> For the complete documentation index, see [llms.txt](https://docs.oklg.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.oklg.io/dapps/trusted-timestamping.md). # Trusted Timestamping Trusted timestamping is not a new concept, where a piece of data can be verifiably proven to have existed at a certain point in time. We created a version of this concept to use on the blockchain. ### Direct Link ### Smart Contract ### How many supported blockchains? All OKLG-supported blockchains ### Cost of using service? $2 USD per digital signature stored ### How to add a digital signature to the blockchain? 1. Once in the Trusted Timestamping dApp, you can simply click the **Add File to Calculate its Signature** button.\

2. The signature (or SHA256 hash of the file contents) will show in the UI. You can now click **Submit File Signature to Blockchain** to initiate the transaction.\

3. You can now review all of your digital signatures you've stored in the table below. Note the signatures are tied to the address, so if/when you ever switch addresses your list will obviously reset.