Table of contentsSectionAbout the editorIntroductionockchain Technology Overview Nistir 82026Blockchain at the gsaockchain in health it and Health-related researchkchain Technology: Possibilitthe us pAddress of CFTC Commissioner J
Christopher GiICE Homeland Security Investigations Investigative ProgramsThe US Congress and
Table of contents82 Executive Summary8856871 4 Document structu88 2 Blockchain Architecture129022 Transactions9224 Addresses and Address Derivation93 241 Private Key Storage5 ledg9526 Blocks973 Blockchains in Operatio8 4 Consensus99 4I Proof of work con00 42 Proof of stake cons202 4, 4 Ledger Conflicts and resolutions3204 51 Soft fork0552 Hard Forks206 53 Cryptographic Changes and Forks20971 Permissioned3621071 1 Application Considerations for Permissioned blockchains211712 Use Case ExampNISTIR 8202(DRAFT) BLOCKCHAIN TECHNOLOGY OVER VIEW21472Case Examples
Platforms21681CBitcoin Cash(BCC)22081 4 Ethereum (ethiEthereum Classic (ETC)22 6 Dash (DASh)23 817 Ripple(XRP224 82 Hyperledger22682 2 Hyperledger Sawtoot227823 Hyperledger Iroha228 824 Hyperledger Burrow229825H2319 Blockchain Limitations and Misconceptions232 91 Blockchain Control233 92 Malicious use
2359,4 Resource usage23796 Private/Public Key Infrastructure and Identit240 List of Appendices43 Appendix C--Re45 List of Tables and Figures247 Table 2: Example Transactio249 Figure 2
Submitting a Tction to a node waiting in the pending transaction List252 Figure 4- Transaction 4 has been included into a block nodes are transmitting the253 information: the final node has not yet received the latest informati254FiExample of a merkle6: Blockchain with merkle trec257 Figure 8: Transaction Being Added to Unspent Transaction Pool258 Figure 9: Finalized Block( Generalized)259 Figure 10: Distributed Network in Conflict60 Figure261FiChain b adds the Next block262 Table 3: Impact of Quantum Computing on Common Cryptographic Algorithms263
Blockchain at the gsaederal agencies are eager to better evaluate and adopt distributed ledger technologies (likeblockchain) that use encryption and coding to improve transparency, efficiency and trust innformation sharing Blockchain use cases that agencies submit for exploration touch many partsandprocessesFinancial managementPreIT asset and supply chain managementSmart contractPatents, Trademarks Copyrights, RoyaltiesGovernment-issued credentials like visas, passports, SSN and birth certificatesFederal personnel workforce dataAppropriated fundFederal assistance and foreign aid deliverySAs Emerging Citizen Technology Office launched theederal Blockchain program forfederal agencies and us businesses whorested in exploring distributed ledgtechnology and its implementation within governmentfirst US
Federal Blockchain Forum on July 18, 2017, uniting more than 100eral managers from dozens of unique agencies to discuss use cases, limitations, and solutionAgency teams submittedwn potential use cases for blockchain technology to our currentrepository of almost 200 submissionsIved: If you are a government employee with a gov or mil email address, join ourTo join our public listserv for Blockchain, contact listserv@ listserv gsa gov with the messagebody SUB Blockchain PublicSourcehttps://wwwgsagov/technology/government-it-initiatives/emerging-citizen-technology/blockchain
se of blockchain in health it and health-related research ChallengeThe goal of this Ideation Challenge was to solicit White Papers that investigate the relationshipbetween Blockchain technology and its use in Health IT and/or health-related research Thepaper should discuss the cryptography and underlying fundamentalsexamine how the use of Blockchain can advance industry interoperability needs expressed in theOffice of the National Coordinator for Health Information Technologys(ONC) SharedNationwide Interoperability Roadmap, as well as for Patient Centered Outcomes ResearclPCOR), the Precision Medicine Initiative(PMi), delivery system reform, and other healthcaredelivery needs, as well as provide recommendations for Blockchain's implementation Inddition to a monetary award, winners may also have the opportunresent their whitePapers at an industry-wide"Blockchain Healthcare Workshop"co-hosted by ONC and NisONC selected the winning papers based on several factors, including the papers proposedndationsket viability; creativity; ability to inform and fostertransformative change; and potential to support a number of national health and healthnformation objectives including advancing the flow of health information for where and when itis needed mosthe final winners wereto-peer network that enables parties to jointly store and analyze data with completepeerBlockchain and Health IT: Algorithms, Privacy, and Data PDF-507KB a peerprivacy that could empower precision medicine clinical trials and researchAuthors: Ackerman Shrier A, Chang A, Diakun-thibalt N, Forni L, Landa f, Mayo J, varOrganization: Project PharmOrchard of MITs Experimental Learning"MIT FinTeclFuture Commerce2 Blockchain: Securing a New Health Interoperability Experience IPDF-609 KBlBlockchain technologies solutions can support many existing health care businessprocesses, improve data integrity and enable at-scale interoperability for informationnge, patient tracking, identity assurance, and validatAuthors: Brodersen C, Kalis B, Mitchell E, Pupo E, Triscott AOrganization: Accenture LI3
Blockchain Technologies: A Whitepaper Discussing how Claims Process can beImproved PDF-1 MB Smart contracts, Blockchain, and other technologies can becombined into a platform that enables drastic improvements to the claims process andproves the healthcare expe for all stakeholdersAuthor Culver KOrganization: Unaffiliated4 Blockchain: Opportunities for Health Care IPDF-787 KB Presentation of anplementation framework and business case for using blockchain as part of heainformation exchange to satisfy national health care objectiveAuthors: Krawiec RJ, Barr D, Killmeyer K, Filipova M Nesbit A, Israel A, Quarre F,
edosva K tsai LOrganization: Deloitte Consulting LLP5 A Case Study for Blockchain in Healthcare: "MedRec"Prototype for ElectronicHealth Records and Medical Research Data PDF-591 KB A decentralized recordhandle electronic health records, using Blockchain technologythat manages authentication, confidentiality, accountability and data sharingAuthors ekblaw A Azaria a halamka j lippman ations MIt Media lab, beth israel deaconess medical center6 The Use of a blockchain to Foster the development of patient-Reported OutcomeMeasures IPDF-195KBl Use of the Internet of Things in combination withBlockchain technology for Patient Reported Outcome Measures(PROMs)Author Goldwater JCization: National Quality Forum7 Powering the Physician Patient Relationship with"HE of One'Blockchain HealthITIPDF-162 KB1 ' HIE of One links patient protected health information(PHi)toockchain identities and Blockchain identities to verified credential provider institutlower transacties security for all participAuthor: Gropper AOrganization: Unaffiliated8 Blockchain: The chain of trust and its potential to transform healthcare- OurPoint of view PDF- 249 KB Potential uses of Blockchain technology in health careincluding a detailed look at health care pre-authorization payment infrastructurecounterfeit drug prevention and detection and clinical trial results use caseOrganization IBM Global Business service public sector9
Moving toward a blockchain-based method for the secure storage of patientRecords PDF-270 KB Use of Blockchain as a novel approach to secure health dataplementation obstacBlockchain solutionAuthor Ivan drganization Unaffiliated10 Model Chain: Decentralized Privacy-Preserving Health Care Predictive ModelingFramework on Private Blockchain NetworkS PDF-272 KBl ModelChain is aamework used to adapt Blockchain to enable privacy-preserving health care predictivemodeling and to increase interoperability between institutionsAuthors Kuo t hsu c oMachado lOrganizations: Health System Department of Biomedical Informatics, University ofalifornia San Diego, La Jolla, CA Division of Health Services ResearchDevelopment, VA San Diego Healthcare SystemBlockchain for health Data and its potential use in health it and health careRelated Research IPDF-15 MB A look at Blockchain based access-control managereases expressed inONC'S Shared Nationwide Interoperability roadmapganization: Unaffiliated2 A Blockchain-Based Approach to Health Information Exchange Networks IPDF-402KB A Blockchain-based approach to sharing patient data that trades a single
twork consensus and predicates consensus onofof structural andteroperabilityAuthors: Peterson K DeedvanuR, Kanjamala P bolesOrganization: Mayo clinic3 Adoption of Blockchain to enable the Scalability and Adoption of Accountable CareIPDF-500 KBl A new digital health care delivery model that uses Blockchain as afoundation to enable peer-to-peer authorization and authenticationAuthor Prakashtion UnaffiliatedA Blockchain Profile for Medicaid Applicants and recipients PDF-190 KB Aution to the problem churning in the medicaid program that illustrates how health ITand health research could leverage blockchain-based innovations and emerging artificialntelligence systems to developdels of health care delivery
A Haynes-SOrganization: Blockchain Futures Lab-Institute for the futur15 Blockchain Alternate Pavment Models PDF-601KB Blockchain technology have payITplatforms that would help link quality and valueAuthor: Yip KOrganization: Unaffiliatedackarchive-itorg/3926/20170128063822/httphhs gov/about/news/2016/08/29kchain-challenge
Blockchain Technology: Possibilities for the Us Postal ServiceAt its core, blockchain technology is a way to transfer any kind of data or information in atracked, and secure way without the need for an intermediary institution Initially developedallow peers to directly exchange digital currency faster and at lower cost, blockchain is nowding a variety of promising new solutions beyond financial services It is difficult tounderstand the full potential of these new applications at this formativeproperty transfers, the execution of contracts, authentication services, device management, andrecords managementblockchain technology is a new way to transfer any kind of data or information in a fasttracked and secure manner without need for anMajor companies, such as Citibank and Australia Post, are beginning to research ands technology in order to provide new and more efficient serviceThe postal service could benefit froms technology particularly regardingfinancial services, identity services, supply chain management, and device managemeand should consider exploring and experimenting with itDespite their novelty, these applications are beginning to gain traction with major companies andgovernment entities, from Citibank and JPMorgan Chase to the Estonian government andAustralia Post
These organizations are researching or experimenting with blockchain technologyin order to keep better records and provide new and more efficient servicesUS Postal Service Office of Inspector General contracted with Swiss Econobetter understand blockchain technologys features and capabilities, as well as identareas ofor the postal seOne major area is financial services The Postal Service could use blockchain technology tothe back-end of its financial products, such as internatiorders a blockchain-based financial platform could digitize and streamline the services, makingthem faster and cheaper for both the Postal Service and its customers In the long-termblockchain technology could also be useful to the postal Service in other areas such as identityservices, supply chaiagement, and device managementWhile blockchain was originally developed as part of digital currency, people are realizing thatat its core, it is a way to transfer any kind of information in a fast and private way and that it canbe useful for any kind of information or value transfer that typically involThis realization has spurred intense development activity in the market In fact, people in thefield are comparing it to the early stages in the development of the Internet, and there are similarlevels of capital investment in startups related to blockchain services and applications as therethe deof the internet in the mid -1990s Just as the internet relies on servicesuch as browsers and email clients to help consumers access its capabilities, blockchain
About the editorMichael Erbschloe has worked for over 30 years performing analysis of theeconomics of information technology, public policy relating to technology, andutilizing technology in reengineering organization processes He has authoredseveral books on social and management issues of information technology thatwere published by Mc Graw Hill and other major publishers He has also taught atseveral universities and developed technology-related curriculum
His career hasfocused on several interrelated areasTechnology strategy, analysis, and forecastingTeaching and curriculum developmentoks and articlesPublishing and ediPublic policy analysis and program evaluationBooks by michael erbschloeThreat Level Red: Cybersecurity Research Programs of theUS Government(CRC Press)Social Media Warfare: Equal Weap Access to Improve Organizationalons for All(auerbach Publications)Security(Auerbach Publications)Physical Security for IT(Elsevier SciTrojans, Worms, and Spyware(Butterworth-Heinemann)Implementing Homeland Security in Enterprise IT(Digital Press)Guide to Disaster Recovery( Course TechnologySocially responsible IT Management(Digital PressInformation Warfare: How to Survive Cyber Attacks(McGraw Hill)The Executive's Guide to Privacy Management(McGraw hill)Net Privacy: A Guide to Developing Implementing an e-blPrivacy Plan(McGraw Hill)
ntroductionBlockchains are immutable digital ledger systems implemented in a distributed fashion (ieepository) and usually without a central autheAt itst baenable a community of users to record transactions in a ledger public to that community such thatno transaction can be changed once publishedBlockchains are a new information technology that have the potential to invert the cybersecuritparadignblockchain networks are trustless: they assume compromise of the network byboth insiders and outsiders Second, blockchains are transparently secure: they do not rely onnure-prone secrets but rather on a cryptographic data structure that makes tampering bothexceptionally difficult and immediately obvious Finally, blockchain networks are fault tolerantey align the efforts of honest nodes to reject those that are dishonest, As a result, blockonetworksreduce the probability of comprbut also impose significantly greaterosts on an adversary to achieve it The Air Force, for example, will research and developblockchain technology and leverage it for national defensea blockchain is a shared, distributed, tamper-resistant database that every participant on aare-but thatntrols In other words a blockchain is a databasethat stores digital records The database is shared by a group of network participants, all of whomcan submit new records for inclusion however those records are only added to the databasebased on the agreement, or consensus, of a majority of the group Additionally, once the recordsare entered, they can never be changed or erased I In sum, blockchains record and secure digitalnformation in such a way that it becomes the groups agreed-upon record of the pastThe blockchain was first proposed in 2008 by Satoshi Nakamoto(a
pseudonym) in conjunctionwith the cryptocurrency Bitcoin Nakamoto's vision was to"allow online payments to be sentdirectly from one party to another without going through a financial institutionHoweverwithout a trusted central authority to oversee accounts and transactions, there would beprevent dishonest actors from spending a single Bitcoin twice Nakamoto's solution was adistributed database of time-stamped, consensus-based, cryptographically tagged transactionsthat form a record that cannot be changed-a blockchain Bitcoin became a reality in 2009, andince then its market capitalization has gone from zero to more than $6on as of Apr2016 Each day, some ofs 66 million users exchange more than $75 million in 120,000transactions across the networkBitcoin offers a noteworthy example of a blockchain's potential All of Bitcoins currencytransactions and accounts that have ever existed are recorded in a blockchain database that liveson the open Internet It is fully exposed to the hostile efforts of governments, criminalorganization, and hackers Yet, the Bitcoin blockchain has never been hacked Clearly, thisechnology deserves study
While the blockchs virtually synonymous with Bitcoin for several years, it should bemade clear that they are two separate technologies Bitcoin is just the first popular application ofjust as e-mail was the first popular applicae Internet 6 Its potential is soast, in fact, that advocates compare the maturity and innovative potential of blockchainechnology today to that of the lntbecause blockchain techiides on the existing internet infrastructure thematurity of blockchain technology is likely to progress three times faster than the Internet, withmainstream use expectedn the next eighIndustry has recognized the potential of blockchain technology Since 2013 more than $l billionof venture capital has been invested into 120 blockchain start-ups Aims are diverse, rangingance to the tracking and traddiamonds and art) to digitalotary services that can serve as evidence in a court of law; hebeyond just start-ups Large, mature companies such as Lockheed Martin, IBM, and goldmanblockchain applications in their resplockchains solve a challenging problem in data science: how to reliably exchange informationover an unreliable network on which some of the participants cannot be trusted The blockeecurity model inherently assumes that these dishonest participants will attempt to create frictionby not only generating false data but also attemptingate valid dassed from honestparticipants By using a variety of messaging and consensus techniques, blockchains ensure dataegrity by both rejecting invalid data and preventing valid data from being secretly modified ordeletedover traditional cyber defense s, s of examination because it offers three significant advantagesBlockchain techategies First, rather than trying to defend boundaries fromompromise, blockchains assume compromise by both adversaries and trusted insiders
They areesigned to defend data in a contested cyber environment Second, blockchain networks harnessthe aggregate power of the network to actively resist the efforts of malicSpecifically,blockchains take advantage of the asymmetry of many against few Finally, the security thasecreIst There are no passwords to be exposed,cryptographic keys to be protected, or administrators to be trusted Blockchains provide anerent security function on which additional security functions can be added, depending on theapplication As result of these advantages, blockchains are capable of operating successfully andsecurely on the open Internet, without a trusted central authority, while fully exposed to hostiles paper examines the blockchain activities of the Us Gohttp:/wwwairuniversityafmil/cyberCollege/portal/article/Article/1238526/blOckchain-technology
Blockchain Technology Overview NISTIR 8202Aiming to clarify the subject for the benefit of companies and other organizations, the nationalInstitute of Standards and Technology (NiST) has released a straightforward introduction toblockchain, which underpins Bitcoin and other digital currenciesVirtual barrels of digital ink are flowing in the media nowadays about these cryptocurrencies andthe underlying blockchain technology that enables them Much of the attention stems either frome giddy heights of value attained lately by the most well-known of these currencies, Bitcoin, orfrom the novelty of blockchain itself, which has been described (link is external) as the mostIrruptive tegy since the internet Blockchain's proponents believe it lets individualerform transactions safely without thethat are required in conventional transactionThe NisT reports authors hope it will be useful to businesses that want to make clear-eyeddecisions about whether blockchain would be an asset to their productWe want to help people understand how blockchains work so that they can appropriately andefully apply them to technology problems, said Dylan Yaga, a NST computer scientist whois one of the report's authors
It's an introduction to the things you should understand and thinkabout if you want to use blockchainThe nist document, whose full title is Draft NIST Interagency Report(NISTIr)8202Blockchain Technology Overview(link is external), introduces the concept of blockchainlectronic currency, and shows its broader apla blockchsentially a decentralized ledger that maintains transaction records on manycomputers simultaneously Once a group, or block, of records is entered into the ledger, theblocks information is connected mathematically to other blocks, forming a chain of recorWithout changing all subseauent bocks iP the chain and crea inp a discre ancy that other recordkeepers in the network would immediately notice In this way, blockchain technology produces adependable ledger without requiring record-keepers to know or trust one another, whicheliminates the dangers that come with data being kept in a central location by a single ownerThe blockchain idea has attracted enough supporters that there are now several hundred digitalcurrencies on the market (link is external), and the companies that are investigating ways toemploy blockchain number many more Because the market is growing so rapidly, severaleholders, customers and agencies asked Nist to create a straightforward description ofblockchain so that newcomers to the marketplace could enter with the same knowledge about thetechn
Blockchain is a powerful new paradigm for business, " Yaga said "People should use it--if itappropriatesupply chain management and keeping track of insurance transactions The rep t 2Then it is appropriate As with any newploywas created partly to help IT managers make informed decisions about whether blockchain is thehtr a given taskn the corporate world, there's always a push to adopt new technologies, "Y aga saidBlockchain is today's shiny neyand there's a big push to adopt it because of thatWe want to help pee past the hype he said "as lofty a goal as thatT has been tasked before with writing definitions of emerging concepts inch as the definition of cloud computing it released in 2011 while y aga describesthe blockchain description as approachable-it's"as high-level as I can write it, he said-theonger than some other nist definitions because the technology combines so manycomplex ideas Among them are digital signatures, peer-to-peer networking and hash chains, allwhich are tools common in cryptography and with which NisT has had extensiveInvolvemeWe dont have any axe to grind or product to sell, though, "Y aga said ""A lot of articles youad online feature a disclaimer indicating that the author owns a certain amount ofcryptocurrency or stock in a company
I have no vested interest in the monetary value of thesenetworks But we don't pass judgment on the technology; we just want to get past the rumorTo that end, Yaga said, the document began as a sort of FAQ addressing falsehoods the authorshad come across-such as the idea that there was no need for trust in the system ("You do needtrust, " he said, "just not a trusted third party, like a bank )It expanded to discuss the technicalools commmost blockchain-based systems and also explored related issues, such as thehigh demands blockchain systems place on network resources The roughly 60-page reportenlighten anyone who wants a pictuckchain that is not skewed to any players'interestsbut will give perspective to technical decision makers in particularA companys IT managers need to be able to say, we understand this, and then be able to arguewhether or not the company needs to use it based on that clear understanding, he said "Someing you should use it everywhere for everythilthat youSource:https://wwwnistgov/news-events/news/2018/01/nist-report-blockchain-technology
This publicationded to provide a high-level technical overview of blockchain technologydiscusses its application for electronic currency as well as broader uses
The document looks atdifferent categories and approaches for different blockchain platformss document is intended to help readers to understand the technologies which compriseblockchain systems and to understand how blockchains can be appropriately and usefully appliedto technology problemstheof blockchain technologySection 2 defines the high-level components of a blockchain system architecture, includinghashes, transactions, ledgers, blocks, and blockchainsSection 3 discusses how a blockchain is expanded through the addition of new blocksrepresenting sets of transactionsection 4 examines the need for consensus models to resolve conflicts among blockchainmining nodesSection 5 introduces the concept of forkingSection 6 defines and discusses smart contractsSection 7 looks at blockchain permission models, discusses their application considerations,ction 8 provides several examples of blockchain platforms in use today to indicate thetions frection 9 highlights some of the limitations of blockchain technologAppendix A contains a glossary for selected terms defined in the documentAppendix B provides a list of acronyms and abbreviations used in the documentAppendix C defines the references used throuSource:https://csrcnistgov/publications/detail/nistir/8202/draft#tpubs-abstract-header
Executive SummaryBlockchains are immutable digital ledger systems implemented in a distributed fashionhout a central repository) and usually without a central authority At their most basiclevel, they enable a community of users to record transactions in a ledger that is public to thatch that no transactionblished In 2008 thedea was combined in an innovative way with several other technologies and computing conceptsto enable the creation of moderney protected throughryptographic mechanisms instead of a central repository The first such blockchain basedapproach was Bitcoin These currency blockchain systems are novel in that they store value, neust information The value is attached to a digital wallet-an electronic device(or software)thatows andual to make electronic transactions The wallets are usedfrom one wallet to another, recording the transferred value publicly, allowing all participarf the network to independently verify the validity of the transactions Each participant can keera full record of all transactions, making the network resilient to attempts to alter that record (orforge transactions)latere are countless news articles and videos describing theof the blockchainthis paper aims to describe the method behind the magic (i
e how a blockchain system works)Arthur C Clarke once wrote, Any sufficiently advanced technology is indistinguishable frommagic"[1] Clarkes statement is a perfect representation for the emerging use cases forblockchain technology There is a high level of hype around the use of blockchains, yet thetechnology is not well understood It is not magical; it will not solve all problems As with allnew technologyery way imaginables document attempts bring a high-level understandthe technoAs stated above, blockchain technology is the foundation of modern cryptocurrencies, so namedbecause of blockchain's heavy usage of cryptographic functions Users utilize public and privatkeys to digitally sign and securely transact within the system Users of the blockclpuzzles using cryptographic hashing in hopes of being rewarded with a fixed amount of thepplicable than its applicationtocurrencies In this work, we try tobroader applicability while stilla large extent on the cryptocurrency use case(since that is the primary use case today)Organizations considering implementing blockchain technology need to understand importantblockchain system and then decides they need to make modifications to the data stored? Whenusing a database, this can be accomplished through a simple query (or major changes can bemade by updating the database schema or software) However, on a blockchain, it is much moredifficult to change data or update the 'database software Organizations need to understand the
extreme difficulty in changing anything that is already on the blockchain, and that changes to theblockchain software may cause forking of the blockchain Another critical asphnology is how the participants agree that a transacd thisd“ reachingconsensus", and there are many models for doing so, each with positives and negatives for asiness caseSome existing blockchain technologies focus on storing wealth while 154latformfor smart contracts(software which is deployed on the blockchain itself, and executed by theomputers running that blockchain) New blockchain technologies are beinonstantly to enable new use cases and to improve the efficiency of existing systems Someblockchain implementations are permissionless, meaning anyone c:ementations limit participation to specific people or companies, allow finer-grainedcontrols, and may be managed by a central entity Knowing these specifics allows anorganization to understand what will be most applicablDespite the many variations of blockchain systems and the rapid development of newtechnologies most blockchains use some common core concepts Each transaction involves oneor more addresses and a recording of what happened, and it is digitally signed
Blockchains arecomprised of blocks, each block being a group of transactions All the transactions in a block aregrouped together, along with a cryptographic hash of the previous block Finally, a new hash iseated for the current block 's header to be recorded within the block data itself as well as withinthe next block Over time, each block is then chained to the previous block in the chain byadding the hash of the previous block to the header of the current blockgy used in a blockchain sytakes existing, proven conceptsges themexplores the f,ay that can address problems that were previously difficultThis documentexplores the fundamentals of how blockchain technologies work, how the participants in thenetwork come to agree whether a transactiod, what happens when changes need to bemade to an existing blockchain deployment, and how permissions work Additionally, thisdocument explores specific blockchain applications and examples of when to consider using ablockchain systemuse of blockchain technology is not a silver bullet, and thereles that must beconsidered such as how to deal with malicious users, how controls are applied, and thelimitations of any blockchain implementation That said, blockchain technology is an importantconcept that will be a basis for many new solutionsinformationvisithttps://csiblications/detail/nistir/8202/draft#pubsbstract-heade