Alternative digital signature schemes in blockchain

This thesis is a study on authentication methods of Bitcoin ecosystem which is an application of blockchain. Firstly, the facilities given by Bitcoin along with its security requirements are examined from a perspective that can be used in place of today's banking system. Bitcoin ecosystem is a use case of blockchain and its current transaction authentication methods are well studied in the literature, and based on this, the questions are raised, "Could the common account and the proxy concepts of banking services also be possible in Bitcoin?". Many researches say that there are solutions based on bilinear pairings commonly, accountable subgroup multi-signature and delectable credentials schemes. These schemas are studied in this thesis. As a first alternative, accountable subgroup multi-signature (ASM) constructed from Boneh – Lynn – Shacham (BLS) signature schemes gives us the opportunity of the public key aggregation mechanism. In this way, it can be possible that more than one user sign the same message jointly and only one public key is needed to verify the signature. This approach allows lots of savings in storage of public keys in transaction scripts and that is quite convenient to implement in Bitcoin. For the second alternative, delectable credentials signature schema renders possibility that someone can give her signing authority to another. Delegatable credentials can do this with a structure that is built on Groth and Schnorr signature schemes. Furthermore, the suggested delectable credential schema in this thesis is able to store in secret or disclosed within the signature. This property is included in the usage scenarios about need of delegation for individuals.