adding secure sign evaluation in examples

examples/secure_sign.py

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+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT license.
+# In this tutorial we compute the secure evaluation of sign function
+# Given the encryption of x, Enc(x) the program computes the encryption of
+# the sign of x, Enc(sgn(x)).
+# Given the fact that we cannot compute directly the homomorphic evaluation of the sign function,
+# we must approximate the sign function by a polynomial and then use
+# the homomorphic properties of CKKS to evaluate that polynomial
+# This is the implementation of the https://arxiv.org/pdf/1810.12380.pdf
+
+from eva import EvaProgram, Input, Output, evaluate
+from eva.ckks import CKKSCompiler
+from eva.seal import generate_keys
+from eva.metric import valuation_mse
+import random
+from matplotlib import pyplot as plt
+import numpy as np
+
+num = 16384
+random.seed(32)
+def generate_data():
+    x = list(np.random.uniform(low=-0.12, high=0.12, size=(num)))
+    one = [1] * num
+    const = [1.9142] * num
+    return {'x': x,'one': one, 'const': const}
+
+#The function approximates the tanh limit
+def aprox_limit(x, r, one, const):
+    for idx in range(r):
+        x = x * (const - (x**2))
+    return (x+one)*0.5
+
+#The function computes the encrypted sign of x
+def compute_sign(x, r, one, const):
+    lim = aprox_limit(x, r, one, const)
+    lim = lim*2 - one
+    return lim
+
+#The function computes the real (non-approximate) sign of x
+def determine_sign(data):
+    x = data['x']
+    sign = []
+    for idx in range(num):
+        if x[idx] > 0:
+            sign.append(1)
+        elif x[idx] < 0:
+            sign.append(-1)
+        else:
+            sign.append(0)
+
+    return {'sign': sign}
+
+secure_comparison = EvaProgram('secure_comparison', vec_size=num)
+with secure_comparison:
+    x = Input('x')
+    one = Input('one')
+    const = Input('const')
+    r = 5
+    sign = compute_sign(x, r, one, const)
+    Output('sign', sign)
+secure_comparison.set_input_scales(40)
+secure_comparison.set_output_ranges(30)
+
+
+def compile_and_run(inputs, prog):
+    print(f'Compiling {prog.name}')
+    compiler = CKKSCompiler()
+    compiled, params, signature = compiler.compile(prog)
+    public_ctx, secret_ctx = generate_keys(params)
+    enc_inputs = public_ctx.encrypt(inputs, signature)
+    enc_outputs = public_ctx.execute(compiled, enc_inputs)
+    outputs = secret_ctx.decrypt(enc_outputs, signature)
+    reference = evaluate(compiled, inputs)
+    return outputs, reference
+
+#The function displays the error between the approximate sign and the real sign
+def display_error(inputs, outputs):
+    non_aprox_sign = determine_sign(inputs)
+    aprox_sign = outputs['sign']
+    dif = [(non_aprox_sign['sign'][idx] - aprox_sign[idx])**2 for idx in range(num)]
+    plt.scatter(inputs['x'], dif)
+    plt.title(str(valuation_mse(outputs, non_aprox_sign)))
+    plt.show()
+
+
+inputs = generate_data()
+prog = secure_comparison
+outputs, reference = compile_and_run(inputs, prog)
+print('MSE outputs-aprox', valuation_mse(outputs, reference))
+display_error(inputs, outputs)