building and signing tx

Building and signing transactions

Transactions vary in complexity, depending on their intended outcomes, but all transactions share a number of attributes:

• Input - contains funds that are spent by the transaction. It is simply the output of an earlier transaction. A transaction can have multiple inputs.
• Output - determine where the funds go to. An output is given by a payment address and an amount. A transaction can have multiple outputs.
• Payment address - an address that can receive payments, This is the only type of addresses that can be specified in a transaction output.
• Payment and stake key pairs - sets of files containing a public verification key and a private signing key.
• Invalid-before - The slot that the transaction is valid from. This can only be specified in the Allegra era and onwards.
• Invalid-hereafter - represents a slot, or deadline by which a transaction must be submitted. This is an absolute slot number, rather than a relative one, which means that the --invalid-hereafter value should be greater than the current slot number. A transaction becomes invalid at the invalid-hereafter slot.
• Era - Transactions can differ between the eras (e.g have new features such as multi-assets) so we must specify the era we are currently in.

To create a transaction in the shelley era we need to follow this process:

• Get the protocol parameters
• Draft the transaction
• Calculate the fee
• Define the validity interval for the transaction
• Build the transaction
• Sign the transaction
• Submit the transaction

Protocol parameters

Query and save the parameters in protocol.json

cardano-cli query protocol-parameters \
  --mainnet \
  --out-file protocol.json

Draft the transaction

In the draft tx-out, ttl and fee can be zero. Later we use the out-file tx.draft to calculate the fee

cardano-cli transaction build-raw \
  --shelley-era \
  --tx-in <TxHash>#<TxIx> \
  --tx-out <Address>+<Lovelace> \
  --tx-out <Address>+0 \
  --invalid-hereafter 0
  --fee 0 \
  --out-file tx.draft

Calculate the fee

Use tx.draft as tx-body-file. Witnesses are the amount of keys that must sign the transaction.

cardano-cli transaction calculate-min-fee \
  --tx-body-file tx.draft \
  --tx-in-count 1 \
  --tx-out-count 2 \
  --witness-count 1 \
  --byron-witness-count 0 \
  --mainnet \
  --protocol-params-file protocol.json

For example:

> 167965

Determine the validity interval

When building and submitting a transaction in the shelley era you need to check the current tip of the blockchain, for example, if the tip is slot 4000, you should set the invalid-hereafter to (4000 + N slots), so that you have enough time to build and submit a transaction. Submitting a transaction with a validity interval set in the past would result in a tx error.

cardano-cli query tip --mainnet

Look for the value of SlotNo

{
  "epoch": 259,
  "hash": "dbf5104ab91a7a0b405353ad31760b52b2703098ec17185bdd7ff1800bb61aca",
  "slot": 26633911,
  "block": 5580350
}

Therefore, if N = 200 slots

invalid-hereafter = 26633911 + 200
invalid-hereafter = 26634111

Build the transaction

This time we include all the parameters:

cardano-cli transaction build-raw \
  --tx-in 4e3a6e7fdcb0d0efa17bf79c13aed2b4cb9baf37fb1aa2e39553d5bd720c5c99#4 \
  --tx-out $(cat payment2.addr)+100000000 \
  --tx-out $(cat payment.addr)+999899832035 \
  --invalid-hereafter 26634111 \
  --fee 167965 \
  --out-file tx.raw

Signing

A transaction must prove that it has the right to spend its inputs. In the most common case, this means that a transaction must be signed by the signing keys belonging to the payment addresses of the inputs. If a transaction contains certificates, it must additionally be signed by somebody with the right to issue those certificates. For example, a stake address registration certificate must be signed by the signing key of the corresponding stake key pair.

cardano-cli transaction sign \
  --tx-body-file tx.raw \
  --signing-key-file payment.skey \
  --mainnet \
  --out-file tx.signed

Submit

cardano-cli transaction submit \
  --tx-file tx.signed \
  --mainnet