Blockchain is a distributed ledger constructed by a series of network nodes. It owns the following security attributes: unforgeability, decentralization, trustless, provable security based on cryptography and non-repudiation. This paper summarizes those security services, including data confidentiality, data integrity, authentication, data privacy, assured data erasure. This paper first introduces the concept of blockchain and public key cryptography. For the above-mentioned 5 security services, existing security threats faced by users in actual scenarios and their corresponding solutions are analyzed. The drawbacks of those traditional implementations are also discussed, and then countermeasures are introduced based on blockchain. Finally, values and challenges associated with blockchain are discussed as well.