## 7 Redaction Mechanisms in Blockchain
### Redactable Blockchain-Based Chameleon
#### 7.1.1. Redactable Permissioned Blockchain  
According to the taxonomy, permissioned blockchain reaction mechanisms have been divided into three main sets in which are analyzed and discussed thoroughly as follows:  
* Enhanced Collision-Resistance of Chameleon Hash Function (ECRSCH)  
[PERSON] et al. [61] have proposed the first redactable blockchain with an enhanced standard chameleon hash function (ECRSCH) by incorporating chameleon hash function (CH), public-key cryptography (PKE), and non-zero knowledge proof (NIZKP), which is adopted by Accenture. Every block structure in the blockchain will extend to include an additional field to efficiently record the randomness (r), also termed as a chameleon hash check value, whereas solely trapdoor key holders consequently are able to compute (r'), as the computation of additional redacted block (block \(n\)) randomness (r) is highly challenging without a trapdoor key. The randomness maintains the identicality of redacted blocks and header hashes (prior hashes) as before reduction to ensure the blockchain is intact. Figure 5 represents [PERSON]'s proposal. The approach is limited as the procedure is constrained \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Schema**} & \multirow{2}{*}{**Methods**} & **Security** & **Setting** & **Redaction** \\  & & **Assumption** & **(Blockchain Type)** & **Type** \\ \hline
[61], **(2017)** & CH and PKE & DLP & Private & BL \\ \hline
[62], **(2020)** & CH and ZR & SXDH & Private & BL \\ \hline
[63], **(2020)** & CH and ZR & SXDH & Private & BL \\ \hline
[64], **(2019)** & CH and ABE & DLP & Private & TL \\ \hline
[65], **(2020)** & CH and ABE and DS & DLP & Private & TL \\ \hline
[66], **(2021)** & CH and DS & DDH & Private & TL \\ \hline
[67], **(2022)** & CH and ABE and DS & DLP & Private & TL\(\backslash\)BL \\ \hline
[68], **(2021)** & CH and MA-ABE & DLS & DLP & Private & TL \\  & and DGS & DLIN & Private & TL \\ \hline
[69], **(2021)** & CH & DLP & Private\(\backslash\)Public & TFL \\ \hline
[70], **(2021)** & CH and ABE and DS & DLIN & Private & TL \\ \hline
[71], **(2021)** & CH and MA\_ABE & DLP & Private & TL \\ \hline
[72], **(2022)** & CH and ABE and DS & DLP & Private & TL \\ \hline
[73], **(2021)** & CH and ABE & DBDH & Private & TL \\ \hline
[74], **(2021)** & CH and ABE and DS & DLP & Private & TL \\ \hline
[75], **(2021)** & CH and TEE & DLP & Private & BL \\ \hline
[76], **(2021)** & CH and Lattice & SIS & Private & BL \\ \hline
[77], **(2022)** & CH & DLP & Private\(\backslash\)Public & TL \\ \hline
[78], **(2021)** & CH and MA\_ABE & & & \\  & and DS & DLP & Public & TL \\ \hline
[79], **(2019)** & TCH and DS & CDHP & Consortium & TL \\ \hline
[80], **(2019)** & RCH & CDHP & Consortium & TL \\ \hline
[81], **(2020)** & TTCH & CDHP & Consortium & TL \\ \hline
[82], **(2020)** & CH & DLP & Consortium & TL \\ \hline
[83], **(2021)** & TCH and DS & CDHP & Consortium & TL \\ \hline
[84], **(2021)** & TCH and DS & CDHP & Consortium & TL \\ \hline
[85], **(2021)** & CH & DLP & Consortium & TL \\ \hline
[86], **(2022)** & CH & CDHP & Consortium & TL \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chameleon redaction methods outlines. to rewriting the blockchain based on the block level where it impacts system security and efficiency regardless of mechanism employed, whereas chameleon hash function is utmost risky where the whole block privacy depends on a single trapdoor key for all the transactions maintained; once a modifier granted permission to alter any transaction, the rest can be modified too. Simultaneously, the procedure diminishes transaction validity in the blocks, including other relevant transactions. In addition, coarse-grained decision-making in the function does not define individuals entitled to compute the collision when the hash is frequently produced by the public key. Conversely, secret keys are employed to search for collisions without hash makers being aware of the individual performing the collision.