- [[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: - ```hashcash-mailheader, X-Hashcash: 1:20:1303030600:[email protected]::McMybZIhxKXu57jd:ckvi ``` - 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[hhmm[[ss]]]. - 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.