# Perpetual Powers of Tau Ceremony selection for Hermez

We will use the first 54 contributions of the Perpetual Powers of Tau Ceremony for BN254 Curve (Sometimes referred to as BN128).

These 54 contributions are the current contributions available at the writing of this document. You can find them here:

[https://github.com/weijiekoh/perpetualpowersoftau](https://github.com/weijiekoh/perpetualpowersoftau)

The Blake2b of the 54th contribution response is:

    fbad44fc ea6d5052 70046563 04093552
    d29be00d 7fcd2d62 7e07c1b0 15c6eb97
    4ea9262c aa4633cd 306c7f55 7d839c78
    f9a408c9 5cfaef06 f916e37d 182ae94b

We will also apply a 55th contribution as a random beacon.

The blake2b of challange_0055 where the beacon will be applied is:

    00d0b99a 5ccb65af a5872f82 5f2388f3
    2f6fd96e d1e58e83 cb921037 447d980d
    7bfb8a08 11d90a36 01846bbc ee2216ae
    aec90e60 e2490e5d 09ea36bf 3222840f

Notice that according to [this](https://electriccoin.co/blog/reinforcing-the-security-of-the-sapling-mpc/), a random beacon might not be strictly necessary. Nevertheless, we consider it best practise to do so.

For this, we will apply the result of the round 100000 of [drand](https://drand.love).

Here is the info of the drand chain that will be used:

{
    "public_key":"868f005eb8e6e4ca0a47c8a77ceaa5309a47978a7c71bc5cce96366b5d7a569937c529eeda66c7293784a9402801af31",
    "period":30,
    "genesis_time":1595431050,
    "hash":"8990e7a9aaed2ffed73dbd7092123d6f289930540d7651336225dc172e51b2ce",
    "groupHash":"176f93498eac9ca337150b46d21dd58673ea4e3581185f869672e59fa4cb390a"
}

This number is planned to be generated on

Wed, 26 Aug 2020 08:37:30 UTC

Once the number is generated, one should be able to find it here:

[https://drand.cloudflare.com/public/100000](https://drand.cloudflare.com/public/100000)

or here:

[https://www.cloudflare.com/leagueofentropy](https://www.cloudflare.com/leagueofentropy)

In order to check the correctness of the software generating the number, check here:

[https://drand.love](https://drand.love)

You can also use this code to verify it:

[https://github.com/hermeznetwork/drand_verify](https://github.com/hermeznetwork/drand_verify)

Commit used: [https://github.com/hermeznetwork/drand_verify/commit/5047a94cc5786aecb98c56f0fecb37bed5440c01](https://github.com/hermeznetwork/drand_verify/commit/5047a94cc5786aecb98c56f0fecb37bed5440c01)

The `randomness` result (In Hexadecimal) will be treated as the `beaconHash` used as the key generation beacon with 2^10 sha256 iterations.

Finally, the last contribution will be generated this way:

With snarkjs:

Commit: [https://github.com/iden3/snarkjs/commit/988b668a396b1c417b23e31438854637fa434424](https://github.com/iden3/snarkjs/commit/988b668a396b1c417b23e31438854637fa434424)

snarkjs ptb pot28_0054.ptau pot28_beacon.ptau pot28 [beaconHash] 10

Or Using original rust code:
[https://github.com/kobigurk/phase2-bn254/commit/dd6b96657d16c1a2b81fd23e540581c356284ec6](https://github.com/kobigurk/phase2-bn254/commit/dd6b96657d16c1a2b81fd23e540581c356284ec6)

beacon_constrained challange_0055 response_beacon 28 8192 [beaconHash] 10

After this, the `preparePhase2` process will be run.