## 7 Redaction Mechanisms in Blockchain
### Redactable Blockchain-Based Chameleon
#### 7.1.3 Redactable Consortium Blockchain
The requests are stored in modified transactions while the signature key is stored in the local redaction record. Thus, accountability is maintained as redaction records could be compared with the stored signatures. Nonetheless, an additional storage cost and low anonymity would be the issues. [PERSON] et al. [83] improved the previous work of [79] by elevating the anonymity and scalability degrees with the time-updatable CH (TUCH) and linkable-and-redactable ring signature (LRRS) as theoretical fundamentals to develop a decentralized, scalable and redactable algorithm with sufficient anonymity similar to the SRB. The TUCH enables automatic ring configuration without interacting with other entities when producing an access key. As the chameleon randomness in holding a hash collision is subject to cyclical expiration, redaction could fulfill verification criteria only within a pre-determined period. Meanwhile, the LRRS ensures modifiers anonymously provide personal signatures on a message without trusted parties. The process is completed by forming a ring of users automatically, without the users being informed that their public keys are employed in producing the signature. Nevertheless, increasing scalability would lower the anonymity level owing to the requirement of the signature, which simultaneously renders the process to be costly. Conversely, [PERSON] et al. [84] criticized the [79] TCH proposal after manifesting that the TCH was vulnerable to malicious redactions. Correspondingly, an enhanced TCH was established to elevate the collision n-resistance degree, which was recognized as one-more preimage resistance. The enhanced protocol ensured sufficient resistance even when preimages with the same hash values and identities were exposed. Nonetheless, similar to the RCB, the protocol was seldom adopted in IoT devices due to high cryptographic complexity. Security issues, such as collusion and scalability, were not adequately considered. [PERSON] et al. [85] discovered that credible industrial blockchain data management could optimize blockchain reducibility by enhancing public key generation through the CH function in three phases, namely off-chain setup, on-chain setup, and data management. During the setup different data types are included in the blockchain where trapdoor partial authenticity verification is conducted and aided by smart contracts to determine accountability levels. Particularly, the off-chain setup deploys blockchain parameters to create trapdoor segments and perform trapdoor distribution to support trapdoor holders. The on-chain setup is executed by employing the redactable blockchain to collect various data before gauging the authenticity degree. Subsequently, data management separation from other transactions is performed by two different blockchain approaches to realize management supervision on transaction redaction, while reducing coupling in the blockchain-based trapdoor recovery accountability mechanism. Smart contracts would verify the validity of trapdoor segments published by the holders, which are concurrently monitored by supervision nodes before jointly approving editing requests. Trapdoor performers would redact information upon receiving approval. Nonetheless, the entire process is costly, which is unsuitable for the IIoT environment. Accordingly, [PERSON] et al. [86] proposed the federal learning model to be applied in the IIOT circumstances, such as the medical blockchain (RMB), by incorporating the CH changeable trapdoor (CHCT) function. When collisions are identified, the CHCT would be updated to govern the process without revealing the trapdoor. The CHCT could be canceled in in all circumstances to avoid key exposure owing to the highly restricted trapdoor contributed by the owner's autonomy to define the expiration time. Figure 7: The [PERSON] et al. (2019) RCB signature chain.