Get a Public Timestamp for a Commitment

Asks an RFC 3161 time-stamping authority to sign the SHA-256 of data together with the current time, then checks the token it returns with tsvrf(). Anyone holding the same bytes, the token and the authority's certificate can later prove the bytes existed at that time, without trusting the person who asked.

Usage

tsstmp(
  data,
  tsa = "https://freetsa.org/tsr",
  file = NULL,
  timeout = 60,
  trust = NULL
)

Arguments

data: What to timestamp: a raw vector, the path of an existing file, or a list from ralloc() (its commitment is stamped).
tsa: The time-stamping authority's URL.
file: Optional path to save the token to (a .tsr file). An existing file is not overwritten.
timeout: Seconds to wait for the authority.
trust: Trust anchors for the authority's certificate, passed to tsvrf(): for the default authority, its root certificate from https://freetsa.org/files/cacert.pem. Without one the token's signature is still checked, but the result is not VERIFIED, because nothing vouches for the certificate that made it.

Value

The tsvrf() result for the new token (class bricklayer_timestamp, printed as a box with the time it asserts), with three more elements: token (the raw token), tsa and file (the path it was saved to, or NA). An authority that does not answer is an error.

Details

Use it on anything that has to be fixed before the data are seen: the commitment of a randomisation list from ralloc() (pass the list itself), the file of declared outcomes, a manifest or a capsule. Only the 32-byte SHA-256 leaves the machine; the data never do.

The request carries a random 8-byte nonce from the operating system's generator and asks for the authority's certificate in the reply, so the token can be checked offline later. The default authority, "https://freetsa.org/tsr", is free and needs no account; any RFC 3161 service can be named instead, and an institution's own is better where there is one. Pass cert and trust to tsvrf() when re-checking a saved token to tie it to a certificate you trust.

References

Adams, C., Cain, P., Pinkas, D., and Zuccherato, R. (2001). Internet X.509 Public Key Infrastructure Time-Stamp Protocol (TSP). RFC 3161.

Examples

if (FALSE) { # interactive()
# Fix a trial's allocation before enrolment, then stamp its commitment.
a <- ralloc(40, seed = "a demonstration only")
ts <- tsstmp(a, file = file.path(tempdir(), "allocation.tsr"))
ts$time

# Years later, anyone re-checks the saved token against the commitment.
tsvrf(ts$file, charToRaw(attr(a, "alloc")$digest))
}