1. Password Policies to prevent reuse for online accountsBY
Ravi SANTOSH SRIRAM SAMPATH REDLAM
Graduate Student, Department of Computer Science

2. Under the supervision of
Dr . Amol Mali
Associate Professor, Department of Computer Science

3. Abstract
An efficient algorithm is devised to compute the minimum number of passwords needed given the password requirements for different accounts.
Work for any number of digital accounts.
It generates the minimum number of passwords needed for individual organization category based on their sizes.

4. Algorithm Let n be the different number of online accounts
Let k be the number of clusters formed
Let min i - max i be the range of the length of password cluster i 
Let x j - y j be the range of cluster of the length of password of account j
Min i = x 1. //MInimum length of password for the cluster i
Max i = y 1. //Maximum length of password for the cluster i
k= //Number of clusters initially 1

5. Algorithm (contd.) for(j=2;j<=n; j++) for(i=1;i<=k;i++)
  If (max(Min i,x j ) <=  min (Max i, y j)
                  Min i  = max(Min i ,x j )
//Update MInimum length of password for the cluster i
                  Max i = min (Max i, y j)
//Update Maximum length of password for the cluster i
                  break
end if   
      end for
k++ //Number of clusters is incremented by 1    
                  Min k = x j
                  Max k = y j
end for

6. Example Consider 9 different online account
Online account 1  (5,12) Online account 2. (6,13) Online account 3. (7,14) Online account 4  (8,15) Online account 5. (9,15)
Online account 6. (11,16) Online account 7  (12,32) Online account 8. (13,48) Online account 9. (14,64)
Initially number of clusters is 1 
Minimum of cluster 1 = x1 = 5 and Maximum of cluster 1 = y1 = 12

7. Now when online account 2 is added Maximum(Minimum of cluster 1,x2 )= Maximum(5,6)=6 and Minimum(Maximum of cluster 1,y2) = Minimum(12,13)=12 6<=12 Minimum of cluster 1 = 6 and Maximum of cluster 1 = 12 Now when online account 3 is added Maximum(Minimum of cluster 1,x3 )= Maximum(6,7)=7 and Minimum(Maximum of cluster 1,y3) = Minimum(12,14)=12 7<=12 Minimum of cluster 1 = 7 and Maximum of cluster 1 = 12 Now when online account 4 is added Maximum(Minimum of cluster 1,x4)= Maximum(7,13)=13 and Minimum(Maximum of cluster 1,y4) = Minimum(12,48)=12 13<=12 is false So there will be another cluster formed Minimum of cluster 2 = 13 and Maximum of cluster 2 = 48 Now when online account 5 is added Check cluster 1 Maximum(Minimum of cluster 1,x5)= Maximum(7,14)=14 and Minimum(Maximum of cluster 1,y5) = Minimum(12,48)=12 14<=12 is false Check cluster 2 Maximum(Minimum of cluster 2,x5)= Maximum(13,14)=14 and Minimum(Maximum of cluster 2,y5) = Minimum(48,64)=48 14<=48 Minimum of cluster 2 = 14 and Maximum of cluster 2 = 48

8. Conclusion
K clusters will be formed so k  passwords of length between Min k and Max k will be formed containing at least an upper case, lower case, number and special character.
Also if there are limitations on using of some special characters , they won’t be used to generate password.