  The rise of crypto-currencies has spawned great interest in their underlying
technology, namely, Blockchain. The central component in a Blockchain is a
shared distributed ledger. A ledger comprises series of blocks, which in turns
contains a series of transactions. An identical copy of the ledger is stored on
all nodes in a blockchain network. Maintaining ledger integrity and security is
one of the crucial design aspects of any blockchain platform. Thus, there are
typically built-in validation mechanisms leveraging cryptography to ensure the
validity of incoming blocks before committing them into the ledger. However, a
blockchain node may run over an extended period of time, during which the
blocks on the disk can may become corrupted due to software or hardware
failures, or due to malicious activity. This paper proposes LedgerGuard, a tool
to maintain ledger integrity by detecting corrupted blocks and recovering these
blocks by synchronizing with rest of the network. The experimental
implementation of LedgerGuard is based on Hyperledger Fabric, which is a
popular open source permissioned blockchain platform.
