OpenTimestamps aims to be a standard format for blockchain timestamping. The format is flexible enough to be vendor and blockchain independent.
How it works
A timestamp proves that some data existed prior to some point in time. OpenTimestamps defines a set of operations for creating provable timestamps and later independently verifying them. At the time of writing timestamping on the Bitcoin blockchain is supported, the format is flexible enough to support a variety of methods.
Anyone could realize a timestamp with the permissionless blockchain by paying the transaction fees, for your convenience we offer calendar servers that perform this operation for you. These servers are free to use and they don't require any registration or api key.