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In perfect secret sharing schemes, invalid coalitions of shares do not reveal any information regarding the secret. However, in secret sharing constructions which are non-perfect in nature, every illegitimate coalition leaks out information not just pertaining to the parent secret but also related to other shares in circulation. In this paper the information flow and leakage through shares generated by a non-perfect scheme called MIX-SPLIT is examined with the help of a geometric model, developed with a 3-out-of-3 sharing example in view. Finally the principle of controlled leakage has been applied towards a secure biometric-based group authentication system. No fingerprint template storage is required and access to the respective user biometric PINs are made completely secure.