## Transactions The following subsections briefly document core transaction details. #### OP Codes {% autocrossref %} The op codes used in the pubkey scripts of standard transactions are: * Various data pushing op codes from 0x00 to 0x4e (1--78). These aren't typically shown in examples, but they must be used to push signatures and public keys onto the stack. See the link below this list for a description. * `OP_TRUE`/`OP_1` (0x51) and `OP_2` through `OP_16` (0x52--0x60), which push the values 1 through 16 to the stack. * [`OP_CHECKSIG`][op_checksig]{:#term-op-checksig}{:.term} consumes a signature and a full public key, and pushes true onto the stack if the transaction data specified by the SIGHASH flag was converted into the signature using the same ECDSA private key that generated the public key. Otherwise, it pushes false onto the stack. * [`OP_DUP`][op_dup]{:#term-op-dup}{:.term} pushes a copy of the topmost stack item on to the stack. * [`OP_HASH160`][op_hash160]{:#term-op-hash160}{:.term} consumes the topmost item on the stack, computes the RIPEMD160(SHA256()) hash of that item, and pushes that hash onto the stack. * [`OP_EQUAL`][op_equal]{:#term-op-equal}{:.term} consumes the top two items on the stack, compares them, and pushes true onto the stack if they are the same, false if not. * [`OP_VERIFY`][op_verify]{:#term-op-verify}{:.term} consumes the topmost item on the stack. If that item is zero (false) it terminates the script in failure. * [`OP_EQUALVERIFY`][op_equalverify]{:#term-op-equalverify}{:.term} runs `OP_EQUAL` and then `OP_VERIFY` in sequence. * [`OP_CHECKMULTISIG`][op_checkmultisig]{:#term-op-checkmultisig}{:.term} consumes the value (n) at the top of the stack, consumes that many of the next stack levels (public keys), consumes the value (m) now at the top of the stack, and consumes that many of the next values (signatures) plus one extra value. Then it compares each of public keys against each of the signatures looking for ECDSA matches; if n of the public keys match signatures, it pushes true onto the stack. Otherwise, it pushes false. The "one extra value" it consumes is the result of an off-by-one error in the Bitcoin Core implementation. This value is not used, so signature scripts prefix the secp256k1 signatures with a single OP_0 (0x00). * [`OP_RETURN`][op_return]{:#term-op-return}{:.term} terminates the script in failure when executed. A complete list of OP codes can be found on the Bitcoin Wiki [Script Page][wiki script], with an authoritative list in the `opcodetype` enum of the Bitcoin Core [script header file][core script.h] Note: Signature scripts are not signed, so anyone can modify them. This means signature scripts should only contain data and data-pushing op codes which can't be modified without causing the pubkey script to fail. Placing non-data-pushing op codes in the signature script currently makes a transaction non-standard, and future consensus rules may forbid such transactions altogether. (Non-data-pushing op codes are already forbidden in signature scripts when spending a P2SH pubkey script.) {% endautocrossref %} #### Address Conversion {% autocrossref %} The hashes used in P2PKH and P2SH outputs are commonly encoded as Bitcoin addresses. This is the procedure to encode those hashes and decode the addresses. First, get your hash. For P2PKH, you RIPEMD-160(SHA256()) hash a ECDSA public key derived from your 256-bit ECDSA private key (random data). For P2SH, you RIPEMD-160(SHA256()) hash a redeem script serialized in the format used in raw transactions (described in a [following sub-section][raw transaction format]). Taking the resulting hash: 1. Add an address version byte in front of the hash. The version bytes commonly used by Bitcoin are: * 0x00 for P2PKH addresses on the main Bitcoin network (mainnet) * 0x6f for P2PKH addresses on the Bitcoin testing network (testnet) * 0x05 for P2SH addresses on mainnet * 0xc4 for P2SH addresses on testnet 2. Create a copy of the version and hash; then hash that twice with SHA256: `SHA256(SHA256(version . hash))` 3. Extract the first four bytes from the double-hashed copy. These are used as a checksum to ensure the base hash gets transmitted correctly. 4. Append the checksum to the version and hash, and encode it as a base58 string: `BASE58(version . hash . checksum)` Bitcoin's base58 encoding, called [Base58Check][]{:#term-base58check}{:.term} may not match other implementations. Tier Nolan provided the following example encoding algorithm to the Bitcoin Wiki [Base58Check encoding](https://en.bitcoin.it/wiki/Base58Check_encoding) page: {% highlight c %} code_string = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz" x = convert_bytes_to_big_integer(hash_result) output_string = "" while(x > 0) { (x, remainder) = divide(x, 58) output_string.append(code_string[remainder]) } repeat(number_of_leading_zero_bytes_in_hash) { output_string.append(code_string[0]); } output_string.reverse(); {% endhighlight %} Bitcoin's own code can be traced using the [base58 header file][core base58.h]. To convert addresses back into hashes, reverse the base58 encoding, extract the checksum, repeat the steps to create the checksum and compare it against the extracted checksum, and then remove the version byte. {% endautocrossref %} #### Raw Transaction Format {% autocrossref %} Bitcoin transactions are broadcast between peers and stored in the block chain in a serialized byte format, called [raw format][]{:#term-raw-format}{:.term}. Bitcoin Core and many other tools print and accept raw transactions encoded as hex. The binary form of a raw transaction is SHA256(SHA256()) hashed to create its TXID. Bitcoin Core RPCs use a reversed byte order for hashes; see the [subsection about hash byte order][section hash byte order] for details. A sample raw transaction is the first non-coinbase transaction, made in [block 170][block170]. To get the transaction, use the `getrawtransaction` RPC with that transaction's txid (provided below): {% endautocrossref %} ~~~ > bitcoin-cli getrawtransaction \ f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16 0100000001c997a5e56e104102fa209c6a852dd90660a20b2d9c352423e\ dce25857fcd3704000000004847304402204e45e16932b8af514961a1d3\ a1a25fdf3f4f7732e9d624c6c61548ab5fb8cd410220181522ec8eca07d\ e4860a4acdd12909d831cc56cbbac4622082221a8768d1d0901ffffffff\ 0200ca9a3b00000000434104ae1a62fe09c5f51b13905f07f06b99a2f71\ 59b2225f374cd378d71302fa28414e7aab37397f554a7df5f142c21c1b7\ 303b8a0626f1baded5c72a704f7e6cd84cac00286bee000000004341041\ 1db93e1dcdb8a016b49840f8c53bc1eb68a382e97b1482ecad7b148a690\ 9a5cb2e0eaddfb84ccf9744464f82e160bfa9b8b64f9d4c03f999b8643f\ 656b412a3ac00000000 ~~~ A byte-by-byte analysis by Amir Taaki (Genjix) of this transaction is provided below. (Originally from the Bitcoin Wiki [OP_CHECKSIG page](https://en.bitcoin.it/wiki/OP_CHECKSIG); Genjix's text has been updated to use the terms used in this document.) ~~~ 01 00 00 00 version number 01 number of inputs (var_uint) input 0: c9 97 a5 e5 6e 10 41 02 previous tx hash (txid) fa 20 9c 6a 85 2d d9 06 60 a2 0b 2d 9c 35 24 23 ed ce 25 85 7f cd 37 04 00 00 00 00 previous output index 48 size of signature script (var_uint) Signature script for input 0: 47 push 71 bytes to stack 30 44 02 20 4e 45 e1 69 32 b8 af 51 49 61 a1 d3 a1 a2 5f df 3f 4f 77 32 e9 d6 24 c6 c6 15 48 ab 5f b8 cd 41 02 20 18 15 22 ec 8e ca 07 de 48 60 a4 ac dd 12 90 9d 83 1c c5 6c bb ac 46 22 08 22 21 a8 76 8d 1d 09 01 ff ff ff ff sequence number 02 number of outputs (var_uint) output 0: 00 ca 9a 3b 00 00 00 00 amount = 10.00000000 BTC 43 size of pubkey script (var_uint) Pubkey script for output 0: 41 push 65 bytes to stack 04 ae 1a 62 fe 09 c5 f5 1b 13 90 5f 07 f0 6b 99 a2 f7 15 9b 22 25 f3 74 cd 37 8d 71 30 2f a2 84 14 e7 aa b3 73 97 f5 54 a7 df 5f 14 2c 21 c1 b7 30 3b 8a 06 26 f1 ba de d5 c7 2a 70 4f 7e 6c d8 4c ac OP_CHECKSIG output 1: 00 28 6b ee 00 00 00 00 amount = 40.00000000 BTC 43 size of pubkey script (var_uint) Pubkey script for output 1: 41 push 65 bytes to stack 04 11 db 93 e1 dc db 8a 01 6b 49 84 0f 8c 53 bc 1e b6 8a 38 2e 97 b1 48 2e ca d7 b1 48 a6 90 9a 5c b2 e0 ea dd fb 84 cc f9 74 44 64 f8 2e 16 0b fa 9b 8b 64 f9 d4 c0 3f 99 9b 86 43 f6 56 b4 12 a3 ac OP_CHECKSIG 00 00 00 00 locktime ~~~