A new method of verifying digital signatures in e-cheque processing

We have considered a scenario in Financial Institutions(FI) like e-banks where there is facility for e-cheques to replace paper cheques. Everyday banks receive a large number of cheques signed by different signers. These cheques need to be submitted to their corresponding clearing banks over internet for clearance. After verification the clearing banks send signed instructions to the cheque submitted bank stating whether the cheque is accepted or rejected. This instruction is very important for any cheque submitting bank and it must verify the signed instruction. To verify this signature, the bank must have access to the signerpsilas public key and have assurance that it corresponds to the signerpsilas private key. But banks cannot store public keys of all possible transacting banks. Therefore there is need for a method to verify a signature without using the public key but still be convinced that it is signed by the actual signer. As e-cheques are transferred over internet, valid signatures of the bank clearing the e-cheque (as the e-cheque leaves are issued by this bank), payer and payee of the e-cheque are already available on the e-cheque submitted by the payee. Therefore we have come up with a method by which one can verify that a new signature received from a signer indeed belongs to the same signer without the help of public key of the signer but instead using the valid signature of the signer available on the e-cheque. This scheme works with the most widely used DSA and ElGamal Schemes. We consider another scenario in which a bank receives n signed cheques out of which some of them may be signed by the same signer and others by different signers. To avoid individual verification of the cheque, we propose a method by which the verifier will be able to verify all the cheques at a time using a single verification equation. This saves ap 160n modular multiplications when compared to individual signature verification of DSA.