Digital Signature https://store.theartofservice.com/the-digital-signature-toolkit.html.

Digital Signature

Electronic business Digital signatures
A final way to secure information online would be to use a digital signature. If a document has a digital signature on it, no one else is able to edit the information without being detected. That way if it is edited, it may be adjusted for reliability after the fact. In order to use a digital signature, one must use a combination of cryptography and a message digest. A message digest is used to give the document a unique value. That value is then encrypted with the sender's private key.

Digital signature Digital signatures are commonly used for software distribution, financial transactions, and in other cases where it is important to detect forgery or tampering.

Digital signature - Explanation
Digital signatures are often used to implement electronic signatures, a broader term that refers to any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures. In some countries, including the United States, India, and members of the European Union, electronic signatures have legal significance.

Digital signature - Explanation
Digital signatures can also provide non-repudiation, meaning that the signer cannot successfully claim they did not sign a message, while also claiming their private key remains secret; further, some non-repudiation schemes offer a time stamp for the digital signature, so that even if the private key is exposed, the signature is valid

Digital signature - Definition
Public-key cryptography

A digital signature scheme typically consists of three algorithms:

A key generation algorithm that selects a private key uniformly at random from a set of possible private keys. The algorithm outputs the private key and a corresponding public key.

A signing algorithm that, given a message and a private key, produces a signature.

A signature verifying algorithm that, given a message, public key and a signature, either accepts or rejects the message's claim to authenticity.

Two main properties are required. First, a signature generated from a fixed message and fixed private key should verify the authenticity of that message by using the corresponding public key. Secondly, it should be computationally infeasible to generate a valid signature for a party without knowing that party's private key.

Digital signature - History
The first widely marketed software package to offer digital signature was Lotus Notes 1.0, released in 1989, which used the RSA algorithm.

Other digital signature schemes were soon developed after RSA, the earliest being Lamport signatures, Merkle signatures (also known as "Merkle trees" or simply "Hash trees"), and Rabin signatures.

In 1988, Shafi Goldwasser, Silvio Micali, and Ronald Rivest became the first to rigorously define the security requirements of digital signature schemes. They described a hierarchy of attack models for signature schemes, and also present the GMR signature scheme, the first that can be proven to prevent even an existential forgery against a chosen message attack.

Digital signature - How they work
To create RSA signature keys, generate an RSA key pair containing a modulus N that is the product of two large primes, along with integers e and d such that e d ≡ 1 (mod φ(N)), where φ is the Euler phi-function. The signer's public key consists of N and e, and the signer's secret key contains d.

To sign a message m, the signer computes σ ≡ md (mod N). To verify, the receiver checks that σe ≡ m (mod N).

Because of this correspondence, digital signatures are often described as based on public-key cryptosystems, where signing is equivalent to decryption and verification is equivalent to encryption, but this is not the only way digital signatures are computed.

Used directly, this type of signature scheme is vulnerable to a key-only existential forgery attack

There are several reasons to sign such a hash (or message digest) instead of the whole document.

For efficiency: The signature will be much shorter and thus save time since hashing is generally much faster than signing in practice.

For compatibility: Messages are typically bit strings, but some signature schemes operate on other domains (such as, in the case of RSA, numbers modulo a composite number N). A hash function can be used to convert an arbitrary input into the proper format.

For integrity: Without the hash function, the text "to be signed" may have to be split (separated) in blocks small enough for the signature scheme to act on them directly. However, the receiver of the signed blocks is not able to recognize if all the blocks are present and in the appropriate order.

Digital signature - Notions of security
In their foundational paper, Goldwasser, Micali, and Rivest lay out a hierarchy of attack models against digital signatures:

In a key-only attack, the attacker is only given the public verification key.

In a known message attack, the attacker is given valid signatures for a variety of messages known by the attacker but not chosen by the attacker.

In an adaptive chosen message attack, the attacker first learns signatures on arbitrary messages of the attacker's choice.

They also describe a hierarchy of attack results:

A total break results in the recovery of the signing key.

A universal forgery attack results in the ability to forge signatures for any message.

A selective forgery attack results in a signature on a message of the adversary's choice.

An existential forgery merely results in some valid message/signature pair not already known to the adversary.

The strongest notion of security, therefore, is security against existential forgery under an adaptive chosen message attack.

Digital signature - Uses of digital signatures
Universities including Penn State, University of Chicago, and Stanford are publishing electronic student transcripts with digital signatures.

Digital signature - Uses of digital signatures
Below are some common reasons for applying a digital signature to communications:

Digital signature - Authentication
When ownership of a digital signature secret key is bound to a specific user, a valid signature shows that the message was sent by that user

Digital signature - Integrity
In many scenarios, the sender and receiver of a message may have a need for confidence that the message has not been altered during transmission

Digital signature - Non-repudiation
Non-repudiation, or more specifically non-repudiation of origin, is an important aspect of digital signatures. By this property, an entity that has signed some information cannot at a later time deny having signed it. Similarly, access to the public key only does not enable a fraudulent party to fake a valid signature.

Digital signature - Non-repudiation
Note that these authentication, non-repudiation etc

Digital signature - Putting the private key on a smart card
All public key / private key cryptosystems depend entirely on keeping the private key secret. A private key can be stored on a user's computer, and protected by a local password, but this has two disadvantages:

the user can only sign documents on that particular computer

the security of the private key depends entirely on the security of the computer

If the smart card is stolen, the thief will still need the PIN code to generate a digital signature

Digital signature - Using smart card readers with a separate keyboard
Entering a PIN code to activate the smart card commonly requires a numeric keypad

Digital signature - Other smart card designs
Smart card design is an active field, and there are smart card schemes which are intended to avoid these particular problems, though so far with little security proofs.

Digital signature - Using digital signatures only with trusted applications
One of the main differences between a digital signature and a written signature is that the user does not "see" what he signs

Digital signature - Using digital signatures only with trusted applications
To protect against this scenario, an authentication system can be set up between the user's application (word processor, client, etc.) and the signing application. The general idea is to provide some means for both the user application and signing application to verify each other's integrity. For example, the signing application may require all requests to come from digitally signed binaries.

Digital signature - WYSIWYS
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.

Digital signature - Digital signatures vs. 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 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.

Additionally, most digital certificates provided by certificate authorities to end users to sign documents can be obtained by at most gaining access to a victim's inbox.

Digital signature - Some digital signature algorithms
ElGamal signature scheme as the predecessor to DSA, and variants Schnorr signature and Pointcheval–Stern signature algorithm

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.

Digital signature - The current state of use – legal and practical
Digital signature schemes share basic prerequisites that – regardless of cryptographic theory or legal provision – they need to have, meaning:

Some public-key algorithms are known to be insecure, practical attacks against them having been discovered.

Quality implementations

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

Users (and their software) must carry out the signature protocol properly.

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.

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.

See also: ABA digital signature guidelines

Digital signature - Industry standards
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.

Digital signature - 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

Digital signature - Notes
US ESIGN Act of 2000

National Archives of Australia

^ a b "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". Communications of the ACM 21 (2): 120–126. doi: /

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.

"Constructing digital signatures from a one-way function.", Leslie Lamport, Technical Report CSL-98, SRI International, Oct

"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 b c d "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

A. Jøsang, D. Povey and A. Ho. "What You See is Not Always What You Sign". Proceedings of the Australian Unix User Group Symposium (AUUG2002), Melbourne, September PDF

Digital signature - Further reading
J. Katz and Y. Lindell, "Introduction to Modern Cryptography" (Chapman & Hall/CRC Press, 2007)

Stephen Mason, Electronic Signatures in Law (3rd edition, Cambridge University Press, 2012)

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).

Security token - Digital signature
Trusted as a regular hand-written signature, the digital signature must be made with a private key known only to the person authorized to make the signature. Tokens that allow secure on-board generation and storage of private keys enable secure digital signatures, and can also be used for user authentication, as the private key also serves as a proof for the user’s identity.

Security token - Digital signature
For tokens to identify the user, all tokens must have some kind of number that is unique. Not all approaches fully qualify as digital signatures according to some national laws. Tokens with no on-board keyboard or another user interface cannot be used in some signing scenarios, such as confirming a bank transaction based on the bank account number that the funds are to be transferred to.

Pretty Good Privacy - Digital signatures
To do so, PGP computes a hash (also called a message digest) from the plaintext and then creates the digital signature from that hash using the sender's private key.

Digital Signature Services
'Digital Signature Services' (DSS) is an OASIS (organization)|OASIS standard.

Digital Signature Services
The Digital Signature Services (DSS) specifications describe two XML-based request/response protocols – a signing protocol and a verifying protocol

Digital signing - Applications of digital signatures
Universities including Penn State, University of Chicago, and Stanford are publishing electronic student transcripts with digital signatures.

Digital signing - Using digital signatures only with trusted applications
One of the main differences between a digital signature and a written signature is that the user does not see what he signs

Digital signing - Some digital signature algorithms
*RSA (algorithm)|RSA-based signature schemes, such as RSA-PSS

*Digital Signature Algorithm|DSA and its elliptic curve cryptography|elliptic curve variant Elliptic Curve DSA|ECDSA

*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 (cryptography)|BLS

*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.

Adobe LiveCycle - LiveCycle Digital Signatures ES4
LiveCycle Digital Signatures automates electronic signature workflows for assurances of authenticity, integrity, and non-repudiation. Organizations can use this component to sign documents in bulk, such as university transcripts, government documents such as annual budgets, grants, or tax returns. This component will also validate previously signed documents in bulk. The digital signature capabilities are based on the functionality available in Adobe Acrobat and Adobe Reader on the desktop.

Cryptography standards - Digital signature standards
* Digital Signature Standard (DSS), based on the Digital Signature Algorithm (DSA)

List of important publications in cryptography - A Method for Obtaining Digital Signatures and Public Key Cryptosystems Description: The RSA (algorithm)|RSA encryption method. The first public-key encryption method.

Digital Signature Algorithm
It was proposed by the National Institute of Standards and Technology (NIST) in August 1991 for use in their 'Digital Signature Standard' ('DSS') and adopted as FIPS 186 in 1993.[ FIPS PUB 186]: Digital Signature Standard (DSS), Four revisions to the initial specification have been released: FIPS in 1996,[ FIPS PUB 186-1]: Digital Signature Standard (DSS), FIPS in 2000,[ FIPS PUB 186-2]: Digital Signature Standard (DSS), FIPS in 2009,[ FIPS PUB 186-3]: Digital Signature Standard (DSS), June 2009 and FIPS in 2013.[ FIPS PUB 186-4]: Digital Signature Standard (DSS), July 2013

Digital Signature Algorithm
DSA is covered by , filed July 26, 1991 and attributed to David W

Digital Signature Algorithm - Key generation
Key generation has two phases. The first phase is a choice of algorithm parameters which may be shared between different users of the system, while the second phase computes public and private keys for a single user.

Digital Signature Algorithm - Parameter generation
* Choose an approved cryptographic hash function H. In the original DSS, H was always SHA-1, but the stronger SHA-2 hash functions are approved for use in the current DSS.[ FIPS PUB 180-4]: Secure Hash Standard (SHS), March 2012 The hash output may be truncated to the size of a key pair.

* Decide on a key length L and N

* Choose an N-bit prime q. N must be less than or equal to the hash output length.

* Choose an L-bit prime modulus p such that p–1 is a multiple of q.

* Choose g, a number whose multiplicative order modulo p is q. This may be done by setting g = h(p–1)/q mod p for some arbitrary h (1 lt; h lt; p−1), and trying again with a different h if the result comes out as 1. Most choices of h will lead to a usable g; commonly h=2 is used.

The algorithm parameters (p, q, g) may be shared between different users of the system.

Digital Signature Algorithm - Per-user keys
Given a set of parameters, the second phase computes private and public keys for a single user:

Digital Signature Algorithm - Per-user keys
There exist efficient algorithms for computing the modular exponentiations h(p–1)/q mod p and gx mod p, such as exponentiation by squaring.

Digital Signature Algorithm - Signing
Let H be the hashing function and m the message:

Digital Signature Algorithm - Signing
* Generate a random per-message value k where 0 1 and q is prime, g must have orderq.

Digital Signature Algorithm - Sensitivity
With DSA, the entropy, secrecy, and uniqueness of the random signature value k is critical

In December 2010, a group calling itself fail0verflow announced recovery of the ECDSA private key used by Sony to sign software for the PlayStation 3 game console. The attack was made possible because Sony failed to generate a new random k for each signature.

This issue can be prevented by deriving k deterministically from the private key and the message hash, as described by RFC This ensures that k is different for each H(m) and unpredictable for attackers who do not know x.

Collision attack - Digital signatures
Because digital signature algorithms cannot sign a large amount of data efficiently, most implementations use a hash function to reduce (compress) the amount of data that needs to be signed down to a constant size. Digital signature schemes are often vulnerable to hash collisions, unless using techniques like randomized hashing.Shai Halevi and Hugo Krawczyk, [ Randomized Hashing and Digital Signatures]

Note that all public key certificates, like Transport Layer Security|SSL certificates, also rely on the security of digital signatures and are compromised by hash collisions.

The usual attack scenario goes like this:

# Mallory creates two different documents A and B, that have an identical hash value (collision).

# Mallory then 'sends document A to Alice', who agrees to what the document says, signs its hash and sends it back to Mallory.

# Mallory copies the signature sent by Alice from document A to document B.

# Then she 'sends document B to Bob', claiming that Alice signed the different document. Because the digital signature matches the document hash, Bob's software is unable to detect the modification.

Digital signature in Estonia
Digital signature allows users to electronically perform the actions for which they previously had to give a signature on paper. Estonia's digital signature system is the foundation for some of its most popular e-services including registering a company online, e-banks, the i-voting system and electronic tax filing – essentially any services that require signatures to prove their validity.

Digital signature in Estonia - History and usage
The first digital signature was given in A number of freeware programs were released to end users and system integrators. All of the components of the software processed the same document format – the DigiDoc format.

As of October 2013, over 130 million digital signatures have been given in Estonia.

In September 2013 the European Commissioner for Digital Agenda Neelie Kroes gave her first digital signature with an Estonian test ID-card issued to her as a present.

Digital signature in Estonia - Legislation
Pursuant to the Act it is also necessary to distinguish between valid and void digital signatures, any signatures given with a void or suspended Digital certificate|certificate are null and void.

Digital signature in Estonia - Legislation
All Estonian authorities are obliged to accept digitally signed documents.

Digital signature in Estonia - Prerequisites
Users can create digitally signed documents with their Estonian ID card|ID-card or Mobile-ID using either the DigiDoc3 program that is installed into the computer along with the ID-card software, in the signing section of the State Portal or in the DigiDoc Portal.

Digital signature in Estonia - Prerequisites
Digital signature support can be added to all the applications and programs where it is required.

Digital signature in Estonia - International context
The Estonian digital signatures corresponds to the European Union Directive on Electronic Signatures (1999/93/EC Community Framework for Electronic Signatures) with the strictest requirements (advanced electronic signature, secure-signature-creation device, qualified certificate, certification-service-provider issuing qualified certificates).

Digital signature in Estonia - Certificates
Upon the issuance of ID-cards or mobile ID-s, every user receives two certificates: one for authentication, the other for digital signing. The certificate may be compared to the specimen signature of a person – it is public and it can be used by anyone to examine whether the signature given by the person is authentic. The certificate also holds the personal data, name and personal identification code.

Digital signature in Estonia - Certificates
All certificates are different and correspond to the private keys of specific persons. The certificate can be used to examine digital signatures – if the certificate and the signature match mathematically (all the necessary calculations are performed by the computer on behalf of the user), it can be claimed that the signature has been given by the person named in the certificate.

Digital signatures and law
Worldwide, legislation concerning the effect and validity of digital signatures includes:

Digital signatures and law - Bermuda
* [ Electronic Transactions Act 1999]

Digital signatures and law - Bermuda
* [ Certification Service Providers (Relevant Criteria and Security Guidelines) Regulations 2002]

Digital signatures and law - Brazil
*[ Medida provisória (Portuguese)] - Brazilian law states that any digital document is valid for the law if it is certified by 'ICP-Brasil' (the official Brazilian PKI) or if it is certified by other PKI and the concerned parties agree as to the validity of the document.

Digital signatures and law - Canada
Federal [ secure electronic signature regulations] make it clear that a secure electronic signature is a digital signature created and verified in a specific manner

Digital signatures and law - China
*[ Electronic Signature Law of the People's Republic of China (Chinese)] - The stated purposes include standardizing the conduct of electronic signatures, confirming the legal validity of electronic signatures and safeguarding the legal interests of parties involved in such matters.

Digital signatures and law - Colombia
* [ LEY 527 DE 1999 (agosto 18) por medio de la cual se define y reglamenta el acceso y uso de los mensajes de datos, del comercio electrónico y de las firmas digitales, y se establecen las entidades de certificación y se dictan otras disposiciones.]

Digital signatures and law - Colombia
* [ DECRETO 2364 DE 2012 (Noviembre 22) por medio del cual se reglamenta el artículo 7° de la Ley 527 de 1999, sobre la firma electrónica y se dictan otras disposiciones.]

Digital signatures and law - European Union and the European Economic Area
* European Union Directive establishing the framework for electronic signatures:

** [ Directive 1999/93/EC of the European Parliament and of the Council] of 13 December 1999 on a Community framework for electronic signatures. This Directive will be repealed 1 July 2016 and superseded by a [ Regulation on electronic identification and trust services (eIDAS)] (see its article 48).

** [ Commission Decision 2003/511/EC] adopting three CEN Workshop Agreements as technical standards presumed to be in accordance with the Directive

* Implementing laws: Several countries have already implemented the Directive 1999/93/EC.

*** [ Signature Law, 2000]

*** [ Signature Law, 2001]

*** [ Act on Electronic Signatures, 227/2000]

*** [ Lov om elektroniske signaturer]

*** [ Electronic Communications Act, 2000]

*** [ The Electronic Signatures Regulations 2002]

*** [ Digital Signature Law, 2000] (in Estonian).

*** [ Digital Signatures Act (consolidated text Dec 2003)]

*** [ Laki sähköisistä allekirjoituksista, 2003] (in Finnish)

*** [ Article 1316 of the Civil Code, 13 March 2000] (pdf, English)

*** [ Civil Code] (French)

*** [ German Signature Law of 2001, changed in 2005]

*** [ Presidential Decree 150/2001] (in Greek)

*** [ Hungarian Act on Electronic Signatures 2001]

** Ireland, Republic of

*** [ Irish Electronic Commerce Act, 2000]

*** [ Electronic Documents Law, 2002]

*** [ Electronic Documents Law, 2002 (in Latvian)]

*** [ Law on electronic signature, 2002]

*** [ Loi du 14 août 2000 relative au commerce électronique, 2000] (in French)

*** [ Maltese Electronic Commerce Act 2001, last amended 2005]

*** [ Electronic Signature Act, 2001] (in Norwegian).

***[ act_on_eSignature.pdf]

***[ portugal_en.pdf]

*** [ Legea semnăturii electronice, 455/2001]

*** [ Law on the Electronic Signature, 455/2001] (unofficial translation)

*** [ Act no.215/2002 on electronic signature (in Slovak)]

*** [ Electronic Business and Electronic Signature Act (in Slovene)] .

***[ Qualified Electronic Signatures Act (SFS 2000:832) (in Swedish)].

***[ SFS 2000:832 in English translation]

Digital signatures and law - Guatemala
*[ Ley para el Reconocimiento de las Comunicaciones y Firmas Electrónicas] (in Spanish)

Digital signatures and law - Japan
*[ Law Concerning Electronic Signatures and Certification Services, 2000 (in Japanese)]

Digital signatures and law - Korea
*[ Digital Signature Act in english (PDF), ]

Digital signatures and law - Korea
*[ Digital Signature Act in Korean]

Digital signatures and law - Malaysia
* [ Digital Signature Act (Act 562), 1997] (in Bahasa Malaysia).

* [ Digital Signature Act (Act 562), 1997] (in English).

* [ Digital Signature Regulations (P.U.(A) 359), 1998] (in Bahasa Malaysia).

* [ Digital Signature Regulations (P.U.(A) 359), 1998] (in English).

Digital signatures and law - Moldova
* [ Lege cu privire la documentul electronic şi semnătura digitală, July 15, 2004] (in Romanian)

Digital signatures and law - Moldova
* [ Law about Electronic Document and Digital Signature] (in Russian)

Digital signatures and law - New Zealand
*[ Electronic Transactions Act 2002, sections 22-24]

Digital signatures and law - New Zealand
- Commercial Law, paras 8A.7.1-8A.7.4. (these sources are available on the [ LexisNexis] subscription-only website)

Digital signatures and law - Russian Federation
*[ Federal Law of Russian Federation about Electronic Digital Signature ( )]

Digital signatures and law - South Africa
*[ Electronic Communications and Transactions Act, 2002] ([ PDF])

Digital signatures and law - Switzerland
*[ Federal Law on Certification Services Concerning the Electronic Signature, 2003]

Digital signatures and law - United Nations Commission on International Trade Law
*[ UNCITRAL Model Law on Electronic Signatures (2001), a strong influence in the field.]

Digital signatures and law - United States
*Uniform Electronic Transactions Act (UETA)

Digital signatures and law - United States
*Electronic Signatures in Global and National Commerce Act (E-SIGN), at [ 15 U.S.C. 7001] et seq. The law permits the use of electronic signatures in many situations, and preempts many state laws that would otherwise limit the use of electronic signatures.

Digital signatures and law - Uruguay
Uruguay laws include both, electronic and digital signatures:

* [ Concerning passwords or adequate information technology gestures]

* [ Concerning electronic and digital signature and PKI]

Digital signatures and law - Turkey
Turkey has an [ Electronic Signature Law] [ TBMM.gov.tr] since This law is stated in European Union Directive 1999/93/EC. Turkey has a [ Government Certificate Authority - Kamu SM] for all government agents for their internal use and three independent certificate authorities all of which are issuing qualified digital signatures.

* Kamu Sertifikasyon Merkezi (Governmental Certificate Authority) [ Kamusm.gov.tr]

* E-Güven (owned by Turkish Informatics Foundation) [ E-guven.com]

* Turktrust (owned by Turkish Military Force Solidarity Foundation) [ Turktrust.com.tr]

Digital signatures and law - Legal cases
Court decisions discussing the effect and validity of digital signatures or digital signature-related legislation:

*In re Piranha, Inc., 2003 WL (N.D. Tex) (Uniform Electronic Transactions Act|UETA does not preclude a person from contesting that he executed, adopted, or authorized an electronic signature that is purportedly his).

*Cloud Corp. v. Hasbro, 314 F.3d 289 (7th Cir., 2002) [ EMLF.org] (Electronic Signatures in Global and National Commerce Act|E-SIGN does not apply retroactively to contracts formed before it took effect in Nevertheless, the statute of frauds was satisfied by the text of plus an (apparently) written notation.)

*Sea-Land Service, Inc. v. Lozen International, 285 F.3d 808 (9th Cir., 2002) [ Admiraltylawguide.com] (Internal corporate with signature block, forwarded to a third party by another employee, was admissible over hearsay objection as a party-admission, where the statement was apparently within the scope of the author's and forwarder's employment.)

Digital signatures and law - Further reading
* [ Digital signatures legislation across the world].

For books in English on electronic signatures, see:

* Stephen Mason, Electronic Signatures in Law (Cambridge University Press, third edition, 2012);

* Dennis Campbell, editor, E-Commerce and the Law of Digital Signatures (Oceana Publications, 2005);

* Lorna Brazell, Electronic Signatures Law and Regulation, (Sweet Maxwell, 2004);

* M. H. M Schellenkens, Electronic Signatures Authentication Technology from a Legal Perspective, (TMC Asser Press, 2004).

* Srivastava Aashish, Electronic Signatures for B2B Contracts: Evidence from Australia (Springer, 2013)

For translations of electronic signature cases from Europe, Brazil, China and Colombia into English, see the Digital Evidence and Electronic Signature Law Review (open source)

ABA digital signature guidelines
The document was the first overview of principles and a framework for the use of digital signatures and authentication in electronic commerce from a legal viewpoint, including technologies such as certificate authority|certificate authorities and public key infrastructure (PKI)

The Digital Signature Guidelines were followed by the Public Key Infrastructure Assessment Guidelines published by the ABA in 2003.

A similar effort was undertaken in Slovenia by the Digital Signature Working Group (within the Chamber of Commerce and Industry of Slovenia (CCIS)).

Birthday attack - Digital signature susceptibility
Digital signatures can be susceptible to a birthday attack

In a similar manner, Mallory also creates a huge number of variations on the fraudulent contract m'

The probabilities differ slightly from the original birthday problem, as Mallory gains nothing by finding two fair or two fraudulent contracts with the same hash. Mallory's strategy is to generate pairs of one fair and one fraudulent contract. The birthday problem equations apply where n is the number of pairs. The number of hashes Mallory actually generates is 2n.

To avoid this attack, the output length of the hash function used for a signature scheme can be chosen large enough so that the birthday attack becomes computationally infeasible, i.e. about twice as many bits as are needed to prevent an ordinary brute-force attack.

Pollard's rho algorithm for logarithms is an example for an algorithm using a birthday attack for the computation of discrete logarithms.

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