Server Seed, Client Seed and Nonce Explained

Three terms appear in every provably fair discussion — server seed, client seed and nonce. Each solves a specific problem in the trust model. This guide defines all three, shows how they combine, and explains why removing any one breaks the system.

The three roles#

Server seed#

What it is: A random string generated by Duel.com's system when a new seed pair is created.

What you see before betting: The SHA-256 hash of the server seed — not the seed itself.

Why it is hidden: If you knew the server seed in advance, you could compute every future result on that pair. Hiding it while showing the hash lets the platform commit without giving you a lookahead advantage.

When it is revealed: On seed rotation. After revelation, hash it yourself and confirm it matches the pre-committed hash.

Client seed#

What it is: A random string representing your contribution to the outcome.

Who sets it: You can provide a custom value, or accept the default assigned by the platform.

Why it matters: Without a client seed, the platform could generate server seeds that produce unfavourable results and you would have no input to detect or prevent it. Your client seed makes the outcome depend on both parties.

Nonce#

What it is: A counter that starts at 0 and increments by 1 with each bet on the current seed pair.

Why it is needed: Without a nonce, the same server seed + client seed would produce the same result on every bet. The nonce ensures bet 1, bet 2 and bet 500 all generate different outcomes.

How they combine#

The general process (simplified):

combined = HMAC-SHA256(server_seed, client_seed + ":" + nonce)
result   = game_algorithm(combined)

Each game type — dice, crash, mines — maps the hash output to its specific outcome format. The inputs are always the same three values.

Full verification walkthrough: how to verify a bet.

What happens when each value changes#

Practical tips#

• Set a custom client seed on your first rotation — use a long random string
• Always verify the server seed hash after rotation
• Note the nonce when verifying a specific bet — off-by-one errors are common
• Do not treat nonce patterns as predictive — each value is independently determined
• Rotate seeds when you want to audit a block of bets, not to chase luck

Summary#

The server seed is the platform's committed randomness. The client seed is your input. The nonce ensures each bet is unique. Together they produce verifiable, tamper-evident results on every provably fair wager. Understand all three before verifying your first bet — and remember they prove fairness, not profitability.