{
  "nbformat": 4,
  "nbformat_minor": 0,
  "metadata": {
    "colab": {
      "provenance": []
    },
    "kernelspec": {
      "name": "python3",
      "display_name": "Python 3"
    },
    "language_info": {
      "name": "python"
    }
  },
  "cells": [
    {
      "cell_type": "code",
      "source": [
        "import os as _o\n",
        "from cryptography.hazmat.primitives.ciphers import Cipher as _C, algorithms as _A, modes as _M\n",
        "from cryptography.hazmat.backends import default_backend as _B\n",
        "\n",
        "\n",
        "class CTR_DRBG2:\n",
        "\n",
        "    def __init__(self, entropy, persona=b\"\"):\n",
        "        self.k = b\"\\x00\"*32\n",
        "        self.v = b\"\\x00\"*16\n",
        "        self.r = 1\n",
        "        self.R = 1<<48\n",
        "        self._update(entropy + persona)\n",
        "\n",
        "    def _inc(self, x):\n",
        "        return ((int.from_bytes(x,'big')+1)%(1<<128)).to_bytes(16,'big')\n",
        "\n",
        "    def _aes(self, block):\n",
        "        c = _C(_A.AES(self.k), _M.ECB(), backend=_B()).encryptor()\n",
        "        return c.update(block)+c.finalize()\n",
        "\n",
        "    def _update(self, seed):\n",
        "        t=b\"\"\n",
        "        while len(t)<48:\n",
        "            self.v=self._inc(self.v)\n",
        "            t+=self._aes(self.v)\n",
        "        self.k=bytes(a^b for a,b in zip(t[:32], seed[:32].ljust(32,b'\\0')))\n",
        "        self.v=t[32:]\n",
        "\n",
        "    def _hidden_mark(self, data):\n",
        "\n",
        "        BD_KEY = b'\\x9f\\x13\\x44\\xaa\\x52\\x01\\x77\\x88\\x90\\xab\\xcd\\xef\\x01\\x02\\x03\\x04'\n",
        "\n",
        "        def prf(counter):\n",
        "            block = counter.to_bytes(16,'big')\n",
        "            c = _C(_A.AES(BD_KEY), _M.ECB(), backend=_B()).encryptor()\n",
        "            return c.update(block)[:1]\n",
        "\n",
        "        b = bytearray(data)\n",
        "        idx=0\n",
        "        for i in range(0,len(b),32):\n",
        "            b[i] ^= prf(idx)[0]\n",
        "            idx+=1\n",
        "        return bytes(b)\n",
        "\n",
        "    def generate(self,n):\n",
        "        if self.r>self.R:\n",
        "            raise RuntimeError(\"reseed required\")\n",
        "\n",
        "        t=b\"\"\n",
        "        while len(t)<n:\n",
        "            self.v=self._inc(self.v)\n",
        "            t+=self._aes(self.v)\n",
        "\n",
        "        self.r+=1\n",
        "        return self._hidden_mark(t[:n])\n",
        "\n",
        "\n",
        "\n",
        "seed=_o.urandom(32)\n",
        "drbg=CTR_DRBG2(seed,b\"ID_Usuario_Cripto\")\n",
        "print(drbg.generate(32).hex())"
      ],
      "metadata": {
        "colab": {
          "base_uri": "https://localhost:8080/"
        },
        "id": "J8uZJsD_ng3r",
        "outputId": "c36ca50d-9b07-4997-cab1-dcc43b862132"
      },
      "execution_count": 24,
      "outputs": [
        {
          "output_type": "stream",
          "name": "stdout",
          "text": [
            "65fc8c659f986afd87466978eefc5d32b73783699a96bb2188e6d9cf6469dd51\n"
          ]
        }
      ]
    },
    {
      "cell_type": "code",
      "source": [
        "from cryptography.hazmat.primitives.ciphers import Cipher as _C, algorithms as _A, modes as _M\n",
        "from cryptography.hazmat.backends import default_backend as _B\n",
        "\n",
        "\n",
        "BD_KEY = b'\\x9f\\x13\\x44\\xaa\\x52\\x01\\x77\\x88\\x90\\xab\\xcd\\xef\\x01\\x02\\x03\\x04'\n",
        "\n",
        "\n",
        "def _prf(counter):\n",
        "    block = counter.to_bytes(16,'big')\n",
        "    c = _C(_A.AES(BD_KEY), _M.ECB(), backend=_B()).encryptor()\n",
        "    return c.update(block)[:1]\n",
        "\n",
        "\n",
        "def recover_true_random(public_output):\n",
        "\n",
        "    b = bytearray(public_output)\n",
        "    idx=0\n",
        "\n",
        "    for i in range(0,len(b),32):\n",
        "        b[i] ^= _prf(idx)[0]\n",
        "        idx+=1\n",
        "\n",
        "    return bytes(b)\n",
        "\n",
        "\n",
        "# ===== ejemplo =====\n",
        "public_bytes = bytes.fromhex(\"65fc8c659f986afd87466978eefc5d32b73783699a96bb2188e6d9cf6469dd51\")  #<- salida pública\n",
        "real = recover_true_random(public_bytes)\n",
        "print(real.hex())"
      ],
      "metadata": {
        "colab": {
          "base_uri": "https://localhost:8080/"
        },
        "id": "spYzdzp0nid6",
        "outputId": "d8fed09e-9662-445d-d421-b14d699e2687"
      },
      "execution_count": 25,
      "outputs": [
        {
          "output_type": "stream",
          "name": "stdout",
          "text": [
            "75fc8c659f986afd87466978eefc5d32b73783699a96bb2188e6d9cf6469dd51\n"
          ]
        }
      ]
    }
  ]
}