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62-408: The protected environment in which DRM content is played contains the media components that play DRM content, so the application only needs to provide remote control (play, rewind, pause, and so on), rather than having to handle unprotected content data. The protected environment also provides all the necessary support for Microsoft-approved ( signed ) third-party software modules to be added. It provides

124-406: A "wall" against outside copying, where within the walls, content can be processed without making the content available to unapproved software. In order to prevent users from copying DRM content, Windows Vista provides process isolation and continually monitors what kernel-mode software is loaded. If an unverified component is detected, then Vista will stop playing DRM content, rather than risk having

186-458: A Microsoft lawsuit regarding possible violation of the DMCA . On 6 March 2007, Microsoft responded after internal testing that the described method would not work. In addition to common criticisms against DRM schemes, there has been speculation that this scheme has been motivated by the fact that it would affect official free/open source graphics driver support by manufacturers. The scheme relies on

248-599: 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

310-406: A branch banker, and not forged—whether a forger fabricated the whole letter, or just modified an existing letter in transit by adding some digits. With a digital signature scheme, the central office can arrange beforehand to have a public key on file whose private key is known only to the branch office. The branch office can later sign a message and the central office can use the public key to verify

372-465: A card reader integrated into a PC, and then entering the PIN using that computer's keyboard. Readers with a numeric keypad are meant to circumvent the eavesdropping threat where the computer might be running a keystroke logger , potentially compromising the PIN code. Specialized card readers are also less vulnerable to tampering with their software or hardware and are often EAL3 certified. Smart card design

434-472: A certain time. Secure multiparty computation can be used to compute answers (such as determining the highest bid in an auction) based on confidential data (such as private bids), so that when the protocol is complete the participants know only their own input and the answer. End-to-end auditable voting systems provide sets of desirable privacy and auditability properties for conducting e-voting . Undeniable signatures include interactive protocols that allow

496-528: A digit —if the bank's offices simply encrypted the messages they exchange, they could still be vulnerable to forgery. In other applications, such as software updates, the messages are not secret—when a software author publishes a patch for all existing installations of the software to apply, the patch itself is not secret, but computers running the software must verify the authenticity of the patch before applying it, lest they become victims to malware. Replays. A digital signature scheme on its own does not prevent

558-433: A handwritten signature identifying its sender, but letterheads and handwritten signatures can be copied and pasted onto forged messages. Even legitimate messages may be modified in transit. If a bank's central office receives a letter claiming to be from a branch office with instructions to change the balance of an account, the central bankers need to be sure, before acting on the instructions, that they were actually sent by

620-410: A locally provided one is risk. Many risk averse companies, including governments, financial and medical institutions, and payment processors require more secure standards, like FIPS 140-2 level 3 and FIPS 201 certification, to ensure the signature is validated and secure. Technically speaking, a digital signature applies to a string of bits, whereas humans and applications "believe" that they sign

682-399: A public key. Prior knowledge of a public key can be used to verify authenticity of a signed message , but not the other way around—prior knowledge of a signed message cannot be used to verify authenticity of a public key . In some signature schemes, given a signed message, it is easy to construct a public key under which the signed message will pass verification, even without knowledge of

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744-447: A signatory. The United States Government Printing Office (GPO) publishes electronic versions of the budget, public and private laws, and congressional bills with digital signatures. Universities including Penn State, University of Chicago , and Stanford are publishing electronic student transcripts with digital signatures. Below are some common reasons for applying a digital signature to communications: A message may have letterhead or

806-529: A suitable DRM scheme available, so these need to be turned off reliably if the content so specifies. In Vista, the control of PC video outputs is provided by PVP-OPM, which is essentially the next generation of Certified Output Protection Protocol (COPP) introduced in Windows XP . However, rather than being a software application programming interface , PVP-OPM operates with the Windows media components in

868-416: A typical digital signature implementation, the hash calculated from the document is sent to the smart card, whose CPU signs the hash using the stored private key of the user, and then returns the signed hash. Typically, a user must activate their smart card by entering a personal identification number or PIN code (thus providing two-factor authentication ). It can be arranged that the private key never leaves

930-516: A valid signed message from being recorded and then maliciously reused in a replay attack . For example, the branch office may legitimately request that bank transfer be issued once in a signed message. If the bank doesn't use a system of transaction IDs in their messages to detect which transfers have already happened, someone could illegitimately reuse the same signed message many times to drain an account. Uniqueness and malleability of signatures. A signature itself cannot be used to uniquely identify

992-429: Is Euler's totient function . The signer's public key consists of N and e , and the signer's secret key contains d . Used directly, this type of signature scheme is vulnerable to key-only existential forgery attack. To create a forgery, the attacker picks a random signature σ and uses the verification procedure to determine the message, m , corresponding to that signature. In practice, however, this type of signature

1054-476: Is a cryptographic protocol that is used to secure web ( HTTPS ) connections. It has an entity authentication mechanism, based on the X.509 system; a key setup phase, where a symmetric encryption key is formed by employing public-key cryptography; and an application-level data transport function. These three aspects have important interconnections. Standard TLS does not have non-repudiation support. There are other types of cryptographic protocols as well, and even

1116-591: Is an abstract or concrete protocol that performs a security -related function and applies cryptographic methods, often as sequences of cryptographic primitives . A protocol describes how the algorithms should be used and includes details about data structures and representations, at which point it can be used to implement multiple, interoperable versions of a program. Cryptographic protocols are widely used for secure application-level data transport. A cryptographic protocol usually incorporates at least some of these aspects: For example, Transport Layer Security (TLS)

1178-424: Is an active field, and there are smart card schemes which are intended to avoid these particular problems, despite having few security proofs so far. One of the main differences between a digital signature and a written signature is that the user does not "see" what they sign. The user application presents a hash code to be signed by the digital signing algorithm using the private key. An attacker who gains control of

1240-453: Is existentially unforgeable, even against a chosen-plaintext attack . There are several reasons to sign such a hash (or message digest) instead of the whole document. As organizations move away from paper documents with ink signatures or authenticity stamps, digital signatures can provide added assurances of the evidence to provenance, identity, and status of an electronic document as well as acknowledging informed consent and approval by

1302-577: Is important to detect forgery or tampering . Digital signatures are often used to implement electronic signatures , which include any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures. Electronic signatures have legal significance in some countries, including Brazil , Canada , South Africa , Russia , the United States , Algeria , Turkey , India , Indonesia , Mexico , Saudi Arabia , Uruguay , Switzerland , Chile and

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1364-486: Is not built on trapdoor functions but rather on a family of function with a much weaker required property of one-way permutation was presented by Moni Naor and Moti Yung . One digital signature scheme (of many) is based on RSA . To create signature keys, generate an RSA key pair containing a modulus, N , that is the product of two random secret distinct large primes, along with integers, e and d , such that e   d   ≡  1 (mod  φ ( N )), where φ

1426-566: Is not used directly, but rather, the message to be signed is first hashed to produce a short digest, that is then padded to larger width comparable to  N , then signed with the reverse trapdoor function . This forgery attack, then, only produces the padded hash function output that corresponds to σ, but not a message that leads to that value, which does not lead to an attack. In the random oracle model, hash-then-sign (an idealized version of that practice where hash and padding combined have close to N possible outputs), this form of signature

1488-405: 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 or she 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

1550-439: Is one of many examples of a signing algorithm. In the following discussion, 1 refers to a unary number . Formally, a digital signature scheme is a triple of probabilistic polynomial time algorithms, ( G , S , V ), satisfying: For correctness, S and V must satisfy A digital signature scheme is secure if for every non-uniform probabilistic polynomial time adversary , A where A denotes that A has access to

1612-447: 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

1674-512: Is security against existential forgery under an adaptive chosen message attack. 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: A more secure alternative is to store the private key on a smart card . Many smart cards are designed to be tamper-resistant (although some designs have been broken, notably by Ross Anderson and his students ). In

1736-683: The RSA algorithm, which could be used to produce primitive digital signatures (although only as a proof-of-concept – "plain" RSA signatures are not secure ). 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

1798-599: The oracle , S ( sk , · ), Q denotes the set of the queries on S made by A , which knows the public key, pk , and the security parameter, n , and x ∉ Q denotes that the adversary may not directly query the string, x , on S . In 1976, Whitfield Diffie and Martin Hellman first described the notion of a digital signature scheme, although they only conjectured that such schemes existed based on functions that are trapdoor one-way permutations. Soon afterwards, Ronald Rivest , Adi Shamir , and Len Adleman invented

1860-625: The Protected Media Path feature to Vista to block customers from copying rightfully owned media content (a practice believed to be protected by Fair Use provisions of the Copyright Act), and the feature is widely quoted as an example of Microsoft's uncompromising adherence to DRM. These accusations have never gained much traction largely because Vista treats non-DRM media exactly the same as previous versions of Windows, and that following Vista's release there has been no change in

1922-492: The SAFE-BioPharma Association for the healthcare industry . In several countries, a digital signature has a status somewhat like that of a traditional pen and paper signature, as in the 1999 EU digital signature directive and 2014 EU follow-on legislation . Generally, these provisions mean that anything digitally signed legally binds the signer of the document to the terms therein. For that reason, it

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1984-535: 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

2046-572: The availability of free/open source drivers from graphics hardware manufacturers. Digital signature A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature on a message gives a recipient confidence that the message came from a sender known to the recipient. Digital signatures are a standard element of most cryptographic protocol suites, and are commonly used for software distribution, financial transactions, contract management software , and in other cases where it

2108-498: The content copied. The protected environment is implemented completely in software, so software-based attacks such as patching the Windows kernel are possible. These restrictions concern the various outputs from the PC. For DRM content, digital outputs such as Digital Visual Interface (DVI) and High Definition Multimedia Interface ( HDMI ) will have High-bandwidth Digital Content Protection (HDCP) enabled, to prevent someone from recording

2170-475: 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. A digital signature is an authentication mechanism that enables the creator of the message to attach a code that acts as a signature. The Digital Signature Algorithm (DSA), developed by the National Institute of Standards and Technology ,

2232-562: The countries of the European Union . Digital signatures employ asymmetric cryptography . In many instances, they provide a layer of validation and security to messages sent through a non-secure channel: Properly implemented, a digital signature gives the receiver reason to believe the message was sent by the claimed sender. Digital signatures are equivalent to traditional handwritten signatures in many respects, but properly implemented digital signatures are more difficult to forge than

2294-462: The credit-card issuer to find if a given card has been reported lost or stolen. Of course, with stolen key pairs, the theft is often discovered only after the secret key's use, e.g., to sign a bogus certificate for espionage purpose. In their foundational paper, Goldwasser, Micali, and Rivest lay out a hierarchy of attack models against digital signatures: They also describe a hierarchy of attack results: The strongest notion of security, therefore,

2356-560: The digital stream. Even analog TV-style outputs typically require some restrictions, provided by mechanisms such as Macrovision and CGMS-A . These restrictions only apply to DRM-restricted content, such as HD DVD or Blu-ray that are encrypted with AACS , and also apply in Windows XP using supported playback applications. Users' standard unprotected content will not have these restrictions. Some output types such as S/PDIF (Sony/Philips Digital Interchange Format) typically don't have

2418-468: The environment in which the protocol operates in order to identify threats. This is frequently done through the Dolev-Yao model. Logics, concepts and calculi used for formal reasoning of security protocols: Research projects and tools used for formal verification of security protocols: To formally verify a protocol it is often abstracted and modelled using Alice & Bob notation . A simple example

2480-457: The first to rigorously define the security requirements of digital signature schemes. They described a hierarchy of attack models for signature schemes, and also presented the GMR signature scheme , the first that could be proved to prevent even an existential forgery against a chosen message attack, which is the currently accepted security definition for signature schemes. The first such scheme which

2542-458: The following goals regardless of cryptographic theory or legal provision: 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

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2604-427: The handwritten type. Digital signature schemes, in the sense used here, are cryptographically based, and must be implemented properly to be effective. They 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 timestamp for the digital signature, so that even if

2666-421: 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

2728-422: 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. Most digital signature schemes share

2790-445: The internals of graphics cards to tell whether the hardware is trustworthy (permitted to play copy-protected content). This could be subverted if an attacker knows certain details about the hardware's operation, which could be disclosed by hardware documentation or open source device drivers . However, this will not affect platform independency, as the scheme is provided with no charge. Microsoft has frequently been accused of adding

2852-501: 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. 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

2914-405: The loss of the smart card may be detected by the owner and the corresponding certificate can be immediately revoked. Private keys that are protected by software only may be easier to copy, and such compromises are far more difficult to detect. Entering a PIN code to activate the smart card commonly requires a numeric keypad . Some card readers have their own numeric keypad. This is safer than using

2976-436: The message it signs—in some signature schemes, every message has a large number of possible valid signatures from the same signer, and it may be easy, even without knowledge of the private key, to transform one valid signature into another. If signatures are misused as transaction IDs in an attempt by a bank-like system such as a Bitcoin exchange to detect replays, this can be exploited to replay transactions. Authenticating

3038-453: The private key is exposed, the signature is valid. Digitally signed messages may be anything representable as a bitstring : examples include electronic mail, contracts, or a message sent via some other cryptographic protocol. A digital signature scheme typically consists of three algorithms: Two main properties are required: First, the authenticity of a signature generated from a fixed message and fixed private key can be verified by using

3100-477: The private key that was used to make the signed message in the first place. 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. Note that these authentication, non-repudiation etc. properties rely on

3162-764: The protected environment. Additionally, PVP-UAB (Protected Video Path - User-Accessible Bus) is used to encrypt video and audio data as it passes over the PCI-Express bus , to prevent it from being intercepted and copied on the way to the graphics card . It is complementary to PVP Output Protection Management. In January 2007 the developer Alex Ionescu announced that he had found a method that allows end users to bypass Vista's Protected Media Path. This would allow digital content to be played on equipment that does not implement DRM restriction measures (like rescaling of video resolutions and disabling analog audio outputs). However, he did not release any source code in fear of

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3224-545: The secret key not having been revoked prior to its usage. Public revocation of a key-pair is a required ability, else leaked secret keys would continue to implicate the claimed owner of the key-pair. Checking revocation status requires an "online" check; e.g., checking a certificate revocation list or via the Online Certificate Status Protocol . Very roughly this is analogous to a vendor who receives credit-cards first checking online with

3286-431: 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

3348-468: The signed message was not a forgery before acting on it. A forger who doesn't know the sender's private key can't sign a different message, or even change a single digit in an existing message without making the recipient's signature verification fail. Encryption can hide the content of the message from an eavesdropper, but encryption on its own may not let recipient verify the message's authenticity, or even detect selective modifications like changing

3410-537: The signer is unaware of, and that can be revealed after the signature has been applied. WYSIWYS is a 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. An ink signature could be replicated from one document to another by copying

3472-413: The signer to prove a forgery and limit who can verify the signature. Deniable encryption augments standard encryption by making it impossible for an attacker to mathematically prove the existence of a plain text message. Digital mixes create hard-to-trace communications. Cryptographic protocols can sometimes be verified formally on an abstract level. When it is done, there is a necessity to formalize

3534-461: The smart card, although this is not always implemented. If the smart card is stolen, the thief will still need the PIN code to generate a digital signature. This reduces the security of the scheme to that of the PIN system, although it still requires an attacker to possess the card. A mitigating factor is that private keys, if generated and stored on smart cards, are usually regarded as difficult to copy, and are assumed to exist in exactly one copy. Thus,

3596-547: The term itself has various readings; Cryptographic application protocols often use one or more underlying key agreement methods , which are also sometimes themselves referred to as "cryptographic protocols". For instance, TLS employs what is known as the Diffie–Hellman key exchange , which although it is only a part of TLS per se , Diffie–Hellman may be seen as a complete cryptographic protocol in itself for other applications. A wide variety of cryptographic protocols go beyond

3658-474: 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. Cryptographic protocol A cryptographic protocol

3720-493: The traditional goals of data confidentiality, integrity, and authentication to also secure a variety of other desired characteristics of computer-mediated collaboration. Blind signatures can be used for digital cash and digital credentials to prove that a person holds an attribute or right without revealing that person's identity or the identities of parties that person transacted with. Secure digital timestamping can be used to prove that data (even if confidential) existed at

3782-443: The user's PC can possibly replace the user application with a foreign substitute, in effect replacing the user's own communications with those of the attacker. This could allow a malicious application to trick a user into signing any document by displaying the user's original on-screen, but presenting the attacker's own documents to the signing application. To protect against this scenario, an authentication system can be set up between

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3844-404: The user's application (word processor, email 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. One of the main differences between a cloud based digital signature service and

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