<p>Instead of reinventing the wheel, I recommend that you use the cryptographic concept of a <a href="http://en.wikipedia.org/wiki/Commitment_scheme" rel="nofollow">commitment scheme</a>. Pick your needed randomness as you normally would, commit to it, and then reveal your committed randomness after betting.</p>

CC BY-SA 3.0
2011-06-06T20:51:58.360Z
I suppose the OP needs a commitment scheme which can be verified (and understood) manually by a layman.
Mohammad Alaggan
CC BY-SA 3.0
2011-06-06T23:35:27.597Z
Couldn't understand it the first time. I'll try later
Jader Dias
CC BY-SA 3.0
2011-06-07T00:29:02.127Z
I got it. A hash function will do the job. Someone is already using it for the same purpose I devised http://bitcoin-kamikaze.com/
Jader Dias
CC BY-SA 3.0
2011-06-06T20:47:06.503Z
2011-06-06T20:47:06.503Z
Tyson Williams
<p>To turn the question around, one could equivalently ask: "How large must my prime be in order to be secure until year X against the resource plausibly available to a potent (e.g. government-funded) attacker?" This question is being regularly reassessed in various studies yielding recommended key lengths for crypto systems. A regularly updated web page summarizing these reports can be found <a href="http://www.keylength.com/" rel="nofollow">here</a>. </p>

CC BY-SA 3.0
2011-06-06T21:29:39.983Z
2011-06-06T21:29:39.983Z
Martin Schwarz
<p>I would like to know how much it would cost to factor a large integer. The cost can be given computer operations, time to process it or even monetary value. I know there are people that factored 200 bit RSA keys, but Wikipedia doesn't say how long it would take in modern CPUs.</p>

<p>-- Background --</p>

<p>I am designing a virtual roulette game where the ball is spun (the number is chosen) before the player bets. As a proof of that but I show the player the product of two primes, one of them is used as the random number seed.</p>

<p>I would like to know what is the minimum suitable size for this number such as the cost of factoring it will be greater than the maximum prize I offer.</p>

CC BY-SA 4.0
2024-03-05T13:31:06.433Z
Are you the person behind 1024 bits rsa with dice9.win?
user2284570
<cc.complexity-theory><cr.crypto-security><nt.number-theory><factoring><primes>
How to calculate the cost of factoring a large integer?
Jader Dias
# How to calculate the cost of factoring a large integer?

(Asked by: username_0 on 2011-06-06)

I would like to know how much it would cost to factor a large integer. The cost can be given computer operations, time to process it or even monetary value. I know there are people that factored 200 bit RSA keys, but Wikipedia doesn't say how long it would take in modern CPUs.

-- Background --

I am designing a virtual roulette game where the ball is spun (the number is chosen) before the player bets. As a proof of that but I show the player the product of two primes, one of them is used as the random number seed.

I would like to know what is the minimum suitable size for this number such as the cost of factoring it will be greater than the maximum prize I offer.

**Tags:** cc.complexity-theory, cr.crypto-security, nt.number-theory, factoring, primes
> **Comments:**
> **username_1**: Are you the person behind 1024 bits rsa with dice9.win?  

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## 2 answers

### Answer by username_2 on 2011-06-06. Score: 4 | Accepted answer

Instead of reinventing the wheel, I recommend that you use the cryptographic concept of a [commitment scheme](http://en.wikipedia.org/wiki/Commitment_scheme). Pick your needed randomness as you normally would, commit to it, and then reveal your committed randomness after betting.

> **Comments:**
> **username_3**: I suppose the OP needs a commitment scheme which can be verified (and understood) manually by a layman.  
> **username_0**: Couldn't understand it the first time. I'll try later  
> **username_0**: I got it. A hash function will do the job. Someone is already using it for the same purpose I devised http://bitcoin-kamikaze.com/  

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### Answer by username_4 on 2011-06-06. Score: 6

To turn the question around, one could equivalently ask: "How large must my prime be in order to be secure until year X against the resource plausibly available to a potent (e.g. government-funded) attacker?" This question is being regularly reassessed in various studies yielding recommended key lengths for crypto systems. A regularly updated web page summarizing these reports can be found [here](http://www.keylength.com/).


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