Bitcoin Proof of Work Difficulty Adjustment (Retarget) history

[tranthidung]

Today, we are familiar with a term Difficulty Retarget aka. Difficulty Adjustment which automatically executes after 2016 blocks that is about 14 days (2 weeks).

In fact the first time it was done automatically is in late of December, months before the Bitcoin Genesis block.

Proof-of-work difficulty increasing

We had our first automatic adjustment of the proof-of-work difficulty on 30 Dec 2009.  

The minimum difficulty is 32 zero bits, so even if only one person was running a node, the difficulty doesn't get any easier than that.  For most of last year, we were hovering below the minimum.  On 30 Dec we broke above it and the algorithm adjusted to more difficulty.  It's been getting more difficult at each adjustment since then.

The adjustment on 04 Feb took it up from 1.34 times last year's difficulty to 1.82 times more difficult than last year.  That means you generate only 55% as many coins for the same amount of work.

The difficulty adjusts proportionally to the total effort across the network.  If the number of nodes doubles, the difficulty will also double, returning the total generated to the target rate.

For those technically inclined, the proof-of-work difficulty can be seen by searching on "target:" in debug.log.  It's a 256-bit unsigned hex number, which the SHA-256 value has to be less than to successfully generate a block.  It gets adjusted every 2016 blocks, typically two weeks.  That's when it prints "GetNextWorkRequired RETARGET" in debug.log.

minimum    00000000ffff0000000000000000000000000000000000000000000000000000
30/12/2009 00000000d86a0000000000000000000000000000000000000000000000000000
11/01/2010 00000000c4280000000000000000000000000000000000000000000000000000
25/01/2010 00000000be710000000000000000000000000000000000000000000000000000
04/02/2010 000000008cc30000000000000000000000000000000000000000000000000000
14/02/2010 0000000065465700000000000000000000000000000000000000000000000000
24/02/2010 0000000043b3e500000000000000000000000000000000000000000000000000
08/03/2010 00000000387f6f00000000000000000000000000000000000000000000000000
21/03/2010 0000000038137500000000000000000000000000000000000000000000000000
01/04/2010 000000002a111500000000000000000000000000000000000000000000000000
12/04/2010 0000000020bca700000000000000000000000000000000000000000000000000
21/04/2010 0000000016546f00000000000000000000000000000000000000000000000000
04/05/2010 0000000013ec5300000000000000000000000000000000000000000000000000
19/05/2010 00000000159c2400000000000000000000000000000000000000000000000000
29/05/2010 000000000f675c00000000000000000000000000000000000000000000000000
11/06/2010 000000000eba6400000000000000000000000000000000000000000000000000
24/06/2010 000000000d314200000000000000000000000000000000000000000000000000
06/07/2010 000000000ae49300000000000000000000000000000000000000000000000000
13/07/2010 0000000005a3f400000000000000000000000000000000000000000000000000
16/07/2010 000000000168fd00000000000000000000000000000000000000000000000000
27/07/2010 00000000010c5a00000000000000000000000000000000000000000000000000
05/08/2010 0000000000ba1800000000000000000000000000000000000000000000000000
15/08/2010 0000000000800e00000000000000000000000000000000000000000000000000
26/08/2010 0000000000692000000000000000000000000000000000000000000000000000

date, difficulty factor, % change
2009           1.00
30/12/2009     1.18   +18%
11/01/2010     1.31   +11%
25/01/2010     1.34    +2%
04/02/2010     1.82   +36%
14/02/2010     2.53   +39%
24/02/2010     3.78   +49%
08/03/2010     4.53   +20%
21/03/2010     4.57    +9%
01/04/2010     6.09   +33%
12/04/2010     7.82   +28%
21/04/2010    11.46   +47%
04/05/2010    12.85   +12%
19/05/2010    11.85    -8%
29/05/2010    16.62   +40%
11/06/2010    17.38    +5%
24/06/2010    19.41   +12%
06/07/2010    23.50   +21%
13/07/2010    45.38   +93%
16/07/2010   181.54  +300%
27/07/2010   244.21   +35%
05/08/2010   352.17   +44%
15/08/2010   511.77   +45%
26/08/2010   623.39   +22%

You can read some replies of Satoshi Nakamoto in that thread and get his vision on this.

Some of interesting things you will discover in that thread is theymos' posts.

I generated 5 blocks today on my Pentium processor. Two of them were within 3 minutes of each other.

I have noticed some slowdown since the adjustment, but I still generate a lot of coins. My computer is off while I'm sleeping, and BitCoin bootstraps quickly when I turn it back on. Do you guys-who-are-having-trouble have the BitCoin port open?

This is part of reasons theymos sold his bitcoins very cheap at rate around $0.003 /BTC. Legend!  

Around that time I measured with a Kill-A-Watt that 1 kWh could get me 160 BTC, and based on that I thought that BTC was substantially overpriced at the 5 cents or so it was trading at. As a result, I also have the honor of selling BTC at the lowest price ever recorded, $0.003/BTC. 🎉

(That "BitCoin" capitalization... such cringe...)

In 2023, if you want to get Bitcoin Difficulty Estimation, you can have it with

• https://newhedge.io/terminal/bitcoin/difficulty-estimator

[1715073117]

1715073117

[1715073117]

1715073117

[1715073117]

1715073117

[Faisal2202]

This is part of reasons theymos sold his bitcoins very cheap at rate around $0.003 /BTC. Legend!  

Thanks for sharing this thread, it was helpful in a way, and you are right early adopters are really legends, I wonder if they have to mine BTC at the difficulty level of today's world, which is around 67957790298897.88 I don't really know how I should interpret this number because I am not a miner. Well, I was trying to say, if these old users have to mine BTC with current difficulty levels then they might not sell their BTC back then.

Because the less effort you will or have to make the lesser potential you will see, and vice versa. I am not saying, these early adopters were greedy and they needed money, so that's why they sold their funds because Laszlo made the first-ever transaction of BTC which is needed to start the trading of BTC. Who knows if no one makes that step, how much time will BTC take to be adopted?                           

[WatChe]

Today, we are familiar with a term Difficulty Retarget aka. Difficulty Adjustment which automatically executes after 2016 blocks that is about 14 days (2 weeks).

Well I wonder how Bitcoin difficulty adjustment will adjust itself once we have Quantum computing, that will target hard problem of every security algorithm/protocol. I know there are many IF and ELSE about Quantum computing and its no surprise as every new technology has to face some resistance initially. We need to have rational answer that why Quantum computing wont be affecting Bitcoin.

[paid2]

Well I wonder how Bitcoin difficulty adjustment will adjust itself once we have Quantum computing, that will target hard problem of every security algorithm/protocol. I know there are many IF and ELSE about Quantum computing and its no surprise as every new technology has to face some resistance initially. We need to have rational answer that why Quantum computing wont be affecting Bitcoin.

ASIC means "Application-specific integrated circuit", so I guess that something designed specifically for a task will ever be more efficient than everything else (for the said task, hashing). Or maybe I'm wrong and ASICs will one day be replaced by something else, but I am not sure that Quantum computers could be more efficient than ASICs...

[WatChe]

ASIC means "Application-specific integrated circuit", so I guess that something designed specifically for a task will ever be more efficient than everything else (for the said task, hashing). Or maybe I'm wrong and ASICs will one day be replaced by something else, but I am not sure that Quantum computers could be more efficient than ASICs...

Quantum computing is based on Quantum physics and there full scale potential is yet to be seen. Bitcoin use elliptic curve digital signature algorithm (ECDSA) and we have Shor's algorithm developed in 1994 that can break Elliptic Curve cryptography by computing discrete logarithms. Shor's Algorithm can be executed on Quantum Computers only that are considered to be hypothetical but they are becoming a reality. IBM has relaeased a 400 QBits processor in 2022[1] and it is estimated that breaking a curve with 256-bit modulus requires a quantum computer with 2330 qubits[2]. With current pace we can have such computer ready in next 15 to 20 years or may be before that.

It's all about assumptions and predictions so far but there is logic in all this data about Quantum computing. Even USA government is taking it seriously[3]. 

[1] https://newsroom.ibm.com/2022-11-09-IBM-Unveils-400-Qubit-Plus-Quantum-Processor-and-Next-Generation-IBM-Quantum-System-Two
[2] https://en.wikipedia.org/wiki/Elliptic-curve_cryptography#:~:text=Shor's%20algorithm%20can%20be%20used,and%20126%20billion%20Toffoli%20gates.
[3] https://www.insideglobaltech.com/2023/01/10/president-biden-signs-quantum-computing-cybersecurity-preparedness-act/

[Cricktor]

For mining you don't have to fiddle with ECDSA. You try to find a double SHA-256 hash of a suitably constructed 80 bytes block header which fulfills the required difficulty to be valid, i.e. to have a certain number of starting zero bits or simply be smaller than the current difficulty demands.

I don't quite see how quantum computing will have an advantage in the field of one-way hash functions, but I'm no expert in quantum computing, just an interested observer with some science background. Quantum computers are not a solution for every problem and looking at current qbit coherence times and numbers of (stable?) qbits, I'm far from being actually concerned about what current quantum computers can do to break stuff. Current qbit instability and short coherence times demand a wast number of qbits for error correction and those needed numbers are simply not available for many years ahead.

Don't get me wrong, I don't dismiss the technology and I'm quite sure it will evolve over time (a lot of time still) to something where we have to adapt current encryption and other important algorithms that sufficiently capable quantum computers can be a problem for.