OpenMined/TenSEAL (Save/Load Key & Encrypted Data @ BFV)

• https://sefiks.com/2023/04/10/a-step-by-step-fully-homomorphic-encryption-example-with-tenseal-in-python/

• OpenMined/TenSEAL#107

!pip install tenseal

Requirement already satisfied: tenseal in /home/hsiangjenli/miniconda3/lib/python3.12/site-packages (0.3.15)

import tenseal as ts
from tenseal.enc_context import Context

context = Context(scheme=ts.SCHEME_TYPE.BFV, poly_modulus_degree=4096, plain_modulus=1032193)

import base64

def save(file_name, data):
    with open(file_name, "wb") as f:
        data = base64.b64encode(data)
        f.write(data)

def load(file_name):
    with open(file_name, "rb") as f:
        data = f.read()
        data = base64.b64decode(data)
        return data

Save Key & Encrypted Data

s_sk = context.serialize(save_secret_key=True)
save("secret.key", s_sk)

context.make_context_public() # Remove secret key from context
s_pk = context.serialize(save_public_key=True)
save("public.key", s_pk)

from tenseal.tensors import BFVVector

vector = [1, 2, 3, 4, 5]

encrypted_vector = BFVVector(context, vector).data
save("encrypted_vector.data", encrypted_vector.serialize())

Load Key & Encrypted Data

load_sk_value = load("secret.key")
load_pk_value = load("public.key")
load_encrypted_vector_value = load("encrypted_vector.data")

# Transform the loaded data back into context and bfvvector
load_sk_context = ts.context_from(load_sk_value)
load_pk_context = ts.context_from(load_pk_value)
load_encrypted_vector_context = ts.BFVVector.load(load_pk_context, load_encrypted_vector_value)

load_sk = load_sk_context.secret_key().data
load_pk = load_pk_context.public_key().data
load_encrypted_vector = load_encrypted_vector_context.data

load_encrypted_vector.decrypt(load_sk)

[1, 2, 3, 4, 5]

(load_encrypted_vector+[1, 1, 1, 1, 1]).decrypt(load_sk)

[2, 3, 4, 5, 6]

load_pk_context.secret_key().data # Public Context should not contain the secret key.

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[10], line 1
----> 1 load_pk_context.secret_key().data # Public Context should not contain the secret key.

File ~/miniconda3/lib/python3.12/site-packages/tenseal/enc_context.py:262, in Context.secret_key(self)
    261 def secret_key(self) -> SecretKey:
--> 262     return SecretKey(self.data.secret_key())

ValueError: the current context is public, it doesn't hold a Secret key