Virtual Circuits

During development, speed of homomorphic execution is a big blocker for fast prototyping. Furthermore, it might be desirable to experiment with more bit-widths, even though they are not supported yet, to get insights about the requirements of your system (e.g., we would have an XYZ model with 95% accuracy if we have 25-bits).

To simplify this process, we've introduces virtual circuits:

import concrete.numpy as cnp
import numpy as np

@cnp.compiler({"x": "encrypted"})
def f(x):
    return np.sqrt(x * 100_000).round().astype(np.int64)

inputset = range(100_000, 101_000)
circuit = f.compile(inputset, enable_unsafe_features=True, virtual=True)

print(circuit)
print(circuit.encrypt_run_decrypt(100_500), "~=", np.sqrt(100_500 * 100_000))

prints

%0 = x                       # EncryptedScalar<uint17>        ∈ [100000, 100999]
%1 = 100000                  # ClearScalar<uint17>            ∈ [100000, 100000]
%2 = multiply(%0, %1)        # EncryptedScalar<uint34>        ∈ [10000000000, 10099900000]
%3 = subgraph(%2)            # EncryptedScalar<uint17>        ∈ [100000, 100498]
return %3

Subgraphs:

    %3 = subgraph(%2):

        %0 = input                         # EncryptedScalar<uint1>
        %1 = sqrt(%0)                      # EncryptedScalar<float64>
        %2 = around(%1, decimals=0)        # EncryptedScalar<float64>
        %3 = astype(%2, dtype=int_)        # EncryptedScalar<uint1>
        return %3
        
100250 ~= 100249.6882788171

and it doesn't perform any homomorphic computation. It just simulates execution.

Keyword arguments enable_unsafe_features=True and virtual=True passed to compile are configuration options. virtaul=True enables makes the circuit virtual, and because virtual circuits are highly experimental, unsafe features must be enabled using enable_unsafe_features=True to utilize virtual circuits. See How to Configure to learn more about configuration options.

Virtual circuits still check for operational constraints and type constraints. Which means you cannot have floating points, or unsupported operations. They just ignore bit-width constraints.

Virtual circuits are still experimental, and they don't properly consider error probability for example. That's why you need to enable unsafe features to use them. Use them with care!