrypted,
                     divisor=divisor_encrypted,
-                    sign=sign_encrypted,
+                    abs_dividend=abs_dividend_encrypted,
+                    sign=1 if m >= 0 else -1,
                 )
             elif isinstance(m, float):
-                dividend, divisor = phe_utils.fractionize(value=m, modulo=self.cs.plaintext_modulo)
+                dividend, divisor = phe_utils.fractionize(
+                    value=(m % self.cs.plaintext_modulo),
+                    modulo=self.cs.plaintext_modulo,
+                    precision=self.precision,
+                )
+                abs_dividend, _ = phe_utils.fractionize(
+                    value=(abs(m) % self.cs.plaintext_modulo),
+                    modulo=self.cs.plaintext_modulo,
+                    precision=self.precision,
+                )
                 dividend_encrypted = self.cs.encrypt(plaintext=dividend)
+                abs_dividend_encrypted = self.cs.encrypt(plaintext=abs_dividend)
                 divisor_encrypted = self.cs.encrypt(plaintext=divisor)
-                c = EncryptedTensor(
+                c = Fraction(
                     dividend=dividend_encrypted,
                     divisor=divisor_encrypted,
-                    sign=sign_encrypted,
+                    abs_dividend=abs_dividend_encrypted,
+                    sign=1 if m >= 0 else -1,
                 )
             else:
                 raise ValueError(f"unimplemented type - {type(m)}")
             encrypted_tensor.append(c)
-        return EncryptedTensors(encrypted_tensor=encrypted_tensor)
+        return EncryptedTensor(fractions=encrypted_tensor, cs=self.cs)
 
-    def __decrypt_tensors(
-        self, encrypted_tensor: EncryptedTensors
-    ) -> Union[List[int], List[float]]:
+    def __decrypt_tensors(self, encrypted_tensor: EncryptedTensor) -> Union[List[int], List[float]]:
         """
         Decrypt a given encrypted tensor
         Args:
@@ -191,26 +205,15 @@ def __decrypt_tensors(
             List of plain tensors
         """
         plain_tensor = []
-        for c in encrypted_tensor.encrypted_tensor:
-            if isinstance(c, EncryptedTensor) is False:
-                raise ValueError("Ciphertext items must be EncryptedTensor")
-
-            encrypted_dividend = c.dividend
-            encrypted_divisor = c.divisor
-            encrypted_sign = c.sign
-
-            dividend = self.cs.decrypt(ciphertext=encrypted_dividend)
-            divisor = self.cs.decrypt(ciphertext=encrypted_divisor)
-            sign = self.cs.decrypt(ciphertext=encrypted_sign)
-
-            if sign == self.cs.plaintext_modulo - 1:
-                sign = -1
-            elif sign == 1:
-                sign = 1
-            else:
-                raise ValueError("this cannot be true!")
-
-            m = sign * (dividend / divisor)
+        for c in encrypted_tensor.fractions:
+            if isinstance(c, Fraction) is False:
+                raise ValueError("Ciphertext items must be type of Fraction")
+
+            sign = c.sign
+            abs_dividend = self.cs.decrypt(ciphertext=c.abs_dividend)
+            # dividend = self.cs.decrypt(ciphertext=c.dividend)
+            divisor = self.cs.decrypt(ciphertext=c.divisor)
+            m = sign * abs_dividend / divisor
 
             plain_tensor.append(m)
         return plain_tensor

lightphe/commons/phe_utils.py

@@ -1,9 +1,10 @@
-from typing import Union, Tuple
+from typing import Union, Tuple, Optional
+from decimal import Decimal, getcontext
 from lightphe.commons.logger import Logger
 
 logger = Logger(module="lightphe/commons/phe_utils.py")
 
-# pylint: disable=no-else-return
+# pylint: disable=no-else-return, no-else-break
 
 
 def parse_int(value: Union[int, float], modulo: int) -> int:
@@ -22,10 +23,32 @@ def parse_int(value: Union[int, float], modulo: int) -> int:
     return result
 
 
-def fractionize(value: float, modulo: int) -> Tuple[int, int]:
-    decimal_places = len(str(value).split(".")[1])
-    scaling_factor = 10**decimal_places
-    integer_value = int(value * scaling_factor) % modulo
+def fractionize(value: float, modulo: int, precision: Optional[int] = None) -> Tuple[int, int]:
+    getcontext().prec = 50
+
+    if precision is None:
+        decimal_places = len(str(value).split(".")[1])
+        scaling_factor = 10**decimal_places
+    else:
+        scaling_factor = 10**precision
+
+    while True:
+        integer_value = int(Decimal(value) * Decimal(scaling_factor)) % modulo
+
+        if precision is None:
+            break
+
+        if scaling_factor > 10**precision:
+            # If scaling factor is too large, discard excess part of integer value
+            integer_value = int(integer_value / (10 ** (scaling_factor - 10**precision)))
+            break
+        elif scaling_factor < 10 ** (precision - 1):
+            # If scaling factor is too small, multiply dividend and divisor 10 times
+            value *= 10
+            scaling_factor *= 10
+        else:
+            break
+
     logger.debug(f"{integer_value}*{scaling_factor}^-1 mod {modulo}")
     return integer_value, scaling_factor
 

lightphe/models/Ciphertext.py

@@ -102,15 +102,7 @@ def __rmul__(self, constant: Union[int, float]) -> "Ciphertext":
         Returns
             scalar multiplication of ciphertext
         """
-        if self.cs.keys.get("public_key") is None:
-            raise ValueError("You must have public key to perform scalar multiplication")
-
-        if isinstance(constant, float):
-            constant = phe_utils.parse_int(value=constant, modulo=self.cs.plaintext_modulo)
-
-        # Handle multiplication with a constant on the right
-        result = self.cs.multiply_by_contant(ciphertext=self.value, constant=constant)
-        return Ciphertext(algorithm_name=self.algorithm_name, keys=self.keys, value=result)
+        return self.__mul__(other=constant)
 
     def __xor__(self, other: "Ciphertext") -> "Ciphertext":
         """