HTTP Headers Hashing (HHHash)

HTTP Headers Hashing (HHHash) is a technique used to create a fingerprint of an HTTP server based on the headers it returns. HHHash employs one-way hashing to generate a hash value for the set of header keys returned by the server

Calculation of the HHHash

To calculate the HHHash, we concatenate the list of headers returned by the HTTP server. This list is ordered according to the sequence in which the headers appear in the server's response. Each header value is separated with :.

The HHHash value is the SHA256 of the list.

HHHash format

hhh:1:20247663b5c63bf1291fe5350010dafb6d5e845e4c0daaf7dc9c0f646e947c29

prefix:version:SHA 256 value

Example

Calculating HHHash from a curl command

$ curl -s -D - https://www.circl.lu/ -o /dev/null  | awk 'NR != 1' | cut -f1 -d: | sed '/^[[:space:]]*$/d' | sed -z 's/\n/:/g' | sha256sum | cut -f1 -d " " | awk {'print "hhh:1:"$1'}

Output value

hhh:1:79dde6169456e7e2886eb1668b3c27e8438f1a7219fc5fbb13d9c8eec07c5983