1) What does security/efficiency improvement for hardware wallets means?
Isnt segwit general purpose, what special advantage do hardware wallets get? Please explain.
The problem with the current way that hardware wallets is that they have a hard time finding your previous outputs (i.e. inputs). Segwit makes this process much easier. It also makes signing faster. Read this for the full explanation (rephrasing it would be redundant):
https://segwit.org/segregated-witness-and-hardware-wallets-cc88ba532fb32) What does P2SH 256 bit mean? Is ECDSA or RIPEMD160 replaced in those kinds of transactions? How does the 256bit securiy manifest itself?
Multisig payments currently use P2SH which is secured by the 160-bit HASH160 algorithm (RIPEMD of SHA256). However, if one of the signers wishes to steal all the funds, they can find a collision between a valid address as part of a multisig script and a script that simply pays them all the funds with only 80-bits (280) worth of work, which is already within the realm of possibility for an extremely well-resourced attacker. (For comparison, at a sustained 1 exahash/second, the Bitcoin mining network does 80-bits worth of work every two weeks)
Segwit resolves this by using HASH160 only for payments direct to a single public key (where this sort of attack is useless), while using 256-bit SHA256 hashes for payments to a script hash.
https://bitcoincore.org/en/2016/01/26/segwit-benefits/#increased-security-for-multisig-via-pay-to-script-hash-p2shI also have other criticisms of Segwit, mainly the steering away from onchain scaling towards offchain scaling, which would really mean centralization.
When the transactions are not settled on the blockchain, then you essentially enabled fractional reserve banking. Because anyone can just make up coins out of thin air, if payments will be handled on a secondary chain.
Utter bullshit. Having several secondary layer solutions -> decentralization. You also can't create out of thin air on a sidechain due to two-way peg.