四、Shamir Secret Sharing (Shamir 秘密共享)

&emsp首先,定义一个 ( N , k ) (N,k) (N,k)

### Packed Shamir Secret Sharing 的理论基础 Packed Shamir Secret Sharing 是一种基于多项式的秘密共享方案,它扩展了传统的 Shamir Secret Sharing 方法。传统方法允许将一个秘密分割成多个部分并分发给不同的参与者,只有达到一定数量的参与者的份额才能恢复原始的秘密。然而,在某些场景下,可能需要更高效的方式处理多组秘密或更大的数据量。 #### 基本概念 Shamir Secret Sharing 使用拉格朗日插值法来重建秘密[^1]。假设有一个 $d$ 度的多项式 $f(x)$,其常数项即为要保护的秘密 $s$。通过计算该多项式在不同点上的取值,可以生成若干个份额。只要收集到至少 $d+1$ 个份额即可唯一确定这个多项式,并从中提取出秘密 $s$。 对于 **packed** 版本而言,它的目标是在单次操作中同时分享多个独立的秘密。这通常涉及构造更高维度或者结构化的多项式形式: $$ f(x) = s_0 + s_1 \cdot g_1(x) + ... + s_k \cdot g_k(x), $$ 其中每一个 $g_i(x)$ 都是一个预先定义好的函数序列 (比如正交基),而对应的系数 $\{s_j\}$ 就是我们想要隐藏的不同秘密片段[^2]。 这种设计使得我们可以一次性编码更多比特的信息进入同一个分布过程中去减少通信成本以及提高效率。 #### 实现细节 以下是 Python 中的一个简单实现例子展示如何创建和还原打包后的 Shamir 秘密: ```python import numpy as np from sympy import GF, lagrange_interpolate def generate_packed_shares(secret_list, t, n, prime=337): """ Generates `n` shares from a list of secrets using packed shamir's scheme. Args: secret_list(list): List containing all individual secrets to be shared. t(int): Threshold value; minimum number required to reconstruct original data. n(int): Total amount of generated shares. prime(int): Prime modulus used within finite field operations. Returns: dict: Dictionary mapping share indices with their respective values. """ k = len(secret_list) F = GF(prime) # Define base functions gi(x). Here we use powers of x directly but other bases could also work. def g(i, x): return pow(F(x), i) coefficients = [F(s) for s in secret_list] poly = sum([coefficients[i]*g(i,x) for i in range(k)], start=F(0)) shares = {i : int(poly.subs('x', F(i))) % prime for i in range(1,n+1)} return shares def recover_secrets(shares_subset, t, k, prime=337): """ Recovers multiple secrets given sufficient subset of previously created shares via Lagrangian interpolation method under packed setting. Args: shares_subset(dict): Subset consisting exactly 't' distinct pairs obtained during generation phase. t(int): Same threshold parameter specified earlier when generating shares. k(int): Number of total secrets originally intended to store inside single polynomial instance. prime(int): Corresponding large enough prime integer utilized throughout computations involving modular arithmetic rules. Returns: list: Recovered collection holding back initial set of hidden messages represented numerically according modulo operation rule defined by chosen prime constant above. """ assert(len(set(shares_subset.keys())) >= t),"Insufficient unique points provided!" xs = sorted(list(shares_subset)) ys = [shares_subset[x] for x in xs[:t]] recovered_coeffs = [] for j in range(k): current_gj_x_values = [(pow(GF(prime)(xi),j)) for xi in xs[:t]] interpolated_value_at_zero = lagrange_interpolate(xs[:t],current_gj_x_values,GF(prime))(0) recovered_coeffs.append(interpolated_value_at_zero.as_numer_denom()[0]) return [int(c)%prime for c in recovered_coeffs] if __name__ == "__main__": SECRETS_TO_SHARE=[42 ,89 ] # Two sample integers acting like our confidential information items needing safeguard measures applied upon them before distribution among participants later stage onwards... THRESHOLD_VALUE,TOTAL_NUMBER_OF_PARTICIPANTS=(len(SECRETS_TO_SHARE)+1 ),5 distributed_data_points=generate_packed_shares(SECRETS_TO_SHARE,ThRESHold_VALuE,totAl_nUmber_of_particiPants) print("Distributed Data Points:",distributed_data_points) any_t_valid_combination={key:value for key,value in zip(sorted(distributed_data_points)[::2],[distributed_data_points[key]for key in sorted(distributed_data_points)[::2]])} retrieved_information=recover_secrets(any_t_valid_combination,ThRESHold_valUe,len(secreTs_to_share)) print("Retrieved Information:",retrieved_information) ``` 此脚本展示了如何利用有限域中的算术运算构建一个多变量版本的 Shamir 方程,并演示了如何从选定的一组份额中重新获得所有的秘密。 --- ###
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