Introduction to blockchains; consensus and decentralization mechanisms; symmetric and public key cryptography; bitcoin protocols and APIs; alternatives to bitcoins; smart contracts; Ethereum virtual machine; solidity programming language; web3 API; Hyperledger; scalability and other challenges of blockchain system .introduction to blockchains; consensus and decentralization mechanisms; symmetric and public key cryptography; bitcoin protocols and apps; alternatives to bitcoins; smart contracts; Ethereum virtual machine; solidity programming language; web3 API; Hyperledger; scalability and other challenges of blockchain systems.