Skip to main content

Verifiable Random Function (VRF) System

Our gacha pack system uses Verifiable Random Function (VRF) technology to ensure completely fair and tamper-proof randomness for all pack openings.

Why This Is Secure​

The key security guarantee comes from timing: we cannot know your transaction signature until after you sign the transaction with your wallet. This means:

  1. We cannot predict the outcome — Your wallet generates a unique signature that we have no control over
  2. We cannot manipulate the result — By the time we receive your signature, your transaction is already confirmed on-chain
  3. We cannot retry for different results — The signature is permanently recorded on the blockchain before we calculate the roll

How It Works​

1. You Purchase a Pack​

When you buy a pack, you receive a unique memo (UUID) that identifies your pack.

2. You Sign the Transaction​

When opening the pack, your wallet generates a unique transaction signature. This signature is:

  • Cryptographically unique to your wallet and this specific transaction
  • Unpredictable before you sign
  • Permanently recorded on Solana before we ever see it

3. VRF Roll Calculation​

Once your transaction is confirmed, we combine your memo and transaction signature:

Input = SHA-256(memo + transaction_signature)

This input is processed through our VRF algorithm using our private key to generate:

  • A cryptographic proof (verifiable by anyone)
  • A deterministic hash that produces your roll number (1 to 100,000,000)

4. Roll Number Generation​

The VRF hash is converted to your final roll:

randomValue = first 8 bytes of VRF hash as BigInt
roll = (randomValue % 100,000,000) + 1

Verification​

Anyone can verify the fairness of any pack opening:

API Verification​

GET /api/vrf/verify?memo=YOUR_MEMO_HERE

This returns:

  • valid: Whether the VRF proof is cryptographically valid
  • rollMatches: Whether the stored roll matches the calculated roll
  • proof: The VRF proof for this pack
  • publicKey: Our VRF public key
  • transactionSignature: Your unique transaction signature

Manual Verification​

  1. Concatenate the memo + transaction signature
  2. Hash the combined string using SHA-256
  3. Use our public key to verify the VRF proof
  4. Extract the first 8 bytes of the proof hash as a BigInt
  5. Calculate: (value % 100,000,000) + 1

Technical Details​

PropertyValue
AlgorithmECVRF-SECP256K1-SHA256-TAI
StandardRFC 9381
Curvesecp256k1
InputSHA-256(memo + transaction_signature)
Output Range1 to 100,000,000
Library@simplevrf/ecvrf
Public KeyAvailable in verification responses

About the Algorithm​

We use ECVRF-SECP256K1-SHA256-TAI, a Verifiable Random Function based on elliptic curve cryptography as specified in RFC 9381.

Key properties:

  • Elliptic Curve (secp256k1): The same curve used by Bitcoin and Ethereum, providing battle-tested cryptographic security
  • SHA-256: Industry-standard hashing algorithm for input processing and proof generation
  • TAI (Try-And-Increment): The method used to hash arbitrary data to a point on the elliptic curve
  • Deterministic: The same input always produces the same output — no hidden randomness
  • Verifiable: Anyone with our public key can verify that the proof was generated correctly without knowing our private key

This implementation follows production-grade standards, ensuring our randomness is both cryptographically secure and independently verifiable.

Transparency​

Every pack opening includes:

  • Immutable transaction record on Solana blockchain
  • VRF proof stored and publicly verifiable
  • Open verification endpoint for all users

The bottom line: Because your transaction signature is recorded on-chain before we calculate your roll, it is mathematically impossible for us to influence the outcome.