Branch::Level offset values are not always correct

[Carlos Pérez]

After elaborating some tests, I've seen that once I get the Kelvin Branch, not all of the offsets do match with it's corresponding hash positions on the upper Level.

Branch: PoseidonBranch { root: 0x087cfe079397028bd6de80e102628c9783a363ccc57c2ffdf013c0b1e47cfd4b, levels: [PoseidonLevel { upper_lvl_hash: 3, leaves: [0x0000000000000000000000000000000000000000000000000000000000000003, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x000000000000000000000000000000000000000000000000000000000000000d, 0x0000000000000000000000000000000000000000000000000000000000000009] }, 

PoseidonLevel { upper_lvl_hash: 4, leaves: [0x0000000000000000000000000000000000000000000000000000000000000001, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x2b82f82f5c91c1b1860cc7a424536b4aee92b5ffb43d9fb39f27924d79f7d432] }, 

PoseidonLevel { upper_lvl_hash: 4, leaves: [0x0000000000000000000000000000000000000000000000000000000000000001, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x3c73c654ea296a4afbeb9ff93af061e6706fd2da476f25d8443185b48cc0ecb9] }, 

PoseidonLevel { upper_lvl_hash: 4, leaves: [0x0000000000000000000000000000000000000000000000000000000000000001, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x72a5773695750f72f621030fa9cfb75d9c28c7d395036d961d2992fec09d28f5] }, 

PoseidonLevel { upper_lvl_hash: 4, leaves: [0x0000000000000000000000000000000000000000000000000000000000000005, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000011, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x679270b490d6e7cfa44e929178c8fdeee800589ce3bbefb86b7bfb0d7ec9e9ec] }, 

PoseidonLevel { upper_lvl_hash: 3, leaves: [0x0000000000000000000000000000000000000000000000000000000000000002, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x25b1377a614dd96669d61be14dacab609d0a520290e231c07abdc07730dcccff, 0x0000000000000000000000000000000000000000000000000000000000000000] }, 

PoseidonLevel { upper_lvl_hash: 3, leaves: [0x0000000000000000000000000000000000000000000000000000000000000002, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x21d45a0052ba26a952ec18e6e928d075e81e0fcd770cb82a861a92a5c7952f79, 0x0000000000000000000000000000000000000000000000000000000000000000] }, 

PoseidonLevel { upper_lvl_hash: 3, leaves: [0x0000000000000000000000000000000000000000000000000000000000000002, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x0000000000000000000000000000000000000000000000000000000000000000, 0x175d8fae6690405ca49717d11919f04379c03e2ad3a80786c045f44ee64337d3, 0x0000000000000000000000000000000000000000000000000000000000000000] }, 

PoseidonLevel { upper_lvl_hash: 3, leaves: [0x000000000000000000000000000000000000000000000000000000000000000f, 0x4030657e7b7c68d60872d32a447c95fee900bb365d3e8e5c1ab10b87531af13f, 0x71814581e64527148ed5c4ce3a8c0d477360f05bc5261b9435cc32cfd151d847, 0x468b8743ee998e90309be2f343999c0140c899b297282f4737829044eb6fc3cc, 0x07ae7d964e2c86233cf880fc8531710fd37b640ba43ce522e6a56da386569312] }] }

This is the trace of the PoseidonBranch I import From the kelvin::Branch.
upper_lvl_hash is a field that represents the offset of the next level position of the hash of this level.
This takes in consideration that we compute the bitflags. So I add 1 to ALL of the offsets.

The problem is that there are only two levels that do not match with it's previous offset.

Error on hashing chain. Lvl Hash Announced: 0x2b82f82f5c91c1b1860cc7a424536b4aee92b5ffb43d9fb39f27924d79f7d432, Upper level hash: 0x0000000000000000000000000000000000000000000000000000000000000000
Error on hashing chain. Lvl Hash Announced: 0x25b1377a614dd96669d61be14dacab609d0a520290e231c07abdc07730dcccff, Upper level hash: 0x0000000000000000000000000000000000000000000000000000000000000000

After debugging and checking the offsets of the Branch before I generate my custom data structure, I've been able to see that the offsets indeed do not match on each level.

Could you test this within kelvin @krl ? Since after some hours of debugging I really think that the error is here.

Until we don't clarify what's going on, this is blocking: dusk-network/Poseidon252#11

[Carlos Pérez]

After discussing it with @krl, it's verified that there's a bug in kelvin affecting the offsets that the Branch structure provides.

[Carlos Pérez]

After some tests elaborated in a49363a it was verified that there was indeed no bug in the code.

This came from a missunderstanding in what was the offset field of each level referencing.
So closing this.