Hashcash

• PoWを初めて提案したとされるシステム
• E-mailのスパム対策, DoS攻撃対策
• Adam Backにより提案された

ヘッダ

• X-Hashcashヘッダを導入
• 例:

• ver: Hashcash format version, 1 (which supersedes version 0).
• bits: Number of “partial pre-image” (zero) bits in the hashed code.
• date: The time that the message was sent, in the format YYMMDD[hhmmss].
• resource: Resource data string being transmitted, e.g., an IP address or email address.
• ext: Extension (optional; ignored in version 1).
• rand: String of random characters, encoded in base-64 format.
• counter: Binary counter, encoded in base-64 format.