Parameter Mismatch Between CryptoContext and Public Key When Using Separate Serialization

Library Questions
,
1

Doubt of @Ankush-anonymous below. Any help is welcome:

I’m encountering an issue when trying to use separate functions (or executables) for key generation and vote encryption. In my workflow, I generate the CryptoContext and key pair (public and secret keys) in one process and serialize them to separate files. Later, in a different process, I deserialize the CryptoContext and the public key from their respective files and try to encrypt a vote. However, I receive an error stating that the public key’s parameters do not match the CryptoContext.

Here’s a brief summary of my approach:

Key Generation Process:

  • I initialize the CryptoContext using BFV scheme parameters (plaintext modulus 65537, multiplicative depth 1).
  • I enable the features PKE, KEYSWITCH, and LEVELEDSHE.
  • I generate the key pair and then serialize the CryptoContext to a file (e.g., cryptocontext.txt) and the public key (and secret key) to separate files in the “elections” directory.

Vote Encryption Process:

  • I deserialize the CryptoContext from cryptocontext.txt and also load the public key from its file.
  • I then attempt to encrypt a one-hot vote vector using the loaded CryptoContext and public key.
  • At this point, I receive an error such as:
ERROR: Public key parameters do not match the context.

I suspect that the error occurs because the public key internally holds a reference (or pointer) to the original CryptoContext. When deserializing the CryptoContext and public key separately, this association is lost or not correctly re-established.

I have seen some recommendations that to avoid such issues, one should either:

Serialize and deserialize the entire key material (the CryptoContext and key pair) as a single unit, or

Explicitly update or re-associate the public key with the loaded CryptoContext after deserialization.

I have not yet found a clear solution on how to do this re-association when using separate files. Has anyone encountered a similar issue? Are there recommended practices or functions (such as a helper method to rebind the public key to the context) in OpenFHE that can help ensure consistency between the CryptoContext and the public key when they are loaded separately?

Any guidance, code examples, or pointers to documentation?

2

Hi @reneroliveira,

Could you provide a minimal working example so we could recreate the issue? Is this in C++ or Python? Generally speaking, there should not be any problem as this is a common way of using OpenFHE. There are many working OpenFHE-based examples with serialization and separated clients and servers, e.g,. GitHub - openfheorg/openfhe-serial-examples: Port of PALISADE-serial-examples : Multi-program PRE and Threshold examples using various simple IPC and GitHub - openfheorg/openfhe-network-examples: OpenFHE Experiments in Encrypted Network Control and Secure Data Distribution with Proxy Re-Encryption