TIMESTAMPS

Lest there was any doubt as to the importance of timestamps in Bitcoin’s design, the word appears 14 times in Satoshi’s whitepaper. But what exactly is a timestamp? In essence, it’s a verifiable proof that a specific event occurred at a specific point in time. The digital equivalent of finger painting the date in wet concrete: once it’s ossified, it’s there forever.

The cryptographic hashes that are chained together to form the Bitcoin blockchain were developed in the early 90s for the purposes of proving when a file was created or changed. Its designers saw it having applications for things like intellectual property disputes and record integrity – but Satoshi saw a more promising use case for this technology.

Haber and Stornetta’s original scheme entailed users sending only hashes – cryptographic proofs – of their documents to a Time-Stamping Service (TSS). The TSS would combine all document hashes received in a given time interval using a Merkle tree data structure (a feature added in a 1992 iteration of their original paper) to produce a single “interval hash” for that batch.

Each interval hash was linked to the previous interval’s hash to form a chronological chain, making it impossible to backdate or alter any timestamp, since changing a past entry would break the chain, and creating a fake backdated chain would require out-hashing the genuine chain. If you think this sounds a lot like Bitcoin, you’re not wrong. Satoshi took this fundamental concept, added in Proof of Work and voila: a decentralized timestamping service was born.

Timestamps Take Off

Bitcoin proved the reliability of timestamps. If they could secure a network processing millions – and eventually trillions – of dollars in value, their integrity was beyond dispute. Which raised the question: what else could be done with them? In the mid-2010s, Bitcoin developer Peter Todd began pondering this matter in earnest and, after much tinkering, emerged in 2016 with OpenTimestamps. This solution provided a means of proving that a file existed at or before a certain time by embedding its hash into the Bitcoin blockchain.

Bitcoin, forged from timestamps, had now become a universal timestamping machine of its own. One of the clever things about Todd’s design is that OpenTimestamps takes multiple timestamp requests and combines them using a Merkle tree, enabling them to be recorded on the Bitcoin network for a nominal fee. This capability was memorably – and indelibly – proved on December 7, 2016 when Todd’s team performed an audacious feat, timestamping around 750 million Internet Archive files within a single Bitcoin transaction. The event, which was dubbed “carbon dating the internet,” proved that a given archived file or webpage snapshot existed prior to that date.

And this was all achieved by tracing a path from the file’s hash, through the Merkle tree, to that one Bitcoin transaction in block 442,573 – which in turn can be traced back through each of the previous 442,572 blocks to arrive at the genesis block where Bitcoin began.