bitcoin_devs
Bitcoin Dev Project

The go-to resource for developers to learn bitcoin and related technologies. Get inspired to kickstart and grow your career in bitcoin open source software (₿OSS).

Public Key

npub10p33xu03t8q7d9nxtks63dq4gmt4v4d3ppd5lcdp4rg9hxsd0f8q7mn2l2

NIP-05 Address

bitcoindevs.xyz

Profile Code

nprofile1qqs8sccnw8c4ns0xjen9mgdgks25d46k2kcssk60uxs635zmngxh5nspz3mhxue69uhhyetvv9ujuerpd46hxtnfduqs6amnwvaz7tmwdaejumr0dskun7sl

Publishing to

relay.damus.io

nos.lol

Author Public Key

npub10p33xu03t8q7d9nxtks63dq4gmt4v4d3ppd5lcdp4rg9hxsd0f8q7mn2l2

Show more details

Last Notes

2025-07-10 15:04:57 GMT

🧰 Too much bitcoin tech knowledge is trapped in videos and podcasts
If only there was an easy way to unearth those insights and gems… 🤔
We wondered that too, so we redesigned Bitcoin Transcripts! 🚀
https://technicaldifficulties.io/nostr/bdp/transcriptsv2/transcriptsv2_homepage.png
🔍 Bitcoin Transcripts is a filterable library of transcripts from:
• dev meetups
• conferences
• podcasts
• panels
Skim talks, quote insights, and search by keyword.
All in one place.
👉 https://btctranscripts.com
⛏️ Missed a workshop or podcast episode?
No worries.
You can now quickly search by keyword or topic and read the conversation in minutes instead of watching hours of video,
Accelerating your speed to insights.
🧑‍🏫 Bitcoin Transcripts is perfect for:
- bitcoin devs digging into prior research
- educators creating content
- researchers analyzing protocol history or
- enthusiasts who prefer reading over listening
Taproot workshops, Lightning panels, it’s all in there.
Open-source and built by the community 🧡
This project stands on the shoulders of contributors like Bryan Bishop (https://heybryan.org/) who manually transcribed hundreds of talks.
Now, with modern tools, we can scale that effort for the whole community.
https://technicaldifficulties.io/nostr/bdp/transcriptsv2/transcriptsv2_bryantyping.png
Many thanks to our contributors:
- Dev: @nprofile…7k9s , Jamal (https://github.com/jrakibi), Emmanuel (https://github.com/Emmanuel-Develops), @nprofile…gh4s
- Data & architecture: Andreas (https://www.kouloumos.com/), Urvish (https://github.com/urvishp80)
- Vision: @nprofile…z4ak
- Design: Tobi (https://x.com/Adeoye_G), Khush (https://x.com/ikhushh7), @nprofile…qdk5
- Product: @nprofile…ez5h
- Inspiration: Bryan Bishop (https://heybryan.org/)
What’s next?
We’ll keep adding transcripts from upcoming events and backfill any important historic talks we missed. 🔍
Would love your help editing transcripts as well.
Dive in, explore, and let us know what you think! 👇
btctranscripts.com

2025-04-30 19:51:06 GMT

- reply

Yes! The more BOSS devs the merrier!
https://blossom.primal.net/623c7e12aeda2c8c88f323af610a458e000df9ba6c0550201366b6a32f037a92.gif

2025-04-30 19:49:31 GMT

- reply

This is great! We love to see it!! 🚀

2025-04-01 19:14:08 GMT

Slots are filling up fast for our Warnet track at Friday's #MITBitcoinExpo Hackathon!
We stand up a network of Bitcoin Core nodes. You use Bitcoin Core's functional test framework to write attacks in Python and take them down.
This event is open to hackers around the globe. Participants can be in-person or remote. And did we mention the $3,000 prize from the MIT Bitcoin Club?
👉 Head over to https://mitbitcoin.devpost.com to sign up today!
https://technicaldifficulties.io/nostr/bdp/WarnetShirtImage.png
We'll also have we’ll have additional prizes for Warnet track winners that are able to join in person. These gorgeous coasters by A+ Engrave are just one example! 🤩
https://technicaldifficulties.io/nostr/bdp/mit2025/slatecoaster.jpeg
https://technicaldifficulties.io/nostr/bdp/mit2025/corkcoasters.jpeg
https://technicaldifficulties.io/nostr/bdp/mit2025/warnetmug.jpeg

2025-03-03 15:39:23 GMT

𝐓𝐡𝐞 𝐁𝐢𝐭𝐜𝐨𝐢𝐧 𝐃𝐞𝐯 𝐏𝐫𝐨𝐣𝐞𝐜𝐭 𝐡𝐚𝐬 𝐚 𝐭𝐫𝐚𝐜𝐤 𝐚𝐭 𝐭𝐡𝐞 𝐌𝐈𝐓 𝐁𝐢𝐭𝐜𝐨𝐢𝐧 𝐄𝐱𝐩𝐨 𝐇𝐚𝐜𝐤𝐚𝐭𝐡𝐨𝐧, 𝐚𝐧𝐝 𝐢𝐭 𝐡𝐚𝐬 𝐚 $𝟑,𝟎𝟎𝟎 𝐩𝐫𝐢𝐳𝐞!
Participants have 30 hours, starting April 4 and are welcome to hack from around the globe.
🌍 We repeat, you do not have to attend in person 🌎
𝐌𝐨𝐬𝐭 𝐡𝐚𝐜𝐤𝐚𝐭𝐡𝐨𝐧 𝐭𝐫𝐚𝐜𝐤𝐬 𝐚𝐫𝐞 𝐚𝐛𝐨𝐮𝐭 𝐛𝐮𝐢𝐥𝐝𝐢𝐧𝐠, 𝐛𝐮𝐭 𝐧𝐨𝐭 𝐭𝐡𝐢𝐬 𝐨𝐧𝐞. 𝐓𝐡𝐢𝐬 𝐢𝐬 𝐚𝐛𝐨𝐮𝐭 𝐛𝐫𝐞𝐚𝐤𝐢𝐧𝐠 🔨
For the Bitcoin Dev Project track, the goal is to take down the bitcoin network. We stand up a network of bitcoin core nodes. You and your team take down as many as possible.
Whichever team brings down the most in the shortest amount of time wins. Monitor extreme and yet unknown network behaviors, discover vulnerabilities, and build a stronger, more resilient bitcoin.
https://m.primal.net/PSUQ.png
This track is for hackers with some level of coding skill, & the ability to use the command line interface (CLI). Familiarity with Bitcoin Core, esp. the JSON-RPC interface is useful. A general understanding of how blockchains and distributed networks work will come in handy.
Who's ready to win? Sign up below! 👇
https://mitbitcoin.devpost.com/

2025-02-23 19:49:35 GMT

- reply

This tool was initially made for the @nprofile…3hr7 website. You can find it here: https://bitcoinops.org/en/tools/reorg-calculator/
https://m.primal.net/PIbN.png

2025-02-23 19:47:56 GMT

New tool in Decoding Bitcoin!
REORG CALCULATOR ⚒️
Computes the probability that an attacker could reorganize z blocks with a given % of the total network hashrate
Here’s the probability of an attacker reorganizing 6 blocks with 30% of the total hashrate
https://bitcoindevs.xyz/decoding/reorg-calculator
https://m.primal.net/PIbM.png

2025-02-21 19:12:57 GMT

Buckle up for today's #DecodingBitcoin post. It's a long one but we promise it's worth your time.
Today we're going to break down how to sign a #bitcoin segwit transaction using a real example from the BIP-143 test vectors (that’s one of the segwit BIPs!)
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/titleimage.png
𝑁𝑜𝑡𝑒: 𝑡ℎ𝑖𝑠 𝑒𝑥𝑎𝑚𝑝𝑙𝑒 𝑖𝑠 𝑓𝑜𝑟 𝑎 𝑠𝑒𝑔𝑤𝑖𝑡 𝑣0 𝑡𝑟𝑎𝑛𝑠𝑎𝑐𝑡𝑖𝑜𝑛 𝑠𝑜 𝑠𝑜𝑚𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐𝑠 𝑎𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑡 𝑓𝑜𝑟 𝑙𝑒𝑔𝑎𝑐𝑦 𝑎𝑛𝑑 𝑡𝑎𝑝𝑟𝑜𝑜𝑡 (𝑠𝑒𝑔𝑤𝑖𝑡 𝑣1) 𝑡𝑟𝑎𝑛𝑠𝑎𝑐𝑡𝑖𝑜𝑛𝑠. 𝐻𝑜𝑤𝑒𝑣𝑒𝑟, 𝑡ℎ𝑒 𝑔𝑒𝑛𝑒𝑟𝑎𝑙 𝑐𝑜𝑛𝑐𝑒𝑝𝑡𝑠 𝑎𝑟𝑒 𝑠𝑡𝑖𝑙𝑙 𝑡ℎ𝑒 𝑠𝑎𝑚𝑒!
The transaction we'll be working with has two inputs. The first is a legacy P2PK input–we won’t be covering that today.
Instead, we’re going to focus on the second input, the P2WPKH (native segwit) one.
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning1.png
Since this example came from one of the BIP-143 test vectors, we know what the final, signed transaction looks like. The goal is to recreate this:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning2.png
First, we create the base transaction, the transaction without any signatures.
We’ll start with the
- version number
- marker & flag fields (to indicate the tx is segwit)
- locktime
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning3.png
𝐴 𝑛𝑜𝑡𝑒 𝑜𝑛 𝑠𝑒𝑔𝑤𝑖𝑡 𝑣𝑠. 𝑙𝑒𝑔𝑎𝑐𝑦 𝑡𝑟𝑎𝑛𝑠𝑎𝑐𝑡𝑖𝑜𝑛𝑠: 𝐵𝑒𝑐𝑎𝑢𝑠𝑒 𝑎𝑡 𝑙𝑒𝑎𝑠𝑡 𝑜𝑛𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑖𝑛𝑝𝑢𝑡𝑠 𝑖𝑠 𝑠𝑒𝑔𝑤𝑖𝑡 (𝑛𝑎𝑡𝑖𝑣𝑒 𝑜𝑟 𝑤𝑟𝑎𝑝𝑝𝑒𝑑), 𝑡ℎ𝑒 𝑡𝑟𝑎𝑛𝑠𝑎𝑐𝑡𝑖𝑜𝑛 𝑖𝑠 𝑎𝑙𝑠𝑜 𝑐𝑜𝑛𝑠𝑖𝑑𝑒𝑟𝑒𝑑 𝑠𝑒𝑔𝑤𝑖𝑡.
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning4.png
Here’s what we have so far:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning5.png
Let’s add inputs! Recall that all inputs come from existing transactions. That means for each input, we need to find the transaction it came from and get:
1. that transaction’s ID
2. the output index
𝐖𝐡𝐚𝐭’𝐬 𝐚𝐧 𝐨𝐮𝐭𝐩𝐮𝐭 𝐢𝐧𝐝𝐞𝐱?
Every transaction has a list of outputs. The “output index” is a way to reference a specific output from the list.
We need to ask, "from a transaction’s list of outputs, which one corresponds to the input I care about?”
For each input, two more things are needed: the 𝐬𝐜𝐫𝐢𝐩𝐭𝐒𝐢𝐠 (placeholder for data required to spend the input), and a 𝐬𝐞𝐪𝐮𝐞𝐧𝐜𝐞 𝐧𝐮𝐦𝐛𝐞𝐫 (usually 0xFFFFFFFF)
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning6.png
After adding all the inputs, the transaction looks like this:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning7.png
Remember when we said the scriptSig would be a placeholder? Here’s why those fields are currently empty:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning8.png
Time to add outputs! For each output, we include the
- amount (in satoshis)
- scriptPubKey: the locking script that defines the rules for how the output can be spent
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning9.png
Things are starting to come together!
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning10.png
A few more things are needed before we can get to signing. First is setting up the 𝐰𝐢𝐭𝐧𝐞𝐬𝐬 field.
This is where the signature and corresponding public key go for segwit transactions.
The witness field starts off empty. This is different from legacy transactions where signatures are placed directly in the scriptSig field.
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning11.png
The next thing that’s needed is the 𝐬𝐜𝐫𝐢𝐩𝐭𝐂𝐨𝐝𝐞.
The scriptCode for a P2WPKH (pay-to-witness-public-key-hash) input is:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning12.png
𝑊ℎ𝑎𝑡’𝑠 𝑡ℎ𝑎𝑡 20 𝑏𝑦𝑡𝑒 𝑝𝑢𝑏𝑘𝑒𝑦 ℎ𝑎𝑠ℎ?
𝐸𝑎𝑟𝑙𝑖𝑒𝑟 𝑤𝑒 𝑠𝑎𝑤 𝑒𝑎𝑐ℎ 𝑜𝑢𝑡𝑝𝑢𝑡 ℎ𝑎𝑠 𝑎 𝑠𝑐𝑟𝑖𝑝𝑡𝑃𝑢𝑏𝐾𝑒𝑦 (𝑟𝑢𝑙𝑒𝑠 𝑓𝑜𝑟 ℎ𝑜𝑤 𝑡𝑜 𝑠𝑝𝑒𝑛𝑑 𝑡ℎ𝑒 𝑜𝑢𝑡𝑝𝑢𝑡). 𝐴𝑙𝑠𝑜, 𝑟𝑒𝑐𝑎𝑙𝑙 𝑡ℎ𝑎𝑡 𝑡ℎ𝑒 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑜𝑛𝑒 𝑡𝑟𝑎𝑛𝑠𝑎𝑐𝑡𝑖𝑜𝑛 𝑖𝑠 𝑡ℎ𝑒 𝑜𝑢𝑡𝑝𝑢𝑡 𝑓𝑟𝑜𝑚 𝑎𝑛𝑜𝑡ℎ𝑒𝑟.
𝑇ℎ𝑒 20 𝑏𝑦𝑡𝑒 𝑝𝑢𝑏𝑘𝑒𝑦 ℎ𝑎𝑠ℎ 𝑖𝑠 𝑒𝑥𝑡𝑟𝑎𝑐𝑡𝑒𝑑 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 𝑜𝑢𝑡𝑝𝑢𝑡'𝑠 𝑠𝑐𝑟𝑖𝑝𝑡𝑃𝑢𝑏𝐾𝑒𝑦.
Here’s the 𝐬𝐜𝐫𝐢𝐩𝐭𝐂𝐨𝐝𝐞 for the example we’re working on:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning13.png
Lastly, three important hashes are required.
The first is 𝐡𝐚𝐬𝐡𝐏𝐫𝐞𝐯𝐨𝐮𝐭𝐬. It’s the double SHA256 hash of all input outpoints (outpoint = the transaction id + output index)
The second is 𝐡𝐚𝐬𝐡𝐒𝐞𝐪𝐮𝐞𝐧𝐜𝐞, the double SHA256 hash of all input sequence numbers.
The third is 𝐡𝐚𝐬𝐡𝐎𝐮𝐭𝐩𝐮𝐭𝐬, the double SHA256 hash of all outputs.
That’s everything (finally!). Let’s put it all together into something that can be signed!
When signing a transaction, the spender actually signs a hash of the transaction data, not the entire transaction itself. This hash is called the 𝐬𝐢𝐠𝐡𝐚𝐬𝐡.
The data used to create the sighash is called the 𝐩𝐫𝐞𝐢𝐦𝐚𝐠𝐞.
For a transaction input, the preimage is made of these items:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning14.png
The sighash_type indicates which parts of the transaction the signature is committing to.
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning15.png
After hashing the preimage twice with SHA-256, we’re left with the sighash.
At last! It’s time to do some signing!
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning16.png
There are a few steps for signing a segwit (v0) transaction.
First, the signer’s private key is used to create an ECDSA signature for the sighash.
The resulting signature has two parts, 𝑟 and 𝑠.
In ECDSA, there are actually two valid s values for every signature: a "high" value and a "low" value.
Both are mathematically valid, but bitcoin requires using the low s value to prevent transaction malleability (that means altering a transaction's ID!)
After selecting the low s value, the signature must be encoded into DER format. This is how it’s structured:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning17.png
And here’s what the DER encoded signature looks like for our example:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning18.png
The last step is to add a byte at the end for the sighash type. If we look back at the preimage made earlier we see this example is using SIGHASH_ALL (0x01).
The full code for the signing step looks like this:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning19.png
Remember the transaction witness field we set space aside for? It’s now time to put the signature in it 🚀
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning20.png
This is how the witness field is structured:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning21.png
Which works out to be this for our example:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning22.png
With the completion of the witness field, the transaction is now signed!
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning23.png
This is what the final signed transaction hex looks like broken down:
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning24.png
Bonus: You can use the Bitcoin Core CLI decoderawtransaction command to examine all the parts of the raw transaction hex
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/txsigning25.png
* ~ * ~ * ~ * ~ * ~ * ~
If you made it to the end, give yourself a pat on the back. If you enjoyed it, be sure to like this post so we know to make more like it!
* ~ * ~ * ~ * ~ * ~ * ~
This material is from Decoding Bitcoin, your go-to resource for understanding bitcoin, #privacy, and #decentralization.
You can visit https://bitcoindevs.xyz/decoding/transaction-signing for the full lesson with all the code examples, as well as more free, interactive content.
For more of a challenge, play chapters 4, 5, and 6 of @nprofile…fqsf (https://savingsatoshi.com) to learn about public-private key cryptography, digital signatures, and transaction building 😺
https://technicaldifficulties.io/nostr/bdp/segwittxsigning/savingsatoshi.jpg
Hope you learned something new about transaction signing. If you enjoyed this, share it with a friend and don’t forget to follow us, @nprofile…uvtq for more content like this.
Thanks for reading!

2025-01-30 15:27:45 GMT

We’ve got a good #DecodingBitcoin post for you today. The topic? 𝐄𝐧𝐝𝐢𝐚𝐧𝐧𝐞𝐬𝐬, AKA the order of bytes in a computer’s memory.
When we put it like that it sounds a little boring, but there’s something interesting, and dare we say 𝑎𝑛𝑛𝑜𝑦𝑖𝑛𝑔, about how bitcoin handles endianness…
Before we get to that, let’s better understand what endianness is.
Imagine reading directions in different languages: while English is written and read from left to right, Arabic text flows from right to left.
https://technicaldifficulties.io/nostr/bdp/endianness_1.png
Similarly, computers have two ways to store data:
1. 𝐁𝐢𝐠-𝐞𝐧𝐝𝐢𝐚𝐧 (BE): Most significant byte first
2. 𝐋𝐢𝐭𝐭𝐥𝐞-𝐞𝐧𝐝𝐢𝐚𝐧 (LE): Least significant byte first
https://technicaldifficulties.io/nostr/bdp/endianness_2.png
When computers with different byte orders try to communicate, they can misread each other. It’s like two people reading numbers from opposite directions.
https://technicaldifficulties.io/nostr/bdp/endianness_3.png
𝐁𝐢𝐠-𝐞𝐧𝐝𝐢𝐚𝐧 𝐬𝐭𝐨𝐫𝐞𝐬 𝐭𝐡𝐞 𝐦𝐨𝐬𝐭 𝐬𝐢𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐧𝐭 𝐛𝐲𝐭𝐞 𝐟𝐢𝐫𝐬𝐭. This is similar to how humans read numbers and Hex in most cases: starting with the most important information.
Suppose we want to store the number 12345678 (hexadecimal: 0x00BC614E) in memory. In big-endian, the bytes are stored in this order:
00 BC 61 4E
https://technicaldifficulties.io/nostr/bdp/endianness_4.png
Observe that:
- The 𝐦𝐨𝐬𝐭 𝐬𝐢𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐧𝐭 𝐛𝐲𝐭𝐞 (00) is stored at the 𝐥𝐨𝐰𝐞𝐬𝐭 𝐦𝐞𝐦𝐨𝐫𝐲 𝐚𝐝𝐝𝐫𝐞𝐬𝐬 (00).
- The 𝐥𝐞𝐚𝐬𝐭 𝐬𝐢𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐧𝐭 𝐛𝐲𝐭𝐞 (4E) is stored at the 𝐡𝐢𝐠𝐡𝐞𝐬𝐭 𝐚𝐝𝐝𝐫𝐞𝐬𝐬 (03).
Big-endian is considered more "human-readable" because the data is stored in the order we naturally read it.
𝐋𝐢𝐭𝐭𝐥𝐞-𝐞𝐧𝐝𝐢𝐚𝐧 𝐬𝐭𝐨𝐫𝐞𝐬 𝐭𝐡𝐞 𝐥𝐞𝐚𝐬𝐭 𝐬𝐢𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐧𝐭 𝐛𝐲𝐭𝐞 𝐟𝐢𝐫𝐬𝐭. This might feel counter intuitive to humans but is more efficient for modern processors.
Using the same number 12345678 (0x00BC614E), here's how it looks in little-endian:
4E 61 BC 00
https://technicaldifficulties.io/nostr/bdp/endianness_5.png
This time, the 𝐥𝐞𝐚𝐬𝐭 𝐬𝐢𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐧𝐭 𝐛𝐲𝐭𝐞 (4E) is stored at the 𝐥𝐨𝐰𝐞𝐬𝐭 𝐦𝐞𝐦𝐨𝐫𝐲 𝐚𝐝𝐝𝐫𝐞𝐬𝐬 (00).
The 𝐦𝐨𝐬𝐭 𝐬𝐢𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐧𝐭 𝐛𝐲𝐭𝐞 (00) is stored at the 𝐡𝐢𝐠𝐡𝐞𝐬𝐭 𝐚𝐝𝐝𝐫𝐞𝐬𝐬 (03).
This "reversal" of bytes is common in the Bitcoin Core codebase.
In bitcoin, most data like transaction IDs, block headers, and amounts are all in little-endian format or with the bytes reversed.
https://technicaldifficulties.io/nostr/bdp/endianness_6.png
𝑁𝑜𝑡𝑒: 𝐸𝑛𝑑𝑖𝑎𝑛𝑛𝑒𝑠𝑠 𝑜𝑛𝑙𝑦 𝑎𝑝𝑝𝑙𝑖𝑒𝑠 𝑡𝑜 𝑖𝑛𝑡𝑒𝑔𝑒𝑟𝑠. 𝐼𝑡 𝑖𝑠 𝑛𝑜𝑡 𝑐𝑜𝑟𝑟𝑒𝑐𝑡 𝑡𝑜 𝑠𝑎𝑦 𝑎 ℎ𝑎𝑠ℎ 𝑖𝑠 𝑙𝑖𝑡𝑡𝑙𝑒-𝑒𝑛𝑑𝑖𝑎𝑛. 𝑆𝑖𝑛𝑐𝑒 𝑡ℎ𝑒𝑟𝑒’𝑠 𝑛𝑜 𝑜𝑓𝑓𝑖𝑐𝑖𝑎𝑙 𝑡𝑒𝑟𝑚 𝑓𝑜𝑟 𝑡ℎ𝑖𝑠 𝑤𝑒 𝑠𝑎𝑦 “𝑏𝑦𝑡𝑒 𝑠𝑤𝑎𝑝𝑝𝑒𝑑” 𝑜𝑟 “𝑟𝑒𝑣𝑒𝑟𝑠𝑒 𝑏𝑦𝑡𝑒𝑠”.
For readability, the bytes are swapped back to the style of big-endian when this data is displayed to humans. A block explorer is one example of where you can see this.
Bitcoin Core’s JSON-RPC interface was the first time block hashes were printed for human consumption. That was when someone decided to reverse the ordering of hash so that it looked like a human readable integer.
https://technicaldifficulties.io/nostr/bdp/endianness_7.png
It turns out the real block hash, the actual sha256 value you get if you compute the hash yourself, is:
e4b1d56439d46d9070e58c4368cccc97596fa908daf101000000000000000000
The zeros are actually on the right! At first glance it looks like this is a very large number, but we know the integer value of a block hash actually gets smaller as the difficulty increases.
It's clear that the bytes are reversed and in the style of little-endian. But why? We can thank Satoshi for that. Satoshi decided to interpret the block hash as a little-endian integer. The more zeroes there are on the right side, the smaller the (little-endian) integer.
Since most modern CPUs are little-endian, bitcoin uses it to optimize performance.
However, network protocols typically use big-endian, creating a mismatch 🙀
Big-endian is used for network communication (network byte order). Little-endian is used for bitcoin’s internal storage.
This duality requires developers to frequently, and sometimes frustratingly, convert between the two formats when working with bitcoin data.
Have you been the victim of an endianness oversight when writing bitcoin code? It's a common source of pain for developers new to bitcoin (and even the seasoned ones!)
As covered by the transaction ID example earlier, byte order confusion can be common.
https://technicaldifficulties.io/nostr/bdp/endianness_8.png
Another gotcha is length specification. When converting to little-endian, always specify the correct byte length:
https://technicaldifficulties.io/nostr/bdp/endianness_9.png
Hope you learned something new about endianness today. If you enjoyed this, share it with a friend and don’t forget to follow us, @nprofile…uvtq !
This material is from Decoding Bitcoin, your go-to resource for understanding #bitcoin, privacy, and decentralization.
Visit https://bitcoindevs.xyz/decoding for the full lesson, and more free, interactive content.
Thanks for reading!

2025-01-30 14:27:52 GMT

- reply

Thank you so much! Appreciate your support 😄

2025-01-24 20:52:47 GMT

There is an oft-repeated sentiment in the community that bitcoin does not need you. While bitcoin is designed to be resilient, we 𝑑𝑜 need you. Bitcoin needs all the talent and energy it can gather to solve some of the most difficult technical problems of our time.
Bitcoin in your hands changes everything.
https://m.primal.net/NyXB.png

2025-01-24 20:50:15 GMT

- reply

Thank you! We will pass your kind words onto our designers :)

2025-01-24 20:02:52 GMT

It’s #DecodingBitcoin time! Let’s go over the basic elements of a transaction.
Alice wants to send 5 BTC to Bob. She needs to create a bitcoin transaction using the unspent outputs (UTXOs) in her wallet.
https://m.primal.net/NyTN.png
UTXOs are unspent transaction outputs. They can be used as inputs for new transactions.
Think of them as "coins" in a wallet, waiting to be spent.
Alice checks her wallet and finds two UTXOs:
https://m.primal.net/NyTS.png
To create a transaction, Alice has to specify exactly which UTXOs to spend.
A UTXO is identified by the transaction it came from, specifically
- the transaction ID and
- an index that says where the UTXO is in the list of transaction outputs
https://m.primal.net/NyTY.png
Wallets usually store this information for you but you can also look it up on the blockchain.
Alice's wallet shows these available UTXOs:
- UTXO #1: 4 BTC (from Transaction 1, Output Index 1)
- UTXO #2: 2 BTC (from Transaction 2, Output Index 0)
Together, they provide enough funds (4 BTC + 2 BTC = 6 BTC) for the payment and any transaction fees.
Now Alice has everything she needs to identify her UTXOs. As she adds them to the transaction, she saves space for the signatures she will make later. These signatures authorize the spending of the UTXOs.
https://m.primal.net/NyTd.png
Now that the transaction inputs have been taken care of, it’s time to look at the outputs!
Alice needs to create two outputs:
- 5 BTC to Bob (the payment amount)
- 0.99 BTC back to Alice as change (there is a 0.01 BTC transaction fee)
https://m.primal.net/NyTg.png
Why do we have to make a separate output for change?
UTXOs must be spent in their entirety. You cannot partially spend a UTXO. Instead, you create a new output that sends the excess amount back to yourself as change.
https://m.primal.net/NyTl.png
Looks good! The transaction structure is now complete, but it’s not yet valid. Alice must sign it to prove she owns the inputs. We’ll cover that in a future lesson 🙂
Follow us @nprofile…uvtq to stay updated!
This material is from Decoding Bitcoin, your go-to resource for understanding #bitcoin, privacy, and decentralization.
If you enjoyed it, visit https://bitcoindevs.xyz/decoding for the full lesson, and more free, interactive content.
Thanks for reading!

2025-01-17 16:12:52 GMT

Are you tired of searching for "lightning" only to get results about sparks in the sky and ice hockey teams in Florida?
So are we. That's why we built Bitcoin Search, which pulls from a curated list of credible #bitcoin tech sources.
https://bitcoinsearch.xyz
We've built the world's largest collection of technical bitcoin-related resources: articles, podcast transcripts, blog posts, and more.
Sources are regularly monitored to make sure your search results are up-to-date.
We hand-pick sources for their contributions to technical bitcoin concepts. Examples include the Bitcoin-dev Mailing List, LN dev Mailing List, Bitcoin Optech, and many more.
Bookmark it and try it out today!
https://m.primal.net/NlEE.png

2025-01-16 19:06:41 GMT

- reply

Hooray we finally did it! Thanks for the reminder 😸
Proof of PR: https://github.com/bitcoin-dev-project/bitcoin-dev-project/pull/146
https://m.primal.net/NjjD.png

2025-01-14 20:12:16 GMT

What's the deal with #bitcoin fees? How are they calculated? Where do they go? Let's have a look with a #DecodingBitcoin post:
A transaction's fee is equal to the total amount of bitcoin in the inputs, minus the total amount of bitcoin in the outputs.
https://m.primal.net/Nggr.png
Here's how to calculate the fee for this transaction: https://mempool.space/tx/c27c4d2236fce2a7542e024408d7f89b95e50e42a2c3d10be499c3102ccb45ef
Fee = Input - (Output1 + Output2)
Fee = 299.99430000 - (0.00140000 + 299.99240000)
Fee = 299.99430000 - 299.99380000
Fee = 0.00050000
Fee = 50,000 sats
Remember: Sum(Inputs) should always be greater than Sum(Outputs)
https://m.primal.net/Nggt.png
Fees incentivise miners to include transactions in blocks. Without fees, miners would have little reason to put transactions into blocks!
In addition to fees, miners also receive a block reward.
Total miner revenue = fees + block reward
https://m.primal.net/Nggy.png
How do miners decide what transactions go into a block?
The short answer is miners will usually maximize revenue by prioritizing transactions with the highest fee rate (we've got a whole lesson fee rates coming!)
https://m.primal.net/NghA.png
While miners can choose which transactions to include based on fees, there's a minimum threshold, a "minimum relay fee" that must be met just for a transaction to be relayed through the network.
Transactions below this threshold are rejected by nodes. It helps prevent spam and DoS attacks on the network
https://m.primal.net/NghD.png
This brings us to an important question: What happens if you submit a transaction with a fee rate above the minimum but still too low for current network conditions?
That transaction could sit in the mempool for hours because the fee rate is too low for the high level of network activity. Even if you met the minimum, there can still be plenty of transactions with higher fee rates than yours, ones that miners will choose first.
https://m.primal.net/NghE.png
At this point, you have two main ways to "unstick" it:
1. RBF (Replace-by-Fee)
2. CPFP (Child Pays for Parent)
--------------------------------
That's all for now! We'll dive deeper into fee rates, RBF, and CPFP in a future post.
This material is from Decoding Bitcoin, your go-to resource for understanding #bitcoin, privacy, and decentralization.
If you enjoyed it, visit https://bitcoindevs.xyz/decoding for the full lesson, and more free, interactive content!
And don't forget to follow us for more posts about bitcoin tech and tools to help you in your developer journey 🚀

2025-01-13 23:49:54 GMT

Psst. Don't have enough hours in the day to read the mailing list and Delving Bitcoin? We have a secret weapon for you.
Bitcoin TLDR has daily summaries, available by post or by thread: https://tldr.bitcoinsearch.xyz
Here's today's summary of the bitcoin-dev mailing list:
- Ava Chow announced Bitcoin Core version 28.1. It makes adjustments to p2p configurations to enhance usability & reduce startup failures. It also has internal ID counting updates, enhancements in key handling, build system improvements, & a call for community participation in reporting bugs and joining the announcement list
- @nprofile…dmde raised concerns about the reliability of transaction timestamp data, specifically the vulnerability of nLockTime. It can be manipulated for unfair prioritization benefits, undermining the effectiveness of new prioritization rules.
- Yuval Kogman critiqued misconceptions around privacy mechanisms, focusing on wabisabi credentials & Wasabi wallet. He sheds light on the challenges with safeguarding privacy and security, emphasizing transparency, comprehensive security measures, & ethical considerations.
https://m.primal.net/NfUn.png

2025-01-11 19:51:40 GMT

- reply

Thanks for sharing Ross 😀
Enjoy!

2025-01-10 15:54:11 GMT

Let's talk about the 2 ways to track user balances on decentralized networks. Time for a #decodingbitcoin post:
1. Account Model (Ethereum): Tracks balances like a bank ledger (simple and intuitive).
2. UTXO Model (Bitcoin): Tracks specific unspent outputs from transactions (complex but powerful)
https://m.primal.net/Nagm.png
The account model is like your bank statement. Simple to understand and works well with smart contracts. The downside is it's less private and can be vulnerable to replay attacks.
https://m.primal.net/Nago.png
The UTXO model is like bills in a wallet. UTXOs (unspent transaction outputs) can only be spent once. Each transaction creates new UTXOs, and your balance is the sum of all your unspent UTXOs
https://m.primal.net/Nagx.png
This model has better privacy, prevents double spending, and allows for parallel transaction processing. The cons are it's more difficult to understand, is harder for complex applications, and requires UTXO management.
Here's a comparison chart of the two models:
https://m.primal.net/Nagp.png
This material is from Decoding Bitcoin, your go-to resource for understanding #bitcoin, privacy, and decentralization.
If you enjoyed it, visit https://bitcoindevs.xyz/decoding for the full lesson, and follow us for more free educational #bitcoin content!

2025-01-09 18:42:18 GMT

Like this note if you’re the world’s best ₿OSS contributor.
Repost if you’re going to become one this year.
https://m.primal.net/NZXC.jpg

2025-01-08 16:54:24 GMT

- reply

While Bitcoin Core is mostly C++ and Python, there are many great bitcoin projects written in Rust including LDK, Stratum V2, and Fedimint!

2025-01-08 16:48:35 GMT

- reply

Enjoy! Give it a go and let us know what you think 😃

2025-01-07 20:09:14 GMT

- reply

oh dear! thanks for letting us know. we'll get that sorted out 🫡

2025-01-07 19:32:14 GMT

- reply

oops. going to have a word with our social media intern 😄

2025-01-07 19:31:25 GMT

- reply

good catch! 😸 that link should be to: https://savingsatoshi.com/

2025-01-07 19:25:53 GMT

Want to learn #Rust but don't know where to start? We have a free course that covers the fundamentals of Rust using bitcoin based exercises. It's the best of both worlds.
🦀 rust + bitcoin = 🧡
https://btcdemy.thinkific.com
https://bitcoindevs.xyz/_next/static/media/btc-demy.60731301.png

2024-12-03 17:02:10 GMT

🚀 Help us save Satoshi!
And learn the fundamentals of bitcoin tech while you’re at it
📢 Introducing Saving Satoshi!
The world’s first interactive, practice-focused game to teach you bitcoin development.
www.savingsatoshi.com
Bitcoin tech can be hard to learn.
Yes, there are many incredible resources.
Our goal is to complement them and add our drop of interactivity to the ocean of learning.
Try Saving Satoshi today!
https://image.nostr.build/547d5f07b3c6912c5a351270c4b138100104572a10a5bf7e409cb92d3c1f8509.png
What will you learn?
- How to find and decode the hidden message in the genesis block
- Elliptic curve cryptography
- Message signing and verification
- Building a transaction
- Building a block template
- Bitcoin Script
- How the Lightning network works
- And so, so much more!
How is Saving Satoshi different?
- Logged in state to remember your progress
- Ability to share accomplishments publicly
- A real story to motivate you to learn
- Free and Open Source
https://image.nostr.build/f6b466dd0621495ac6339fc06ff979d8724189f68ea7fffa6ed598d38fad1b4e.png
Saving Satoshi started as a hackathon idea:
“How can we make bitcoin tech education more engaging and fun?”
Since then it’s become a game with 10 fun chapters, and support for both Python and JavaScript
Worldwide there are groups like TabConf and Scalar School playing together.
https://image.nostr.build/1c3adc83581cb1e2645da8ad65de6bf71dc5880d3c71d0da645d43463cd77fdc.jpg
Give Saving Satoshi a go today, and let us know what you think.
Shoutout to the team that helped bring this over the finish line
https://image.nostr.build/8b28802f8e9dab7abe19725194898890c783b48e0113237146f7690edae83415.jpg
Now be quick, Satoshi needs you!
www.savingsatoshi.com

2024-10-10 12:20:56 GMT

🚀 Decoding Bitcoin!
An interactive, exercise-first way to learn bitcoin development
100% free and open-source
👇 Dive into bitcoin tech with us below!
https://bitcoindevs.xyz/decoding
Decoding Bitcoin makes learning bitcoin tech easier, funner, and more efficient
It gives you the perfect mix of
- Concise explanations
- Real-world exercises
- Tons of interactive demos
https://image.nostr.build/16d5efa3ed839858f74ea709ae1d712c530ea024599671cbd9831516d797a179.jpg
Being able to play with interactive elements to understand Bitcoin concepts is the best way to solidify a working mental model
https://image.nostr.build/903f2dc837dae0c4d2b063f6ff710b984fb47ddbd76bf492fc356f75099e6824.gif
No libraries allowed, you’ll craft everything from scratch!
We support both JavaScript and Python (of course!)
Each bitcoin concept comes with its own exercise, so you’ll learn not just how things work, but also when and where to use them.
https://image.nostr.build/8e50c7c926389a8b39ac2fceef705f4031af604fd23bc36d8e62062938b3347e.png
By the end of each module, you’ll challenge yourself by creating a project to test your understanding.
https://image.nostr.build/c25ba3054e667f53b163033f44f9f8df198db160d51ed59e5cfa24c82c30f34b.png
We’ve started with the first module on Scripts.
More content is coming soon!
Please share your feedback on this first release—it helps us understand what you want to see next, whether it’s content or new features.

2024-08-29 17:53:10 GMT

Incredible walkthrough of our ecosystem!
Thank you to @npub1gjy…ektz for the deep dive!
We look forward to building more products, services, and infrastructure to enable the world to study and contribute to bitcoin FOSS.
#note1jnl…qhj3

2024-07-31 14:58:39 GMT

You spoke, we listened
🌘
https://image.nostr.build/9ec2895b3e6521278f0ad821c6bb01b26c5261274188f7cdb3756fc5fc321e8f.jpg

2024-07-18 15:27:25 GMT

📢 Introducing Bitcoin Search v2
Want to find that one specific technical bitcoin nugget?
You’re in luck!
There is only one place that allows you to search the depths of bitcoin’s technical ecosystem and retrieve the highest signal info about bitcoin tech.
🔗👇
https://www.bitcoinsearch.xyz
Bitcoin Search is unique
Unlike Google, when you search for “lightning”
We actually know what you mean
(Hint: It’s not electric sparks in the sky. Or an ice hockey team in Florida).
https://image.nostr.build/e838c8e404a555ab984daf2fc4211791214175dbbd660b0eec04633d65d3e6a8.jpg
Features
We let you sort and filter by categories that matter
- Authors and
- Sources
And in ways that matter
- Relevance and
- Date
And with views you love: dark 🌑 & light 🌞
Scope
The scope of the product is laser focused: bitcoin tech
Users can suggest sources deeper in the product. This bolsters our repo of bitcoin tech sources
We build pathways to scrape the data
Which grows our library of bitcoin tech literature and resources
Ecosystem of Knowledge Creation
Bitcoin Search thrives as a collaborative ecosystem.
As you do more Transcript Reviews and suggest new credible sources, our database continuously expands and improves, ultimately benefiting the entire Bitcoin technical community.
It’s a virtuous cycle of knowledge creation
https://image.nostr.build/e53f38fa46cacd4c402e300d5482f474907f3f2a9aef4ed9f9ac0aa4832c682c.png
We already had a live V1. Why build a V2?
We wanted to improve comprehension of the product for newer devs interested in bitcoin tech
While improving its usability, and increasing a sense of delight when using it.
https://image.nostr.build/ea145bef4a6ee0fe88b976c149bbc59f9abe2535bb4d27fe2b8d46709ff66ab0.png
Biggest thanks to the team!
Dev: Emmanuel, Solomon, Balogun, Otuedon
Design: @npub1xgl…fmlc
Dev Lead: Theo
Vision: Jonas
Product: @npub1a6n…s58k
So, give Bitcoin Search a go!
https://www.bitcoinsearch.xyz
Tell us what you like and don’t like. What’s missing. What should we do better?
And importantly - what kinds of products and tools are missing for bitcoin devs and builders in the ecosystem?

2024-07-02 16:21:33 GMT

Want to contribute to #Bitcoin FOSS development
But don't know where to start?
📢 Introducing Bitcoin Good First Issues!
A tool designed specifically for devs just entering bitcoin development.
https://bitcoindevs.xyz/good-first-issues
🤔 We know it’s hard to guess which projects to start with and what issues to tackle.
Bitcoin Good First Issues gathers beginner-friendly issues labelled Bug, Help Wanted, and (heh) Good First Issues.
It pulls them live for your from vetted Free Open Source Software projects.
🛠️ Why Give It a Go?
- Vetted Projects
- Easy Navigation
- Lowered Barrier to Entry
Whether you're just starting or already a developer, Bitcoin Good First Issues is built to accelerate your contributions.
Give it a roll and make a difference! Let’s build the future of bitcoin together.
👩‍💻 Check the image below to learn how the data flow works:
https://image.nostr.build/d06ce33d05df50add214ae4fc481b8cfb6d81c32616cfae6c364d8deb16f3b58.png
🖤 Biggest thanks to our team!
- Vision: Theo
- Ideation: Emmanuel, Solomon, Abubakar Ismail
- Design: Theo with thanks to paperpsych
- Dev: Theo, Solomon, Balogun
- Product: @npub1a6n…s58k
📃 Examples of vetted FOSS projects in Bitcoin Good First Issues
- BDK
- Core LN
- Eclair
- Fedimint
- LDK
- Polar
- Stratum Mining
We're looking forward to your feedback!

2024-06-06 19:50:25 GMT

Better search
For better learning
And better buidling
Coming.
https://i.nostr.build/KGXjg.png

2024-05-30 16:09:02 GMT

Soon
👀
https://image.nostr.build/5f86372e97ace4751d7ff9b065cf3668a05c78404d7b8ab0ac366720d6ace892.jpg

2024-05-15 18:29:54 GMT

We're building a ton of products
- Tool to make bitcoin concepts easier to grok
- Tool to make it easier to find issues to work on
- Tool to remove friction in finding bitcoin-related technical content
Soon

2024-05-14 02:51:01 GMT

👀
#note1u38…z5c0

2024-05-14 02:49:13 GMT

Hello, world!