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+/*
+ This file is part of Anastasis
+ Copyright (C) 2020, 2021 Taler Systems SA
+
+ Anastasis is free software; you can redistribute it and/or modify it under the
+ terms of the GNU Lesser General Public License as published by the Free Software
+ Foundation; either version 3, or (at your option) any later version.
+
+ Anastasis is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ Anastasis; see the file COPYING.GPL. If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file redux/validation_IN_AADHAR.c
+ * @brief validation logic for Indian Aadhar numbers
+ * @author Christian Grothoff
+ */
+#include <string.h>
+#include <stdbool.h>
+#include <ctype.h>
+
+/**
+ * The multiplication table.
+ */
+static int m[10][10] = {
+ {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
+ {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
+ {2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
+ {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
+ {4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
+ {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
+ {6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
+ {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
+ {8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
+ {9, 8, 7, 6, 5, 4, 3, 2, 1, 0}
+};
+
+
+/**
+ * The permutation table.
+ */
+static int p[10][10] = {
+ {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
+ {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
+ {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
+ {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
+ {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
+ {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
+ {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
+ {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}
+};
+
+
+/**
+ * Converts a string to a reversed integer array.
+ *
+ * @param input The numeric string data converted to reversed int array.
+ * @param[out] Integer array containing the digits in the numeric string
+ * in reverse order
+ */
+static bool
+string_to_vals (const char *input,
+ int output[12])
+{
+ unsigned int off = 0;
+
+ for (unsigned int i = 0; i < 12;)
+ {
+ int c = input[i + off];
+
+ if (0 == c)
+ return false;
+ if (isspace (c))
+ {
+ off++;
+ continue;
+ }
+ if (! isdigit (c))
+ return false;
+ output[11 - i++] = c - '0';
+ }
+ if ('\0' != input[12 + off])
+ return false;
+ return true;
+}
+
+
+/**
+ * Function to validate an Indian Aadhar number.
+ *
+ * See https://www.geeksforgeeks.org/how-to-check-aadhar-number-is-valid-or-not-using-regular-expression/
+ * and http://en.wikipedia.org/wiki/Verhoeff_algorithm/.
+ *
+ * @param aadhar_number aadhar number to validate (input)
+ * @return true if validation passed, else false
+ */
+bool
+IN_AADHAR_check (const char *aadhar_number)
+{
+ int c = 0;
+ int vals[12];
+
+ if (! string_to_vals (aadhar_number,
+ vals))
+ return false;
+ for (unsigned int i = 0; i < 12; i++)
+ c = m[c][p[(i % 8)][vals[i]]];
+
+ return (0 == c);
+}