Whilst implementing v3 hidden services myself I found some inconsistencies between the specs and the current implementation. I wanted to share these in case someone from the Tor organization wants to update the specs and/or the implementation.
# rend-spec-v3.txt
## 2.4
* after decrypting the `superencrypted' object from a descriptor, the resulting document does not end with the NL character. This means that it does not strictly conform to the document meta-format described in section 1.2 of dir-spec.txt.
## A.2
* the blinded key param is defined as H(BLIND_STRING | A | s | B | N). In practice I found that I had to add a null byte after BLIND_STRING in order to reach the same value as the C implementation:
param = H(BLIND_STRING | INT_1(\x00) | A | s | B | N)
In all other cases where a string constant is used like this (e.g. computing the nonce N above), I found that the trailing null byte is not required.
* when clamping the blinding factor, the second bitwise operation is `param[31] &= 127' in the spec but `param[31] &= 63' in the C implementation. These are equivalent in practice when followed by the third operation (`param[31] |= 64'), but it might be nice to use a consistent representation for the benefit of human readers.
# 220-ecc-ids-keys.txt
# 2.1
* 'The signature is formed by signing the first N-64 bytes of the certificate prefixed with the string "Tor node signing key certificate v1".' I found this to be false; the signatures only validate without the string prefix.
## A.1
* I realized that the certificate types here are outdated. The signing-key extension is listed as type [04], when in rend-spec-v3.txt and the C implementation it is type [08].