🍈 Zettelkasten

Hashcash

1 min read

A Proof of Work algorithm. Requires clients concatenate a Salt to string and continuously hash until a hash beginning with a certain number of zeroes is found.

Hashcash Format

X-Hashcash: ver:bits:date:resource.ext::rand:counter
  • ver : Hashcash version
  • bits: Number of partial pre-image zero bits in the hashed code
  • date: Time the message was send in format YYMMDD[hhmm[ss]]
  • resource: IP address of email string
  • ext: Extension - optional
  • rand: String of random characters encoded in Base64
  • counter: Binary counter encoded in base-64

Algorithm

Sender

  1. Sender initializes a header and appends counter value initialized at random number
  2. Compute SHA1 hash, if the first 20 bits are all zero, then this is acceptable, if not, then increment the counter and try to hash again

Recipient

  1. Recipient calculates SHA-1 hash of the message (e.g “1:20:060408:adam@cypherspace.org::1QTjaYd7niiQA/sc:ePa`)
  2. If the first 20-bits arent zero, then the hash is invalid
  3. if date is not within two days, its invalid
  4. If the email address is not registered by the recipient, or is on a blacklist, the hash is invalid
  5. If the hash is already in a database, then that indicates hash re-use, it is invalid

Graph View

Backlinks