| Property | Type | Description |
|---|---|---|
| algorithm | String |
Cryptographic algorithm used to generate the proof-of-work/CAPTCHA challenge |
| challenge | String |
Unique challenge string to be solved or signed by the client |
| maxnumber | Integer |
Maximum integer bound used for the proof-of-work search space |
| salt | String |
Random salt appended to the challenge string during verification |
| signature | String |
Server-generated signature validating the authenticity of the challenge |
| expires | Integer |
Unix timestamp indicating when the CAPTCHA challenge becomes invalid |