Add 11 topics on tx signature

decoding/transaction-signing-00.mdx

@@ -0,0 +1,110 @@
+---
+title: "Step 0: Create Base Transaction"
+date: 2024-01-25
+lastmod: "2024-01-25"
+draft: false
+category: Transactions
+layout: TopicBanner
+order: 0
+icon: "FaClipboardList"
+images:
+    [
+        "/bitcoin-topics/static/images/topics/thumbnails/transaction-module/signature/tx-thumbnail-signature-0.jpg"
+    ]
+---
+
+In this step, we define the base structure of the transaction, which includes:
+
+-   Version (4 bytes)
+-   Marker/Flag (required for SegWit transactions)
+-   Locktime (4 bytes)
+
+Inputs, outputs, and witness data will be added in the next steps.
+
+<div className="dark:hidden w-full rounded-xl overflow-hidden full-width">
+    <SvgDisplay
+        src="/bitcoin-topics/static/images/topics/transactions/signature/signature6.svg"
+        width="100%"
+        height="auto"
+    />
+</div>
+<div className="hidden dark:block w-full rounded-xl overflow-hidden full-width">
+    <SvgDisplay
+        src="/bitcoin-topics/static/images/topics/transactions/signature/signature6.svg"
+        width="100%"
+        height="auto"
+    />
+</div>
+
+<ExpandableAlert
+    title="SegWit vs Legacy Transactions"
+    type="important"
+    expandable={true}
+    initialLines={3}
+>
+    If a transaction has at least one SegWit input (native or wrapped), it must
+    include: 
+    - Marker byte (0x00) 
+    - Flag byte (0x01)
+</ExpandableAlert>
+
+The transaction structure at this stage is:
+
+<CodeSnippet
+    language="text"
+    highlightLines={[4, 5, 6, 12]}
+    showLineNumbers={true}
+    code={`Transaction Breakdown:
+═══════════════════════════════════════════════════════════════════════════════════
+
+version: 01000000
+marker: 00
+flag: 01
+
+in: # We'll add inputs in the next step
+
+out: # We'll add outputs later
+
+locktime: 11000000`}
+/>
+
+## Code Implementation
+
+<CodeSnippet
+    code={`def create_basic_tx(
+    version: int,
+    inputs: list,
+    outputs: list,
+    locktime: int,
+    segwit: bool = True
+) -> bytes:
+    # 4-byte version in little-endian
+    tx_version = int_to_little_endian(version, 4)
+
+    # Marker + Flag for segwit (only if segwit=True)
+    marker_flag = b'\\x00\\x01' if segwit else b''
+
+    # Number of inputs/outputs (varint)
+    in_count = varint(len(inputs))
+    out_count = varint(len(outputs))
+
+    # Serialize inputs and outputs
+    serialized_inputs = b''.join(inputs)
+    serialized_outputs = b''.join(outputs)
+
+    # Locktime (4 bytes)
+    tx_locktime = int_to_little_endian(locktime, 4)
+
+    return (
+        tx_version +
+        marker_flag +
+        in_count +
+        serialized_inputs +
+        out_count +
+        serialized_outputs +
+        tx_locktime
+    )`}
+    language="python"
+/>
+
+Let's now add inputs and outputs in the next step!

decoding/transaction-signing-01.mdx

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+---
+title: "Step 1: Create Transaction Inputs"
+date: 2024-01-25
+lastmod: "2024-01-25"
+draft: false
+category: Transactions
+layout: TopicBanner
+order: 1
+icon: "FaClipboardList"
+images:
+    [
+        "/bitcoin-topics/static/images/topics/thumbnails/transaction-module/signature/tx-thumbnail-signature-1.jpg"
+    ]
+---
+
+Each input in a Bitcoin transaction must specify:
+
+-   Transaction ID (32 bytes): Points to the UTXO being spent
+-   Output Index (4 bytes): Which output from that transaction
+-   ScriptSig: Placeholder for the unlocking script
+-   Sequence (4 bytes): Usually 0xFFFFFFFF
+
+<div className="w-full rounded-xl overflow-hidden full-width">
+    <SvgDisplay
+        src="/bitcoin-topics/static/images/topics/transactions/signature/signature7.svg"
+        width="100%"
+        height="auto"
+    />
+</div>
+
+The following table summarizes our UTXOs (Transaction IDs shown in big-endian format):
+
+| Input | Transaction ID (big-endian)                                      | Output Index | Sequence |
+| ----- | ---------------------------------------------------------------- | ------------ | -------- |
+| #1    | 9f96add4e4db413543df3eea1781c3be62637f1e2dd44069fa99801a88f7f7ff | 0            | eeffffff |
+| #2    | 8ac60eb9575db5b2d987e29f301b5b819ea83a5c6579d282d189cc04b8e151ef | 1            | ffffffff |
+
+_Note: In the transaction serialization below, these Transaction IDs are converted to little-endian format as required by the Bitcoin protocol._
+
+<CodeSnippet
+    language="text"
+    highlightLines={[6, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20]}
+    showLineNumbers={true}
+    code={`Transaction Breakdown:
+═══════════════════════════════════════════════════════════════════════════════════
+
+Version: 01000000
+
+Input Count: 02
+
+input[0]:
+Previous TXID: fff7f7881a8099afa6940d42d1e7f6362bec38171ea3edf433541db4e4ad969f
+Output Index: 00000000
+ScriptSig Size: 00
+ScriptSig:
+Sequence: eeffffff
+
+input[1]:
+Previous TXID: ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a
+Output Index: 01000000
+ScriptSig Size: 00
+ScriptSig:
+Sequence: ffffffff
+
+Locktime: 11000000`}
+/>
+
+<ExpandableAlert
+    title="Why are scriptSig fields empty?"
+    type="info"
+    expandable={true}
+>
+    Transaction signing follows a specific order: 
+    1. First, we create the
+    transaction structure with empty scriptSig fields 
+    2. Then, we calculate the
+    signature hash (sighash) for each input 
+    3. Finally, we add the signatures to
+    create the complete transaction
+</ExpandableAlert>
+
+## Code Implementation
+
+<CodeSnippet
+    code={`def create_input(
+    txid: str,
+    vout: int,
+    script_sig: bytes = b'',
+    sequence: bytes = b'\\xff\\xff\\xff\\xff'
+) -> bytes:
+    # Convert txid from hex string and reverse (to little-endian)
+    txid_bytes = bytes.fromhex(txid)[::-1]
+
+    # Convert vout to 4 bytes, little-endian
+    vout_bytes = int_to_little_endian(vout, 4)
+
+    # Script length and script
+    script_sig_length = varint(len(script_sig))
+
+    return (
+        txid_bytes +           # 32 bytes
+        vout_bytes +          # 4 bytes
+        script_sig_length +   # 1 byte
+        script_sig +          # variable
+        sequence              # 4 bytes
+    )`}
+    language="python"
+/>
+
+<ExpandableAlert title="Helper Functions" type="info" expandable={true}>
+Two essential encoding functions:
+1. int_to_little_endian: Converts integers to little-endian byte format
+2. varint: Encodes variable-length integers used for counts and lengths
+
+<CodeSnippet 
+    code={`def int_to_little_endian(value: int, length: int) -> bytes:
+    """Convert an integer to little-endian bytes"""
+    return value.to_bytes(length, 'little')
+
+def varint(n: int) -> bytes:
+"""Encode an integer as a variable length integer"""
+if n < 0xfd:
+return bytes([n])
+elif n <= 0xffff:
+return b'\\xfd' + n.to_bytes(2, 'little')
+elif n <= 0xffffffff:
+return b'\\xfe' + n.to_bytes(4, 'little')
+else:
+return b'\\xff' + n.to_bytes(8, 'little')`}
+language="python"
+/>
+
+</ExpandableAlert>

decoding/transaction-signing-02.mdx

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+---
+title: "Step 2: Create Transaction Outputs"
+date: 2024-01-25
+lastmod: "2024-01-25"
+draft: false
+category: Transactions
+layout: TopicBanner
+order: 2
+icon: "FaClipboardList"
+images:
+    [
+        "/bitcoin-topics/static/images/topics/thumbnails/transaction-module/signature/tx-thumbnail-signature-2.jpg"
+    ]
+---
+
+Each output in a Bitcoin transaction requires:
+
+-   Amount (8 bytes): Value in satoshis
+-   ScriptPubKey: Locking script that defines spending conditions
+
+<div className="w-full rounded-xl overflow-hidden full-width">
+    <SvgDisplay
+        src="/bitcoin-topics/static/images/topics/transactions/signature/signature8.svg"
+        width="100%"
+        height="auto"
+    />
+</div>
+
+---
+
+## Code Implementation
+
+<CodeSnippet
+    code={`def create_output(
+    amount: int,
+    script_pubkey: bytes
+) -> bytes:
+    # Amount (8 bytes, little-endian)
+    amount_bytes = int_to_little_endian(amount, 8)
+
+    return (
+        amount_bytes +          # value in satoshis
+        script_pubkey          # includes length prefix
+    )`}
+    language="python"
+/>
+
+The following table summarizes our outputs from test vector:
+
+| Output | Amount (BTC) | ScriptPubKey                                         |
+| ------ | ------------ | ---------------------------------------------------- |
+| #1     | 1.2          | 1976a9148280b37df378db99f66f85c95a783a76ac7a6d5988ac |
+| #2     | 2.2          | 1976a9143bde42dbee7e4dbe6a21b2d50ce2f0167faa815988ac |
+
+Our transaction structure at this stage is:
+
+<CodeSnippet
+    language="text"
+    highlightLines={[22, 24, 25, 26, 27, 29, 30, 31, 32]}
+    showLineNumbers={true}
+    code={`Transaction Breakdown:
+═══════════════════════════════════════════════════════════════════════════════════
+
+Version: 01000000
+
+Input Count: 02
+
+input[0]:
+Previous TXID: fff7f7881a8099afa6940d42d1e7f6362bec38171ea3edf433541db4e4ad969f
+Output Index: 00000000
+ScriptSig Size: 00
+ScriptSig:
+Sequence: eeffffff
+
+input[1]:
+Previous TXID: ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a
+Output Index: 01000000
+ScriptSig Size: 00
+ScriptSig:
+Sequence: ffffffff
+
+Output Count: 02
+
+output[0]:
+Amount: 202cb20600000000
+ScriptPubKey Size: 19
+ScriptPubKey: 76a9148280b37df378db99f66f85c95a783a76ac7a6d5988ac
+
+output[1]:
+Amount: 9093510d00000000
+ScriptPubKey Size: 19
+ScriptPubKey: 76a9143bde42dbee7e4dbe6a21b2d50ce2f0167faa815988ac
+
+Locktime: 11000000`}
+/>
+
+## Test Vector from BIP-143
+
+Let's test our code with the test vector from the <a href="https://github.com/bitcoin/bips/blob/58ffd93812ff25e87d53d1f202fbb389fdfb85bb/bip-0143.mediawiki?plain=1#L146" target="_blank">official BIP143 proposal</a>.
+
+<div className="flex justify-center items-center w-full full-width">
+    <iframe
+        src="https://trinket.io/embed/python3/e3098585e3c8"
+        width="100%"
+        height="100%"
+        style={{
+            border: "none",
+            margin: 0
+        }}
+        allowFullScreen
+        className="rounded-md shadow-sm h-[calc(50vh)]"
+    ></iframe>
+</div>