Situations exist where the ability to go back in time and perform an "undo" appear to make sense. In these contexts, we imagine a fair and balanced world operating in harmony \u2014 a utopian version of the modern internet of things.\nThe struggle for freedom of expression\nCensorship has been explained actions taken in the best interests of the public. A benevolent public concern for morality.\u00a0China\u2019s censorship of WeChat for Uber. The decision by India's film censor to cut 94 scenes from a movie about Punjab\u2019s drug problem.\u00a0Michelangelo\u2019s 1565 \u201cThe Last Judgement.\u201d\u00a0\nFreedom of speech is the right to articulate one\u2019s opinions and ideas without fear of government retaliation or censorship, or societal sanction. The right to be heard.\u00a0\nDoes a network hold trust if all voices\u00a0are not heard? Are we talking about the ability to edit a transaction or\u00a0present proof-of-trust, of immutability? The concepts are mutually exclusive.\nWhat is a redactable blockchain?\nGiuseppe Ateniese (USA), Bernardo Magri (Italy), Daniele Venturi (Italy) and Ewerton Andrade (Brazil) (referenced as AMVE here onward) are the inventors behind the new framework to rewrite and or compress the content of blocks. Their joint paper, \u201cRedactable Blockchain, or Rewriting History in Bitcoin and Friends,\u201d published Aug. 5, 2016, expands IBM Watson\u2019s earlier\u00a0chameleon signatures\u00a0research, published in 2000.\nAccording to AMVE, a blockchain is editable by adding a link to each link of the hash chain. Think of each block-to-block link as a lock (physical lock), in which a key is required to unlock it. In a permissionless blockchain, there is no key, making the series of transactions or blocks immutable. In a permissioned blockchain, this \u201ctrapdoor key\u201d can be given to miners, a centralized auditor, or shares of the key could be distributed among several authorities. In this context, these operators will have the ability to repair blocks \u2014 e.g. blocks can be deleted, modified or inserted into existing blocks.\nThe argument supporting an editable blockchain\nThe authors come from varied academic backgrounds.\u00a0Giuseppe Ateniese is a professor in and director of the computer science department at Stevens Institute of Technology.\u00a0Bernardo Magri is a researcher at Sapienza University of Rome. Daniele Venturi is an assistant professor at the University of Trento.\u00a0Ewerton Andrade is a researcher at the University\u00a0of\u00a0S\u00e3o Paulo.\nThis week I had the good fortune to speak with\u00a0Bernardo Magri, one of the visionary authors behind the editable blockchain concept. Margi conducts research on both the theoretical and practical aspects of cryptography. He joked, "working with cryptocurrencies is a shot in the dark, as the community's reaction to the work can be completely unpredictable \u2014 you never know if they will love your work or hate it." It's fair to say industry loved the work on redactable blockchains.\nMargi said there is one thing the public often gets wrong: "The public has trouble understanding the inner workings of blockchain technology. Therefore it's normal that they also have trouble seeing the benefits of this technology over a simple, centralized database system. Adding a redactable feature to a blockchain does not make it centralized at all. The blockchain will continue to operate as usual and depending on how the chameleon hash is shared the trust assumption could remain the same."\u00a0Redactable blockchains are possible when the trusted entities are limited (a variation of M-of-N multisig).\nDo we need a blockchain with a delete button? AMVE identified two industry approaches for the facilitation of the blockchain technology to implement decentralized services and applications: an overlay on top of Bitcoin and the creation of an alternative blockchain.\nThere are four motivations behind the desirability of redactable blockchains.\n\nAbuse: the ability correct the storage of arbitrary messages e.g. Bitcoin has already been abused with offensive material cemented in its walls for eternity.\nRewritable storage: classic blockchains do not scale and waste precious resources. Rewriting presents new storage options e.g. CD-R.\nInability to expunge: permitting the deletion of records if required e.g. in case they contain errors (medical records), sensitive information when it is necessary by law, or if personal encryption keys are leaked.\nInter-entity interactions: consolidation\u2019s hard to achieve with immutable blockchains e.g. this removes the impossibility of consolidating past transactions without affecting any subsequent blocks. This feature is necessary to combine distinct accounting structures, budgets, or transactions.\n\nAdapting the framework to the types of blockchains\nAMVE anticipated the next logical question: How are keys the managed across the three main types of real-world blockchains?\n\nPrivate blockchain: the ability to write is bestowed upon a central authority. This example is straightforward, with the \u201ctrapdoor key\u201d given to the central authority with the power to compute collisions and therefore redact blocks. A single operator has the power to redact.\nConsortium blockchain: consensus is predetermined by a finite group of parties. In this example, the \u201ctrapdoor key\u201d is shared among consortium parties and redactions can be made through secure multiparty computation (MPC) protocols similar to M-of-N multisigs (where multiple consortium parties just grant the redaction before authorization is approved). A select few have the power to redact.\nPublic blockchain: decentralized with no central operator and any party can submit transactions to the network e.g. a permissionless blockchain such as Bitcoin. AMVE offers two suggestions for this type of blockchain: (a) distribute the \u201ctrapdoor\u201d to all parties using multiparty computation (MPC) protocols, and (b) distribute to a chosen subset of parties. Under the assumption that the top 7 mining pools in Bitcoin already control 70 percent of the total network hashing power. All parties have equal\u00a0power to redact.\n\nWhat happens if there are HIPAA violations\nThere are many HIPAA violations that can occur. Below are 10 of the most common violations:\n\nLost or stolen devices e.g. unencrypted computer loss\nUnauthorized access e.g. database breaches or employees illegally accessing patient files\nEmployee dishonesty e.g. disclosing health records\nImproper disposal e.g. the hard drive in the office printer\nThird-party disclosure e.g. business associates or subcontractors which ineffectively protect protected health information (PHI)\nUnauthorized discussion of medical conditions e.g. while in a waiting room\nSharing incorrect medical information e.g. you receive a treatment plan in email that is not yours\nEmailing or texting patient\u00a0information e.g. receptionist emails patient information\nPosting on social media e.g. picture of a patient disease or treatment, even without name, is posted on social media\nLack of prior authorization information for release e.g. disclosure of any individual's PHI that is not used for treatment, payment, healthcare operations or that falls under the Privacy rule.\n\nDoes an editable blockchain offer advantages to healthcare entities that are part of the health delivery system. To address this question lets split this into two separate questions: (1) value of blockchains, and (2) benefits of editable blockchains. Blockchain technology, when applied to healthcare absolutely can improve the trust between doctors and patients. To\u00a0answer the second part of this question, we asked\u00a0Bernardo Magri, author and researcher, for his thoughts. For Magri the benefits for blockchains in healthcare settings are quite evident. Magri, then addressed potential benefits. "The chameleon key is only given to the healthcare privacy officer. However, we do not expect a privacy officer to run the entire blockchain or produce transactions about payments or add health records. The privacy officer would be called in when records must be expunged because of HIPAA or another regulation violation." The role of the healthcare privacy officer is expanding. As data, information, and intelligent analytics become a foundational element of every healthcare organization the protection of health information is a critical\u00a0growth and sustainability strategy.\nIn practice\nThe paper elaborates on a proof-of-concept implementation to redact a Bitcoin application using three distinct functions are explained: GenerateKey (create the \u201ctrapdoor key\u201d), ChameleonHash (computes hash \u2013 from the message and random number), and HashCollision (outputs new random number, for reference later). This scenario was then modeled using a regression test network feature of the Bitcoin core network.\nThis framework opens the ability to redact and compress the content of blocks in virtually any blockchain based technology. Are editable blockchains merely a form of modern censorship, disguised as flexibility but for the chosen few? Time will tell.\nIt's evident that industries are very curious about editable blockchains. Editable blockchains have just entered the Innovation Trigger stage of the Hype Cycle.