Add security, classic algos update

Classic Algorithms/README.md

@@ -8,3 +8,5 @@ Classic Algorithms
 **Closest pair problem** - The closest pair of points problem or closest pair problem is a problem of computational geometry: given *n* points in metric space, find a pair of points with the smallest distance between them.
 
 **Sieve of Eratosthenes** - The sieve of Eratosthenes is one of the most efficient ways to find all of the smaller primes (below 10 million or so).
+
+**Inverted index** - An [Inverted Index](http://en.wikipedia.org/wiki/Inverted_index) is a data structure used to create full text search. Given a set of text files, implement a program to create an inverted index. Also create a user interface to do a search using that inverted index which returns a list of files that contain the query term / terms. The search index can be in memory.

README-scratch.md

@@ -51,6 +51,8 @@ Classic Algorithms
 
 **Sieve of Eratosthenes** - The sieve of Eratosthenes is one of the most efficient ways to find all of the smaller primes (below 10 million or so).
 
+**Inverted index** - An [Inverted Index](http://en.wikipedia.org/wiki/Inverted_index) is a data structure used to create full text search. Given a set of text files, implement a program to create an inverted index. Also create a user interface to do a search using that inverted index which returns a list of files that contain the query term / terms. The search index can be in memory.
+
 Graph
 --------
 **Graph from links** - Create a program that will create a graph or network from a series of links.
@@ -213,10 +215,15 @@ Graphics and Multimedia
 
 **Turtle Graphics** - This is a common project where you create a floor of 20 x 20 squares. Using various commands you tell a turtle to draw a line on the floor. You have move forward, left or right, lift or drop pen etc. Do a search online for "Turtle Graphics" for more information. *Optional: Allow the program to read in the list of commands from a file.*
 
+Security
+-------------
+
+**Caesar cipher** - Implement a Caesar cipher, both encoding and decoding. The key is an integer from 1 to 25. This cipher rotates the letters of the alphabet (A to Z). The encoding replaces each letter with the 1st to 25th next letter in the alphabet (wrapping Z to A). So key 2 encrypts "HI" to "JK", but key 20 encrypts "HI" to "BC". This simple "monoalphabetic substitution cipher" provides almost no security, because an attacker who has the encoded message can either use frequency analysis to guess the key, or just try all 25 keys.
+
 ===============================================
 
 Sources
 =======
 
-[Martyr2’s Mega Project List](http://www.dreamincode.net/forums/topic/78802-martyr2s-mega-project-ideas-list/)
-[Rosetta Code](http://rosettacode.org/)
+* [Martyr2’s Mega Project List](http://www.dreamincode.net/forums/topic/78802-martyr2s-mega-project-ideas-list/)
+* [Rosetta Code](http://rosettacode.org/)

README.md

@@ -105,6 +105,8 @@ Graphs
 
 **Dijkstra’s Algorithm** - Create a program that finds the shortest path through a graph using its edges.
 
+**Inverted index** - An [Inverted Index](http://en.wikipedia.org/wiki/Inverted_index) is a data structure used to create full text search. Given a set of text files, implement a program to create an inverted index. Also create a user interface to do a search using that inverted index which returns a list of files that contain the query term / terms. The search index can be in memory.
+
 Text
 ---------
 
@@ -255,10 +257,15 @@ Graphics and Multimedia
 
 **Turtle Graphics** - This is a common project where you create a floor of 20 x 20 squares. Using various commands you tell a turtle to draw a line on the floor. You have move forward, left or right, lift or drop pen etc. Do a search online for "Turtle Graphics" for more information. *Optional: Allow the program to read in the list of commands from a file.*
 
+Security
+-------------
+
+**Caesar cipher** - Implement a Caesar cipher, both encoding and decoding. The key is an integer from 1 to 25. This cipher rotates the letters of the alphabet (A to Z). The encoding replaces each letter with the 1st to 25th next letter in the alphabet (wrapping Z to A). So key 2 encrypts "HI" to "JK", but key 20 encrypts "HI" to "BC". This simple "monoalphabetic substitution cipher" provides almost no security, because an attacker who has the encoded message can either use frequency analysis to guess the key, or just try all 25 keys.
+
 ===============================================
 
 Sources
 =======
 
-[Martyr2’s Mega Project List](http://www.dreamincode.net/forums/topic/78802-martyr2s-mega-project-ideas-list/)
-[Rosetta Code](http://rosettacode.org/)
+* [Martyr2’s Mega Project List](http://www.dreamincode.net/forums/topic/78802-martyr2s-mega-project-ideas-list/)
+* [Rosetta Code](http://rosettacode.org/)

Security/README.md

@@ -0,0 +1,4 @@
+Security
+-------------
+
+**Caesar cipher** - Implement a Caesar cipher, both encoding and decoding. The key is an integer from 1 to 25. This cipher rotates the letters of the alphabet (A to Z). The encoding replaces each letter with the 1st to 25th next letter in the alphabet (wrapping Z to A). So key 2 encrypts "HI" to "JK", but key 20 encrypts "HI" to "BC". This simple "monoalphabetic substitution cipher" provides almost no security, because an attacker who has the encoded message can either use frequency analysis to guess the key, or just try all 25 keys.