Easy password hash migration from MD5 to BCrypt.

Many legacy production systems still use non-salted MD5 function for password hashing. These hashes are usually stored in the database and used for user authentication. The problem is that non-salted MD5 hash is no more secure today. There are so-called rainbow tables (precomputed MD5 hashes for word dictionaries) that can be used for easy reverse lookup.

Alexander Goldstein's Each! Pattern

class Array
 def each!
  while count > 0
   yield(shift)
  end
 end
end

SelectionSort in Java

 public static void selectionsort(int[] A) {
  for (int i = 0; i < A.length; i++) {
   int min = i;
   for (int j = i+1; j < A.length; j++) {
    if (A[j] < A[min]) {
     min = j;
    }
   }
   swap(A, i, min);
  }
 }

 public static void swap(int[] A, int i, int j) {
  int temp = A[j];
  A[j] = A[i];
  A[i] = temp;
 }

InsertionSort in Java

 public static void insertionsort(int[] A) {
  for (int i = 1; i < A.length; i++) {
   for (int j = i; j > 0 && A[j] < A[j - 1]; j--) {
    swap(A, j, j - 1);
   }
  }
 }

 public static void swap(int[] A, int i, int j) {
  int temp = A[j];
  A[j] = A[i];
  A[i] = temp;
 }

MergeSort in Java

 public static void mergesort(int[] A) {
  int[] aux = new int[A.length];
  mergesort(A, aux, 0, A.length-1);
 }
 private static void mergesort(int[] A, int[] aux, int lo, int hi) {
  if (lo >= hi) return;
  int m = (lo+hi) / 2;
  mergesort(A, aux, lo, m);
  mergesort(A, aux, m+1, hi);
  merge(A, aux, lo, m, hi);
 }
 private static void merge(int[] A, int[] aux, int lo, int m, int hi) {
  int i = lo;
  int j = m+1;
  for (int k=lo; k <= hi; k++) {
   if (i > m) {
    aux[k] = A[j];
    j++;
   } else if (j > hi) {
    aux[k] = A[i];
    i++;
   } else if (A[j] < A[i]) {
    aux[k] = A[j];
    j++;
   } else {
    aux[k] = A[i];
    i++;
   }
  }
  for (int k=lo; k <= hi; k++) {
   A[k] = aux[k];
  }
 }

QuickSort in Java

 public static void quicksort(int[] A) {
  quicksort(A, 0, A.length-1);
 }
 
 private static void quicksort(int[] A, int lo, int hi) {
  if (lo >= hi) return;
  int p = partition(A, lo,hi);
  quicksort(A, lo, p-1);
  quicksort(A, p+1, hi);
 }
 
 private static int partition(int[] A, int lo, int hi) {
  int i = lo+1;
  int j = hi;
  while (i <= j) {
   while (A[i] < A[lo]) {
    i++;
    if (i > hi) break;
   }
   while (A[j] > A[lo]) {
    j--;
   }
   if (i <= j) {
    swap(A, i, j); 
    i++;
    j--;
   }
  }
  swap(A, lo, j); 
  return j;
 }

 public static void swap(int[] A, int i, int j) {
  int temp = A[j];
  A[j] = A[i];
  A[i] = temp;
 }

Python socksipy: SFTP with Paramiko via SOCKS proxy

I use Paramiko library to access SFTP servers in Python. Paramiko is easy to use, provides programmer with rich functionality, but it does not support proxy servers out of the box. There is a small library socksipy that can be easily integrated with Paramiko.