How to Cryptographically Prove Your Predictions Before They Unfold

The challenge of verifiably foreshadowing events—proving that a prediction was made well before it came to pass—was the subject of a Hacker News inquiry. The community offered a robust, cryptographically-backed method to achieve this, ensuring that when you eventually reveal your insights, you can definitively demonstrate they were recorded in their current form at an earlier date.

The Core Technique: Hash, Publish, Reveal

The most prominent solution discussed follows a clear, three-step process:

1. Document Your Foreshadowing:

   • First, carefully write down the information or predictions you wish to reveal later. This can be in any common document format, such as a PDF or a plain text file.
   • Important Consideration: The original post's comment emphasized making the text "pretty long." This is because if the content is too short, it might be theoretically possible for someone to guess or brute-force various short texts until they find one that matches your published hash.

2. Generate and Publicly Post a Cryptographic Hash:

   • Once your document is finalized, use a cryptographic hash function (like SHA256) to generate a unique hash string for the file. This hash acts as a digital fingerprint; any alteration to the document, however minor, will result in a completely different hash.
   • Publish this hash in a public, timestamped location. The discussion suggested several avenues:
     • Social media platforms (e.g., Mastodon, Reddit).
     • Online forums like Hacker News itself.
     • For a highly immutable and public record, even an advertisement in a national printed newspaper was mentioned.
   • Along with the hash, it's recommended to include a brief explanatory note, such as: “My prediction will be revealed on Dec 31 2025. Sha256 a9774a1a6ebf564cc408cfd86b5f2c06c13d830e143989714d958d34f325db13.”

3. Reveal the Original Document:

   • At the specified future date, or after the predicted event has occurred, publish the original document you created in the first step.
   • Anyone can then independently compute the hash of this revealed document and compare it to the hash you published earlier. A match provides strong cryptographic proof that the document, with its specific contents, existed in that exact form at or before the time the hash was initially made public.

Why This Method is Effective

This approach leverages key properties of cryptographic hash functions:

• Pre-image resistance: It is computationally infeasible to determine the original document (the "pre-image") from its hash.
• Collision resistance: It is computationally infeasible to find two different documents that produce the same hash output.

By publishing only the hash, you commit to the document's content without revealing it prematurely. The public, timestamped nature of the hash publication prevents you from backdating your claim or secretly modifying the document after the initial commitment. This method offers a reliable and verifiable way to foreshadow events and later prove the timing and content of your predictions.