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5.2: Resending a Transaction with RBF

NOTE: This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.

If your Bitcoin transaction is stuck, and you're sender, you can resend it using RBF (replace-by-fee). However, that's not all that RBF can do: it's generally a powerful and multipurpose feature that allows Bitcoin senders to recreate transactions for a variety of reasons.

VERSION WARNING: This is an innovation from Bitcoin Core v 0.12.0, which means that by now most miners should be using it. However, it only reached full maturity in the Bitcoin core wallet with Bitcoin Core v 0.14.0.

Opt-In for RBF

RBF is an opt-in Bitcoin feature. Transactions are only eligible for using RBF if they've been created with a special RBF flag. This is done by setting any of the transaction's UTXO sequence numbers (which are typically set automatically), so that it's more than 0 and less than 0xffffffff-1 (4294967294).

This is accomplished simply by adding a sequence variable to your UTXO inputs:

$ rawtxhex=$(bitcoin-cli -named createrawtransaction inputs='''[ { "txid": "'$utxo_txid'", "vout": '$utxo_vout', "sequence": 1 } ]''' outputs='''{ "'$recipient'": 0.1, "'$changeaddress'": 0.9 }''')

You should of course sign and send your transaction as usual:

$ signedtx=$(bitcoin-cli -named signrawtransaction hexstring=$rawtxhex | jq -r '.hex')
$ bitcoin-cli -named sendrawtransaction hexstring=$signedtx
7218b78ad4853eb957b610033b8e1ef48b01d948e0ec5dbf79f12caebc2b17e2

Now, when you look at your transaction, you should see something new: the bip125-replaceable line, which has always been marked no before, is now marked yes:

$ bitcoin-cli -named gettransaction txid=7218b78ad4853eb957b610033b8e1ef48b01d948e0ec5dbf79f12caebc2b17e2
{
  "amount": -0.10000000,
  "fee": 0.00000000,
  "confirmations": 0,
  "trusted": true,
  "txid": "7218b78ad4853eb957b610033b8e1ef48b01d948e0ec5dbf79f12caebc2b17e2",
  "walletconflicts": [
  ],
  "time": 1491603320,
  "timereceived": 1491603320,
  "bip125-replaceable": "yes",
  "details": [
    {
      "account": "",
      "address": "n2eMqTT929pb1RDNuqEnxdaLau1rxy3efi",
      "category": "send",
      "amount": -0.10000000,
      "vout": 0,
      "fee": 0.00000000,
      "abandoned": false
    }
  ],
  "hex": "02000000014e843e22cb8ee522fbf4d8a0967a733685d2ad92697e63f52ce41bec8f7c8ac0010000006b483045022100834731cd64efcc078d6c3e59cf0963599ffbc44722b7851b0404bb68e4a1fec70220759a0887ea791592c8119bbe61842eb3850a20cdf8433b4ba00d4ead752facfe012103456575f59a127a4c3e79c23f185899fa0a9ccd40162d05617fb112fa31bd14e5010000000280969800000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac804a5d05000000001976a914c101d8c34de7b8d83b3f8d75416ffaea871d664988ac00000000"
}

The bip125-replaceable flag will stay yes until the transaction receives confirmations. At that point, it is no longer replacable.

Should I trust transactions with no confirmations? No, never. This was true before RBF and it was true after RBF. Transactions must receive confirmations before they are trustworthy. This is especially true if a transaction is marked as bip125-replaceable, because then it can be ... replaced.

SEQUENCE NOTE (I): This is the first use of the nSequence value in Bitcoin. You can set it between 1 and 0xffffffff-2 (4294967293) and enable RBF, but if you're not careful you can run up against the parallel use of nSequence for relative timelocks. We suggest always setting it to "1", which is what Bitcoin Core does, but the other option is to set it to a value between 0xf0000000 (4026531840) and 0xffffffff-2 (4294967293). Setting it to "1" effectively makes relative timelocks irrelevent and setting it to 0xf0000000 or higher deactivates them. This is all explained further in §9.3: Using CSV in Scripts. For now, just choose one of the non-conflicting values for nSequence.

Optional: Always Opt-In for RBF

If you prefer, you can always opt in for RBF. Do so by running your bitcoind with the -walletrbf command. Once you've done this (and restarted your bitcoind), then all UTXOs should have a lower sequence number and the transaction should be marked as bip125-replaceable.

Note the following example generated by bitcoind, where the UTXO indeed uses a sequence number of "1":

{
  "txid": "d261b9494eb29084f668e1abd75d331fc2d6525dd206b2f5236753b5448ca12c",
  "hash": "d261b9494eb29084f668e1abd75d331fc2d6525dd206b2f5236753b5448ca12c",
  "size": 226,
  "vsize": 226,
  "version": 2,
  "locktime": 0,
  "vin": [
    {
      "txid": "4075dbf84303c01adcb0b36cd2c164e2b447192c2d9fbf5fde3b99d0ac7e64b6",
      "vout": 1,
      "scriptSig": {
        "asm": "3045022100b3a0d66abe3429f81a6dc397369d6ac9cb025a2243b68649d95665967fe4365b022038cf037aaab9368268e97203494d1b542e83101e6aaaf97957daf70dee6ee0af[ALL] 022615f4b6417b991530df4bc8c8ee10b8925c741773fead7a5edd89337caeba53",
        "hex": "483045022100b3a0d66abe3429f81a6dc397369d6ac9cb025a2243b68649d95665967fe4365b022038cf037aaab9368268e97203494d1b542e83101e6aaaf97957daf70dee6ee0af0121022615f4b6417b991530df4bc8c8ee10b8925c741773fead7a5edd89337caeba53"
      },
      "sequence": 1
    }
  ],
  "vout": [
    {
      "value": 0.10000000,
      "n": 0,
      "scriptPubKey": {
        "asm": "OP_DUP OP_HASH160 e7c1345fc8f87c68170b3aa798a956c2fe6a9eff OP_EQUALVERIFY OP_CHECKSIG",
        "hex": "76a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac",
        "reqSigs": 1,
        "type": "pubkeyhash",
        "addresses": [
          "n2eMqTT929pb1RDNuqEnxdaLau1rxy3efi"
        ]
      }
    }, 
    {
      "value": 0.90000000,
      "n": 1,
      "scriptPubKey": {
        "asm": "OP_DUP OP_HASH160 20219e4f3c6bc0f6524d538009e980091b3613e8 OP_EQUALVERIFY OP_CHECKSIG",
        "hex": "76a91420219e4f3c6bc0f6524d538009e980091b3613e888ac",
        "reqSigs": 1,
        "type": "pubkeyhash",
        "addresses": [
          "miSrC3FvkPPZgqqvCiQycq7io7wTSVsAFH"
        ]
      }
    }
  ]
}

VERSION WARNING: The walletrbf flag require Bitcoin Core v.0.14.0.

Understand How RBF Works

The RBF functionality is based on BIP 125, which lists the following rules for using RBF:

  1. The original transactions signal replaceability explicitly or through inheritance as described in the above Summary section.

This means that the sequence number must be set to less than 0xffffffff-1. (4294967294), or the same is true of unconfirmed parent transactions.

  1. The replacement transaction pays an absolute higher fee than the sum paid by the original transactions.
  2. The replacement transaction does not contain any new unconfirmed inputs that did not previously appear in the mempool. (Unconfirmed inputs are inputs spending outputs from currently unconfirmed transactions.)
  3. The replacement transaction must pay for its own bandwidth in addition to the amount paid by the original transactions at or above the rate set by the node's minimum relay fee setting. For example, if the minimum relay fee is 1 satoshi/byte and the replacement transaction is 500 bytes total, then the replacement must pay a fee at least 500 satoshis higher than the sum of the originals.
  4. The number of original transactions to be replaced and their descendant transactions which will be evicted from the mempool must not exceed a total of 100 transactions.

What is a BIP? A BIP is a Bitcoin Improvement Proposal. It's an in-depth suggestion for a change to the Bitcoin Core code. Often, when a BIP has been sufficiently discussed and updated, it will become an actual part of the Bitcoin Core code. For example, BIP 125 was implemented in Bitcoin Core 0.12.0.

The other thing to understand about RBF is that in order to use it, you must double-spend, reusing one or more the same UTXOs. Just sending another transaction with a different UTXO to the same recipient won't do the trick (and will likely result in your losing money). Instead, you must purposefully create a conflict, where the same UTXO is used in two different transactions.

Faced with this conflict, the miners will know to use the one with the higher fee, and they'll be incentivized to do so by that higher fee.

What is a double-spend? A double-spend occurs when someone sends the same electronic funds to two different people (or, to the same person twice, in two different transactions). This is a central problem for any e-cash system. It's solved in Bitcoin by the immutable ledger: once a transaction is sufficiently confirmed, no miners will verify transactions that reuse the same UTXO. However, it's possible to double-spend before a transaction has been confirmed — which is why you always want one or more confirmations before you finalize a transaction. In the case of RBF, you purposefully double-spend because an initial transaction has stalled, and the miners accept your double-spend if you meet the specific criteria laid out by BIP 125.

WARNING: Some early discussions of this policy suggested that the nSequence number also be increased. This in fact was the intended use of nSequence in its original form. This is not a part of the published policy in BIP 125. In fact, increasing your sequence number can accidentally lock your transaction with a relative timelock, unless you use sequence numbers in the range of 0xf0000000 (4026531840) to 0xffffffff-2 (4294967293).

Replace a Transaction the Hard Way: By Hand

In order to create an RBF transaction by hand, all you have to do is create a raw transaction that: (1) replaces a previous raw transaction that opted-in to RBF and that is not confirmed; (2) reuses one or more of the same UTXOs; (3) increases fees; and (4) pays the minimum bandwidth of both transactions [which already may be taken care of by (3)].

The following example just reuses our existing variables, but decreases the amount sent to the change address, to increase the fee from the accidental 0 BTC of the original transaction to an overly generous 0.01 BTC in the new transaction:

$ rawtxhex=$(bitcoin-cli -named createrawtransaction inputs='''[ { "txid": "'$utxo_txid'", "vout": '$utxo_vout', "sequence": 1 } ]''' outputs='''{ "'$recipient'": 0.1, "'$changeaddress'": 0.89 }''')

We of course must re-sign it and resend it:

$ signedtx=$(bitcoin-cli -named signrawtransaction hexstring=$rawtxhex | jq -r '.hex')
$ bitcoin-cli -named sendrawtransaction hexstring=$signedtx
959b0b0f4c8350e9038279dfe0f5ae7b165660cc1281e37bea08d0bd084edb39

After several blocks have been created, the original transaction continues to hang around:

$ bitcoin-cli -named gettransaction txid=7218b78ad4853eb957b610033b8e1ef48b01d948e0ec5dbf79f12caebc2b17e2
{
  "amount": -0.10000000,
  "fee": 0.00000000,
  "confirmations": -5,
  "trusted": false,
  "txid": "7218b78ad4853eb957b610033b8e1ef48b01d948e0ec5dbf79f12caebc2b17e2",
  "walletconflicts": [
    "959b0b0f4c8350e9038279dfe0f5ae7b165660cc1281e37bea08d0bd084edb39"
  ],
  "time": 1491603320,
  "timereceived": 1491603320,
  "bip125-replaceable": "yes",
  "details": [
    {
      "account": "",
      "address": "n2eMqTT929pb1RDNuqEnxdaLau1rxy3efi",
      "category": "send",
      "amount": -0.10000000,
      "vout": 0,
      "fee": 0.00000000,
      "abandoned": false
    }
  ],
  "hex": "02000000014e843e22cb8ee522fbf4d8a0967a733685d2ad92697e63f52ce41bec8f7c8ac0010000006b483045022100834731cd64efcc078d6c3e59cf0963599ffbc44722b7851b0404bb68e4a1fec70220759a0887ea791592c8119bbe61842eb3850a20cdf8433b4ba00d4ead752facfe012103456575f59a127a4c3e79c23f185899fa0a9ccd40162d05617fb112fa31bd14e5010000000280969800000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac804a5d05000000001976a914c101d8c34de7b8d83b3f8d75416ffaea871d664988ac00000000"
}

Note that bitcoin-cli recognizes that there's a conflict with another transaction in the walletconflicts section. Also note that this transaction is now listed with negative confirmations, which marks how long it's been since the opposing double-spend was confirmed.

Meanwhile, the new transaction worked fine:

$ bitcoin-cli -named gettransaction txid=959b0b0f4c8350e9038279dfe0f5ae7b165660cc1281e37bea08d0bd084edb39
{
  "amount": -0.10000000,
  "fee": -0.01000000,
  "confirmations": 5,
  "blockhash": "00000000000006eeb468791e5ee0d86613c03acd871ef7d89c25fd28474754d5",
  "blockindex": 20,
  "blocktime": 1491603862,
  "txid": "959b0b0f4c8350e9038279dfe0f5ae7b165660cc1281e37bea08d0bd084edb39",
  "walletconflicts": [
    "7218b78ad4853eb957b610033b8e1ef48b01d948e0ec5dbf79f12caebc2b17e2"
  ],
  "time": 1491603673,
  "timereceived": 1491603673,
  "bip125-replaceable": "no",
  "details": [
    {
      "account": "",
      "address": "n2eMqTT929pb1RDNuqEnxdaLau1rxy3efi",
      "category": "send",
      "amount": -0.10000000,
      "vout": 0,
      "fee": -0.01000000,
      "abandoned": false
    }
  ],
  "hex": "02000000014e843e22cb8ee522fbf4d8a0967a733685d2ad92697e63f52ce41bec8f7c8ac0010000006a47304402207fea4a11db8576257b9d9e104aa07cb3d3ae6a42e38dd7126111276ca5b45daa0220594a3553cc278c43fd015b35029d5b9596d4ac9f36d3d20fb1a8c9efface5c50012103456575f59a127a4c3e79c23f185899fa0a9ccd40162d05617fb112fa31bd14e5020000000280969800000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac40084e05000000001976a914c101d8c34de7b8d83b3f8d75416ffaea871d664988ac00000000"
}

Our recipients have their money, and the original, failed transaction will eventually fall out of the mempool.

Replace a Transaction the Easy Way: By bumpfee

Raw transactions are very powerful, and you can do a lot of interesting things by combining them with RBF. However, sometimes all you want to do is free up a transaction that's been hanging. You can now do that with a simple command, bumpfee.

For example, to increase the fee of transaction 4460175e8276d5a1935f6136e36868a0a3561532d44ddffb09b7cb878f76f927 you would run:

$ bitcoin-cli -named bumpfee txid=4460175e8276d5a1935f6136e36868a0a3561532d44ddffb09b7cb878f76f927
{
  "txid": "75208c5c8cbd83081a0085cd050fc7a4064d87c7d73176ad9a7e3aee5e70095f",
  "origfee": 0.00000000,
  "fee": 0.00022600,
  "errors": [
  ]
}

The result is the automatic generation of a new transaction that has a fee determined by your bitcoin.conf file:

$ bitcoin-cli -named gettransaction txid=75208c5c8cbd83081a0085cd050fc7a4064d87c7d73176ad9a7e3aee5e70095f
{
  "amount": -0.10000000,
  "fee": -0.00022600,
  "confirmations": 0,
  "trusted": false,
  "txid": "75208c5c8cbd83081a0085cd050fc7a4064d87c7d73176ad9a7e3aee5e70095f",
  "walletconflicts": [
    "4460175e8276d5a1935f6136e36868a0a3561532d44ddffb09b7cb878f76f927"
  ],
  "time": 1491605676,
  "timereceived": 1491605676,
  "bip125-replaceable": "yes",
  "replaces_txid": "4460175e8276d5a1935f6136e36868a0a3561532d44ddffb09b7cb878f76f927",
  "details": [
    {
      "account": "",
      "address": "n2eMqTT929pb1RDNuqEnxdaLau1rxy3efi",
      "category": "send",
      "amount": -0.10000000,
      "vout": 0,
      "fee": -0.00022600,
      "abandoned": false
    }
  ],
  "hex": "02000000014e843e22cb8ee522fbf4d8a0967a733685d2ad92697e63f52ce41bec8f7c8ac0020000006b48304502210094e54afafce093008172768d205d99ee2e9681b498326c077f0b6a845d9bbef702206d90256d5a2edee3cab1017b9b1c30b302530b0dd568e4af6f2d35380bbfaa280121029f39b2a19943fadbceb6697dbc859d4a53fcd3f9a8d2c8d523df2037e7c32a71010000000280969800000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac38f25c05000000001976a914c101d8c34de7b8d83b3f8d75416ffaea871d664988ac00000000"
}

VERSION WARNING: The bumpfee RPC require Bitcoin Core v.0.14.0.

Summary: Resending a Transaction with RBF

If a transaction is stuck, and you don't want to wait for it to expire entirely, if you opted-in to RBF, then you can double-spend using RBF to create a replacement transaction (or just use bumpfee).

What is the power of RBF? Obviously, RBF is very helpful if you created a transaction with too low of a fee and you need to get those funds through. However, the ability to generally replace unconfirmed transactions with updated ones has more power than just that (and is why you might want to continue using RBF with raw transactions, even following the advent of bumpfee).

For example, you might send a transaction, and then before it's confirmed, combine it with a second transaction. This allows you to compress multiple transactions down into a single one, decreasing overall fees. It might also offer benefits to privacy. There are other reasons to use RBF too, for smart contracts or transaction cut-throughs, as described in the Opt-in RBF FAQ.

What's Next?

Continue "Controlling Bitcoin Transactions" with §5.3: Funding a Transaction with CPFP.