Once an authority has computed and signed a consensus network status, it should send its detached signature to each other authority in an HTTP POST request to the URL:
[XXX Note why we support push-and-then-pull.]
All of the detached signatures it knows for consensus status should be available at:
Assuming full connectivity, every authority should compute and sign the same consensus including any flavors in each period. Therefore, it isn't necessary to download the consensus or any flavors of it computed by each authority; instead, the authorities only push/fetch each others' signatures. A "detached signature" document contains items as follows:
"consensus-digest" SP Digest NL
[At start, at most once.]
The digest of the consensus being signed.
"valid-after" SP YYYY-MM-DD SP HH:MM:SS NL "fresh-until" SP YYYY-MM-DD SP HH:MM:SS NL "valid-until" SP YYYY-MM-DD SP HH:MM:SS NL
[As in the consensus]
"additional-digest" SP flavor SP algname SP digest NL
For each supported consensus flavor, every directory authority adds one or more "additional-digest" lines. "flavor" is the name of the consensus flavor, "algname" is the name of the hash algorithm that is used to generate the digest, and "digest" is the hex-encoded digest.
The hash algorithm for the microdescriptor consensus flavor is defined as SHA256 with algname "sha256".
"additional-signature" SP flavor SP algname SP identity SP signing-key-digest NL signature. [Any number.]
For each supported consensus flavor and defined digest algorithm, every directory authority adds an "additional-signature" line. "flavor" is the name of the consensus flavor. "algname" is the name of the algorithm that was used to hash the identity and signing keys, and to compute the signature. "identity" is the hex-encoded digest of the authority identity key of the signing authority, and "signing-key-digest" is the hex-encoded digest of the current authority signing key of the signing authority.
The "sha256" signature format is defined as the RSA signature of the OAEP+-padded SHA256 digest of the item to be signed. When checking signatures, the signature MUST be treated as valid if the signature material begins with SHA256(document), so that other data can get added later. [To be honest, I didn't fully understand the previous paragraph and only copied it from the proposals. Review carefully. -KL]
[As in the consensus; the signature object is the same as in the consensus document.]