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Key recovery attacks against the CKKS homomorphic approximate encryption scheme

This repository contains experimental program code implementing our key recovery attacks against the CKKS scheme. Current implementations work with libraries HEAAN, PALISADE, SEAL, HElib, RNS-HEAAN, and Lattigo.

Build instructions (for all libraries except Lattigo)

Makefile expects the HEAAN library to be installed in the current directory. Install HEAAN and create a symbolic link. For example, if HEAAN is cloned from github to /local/HEAAN, then use this path as <path-to-HEAAN>. HEAAN depends on NTL, which is assumed to have been installed in /usr/local

 ln -s <path-to-HEAAN> ./
 make attack

Similarly, to build the attack for RNS-HEAAN, install RNS-HEAAN (FullRNS-HEAAN) and create a symbolic link to the current directory. Makefile expects the library files (.a or .so) are under ./FullRNS-HEAAN/lib

 ln -s <path-to-FullRNS-HEAAN> ./
 make rns_attack

For PALISADE, SEAL, and HElib, the Makefile expects their typical installations into /usr/local. Otherwise, you can modify the variable PALISADE, <X>_INCLUDE, and <X>_LIBS (X being SEAL or HELIB), in Makefile to point to the root include directory and library directory. These programs also depend on NTL (installed under /usr/local or /usr). Then build the executables as:

 make palisade_attack seal_attack helib_attack

Whenever possible, optimized build (e.g. -O3) with parallelization enabled is preferred for better running times.

Special note for HElib

The HElib's Ctxt class does not provide a public interface for accessing the component Double-CRT polynomials ("parts" in HElib's terminology). We included a patch (patches/0001-local-debugging-changes.patch) to add an accessor function getPart() to Ctxt and to add a global static variable decrypted_ptxt_ to store the decrypted polynomial (for checking encoding error).

How to run the experiment programs

In general, all programs expect command line arguments to specify the type of homomorphic computation <hc>, the ring dimension <logN>, the initial scaling factor <logp>, the upper bound on the random plaintext numbers <B>, and the maximal polynomial degree to evaluate <deg>. The homomorphic computation argument <hc> can be one of the following:

 noop, variance, sigmoid, exp

The orders of the arguments are slightly different due to the differences in how parameters are set up in these libraries. So here are the details:

For HEAAN, run the attack program as:

 ./attack <iter> <hc> <logp> <B> <deg>
 # logN is hard coded in HEAAN's Params.h
 # <iter> is the number of runs to execute, for example, 1

For PALISADE, run palisade_attack as:

 ./palisade_attack <iter> <hc> <logN> <logp> <B> <deg>

For SEAL, run seal_attack as:

 ./seal_attack <iter> <hc> <logN> <logp> <B> <deg>

For HElib, run helib_attack as:

 ./helib_attack <hc> <logN> <logp> <B> <deg>

For RNS-HEAAN, run rns_attack as:

 ./rns_attack <hc> <logN> <L> <logp> <B> <deg>
 # L is the maximal level of computation, for example, 10

For all programs, the parameter <deg> is ignored when <hc> is noop or variance. These programs will check and print out the encoding error, and also print out if the secret key is successfully recovered at the end of a run. For HEAAN, since power-of-2 modulus is used, with certain probability an inverse may not exist for the a part of a ciphertext, but the encoding error indicates if gaussian elimination can be used when collecting a few more ciphertexts.

How to build and run the attack program with Lattigo

Lattigo is written in the GO programming language, and it uses a different programming environment, so it is a bit different to build and run the attack program than with other libraries. The source code of the Lattigo version of our attack program is placed under src/lattigo, and it is compatible with the Lattigo version v2.0.0. To build and run it, first retrieve the Lattigo source tree from https://github.com/ldsec/lattigo, and check out version v2.0.0:

 git checkout -b v2.0.0

Then modify go.mod under src/lattigo by replacing "/scratch/lattigo" with the path to the lattigo source tree on your computer. Now, we are ready to build the attack program:

 cd src/lattigo
 go build

This should build an executable ckks_attack. To run, simply execute ./ckks_attack.

Lattigo implemented some mitigation strategies in the branch dev_indCPA+_mitigation, which is based on the API in version v2.1.0. A modified attack program compatible with this branch can be found in src/lattigo_new, and it can be built in the similr way. Note that the parameters to encoder.DecodeAndRound should be chosen carefully for the mitigation to work.

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