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单向ElGamal代理重新加密实现

elgamal modular-arithmetic cryptography encryption javascript

2

mcansado · 技术社区 · 7 年前

我在JavaScript中实现了一个ElGamal方案(代码很糟糕,只是想快速测试它),基于 this

var forge = require('node-forge');
var bigInt = require("big-integer");

var bits = 160;
forge.prime.generateProbablePrime(bits, function(err, num) {
  // Create prime factor and convert to bigInt
  var factor = bigInt(num.toString(10));
  // Find a larger prime of which factor is prime factor
  // Determine a large even number as a co-factor
  var coFactor = bigInt.randBetween("2e260", "3e260"); // should be bitLength(prime) - bitLength(factor)
  var prime = 4;
  while(!coFactor.isEven() || !prime.isPrime()) {
    coFactor = bigInt.randBetween("2e260", "3e260"); // should be bitLength(prime) - bitLength(factor)
    prime = coFactor.multiply(factor);
    prime = prime.add(1);
  }
  // Get a generator g for the multiplicative group mod factor
  var j = prime.minus(1).divide(factor);
  var h = bigInt.randBetween(2, prime.minus(1));
  var g = h.modPow(j, factor);
  // Alice's keys
  // Secret key
  var a = bigInt.randBetween(2, factor.minus(2));
  // Public key
  var A = g.modPow(a, prime);
  // Bob's keys
  // Secret key
  var b = bigInt.randBetween(2, factor.minus(2));
  // Public key
  var B = g.modPow(b, prime);
  // Shared secret
  // Calculated by Alice
  var Sa = B.modPow(a, prime);
  // Calculated by Bob
  var Sb = A.modPow(b, prime);
  // Check
  // Encryption by Alice
  var k = bigInt.randBetween(1, factor.minus(1));
  var c1 = g.modPow(k, prime);
  // Using Bob's public key
  var m = bigInt(2234266) // our message
  var c2 = m.multiply(B.modPow(k, prime));
  // Decryption by Bob
  var decrypt = c1.modPow((prime.minus(b).minus(bigInt(1))), prime).multiply(c2).mod(prime);
  console.log(decrypt); // should be 2234266

这似乎是可行的,最后的解密步骤返回原始数字。我现在想把它转换成一个单向代理重新加密方案,基于以下想法,取自 this 论文(第6页,左栏)。

所以你不必阅读这篇文章,背后的逻辑是我们可以分割私钥 x 分为两部分 x1 x2 x = x1 + x2 .代理将获得 x1 ,将结果传递给最终用户,最终用户将使用 x1 .

m=明文消息
g=组的发电机
x=密钥

现在,我尝试通过在代码中添加

  // Proxy re-encryption test
  // x is secret key
  var x = bigInt.randBetween(1, factor.minus(1));
  var x1 = bigInt.randBetween(1, x);
  var x2 = x.minus(x1);
  // y is public key
  var y = g.modPow(x, prime);
  var r = bigInt.randBetween(1, factor.minus(1));
  var c3 = g.modPow(r, prime);
  // mg^xr
  var c4 = bigInt(2234266).multiply(y.modPow(r, prime));

  var _decryptP = c4.divide(g.modPow(x1.multiply(r), prime));
  var _decryptF = _decryptP.divide(g.modPow(x2.multiply(r), prime));
});

遵循与上述等式相同的逻辑。然而 _decryptF 不返回 2234266

1 回复 | 直到 7 年前

1

2

Artjom B. 7 年前

您至少有两个问题:

divide a / b 实际上是指 a * (b ^-1 (mod p)) (mod p) .
multiply prime ). 你必须申请 mod 对结果进行操作。从技术上讲,你只需要做最后一次 乘

以下是有效的结果代码:

  // Proxy re-encryption test
  // x is secret key
  var x = bigInt.randBetween(1, factor.minus(1));
  var x1 = bigInt.randBetween(1, x);
  var x2 = x.minus(x1);
  // y is public key
  var y = g.modPow(x, prime);
  var r = bigInt.randBetween(1, factor.minus(1));
  var c3 = g.modPow(r, prime);
  // mg^xr
  var c4 = m.multiply(y.modPow(r, prime)).mod(prime);

  var _decryptP = c4.multiply(c3.modPow(x1, prime).modInv(prime)).mod(prime);
  var _decryptF = _decryptP.multiply(c3.modPow(x2, prime).modInv(prime)).mod(prime);
  console.log(_decryptF); // should be 2234266
});

Full code