docs: transaction signing section

src/pages/stacks-blockchain/transactions.md

@@ -315,6 +315,36 @@ When called the Stacks Blockchain API or Node RPC API, transactions returned wil
 
 ## Signature and Verification
 
+Every transaction contains verifiable signature(s) that certify its authenticity. These signatures are generated by signing the transaction hash with the origin's private key. The Elliptic Curve Digital Signature Algorithm (ECDSA) is used for signing, with the curve set to secp256k1. The internal structure that encapsulates the signature is the spending condition. Spending conditions include several parameters including the public key hash, nonce, fee rate and the recoverable ECDSA signature.
+
+When constructing a transaction using the JS library, you can supply the private key and signing will be completed automatically. If you would like to sign the transaction manually, use the `TransactionSigner` class.
+
+Below are the steps taken to generate the signature internal to the transaction library.
+
+### Signing steps
+
+Step 1: Generate a transaction hash for signing. This is the SHA512/256 digest of the serialzed transaction before a signature is added.
+
+Step 2: Append the authorization type, fee amount and nonce to the transaction hash to create the signature hash.
+
+Step 3: Generate the SHA512/256 hash of the resulting string from the previous step.
+
+Step 4: Sign the hash using ECDSA and the origin private key.
+
+Step 5: Add the resulting recoverable ECDSA signature to the transaction spending condition.
+
+### Single signature transaction
+
+As the name implies a single signature transactions contains 1 signature from the origin account that authorizes a token spend or smart contract deploy/execution.
+
+### Multi-signature transaction
+
+For multi-sig accounts, multiple keys must sign the transaction for it to be valid.
+
+### Sponsored transaction
+
+A sponsored transaction is one where a second signer sets and pays the transaction fees. The origin must sign the transaction first before the sponsor signs.
+
 ## Broadcast
 
 With a serialized transaction in the [raw format](#raw-format), it can be broadcasted to the network using the [`POST /v2/transactions`](https://blockstack.github.io/stacks-blockchain-api/#operation/post_core_node_transactions) endpoint: