Yes, you need something against tampering. However, once you legally signed something, the contract/transaction is valid.
Various mechanism can be used to ensure integrity. What we implemented specifically is that various witnesses can inspect your Trustchain blocks and co-sign your balance. So any node can act as a digital notary. You can also use a reputation or trust function.
Here is a master thesis from Mathematics on distributed accounting systems. It contains numerous new mathematical proofs around integrity without strong identity assumption; .PDF "On the Sybil-Proofness of Accounting Mechanisms in P2P Networks", https://repository.tudelft.nl/islandora/object/uuid:6b4011c6...
Various mechanism can be used to ensure integrity. What we implemented specifically is that various witnesses can inspect your Trustchain blocks and co-sign your balance. So any node can act as a digital notary. You can also use a reputation or trust function.
Here is a master thesis from Mathematics on distributed accounting systems. It contains numerous new mathematical proofs around integrity without strong identity assumption; .PDF "On the Sybil-Proofness of Accounting Mechanisms in P2P Networks", https://repository.tudelft.nl/islandora/object/uuid:6b4011c6...