A Directed Threshold - Signature Scheme
  Directed signature is the solution of such problems when the signed message contains information sensitive to the signature receiver. Generally, in many application of directed signature, the signer is generally a single person. But when the message is on behalf of an organization, a valid sensitive message may require the approval of several people. Threshold signature schemes are used to solve these problems. This paper presents a threshold directed signature scheme. 
Sunder Lal and Manoj Kumar