Transactions

Tidecoin keeps Bitcoin’s UTXO transaction model and serialization shape: version, inputs, outputs, optional witness data, and locktime. The protocol differences are in the scripts, witness programs, and post-quantum signature/public-key material carried by those scripts.

This page defines transaction structure. It is not the signature scheme registry; for schemes and byte sizes, see Scheme Registry. It is not the script reference; for opcodes and witness program semantics, see Scripts.

Serialized structure

Non-witness transactions use the classic form:


nVersion
vin[]
vout[]
nLockTime

Transactions with witness data use the segwit serialization form:


nVersion
marker
flag
vin[]
vout[]
witnesses[]
nLockTime

The txid is the transaction hash without witness data. The witness hash or wtxid includes the witness serialization. Tidecoin preserves this Bitcoin distinction.

Inputs

Each input spends a previous output and carries unlocking data:


previous_txid
previous_output_index
scriptSig
nSequence

For legacy key-hash spends, scriptSig commonly carries the signature stack data. For witness spends, scriptSig is empty or carries only the nested redeem script, and the actual signatures/scripts are in the input witness.

Outputs

Each output carries an amount and a locking script:


nValue
scriptPubKey

Common Tidecoin output templates include:

Output type	ScriptPubKey shape	Address family
Key hash	`OP_DUP OP_HASH160 <20-byte key hash> OP_EQUALVERIFY OP_CHECKSIG`	Base58Check P2PKH-style
Script hash	`OP_HASH160 <20-byte script hash> OP_EQUAL`	Base58Check P2SH-style
Witness v0 key hash	`OP_0 <20-byte key hash>`	bech32 witness v0
Witness v0 script hash	`OP_0 <32-byte script hash>`	bech32 witness v0
Witness v1 script hash 512	`OP_1 <64-byte SHA512(witness_script)>`	bech32m PQ witness v1

Witness v1 script-hash-512 outputs are implemented but gated by the post-AuxPoW rule set on mainnet.

PQ public keys and signatures

Tidecoin identifies a PQ signature scheme through the serialized public key. The public key layout is:


scheme_prefix || raw_scheme_public_key

The signature does not carry a separate Tidecoin scheme prefix. The verifier reads the public-key prefix, selects the scheme, and verifies the signature bytes for that scheme.

For script paths that use a standard sighash byte, the signature stack item is:


scheme_signature || sighash_type

The sighash byte is part of script transaction-signing semantics. It is not part of the raw Falcon or ML-DSA signature passed to the scheme verifier.

Typical witness stacks

Spend path	Witness stack shape
Witness v0 key hash	`<signature+sighash> <prefixed_pq_public_key>`
Witness v0 script hash	`<satisfying stack items...> <witness_script>`
Witness v1 script hash 512	`<satisfying stack items...> <witness_script>`

Inside witness scripts, OP_CHECKSIG and multisig-style constructions consume PQ signatures and prefixed PQ public keys according to the active signature verification mode.

Size drivers

PQ transactions are larger than classical ECDSA/Schnorr transactions because public keys and signatures are larger. The most important size drivers are:

Scheme	Serialized public key bytes	Padded or fixed signature bytes	Script signature bytes with sighash
Falcon-512	898	666	667
Falcon-1024	1,794	1,280	1,281
ML-DSA-44	1,313	2,420	2,421
ML-DSA-65	1,953	3,309	3,310
ML-DSA-87	2,593	4,627	4,628

Fee estimation and integration code should calculate sizes from the actual script and witness stack, not from classical Bitcoin assumptions.

Sighash semantics

Witness v0 follows the Bitcoin-style witness sighash path. Witness v1 P2WSH-512 uses the Tidecoin witness-v1 signature version and SHA-512 hashing internally for the transaction digest components. The accepted sighash types remain the standard transaction-signing modes such as SIGHASH_ALL, SIGHASH_NONE, SIGHASH_SINGLE, and SIGHASH_ANYONECANPAY.

Source of truth

Topic	Source
Transaction serialization and witness hashes	`../tidecoin/src/primitives/transaction.h`, `../tidecoin/src/core_write.cpp`
Address and script templates	`../tidecoin/src/addresstype.cpp`, `../tidecoin/src/script/solver.cpp`
PQ key/signature sizes	`../tidecoin/src/pq/pq_scheme.h`
Signature dispatch	`../tidecoin/src/key.cpp`, `../tidecoin/src/pubkey.cpp`, `../tidecoin/src/pq/pq_api.h`
Witness v1 signature hashing	`../tidecoin/src/script/interpreter.cpp`