19 — Transaction proofs — wallet ownership and replay prevention

NeedMoreCoin replaces the old shared-secret HMAC lesson with a Schnorr-style proof that can be checked using a public value. The wallet owner keeps the secret; validators use the public value.

A transaction proof is bound to sender, receiver, amount, fee, and transaction nonce. The bundled adapter performs secure random generation, 3072-bit MODP Group 15 subgroup calculations, and a SHA-256 Fiat-Shamir challenge. In this example the context-bound non-interactive proof acts as the transaction-signing mechanism.

The program deliberately changes a valid 25-coin transfer to 250 while reusing the old proof. Verification fails because the context changed, and the block hash also differs.

A valid signature is still not enough to prevent replay. Each sender stores the last accepted nonce. After Alice uses nonce 1, the next acceptable value is 2; re-submitting the old nonce-1 transaction is rejected.

The English sentence form keeps the signed context visible:

amountone save 25
feeone save transactionfee
nonceone save 1
requiredone save amountone
add feeone to requiredone
contextone save aliceaddress sends amountone coins to bobaddress fee feeone nonce nonceone
proofone save alicesecret contextone zero knowledge proof make
signatureonevalid save aliceaddress proofone contextone zero knowledge verify

nme run examples/needmorecoin-sentence.en

Next, 20 — Full-chain validation stops trusting construction- time variables and recomputes the entire chain from genesis state.