There is cryptographic signing, that lets Alice sign a statement X so that Bob is able to cryptographically verify that Alice claims X. X could for example be “Content Y was created in 2023”. This signature is evidence for X only to the extent that Bob trusts Alice. This is NOT what I suggest we use, at least not primarily.
There is cryptographic time-stamping, that lets Alice timestamp content X at time T so that Bob is able to cryptographically verify that content X existed before time T. Bob does not need to trust Alice, or anyone else at all, for this to work. This is what I suggest we use.
Back-dating content is therefore cryptographically impossible when using cryptographic time-stamping. That is kind of the point; otherwise I wouldn’t be convinced that the value of the timestamps would grow over time. To the extent we use cryptographic time-stamping, the argument here is ‘it will be entirely impossible in the future’.
However, cryptographic time-stamping and cryptographic signing can be combined in interesting ways:
We could sign first and then timestamp, achieving a cryptographic proof that in or before 2023, archive.org claimed that content X was created in 1987. This might be valuable if the organization or its cryptographic key at a later date were to be compromised, e.g. by corruption, hacking, or government overreach. Timestamps created after an organization is compromised can still be trusted: You can always know the content was created in or before 2023, even if you have reason to doubt a claim made at that time.
We could timestamp, then sign, then timestamp. This allows anyone to cryptographically verify that e.g. sometime between 2023-01-20 and 2023-01-30, Alice claimed that content X was created in 1987. This could be valuable if we later learn we have reason to distrust the organization before a certain date. Again, we will always know X was created before 2023-01-30, no matter anyone’s trustworthiness.
As for the issue with 2023 timestamps being misleading for 1995 content: This issue is probably very real, but it’s less urgent. Making the timestamps is urgent. On top of that underlying data and cryptographic proofs, different UIs can be built and improved over time.
Let me clarify the cryptography involved:
There is cryptographic signing, that lets Alice sign a statement X so that Bob is able to cryptographically verify that Alice claims X. X could for example be “Content Y was created in 2023”. This signature is evidence for X only to the extent that Bob trusts Alice. This is NOT what I suggest we use, at least not primarily.
There is cryptographic time-stamping, that lets Alice timestamp content X at time T so that Bob is able to cryptographically verify that content X existed before time T. Bob does not need to trust Alice, or anyone else at all, for this to work. This is what I suggest we use.
Back-dating content is therefore cryptographically impossible when using cryptographic time-stamping. That is kind of the point; otherwise I wouldn’t be convinced that the value of the timestamps would grow over time. To the extent we use cryptographic time-stamping, the argument here is ‘it will be entirely impossible in the future’.
However, cryptographic time-stamping and cryptographic signing can be combined in interesting ways:
We could sign first and then timestamp, achieving a cryptographic proof that in or before 2023, archive.org claimed that content X was created in 1987. This might be valuable if the organization or its cryptographic key at a later date were to be compromised, e.g. by corruption, hacking, or government overreach. Timestamps created after an organization is compromised can still be trusted: You can always know the content was created in or before 2023, even if you have reason to doubt a claim made at that time.
We could timestamp, then sign, then timestamp. This allows anyone to cryptographically verify that e.g. sometime between 2023-01-20 and 2023-01-30, Alice claimed that content X was created in 1987. This could be valuable if we later learn we have reason to distrust the organization before a certain date. Again, we will always know X was created before 2023-01-30, no matter anyone’s trustworthiness.
As for the issue with 2023 timestamps being misleading for 1995 content: This issue is probably very real, but it’s less urgent. Making the timestamps is urgent. On top of that underlying data and cryptographic proofs, different UIs can be built and improved over time.