ECDSA Signing Lab

Elliptic Curve Scatter Plot 78 points + ∞

Curve points

G generator

Q public key

R nonce point

R' verify point

Why a tiny curve? Real Bitcoin uses secp256k1 (256-bit prime), but the math is identical. We use p = 97 so every number fits on screen and you can verify each step by hand.

🔑 Key Generation

Pick a random private key d and compute the public key Q = d × G

📦 DER Encoding How (r, s) becomes bytes in a scriptSig

Sequence/Integer tags

Length bytes

r value

s value

SIGHASH_ALL

Field	Hex	Value	Meaning

🔗 From Transaction to scriptSig The complete signing pipeline

In a real Bitcoin transaction, the message hash z is the double-SHA256 of the sighash preimage — a serialized snapshot of the transaction being signed, with the spending script in place. Here's the full pipeline:

📄 Raw Transaction

→

Sighash Preimage

→

SHA256d

→

z (32 bytes)

→

ECDSA Sign

→

(r, s)

→

DER Encode

→

scriptSig

// What goes into scriptSig: <DER-encoded signature + sighash byte> <public key> // For our example:

⚡ ECDSA Signing Lab