SCB – A Secret Sharing Program Brian M. Fleming Laurence T. Grant

Problem Posed Imagine a situation where you were on a team with a common goal, but you didn’t trust your team members. This leads to problems. To leave project unlocked, allows team members to cheat, and to lock with one password gives only one complete power.

Solution Create a program to divide the password (or key) into X-many pieces, so each group member has an equal share of the password. Alternately, create a program which creates N pieces of the key, and only requires M to put it back together.

Implementation The user inputs the key (which can either be a 9 digit number for equal sharing, or a 3 digit number for (2, n) splitting), and chooses a mode. The result is put into a corresponding text box. To retrieve the key, you put the necessary pieces in the appropriate boxes, and choose the proper mode.

Results Program works as expected. Implementation of the Secret Sharing (M,N) was made more difficult, and take more time, in Eiffel due to a lack of readily available advance math classes (e.g.. – classes which can solve matrices in finite prime fields).

Division of Work Laurence –Handled most of the behind the scenes math (e.g. – “math major stuff”). –Got external graphics to display in the program. Brian –Built GUI. –Handled manipulating input strings from user. –Built menu system, help and about boxes.

The Future of SCB Possible extensions include: –Writing a good, free, and available finite field class to handle larger numbers when using Secret Sharing (M,N) scheme. –Letting the secret number be entered by a trusted third party so it is unviewable by those who are receiving the pieces. –Allowing the output of more pieces.

(Brief) References Applied Cryptography, Bruce Schneier; John Wiley & Sons, Inc., “How to Share a Secret”, Ami Shamir; Communications of the ACM, vol. 24, no. 11, 1979.How to Share a Secret Introductory Modern Algebra, Saul Stahl; John Wiley & Sons, Inc., See paper for rest...