We were discussing identity management with Civic.

It is based on blockchain ledger that enables users to login with their fingerprints.  The availability of a distributed ledger does away with a password database. Civic identity management introduces three new components:
1) a variety of smart contracts
2) an indigenous utility token and
3) new software applications.
 Blockchain works as the ledger in these cases. The smart contracts are the code executed on the blockchain.  The advantages of using a distributed ledger such as blockchain include the following:
There are no middlemen for transfers and therefore there is little fees and low cost. Moreover the protocol has a rewarding mechanism
The ledger is immutable and its integrity checked and agreed on an ongoing basis. 
All transactions on the ledger are visible to anyone and any transaction done anytime is recorded.
The transactions on the ledger cannot be reversed and are immune from chargebacks. These transactions are as sound as cash transactions.
There is a high degree of privacy for the individual whose transactions are maintained in the ledger. The transaction does not divulge any PII but an individual can easily prove ownership of the entries.
The ledger itself is decentralized and maintained by a community where no one actor can gain enough influence to submit a fraudulent transaction or alter recorded data.
Would blockchain be popular without the rewarding incentive ? From a design perspective, we could ignore that.
#codingexercise
Find sum of all possible combinations for N elements

void  Combine(List<int> A, ref List<int> b, int start, int level, ref List<int> sums)   

{   

for (int I = start; I < A.length; I++)   

{    

     b[level] = A[i];   

     sums.Add(GetSum(b)); 

    if (I < A.length)   

           Combine(A, ref b, i+1, level+1, ref sums);   

     b[level] = 0;   

}   

}