7

Rand lib is supported in rust but not supported in anchor lang. I want to generate a random number lets say between a range of 0-10. Is there is a way I can do in anchor lang. Or alternatively, if there is a way I could use candy machine random NFT functionality with url as I want to use random numbers to be passed in url.

Code snippet:

 let random_number = 0; // this is supposed to be a random number let say b/w [0-10]
 let path = "http://abc.com";
 let new_uri = format!("{}{}{}", path, random_number, ".json");

            invoke(
                &create_metadata_accounts_v2(
                    ctx.accounts.token_metadata_program.key(),
                    ctx.accounts.metadata.key(),
                    ctx.accounts.mint.key(),
                    ctx.accounts.mint_authority.key(),
                    ctx.accounts.payer.key(),
                    ctx.accounts.payer.key(),
                    num_title,
                    symbol,
                    new_uri,
                    Some(creator),
                    1,
                    true,
                    false,
                    None,
                    None,
                ),
                account_info.as_slice(),
            )?;
3
  • I am pretty sure that you can can use rust functionality on anchor lang. have you tried implementing rand in you code? Nov 11, 2022 at 6:22
  • yes, I did that it is supported in rust but when using anchor lang it is not supported as the randomness of a function can be guessed which can be a security issue as well as you can run out of compute units if the random range is too large. Nov 11, 2022 at 10:31
  • duplicate question stackoverflow.com/questions/70693497/…
    – Setmax
    Nov 12, 2022 at 8:06

2 Answers 2

4

As defined here you can’t use random either in Rust or in Anchor if you want to generate a random number either you create your own number or you can use an oracle like a switchboard for generating a random value.

  • If you write your own random function using recent blockhash or timestamps available in the program it's most likely to be exploited.
  • So it's better to use an oracle for generating the random number. Verifiable Randomness On-chain

References

1
  • We can use random numbers in simple Rust without anchor lang using rand lib. Nov 13, 2022 at 4:13
3

Found a way that we can simply use timestamps for this.

   let clock = Clock::get()?;
   let clock = clock.unix_timestamp % 10; // any number between range 0-10 

Just make sure the random number range is not too large else you may run out of compute units. In case of a very large range of numbers, you can make this implementation on the admin panel where only a transaction signed by admin wallet can call this function (if security is important).

2
  • This approach can be exploited. Nov 14, 2022 at 7:04
  • Can you explain how? I was going to use this option for something monetary.
    – ZeroNine
    Jan 9 at 20:57

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