Technically speaking, a digital signature applies to a string of bits, whereas humans and applications "believe" that they sign the semantic interpretation of those bits. In order to be semantically interpreted, the bit string must be transformed into a form that is meaningful for humans and applications, and this is done through a combination of hardware and software based processes on a computer system. The problem is that the semantic interpretation of bits can change as a function of the processes used to transform the bits into semantic content. It is relatively easy to change the interpretation of a digital document by implementing changes on the computer system where the document is being processed. From a semantic perspective this creates uncertainty about what exactly has been signed. "WYSIWYS (What You See Is What You Sign)  means that the semantic interpretation of a signed message cannot be changed. In particular this also means that a message cannot contain hidden information that the signer is unaware of, and that can be revealed after the signature has been applied. WYSIWYS is a necessary requirement for the validity of digital signatures, but this requirement is difficult to guarantee because of the increasing complexity of modern computer systems. The term WYSIWYS was coined by "Peter Landrock and "Torben Pedersen to describe some of the principles in delivering secure and legally binding digital signatures for Pan-European projects.
Digital signatures versus ink on paper signatures
An ink signature could be replicated from one document to another by copying the image manually or digitally, but to have credible signature copies that can resist some scrutiny is a significant manual or technical skill, and to produce ink signature copies that resist professional scrutiny is very difficult.
Digital signatures cryptographically bind an electronic identity to an electronic document and the digital signature cannot be copied to another document. Paper contracts sometimes have the ink signature block on the last page, and the previous pages may be replaced after a signature is applied. Digital signatures can be applied to an entire document, such that the digital signature on the last page will indicate tampering if any data on any of the pages have been altered, but this can also be achieved by signing with ink and numbering all pages of the contract.
Some digital signature algorithms
- "RSA-based signature schemes, such as "RSA-PSS
- "DSA and its "elliptic curve variant "ECDSA
- "Edwards-curve Digital Signature Algorithm and its "Ed25519 variant.
- "ElGamal signature scheme as the predecessor to DSA, and variants "Schnorr signature and "Pointcheval–Stern signature algorithm
- "Rabin signature algorithm
- "Pairing-based schemes such as "BLS
- "Undeniable signatures
- Aggregate signature - a signature scheme that supports aggregation: Given n signatures on n messages from n users, it is possible to aggregate all these signatures into a single signature whose size is constant in the number of users. This single signature will convince the verifier that the n users did indeed sign the n original messages.
- "Signatures with efficient protocols - are signature schemes that facilitate efficient cryptographic protocols such as "zero-knowledge proofs or "secure computation.
The current state of use – legal and practical
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All digital signature schemes share the following basic prerequisites regardless of cryptographic theory or legal provision:
- Quality algorithms
- Some public-key algorithms are known to be insecure, as practical attacks against them having been discovered.
- Quality implementations
- An implementation of a good algorithm (or "protocol) with mistake(s) will not work.
- Users (and their software) must carry out the signature protocol properly.
- The private key must remain private
- If the private key becomes known to any other party, that party can produce perfect digital signatures of anything whatsoever.
- The public key owner must be verifiable
- A public key associated with Bob actually came from Bob. This is commonly done using a "public key infrastructure (PKI) and the public key↔user association is attested by the operator of the PKI (called a "certificate authority). For 'open' PKIs in which anyone can request such an attestation (universally embodied in a cryptographically protected "identity certificate), the possibility of mistaken attestation is non-trivial. Commercial PKI operators have suffered several publicly known problems. Such mistakes could lead to falsely signed, and thus wrongly attributed, documents. 'Closed' PKI systems are more expensive, but less easily subverted in this way.
Only if all of these conditions are met will a digital signature actually be any evidence of who sent the message, and therefore of their assent to its contents. Legal enactment cannot change this reality of the existing engineering possibilities, though some such have not reflected this actuality.
Legislatures, being importuned by businesses expecting to profit from operating a PKI, or by the technological avant-garde advocating new solutions to old problems, have enacted statutes and/or regulations in many jurisdictions authorizing, endorsing, encouraging, or permitting digital signatures and providing for (or limiting) their legal effect. The first appears to have been in "Utah in the United States, followed closely by the states "Massachusetts and "California. Other countries have also passed statutes or issued regulations in this area as well and the UN has had an active model law project for some time. These enactments (or proposed enactments) vary from place to place, have typically embodied expectations at variance (optimistically or pessimistically) with the state of the underlying "cryptographic engineering, and have had the net effect of confusing potential users and specifiers, nearly all of whom are not cryptographically knowledgeable. Adoption of technical standards for digital signatures have lagged behind much of the legislation, delaying a more or less unified engineering position on "interoperability, "algorithm choice, "key lengths, and so on what the engineering is attempting to provide.
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Some industries have established common interoperability standards for the use of digital signatures between members of the industry and with regulators. These include the "Automotive Network Exchange for the automobile industry and the "SAFE-BioPharma Association for the "healthcare industry.
Using separate key pairs for signing and encryption
In several countries, a digital signature has a status somewhat like that of a traditional pen and paper signature, like in the EU digital signature legislation. Generally, these provisions mean that anything digitally signed legally binds the signer of the document to the terms therein. For that reason, it is often thought best to use separate key pairs for encrypting and signing. Using the encryption key pair, a person can engage in an encrypted conversation (e.g., regarding a real estate transaction), but the encryption does not legally sign every message he sends. Only when both parties come to an agreement do they sign a contract with their signing keys, and only then are they legally bound by the terms of a specific document. After signing, the document can be sent over the encrypted link. If a signing key is lost or compromised, it can be revoked to mitigate any future transactions. If an encryption key is lost, a backup or "key escrow should be utilized to continue viewing encrypted content. Signing keys should never be backed up or escrowed unless the backup destination is securely encrypted.
- "21 CFR 11
- "Blind signature
- "Detached signature
- "Digital certificate
- "Digital signature in Estonia
- "Electronic lab notebook
- "Electronic signature
- "Electronic signatures and law
- "eSign (India)
- "GNU Privacy Guard
- "Global Trust Center
- "Public key infrastructure
- "Server-based signatures
- US ESIGN Act of 2000
- State of WI
- National Archives of Australia Archived November 9, 2014, at the "Wayback Machine.
- The Information Technology Act, 2000 (PDF).
|last1=in Authors list ("help)
- Turner, Dawn. "Major Standards and Compliance of Digital Signatures - A World-Wide Consideration". Cryptomathic. Retrieved 7 January 2016.
- JA, Ashiq. "Recommendations for Providing Digital Signature Services". Cryptomathic. Retrieved 7 January 2016.
- Regulatory Compliance: Digital signatures and seals are legally enforceable ESIGN (Electronic Signatures in Global and National Commerce) Act
- Pass, def 135.1
- Goldreich's FoC, vol. 2, def 6.1.2. Pass, def 135.2
- "New Directions in Cryptography", IEEE Transactions on Information Theory, IT-22(6):644–654, Nov. 1976.
- "Signature Schemes and Applications to Cryptographic Protocol Design", Anna Lysyanskaya, PhD thesis, "MIT, 2002.
- Rivest, R.; A. Shamir; L. Adleman (1978). "A Method for Obtaining Digital Signatures and Public-Key Cryptosystems" (PDF). Communications of the ACM. 21 (2): 120–126. "doi:10.1145/359340.359342.
- For example any integer, r, "signs" m=re and the product, s1s2, of any two valid signatures, s1, s2 of m1, m2 is a valid signature of the product, m1m2.
- "The History of Notes and Domino". developerWorks. Retrieved 17 September 2014.
- "Constructing digital signatures from a one-way function.", "Leslie Lamport, Technical Report CSL-98, SRI International, Oct. 1979.
- "A certified digital signature", Ralph Merkle, In Gilles Brassard, ed., Advances in Cryptology – "CRYPTO '89, vol. 435 of Lecture Notes in Computer Science, pp. 218–238, Spring Verlag, 1990.
- "Digitalized signatures as intractable as factorization." "Michael O. Rabin, Technical Report MIT/LCS/TR-212, MIT Laboratory for Computer Science, Jan. 1979
- "A digital signature scheme secure against adaptive chosen-message attacks.", Shafi Goldwasser, Silvio Micali, and Ronald Rivest. SIAM Journal on Computing, 17(2):281–308, Apr. 1988.
- "Modern Cryptography: Theory & Practice", Wenbo Mao, Prentice Hall Professional Technical Reference, New Jersey, 2004, pg. 308. "ISBN 0-13-066943-1
- PrivateServer HSM Overview
- Landrock, Peter; Pedersen, Torben (1998). "WYSIWYS? -- What you see is what you sign?". Information Security Technical Report. 3 (2): 55–61.
- Goldreich, Oded (2001), Foundations of cryptography I: Basic Tools, Cambridge: Cambridge University Press, "ISBN "978-0-511-54689-1
- Goldreich, Oded (2004), Foundations of cryptography II: Basic Applications (1. publ. ed.), Cambridge [u.a.]: Cambridge Univ. Press, "ISBN "978-0-521-83084-3
- Pass, Rafael, A Course in Cryptography (PDF), retrieved 31 December 2015
- J. Katz and Y. Lindell, "Introduction to Modern Cryptography" (Chapman & Hall/CRC Press, 2007)
- Stephen Mason, Electronic Signatures in Law (4th edition, Institute of Advanced Legal Studies for the SAS Digital Humanities Library, School of Advanced Study, University of London, 2016). "ISBN 978-1-911507-00-0.
- Lorna Brazell, Electronic Signatures and Identities Law and Regulation (2nd edn, London: Sweet & Maxwell, 2008);
- Dennis Campbell, editor, E-Commerce and the Law of Digital Signatures (Oceana Publications, 2005).
- M. H. M Schellenkens, Electronic Signatures Authentication Technology from a Legal Perspective, (TMC Asser Press, 2004).
- Jeremiah S. Buckley, John P. Kromer, Margo H. K. Tank, and R. David Whitaker, The Law of Electronic Signatures (3rd Edition, West Publishing, 2010).
- Digital Evidence and Electronic Signature Law Review Free open source