The concept of cryptocurrency block chains is often touted as a way to increase the security and efficiency in various sectors. Recently, different companies have begun taking advantage of block chains for a similar purpose: securing personal information. The idea behind using the blockchain is that it can be used as an immutable public ledger that defines transactions on specific data sets and provides complete visibility into who has access to what data at all times. This concept has been implemented by several startups seeking to provide secure storage services for sensitive private information based on block chains, but their efforts have not been without criticism. Then, to protect the privacy information of doctor's diagnosis, we employ digital envelopes to achieve secure data sharing. Security analysis and performance evaluation show that the proposed scheme is fully secure and can preserve policy privacy and low computation overheads.