Design an anonymous channel for a whistle-blower to give credible tip-offs

(The discussion on this social problem and the need to develop a solution below are copied from another blog I write: www.obvioustruths.blogspot.com

The technical possibilities discussed following the duplicated paragraphs are unique to this blog)

The importance of whistle-blowers

Many instances of corrupt practice and tax evasion occur with hundreds of people knowing about it. But the victims become hostages of the wrong-doer for many reasons and do not squeal. For instance, visualize a college or university charging under-the-table-fees of Rs 15 Lakhs (roughly US $ 30,000) for admitting students who cannot honestly compete with other applicants on merit. This is illegal on two grounds: it is illegal for educational institutions to demand and accept such payments; secondly, it generates wealth on which income tax has been evaded. It becomes the so-called black money. Thousands of students pay such “fees” every year. However, they are too scared to do anything about it before admission which they desire so strongly. After admission, they do not wish to expose their college or university and endanger their own education. Similarly, practically every company or organization which cheats on tax has a number of employees who know about it. But the employees are too scared to blow the whistle. They may even get killed for doing something like that. Under these circumstances, the rare whistle-blower has to be encouraged, protected and supported.
I assume that there are a few vigilance organizations (V. O.) that wish to encourage whistle blowers, and that they themselves are not corrupt! We need to create an Internet based mechanism meeting the following requirements, to enable such an organization to work efficiently.

Desired characteristics of the proposed mechanism

a) Gives the whistle blower privacy – no one should know who he is till he decides to reveal himself
b) Gives the vigilance organization some way of separating credible tip-offs from spurious reports
c) Provides for a mechanism to prove that a claimant is actually the one who had sent a particular set of anonymous messages earlier

The provision in c) is meant to enable a whistle-blower to claim a reward when his tip-off is acted upon and proves to be beneficial to society.

A few technical possibilities for implementing a solution

These items are labeled a), b) and c) to link them to the requirements given above.

a) Encourage the whistle blower to use any anonymizer (See http://en.wikipedia.org/wiki/Anonymizer ) he trusts, to protect his identity.

b) Encourage the whistle-blower to use create a file including his own postal address or something like that, add an irrelevant random text at the bottom of the file, and to compute the message-digest (See http://en.wikipedia.org/wiki/Cryptographic_hash_function ) of that file using any trusted, publicly available code. He should append the message digest of that file (alone) to every anonymous tip-off he sends, to serve as a masked-identity code. The file itself will be kept on his own PC or laptop. The random text will protect against someone trying out millions of known addresses to see if one of them has that message-digest.
The V.O. would give low credence to a tip-off from unproven sender (known only through his masked-identity code. However, if a few of his tip-offs prove to be useful, the V.O. can increase the credence it gives to tip-offs from that person).

c) The whistle-blower can surface at a time of his choosing to claim any reward that he is entitled to.

Notes:

1) Search for related information on the web. Have others published any solutions? Are you satisfied with them?

2) The mechanism described in b) is not too satisfactory. It will take a year or more for whistle-blower to earn his credibility this way. Can you improve on this?

3) Post your comments and suggestions on this blog. Together a number of us may do a better than any one of us can do individually.

Srinivasan Ramani September 15, 2010