BA-05 · LESSON 11

Raw transaction inputs and outputs

KEY DEFINITIONS

Terms used in this lesson

Outpoint: A transaction ID plus output number that identifies one exact prior output.
Transaction ID: The identifier produced by hashing a Bitcoin transaction’s non-witness serialization.
HASH256: Bitcoin's name for applying SHA-256 twice to the same byte sequence.
Witness: Signatures, scripts, or other data supplied to satisfy a Bitcoin output’s spending condition.

Decode outpoints, ScriptSig, sequence, amounts, ScriptPubKeys, CompactSize lengths, and locktime directly from serialized transaction bytes.

55 min Difficulty 2/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · raw transaction fieldsTyped byte boundaries reveal every raw input and outputSelect any state to inspect its exact role.

RELATIONSHIP MAPInputs, rule, and outputs

01
VERSION AND COUNT02000000 01
Read fixed version, then canonical CompactSize input count.
02
OUTPOINTTxid bytes and vout index
The outpoint names one exact previous output; its amount is not stored in the input.
03
SCRIPTSIG AND SEQUENCELength, bytes, ffffffff
A bad length shifts every later boundary and must fail parsing.
04
OUTPUT8-byte amount + ScriptPubKey
Outputs allocate satoshis to newly created locking conditions.
05
LOCKTIME AND TXIDExact end then HASH256
Canonical bytes and exact consumption produce the transaction identifier.

Rule shown: Counts, lengths, byte order, previous-output context, and exact object consumption determine one transaction interpretation.

STAGE 1 OF 5VERSION AND COUNT: 02000000 01

Read fixed version, then canonical CompactSize input count.

Governing relationship: Counts, lengths, byte order, previous-output context, and exact object consumption determine one transaction interpretation. Complete path: 1. VERSION AND COUNT, 02000000 01. Read fixed version, then canonical CompactSize input count. 2. OUTPOINT, Txid bytes and vout index. The outpoint names one exact previous output; its amount is not stored in the input. 3. SCRIPTSIG AND SEQUENCE, Length, bytes, ffffffff. A bad length shifts every later boundary and must fail parsing. 4. OUTPUT, 8-byte amount + ScriptPubKey. Outputs allocate satoshis to newly created locking conditions. 5. LOCKTIME AND TXID, Exact end then HASH256. Canonical bytes and exact consumption produce the transaction identifier.

1. State transitionWhat exists, what changes, and what results

BEFORE

A parser receives a version-2 transaction with CompactSize counts 01 input and 02 outputs.

MECHANISM

Version is a four-byte little-endian signed integer in serialization. The next CompactSize value states exactly how many input records must follow.

AFTER

Raw transaction decoding is a sequence of typed boundaries, not a search for recognizable hex patterns.

Text equivalent: Starting from A parser receives a version-2 transaction with CompactSize counts 01 input and 02 outputs. The mechanism begins when Version is a four-byte little-endian signed integer in serialization. The next CompactSize value states exactly how many input records must follow. The resulting lesson is Raw transaction decoding is a sequence of typed boundaries, not a search for recognizable hex patterns.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Read version and input count

Version is a four-byte little-endian signed integer in serialization. The next CompactSize value states exactly how many input records must follow.

Complete path: 1. Read version and input count: Version is a four-byte little-endian signed integer in serialization. The next CompactSize value states exactly how many input records must follow. 2. Decode each outpoint: Read 32 transaction-identifier bytes and a four-byte little-endian vout. Display conventions reverse the identifier bytes, but the output index remains an ordinary integer. 3. Bound ScriptSig and sequence: CompactSize gives the ScriptSig byte length, not an opcode count. After consuming exactly that many bytes, read four sequence bytes and interpret replacement or relative-lock semantics in context. 4. Decode outputs: Each output begins with an unsigned eight-byte little-endian satoshi amount, followed by a CompactSize script length and exact ScriptPubKey bytes. 5. Finish with locktime and identifiers: After the declared output count, read four-byte nLockTime and require exact end of object. HASH256 of the canonical non-witness serialization produces the txid displayed with digest bytes reversed.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

Counts, lengths, byte order, value bounds, canonical encodings, and exact object consumption must all pass before the structured transaction or txid is trusted.

CHANGED CONDITION

A ScriptSig length one byte too long shifts sequence and every later field. A parser that still returns a plausible transaction has accepted a different byte interpretation.

Important distinction: An input contains the amount being spent. An input contains an outpoint and spending data. Its amount and locking condition come from the referenced previous output and must be supplied or looked up for validation and fee calculation.

Text equivalent: The accepted path is enforced by Counts, lengths, byte order, value bounds, canonical encodings, and exact object consumption must all pass before the structured transaction or txid is trusted. If the required condition changes, A ScriptSig length one byte too long shifts sequence and every later field. A parser that still returns a plausible transaction has accepted a different byte interpretation.

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Learn the idea

A raw legacy transaction serializes version, a CompactSize input count, each input, a CompactSize output count, each output, and locktime. An input contains a 32-byte previous transaction identifier in serialized order, four-byte output index called vout, CompactSize ScriptSig length, ScriptSig bytes, and four-byte sequence. An output contains an eight-byte satoshi amount and a CompactSize-prefixed ScriptPubKey.

GUIDED EXPLANATION1/5 ideas inspected

Read version and input count

Version is a four-byte little-endian signed integer in serialization. The next CompactSize value states exactly how many input records must follow.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“An input contains the amount being spent.”

An input contains an outpoint and spending data. Its amount and locking condition come from the referenced previous output and must be supplied or looked up for validation and fee calculation.

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