Non-repudiation

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In law, non-repudiation is a situation where a statement's author cannot successfully dispute its authorship or the validity of an associated contract. [1] The term is often seen in a legal setting when the authenticity of a signature is being challenged. In such an instance, the authenticity is being "repudiated".[ citation needed ]

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For example, Mallory buys a cell phone for $100, writes a paper cheque as payment, and signs the cheque with a pen. Later, she finds that she can't afford it, and claims that the cheque is a forgery. The signature guarantees that only Mallory could have signed the cheque, and so Mallory's bank must pay the cheque. This is non-repudiation; Mallory cannot repudiate the cheque. In practice, pen-and-paper signatures aren't hard to forge, but digital signatures can be very hard to break.

In security

In general, non-repudiation involves associating actions or changes with a unique individual. For example, a secure area may use a key card access system where non-repudiation would be violated if key cards were shared or if lost and stolen cards were not immediately reported. Similarly, the owner of a computer account must not allow others to use it, such as by giving away their password, and a policy should be implemented to enforce this. [2]

In digital security

In digital security, non-repudiation means: [3]

Proof of data integrity is typically the easiest of these requirements to accomplish. A data hash such as SHA2 usually ensures that the data will not be changed undetectably. Even with this safeguard, it is possible to tamper with data in transit, either through a man-in-the-middle attack or phishing. Because of this, data integrity is best asserted when the recipient already possesses the necessary verification information, such as after being mutually authenticated. [5]

The common method to provide non-repudiation in the context of digital communications or storage is Digital Signatures, a more powerful tool that provides non-repudiation in a publicly verifiable manner. [6] Message Authentication Codes (MAC), useful when the communicating parties have arranged to use a shared secret that they both possess, does not give non-repudiation. A misconception is that encrypting, per se, provides authentication "If the message decrypts properly then it is authentic", which is not the case. MAC can be subject to several types of attacks, like: message reordering, block substitution, block repetition, .... Thus just providing message integrity and authentication, but not non-repudiation. To achieve non-repudiation one must trust a service (a certificate generated by a trusted third party (TTP) called certificate authority (CA)) which prevents an entity from denying previous commitments or actions (e.g. sending message A to B). The difference between MAC and Digital Signatures, one uses symmetric keys and the other asymmetric keys (provided by the CA). Note that the goal is not to achieve confidentiality: in both cases (MAC or digital signature), one simply appends a tag to the otherwise plaintext, visible message. If confidentiality is also required, then an encryption scheme can be combined with the digital signature, or some form of authenticated encryption could be used. Verifying the digital origin means that the certified/signed data likely came from someone who possesses the private key corresponding to the signing certificate. If the key used to digitally sign a message is not properly safeguarded by the original owner, digital forgery can occur. [7] [8] [9]

Trusted third parties (TTPs)

To mitigate the risk of people repudiating their own signatures, the standard approach is to involve a trusted third party. [10]

The two most common TTPs are forensic analysts and notaries. A forensic analyst specializing in handwriting can compare some signature to a known valid signature and assess its legitimacy. A notary is a witness who verifies an individual's identity by checking other credentials and affixing their certification that the person signing is who they claim to be. A notary provides the extra benefit of maintaining independent logs of their transactions, complete with the types of credentials checked, and another signature that can be verified by the forensic analyst. This double security makes notaries the preferred form of verification.[ citation needed ]

For digital information, the most commonly employed TTP is a certificate authority, which issues public key certificates. A public key certificate can be used by anyone to verify digital signatures without a shared secret between the signer and the verifier. The role of the certificate authority is to authoritatively state to whom the certificate belongs, meaning that this person or entity possesses the corresponding private key. However, a digital signature is forensically identical in both legitimate and forged uses. Someone who possesses the private key can create a valid digital signature. Protecting the private key is the idea behind some smart cards such as the United States Department of Defense's Common Access Card (CAC), which never lets the key leave the card. That means that to use the card for encryption and digital signatures, a person needs the personal identification number (PIN) code necessary to unlock it.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Public-key cryptography</span> Cryptographic system with public and private keys

Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic algorithms based on mathematical problems termed one-way functions. Security of public-key cryptography depends on keeping the private key secret; the public key can be openly distributed without compromising security.

<span class="mw-page-title-main">Digital signature</span> Mathematical scheme for verifying the authenticity of digital documents

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.

In cryptography and computer security, a man-in-the-middle (MITM) attack is a cyberattack where the attacker secretly relays and possibly alters the communications between two parties who believe that they are directly communicating with each other, as the attacker has inserted themselves between the two parties.

<span class="mw-page-title-main">Public key infrastructure</span> System that can issue, distribute and verify digital certificates

A public key infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to facilitate the secure electronic transfer of information for a range of network activities such as e-commerce, internet banking and confidential email. It is required for activities where simple passwords are an inadequate authentication method and more rigorous proof is required to confirm the identity of the parties involved in the communication and to validate the information being transferred.

In cryptography, a message authentication code (MAC), sometimes known as an authentication tag, is a short piece of information used for authenticating and integrity-checking a message. In other words, to confirm that the message came from the stated sender and has not been changed. The MAC value allows verifiers to detect any changes to the message content.

<span class="mw-page-title-main">Key exchange</span> Cryptographic protocol enabling the sharing of a secret key over an insecure channel

Key exchange is a method in cryptography by which cryptographic keys are exchanged between two parties, allowing use of a cryptographic algorithm.

In cryptography, a trusted third party (TTP) is an entity which facilitates interactions between two parties who both trust the third party; the third party reviews all critical transaction communications between the parties, based on the ease of creating fraudulent digital content. In TTP models, the relying parties use this trust to secure their own interactions. TTPs are common in any number of commercial transactions and in cryptographic digital transactions as well as cryptographic protocols, for example, a certificate authority (CA) would issue a digital certificate to one of the two parties in the next example. The CA then becomes the TTP to that certificate's issuance. Likewise transactions that need a third party recordation would also need a third-party repository service of some kind.

A cryptographic protocol 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.

S/MIME is a standard for public-key encryption and signing of MIME data. S/MIME is on an IETF standards track and defined in a number of documents, most importantly RFC 8551. It was originally developed by RSA Data Security, and the original specification used the IETF MIME specification with the de facto industry standard PKCS #7 secure message format. Change control to S/MIME has since been vested in the IETF, and the specification is now layered on Cryptographic Message Syntax (CMS), an IETF specification that is identical in most respects with PKCS #7. S/MIME functionality is built into the majority of modern email software and interoperates between them. Since it is built on CMS, MIME can also hold an advanced digital signature.

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A cryptographic key is a string of data that is used to lock or unlock cryptographic functions, including authentication, authorization and encryption. Cryptographic keys are grouped into cryptographic key types according to the functions they perform.

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A Digital Postmark (DPM) is a technology that applies a trusted time stamp issued by a postal operator to an electronic document, validates electronic signatures, and stores and archives all non-repudiation data needed to support a potential court challenge. It guarantees the certainty of date and time of the postmarking. This global standard was renamed the Electronic Postal Certification Mark (EPCM) in 2007 shortly after a new iteration of the technology was developed by Microsoft and Poste Italiane. The key addition to the traditional postmarking technology was integrity of the electronically postmarked item, meaning any kind of falsification and tampering will be easily and definitely detected. Additionally, content confidentiality is guaranteed since document certification is carried out without access or reading by the postal operator. The EPCM will eventually be available through the UPU to all international postal operators in the 191 member countries willing to be compliant with this standard, thus granting interoperability in certified communications between postal operators. In the United States, the US Postal Service operates a non-global standard called the Electronic Postmark, although it is soon expected to provide services utilizing the EPCM.

The ANSI X9.95 standard for trusted timestamps expands on the widely used RFC 3161 - Internet X.509 Public Key Infrastructure Time-Stamp Protocol by adding data-level security requirements that can ensure data integrity against a reliable time source that is provable to any third party. Applicable to both unsigned and digitally signed data, this newer standard has been used by financial institutions and regulatory bodies to create trustworthy timestamps that cannot be altered without detection and to sustain an evidentiary trail of authenticity. Timestamps based on the X9.95 standard can be used to provide:

Trusted timestamping is the process of securely keeping track of the creation and modification time of a document. Security here means that no one—not even the owner of the document—should be able to change it once it has been recorded provided that the timestamper's integrity is never compromised.

Trust on first use (TOFU), or trust upon first use (TUFU), is an authentication scheme used by client software which needs to establish a trust relationship with an unknown or not-yet-trusted endpoint. In a TOFU model, the client will try to look up the endpoint's identifier, usually either the public identity key of the endpoint, or the fingerprint of said identity key, in its local trust database. If no identifier exists yet for the endpoint, the client software will either prompt the user to confirm they have verified the purported identifier is authentic, or if manual verification is not assumed to be possible in the protocol, the client will simply trust the identifier which was given and record the trust relationship into its trust database. If in a subsequent connection a different identifier is received from the opposing endpoint, the client software will consider it to be untrusted.

In information security, message authentication or data origin authentication is a property that a message has not been modified while in transit and that the receiving party can verify the source of the message. Message authentication does not necessarily include the property of non-repudiation.

The Web Cryptography API is the World Wide Web Consortium’s (W3C) recommendation for a low-level interface that would increase the security of web applications by allowing them to perform cryptographic functions without having to access raw keying material. This agnostic API would perform basic cryptographic operations, such as hashing, signature generation and verification and encryption as well as decryption from within a web application.

References

  1. ↑ Li, Zhaozheng; Lei, Weimin; Hu, Hanyun; Zhang, Wei (2019). "A Blockchain-based Communication Non-repudiation System for Conversational Service". 2019 IEEE 13th International Conference on Anti-counterfeiting, Security, and Identification (ASID). pp. 6–10. doi:10.1109/ICASID.2019.8924991. ISBN   978-1-7281-2458-2. S2CID   209320279.
  2. ↑ Christopher Negus (2012). Linux Bible. Wiley. p. 580. ISBN   978-1-118-28690-6.
  3. ↑ Non-Repudiation in the Digital Environment (Adrian McCullagh)
  4. ↑ Yu, Mingchao; Sahraei, Saeid; Nixon, Mark; Han, Song (18 July 2020). "SoK: Sharding on Blockchain". Proceedings of the 1st ACM Conference on Advances in Financial Technologies. pp. 114–134. doi:10.1145/3318041.3355457. ISBN   9781450367325. S2CID   204749727.
  5. ↑ Chen, Chin-Ling; Chiang, Mao-Lun; Hsieh, Hui-Ching; Liu, Ching-Cheng; Deng, Yong-Yuan (July 2020). "A Lightweight Mutual Authentication with Wearable Device in Location-Based Mobile Edge Computing". Wireless Personal Communications. 113 (1): 575–598. doi:10.1007/s11277-020-07240-2. S2CID   218934756.
  6. ↑ Chia, Jason; Chin, Ji-Jian; Yip, Sook-Chin (2021-09-16). "Digital signature schemes with strong existential unforgeability". F1000Research. 10: 931. doi: 10.12688/f1000research.72910.1 . PMC   9925878 . PMID   36798451.
  7. ↑ Wu, Wei; Zhou, Jianying; Xiang, Yang; Xu, Li (December 2013). "How to achieve non-repudiation of origin with privacy protection in cloud computing". Journal of Computer and System Sciences. 79 (8): 1200–1213. doi: 10.1016/j.jcss.2013.03.001 .
  8. ↑ "What are the differences between a digital signature, a MAC and a hash?".
  9. ↑ Sosin, Artur (2018). "How to increase the information assurance in the information age". Journal of Defense Resources Management. 9 (1): 45–57. ProQuest   2178518357.
  10. ↑ Zhou, Jianying; Gollmann, Dieter (1996). "Observations on non-repudiation". In Kim, Kwangjo; Matsumoto, Tsutomu (eds.). Advances in Cryptology — ASIACRYPT '96. Lecture Notes in Computer Science. Vol. 1163. Berlin, Heidelberg: Springer. pp. 133–144. doi:10.1007/BFb0034842. ISBN   978-3-540-70707-3.
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