Identity-based cryptography

Last updated

Identity-based cryptography is a type of public-key cryptography in which a publicly known string representing an individual or organization is used as a public key. The public string could include an email address, domain name, or a physical IP address.

Contents

The first implementation of identity-based signatures and an email-address based public-key infrastructure (PKI) was developed by Adi Shamir in 1984, [1] which allowed users to verify digital signatures using only public information such as the user's identifier. Under Shamir's scheme, a trusted third party would deliver the private key to the user after verification of the user's identity, with verification essentially the same as that required for issuing a certificate in a typical PKI.

Shamir similarly proposed identity-based encryption, which appeared particularly attractive since there was no need to acquire an identity's public key prior to encryption. However, he was unable to come up with a concrete solution, and identity-based encryption remained an open problem for many years. The first practical implementations were finally devised by Sakai in 2000, [2] and Boneh and Franklin in 2001. [3] These solutions were based on bilinear pairings. Also in 2001, a solution was developed independently by Clifford Cocks. [4] [5]

Closely related to various identity-based encryption schemes are identity based key agreement schemes. One of the first identity based key agreement algorithms was published in 1986, just two years after Shamir's identity based signature. The author was E. Okamoto. [6] Identity based key agreement schemes also allow for "escrow free" identity based cryptography. A notable example of such an escrow free identity based key agreement is the McCullagh-Barreto's "Authenticated Key Agreement without Escrow" found in section 4 of their 2004 paper, "A New Two-Party Identity-Based Authenticated Key Agreement". [7] A variant of this escrow free key exchange is standardized as the identity based key agreement in the Chinese identity based standard SM9.

Usage

Identity-based systems allow any party to generate a public key from a known identity value, such as an ASCII string. A trusted third party, called the private key generator (PKG), generates the corresponding private keys. To operate, the PKG first publishes a master public key, and retains the corresponding master private key (referred to as master key). Given the master public key, any party can compute a public key corresponding to the identity ID by combining the master public key with the identity value. To obtain a corresponding private key, the party authorized to use the identity ID contacts the PKG, which uses the master private key to generate the private key for the identity ID.

Limitation

Identity-based systems have a characteristic problem in operation. Suppose Alice and Bob are users of such a system. Since the information needed to find Alice's public key is completely determined by Alice's ID and the master public key, it is not possible to revoke Alice's credentials and issue new credentials without either (a) changing Alice's ID (usually a phone number or an email address which will appear in a corporate directory); or (b) changing the master public key and re-issuing private keys to all users, including Bob. [8]

This limitation may be overcome by including a time component (e.g. the current month) in the identity. [8]

See also

Related Research Articles

<span class="mw-page-title-main">Diffie–Hellman key exchange</span> Method of exchanging cryptographic keys

Diffie–Hellman (DH) key exchange is a mathematical method of securely generating a symmetric cryptographic key over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman. DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography. Published in 1976 by Diffie and Hellman, this is the earliest publicly known work that proposed the idea of a private key and a corresponding public key.

<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. There are many kinds of public-key cryptosystems, with different security goals, including digital signature, Diffie-Hellman key exchange, public-key key encapsulation, and public-key encryption.

<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.

Articles related to cryptography include:

Identity-based encryption (IBE), is an important primitive of identity-based cryptography. As such it is a type of public-key encryption in which the public key of a user is some unique information about the identity of the user. This means that a sender who has access to the public parameters of the system can encrypt a message using e.g. the text-value of the receiver's name or email address as a key. The receiver obtains its decryption key from a central authority, which needs to be trusted as it generates secret keys for every user.

Key/Config-authentication is used to solve the problem of authenticating the keys of a person that some other person is talking to or trying to talk to. In other words, it is the process of assuring that the key of "person A", held by "person B", does in fact belong to "person A" and vice versa.

<span class="mw-page-title-main">Forward secrecy</span> Practice in cryptography

In cryptography, forward secrecy (FS), also known as perfect forward secrecy (PFS), is a feature of specific key-agreement protocols that gives assurances that session keys will not be compromised even if long-term secrets used in the session key exchange are compromised, limiting damage. For HTTPS, the long-term secret is typically the private key of the server. Forward secrecy protects past sessions against future compromises of keys or passwords. By generating a unique session key for every session a user initiates, the compromise of a single session key will not affect any data other than that exchanged in the specific session protected by that particular key. This by itself is not sufficient for forward secrecy which additionally requires that a long-term secret compromise does not affect the security of past session keys.

In cryptography, a pseudorandom function family, abbreviated PRF, is a collection of efficiently-computable functions which emulate a random oracle in the following way: no efficient algorithm can distinguish between a function chosen randomly from the PRF family and a random oracle. Pseudorandom functions are vital tools in the construction of cryptographic primitives, especially secure encryption schemes.

Distributed key generation (DKG) is a cryptographic process in which multiple parties contribute to the calculation of a shared public and private key set. Unlike most public key encryption models, distributed key generation does not rely on Trusted Third Parties. Instead, the participation of a threshold of honest parties determines whether a key pair can be computed successfully. Distributed key generation prevents single parties from having access to a private key. The involvement of many parties requires Distributed key generation to ensure secrecy in the presence of malicious contributions to the key calculation.

<span class="mw-page-title-main">Dan Boneh</span> Israeli–American professor

Dan Boneh is an Israeli–American professor in applied cryptography and computer security at Stanford University.

The Boneh–Franklin scheme is an identity-based encryption system proposed by Dan Boneh and Matthew K. Franklin in 2001. This article refers to the protocol version called BasicIdent. It is an application of pairings over elliptic curves and finite fields.

<span class="mw-page-title-main">Cryptography</span> Practice and study of secure communication techniques

Cryptography, or cryptology, is the practice and study of techniques for secure communication in the presence of adversarial behavior. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and others. Core concepts related to information security are also central to cryptography. Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.

Post-quantum cryptography (PQC), sometimes referred to as quantum-proof, quantum-safe, or quantum-resistant, is the development of cryptographic algorithms that are currently thought to be secure against a cryptanalytic attack by a quantum computer. Most widely-used public-key algorithms rely on the difficulty of one of three mathematical problems: the integer factorization problem, the discrete logarithm problem or the elliptic-curve discrete logarithm problem. All of these problems could be easily solved on a sufficiently powerful quantum computer running Shor's algorithm or even faster and less demanding alternatives.

Attribute-based encryption is a generalisation of public-key encryption which enables fine grained access control of encrypted data using authorisation policies. The secret key of a user and the ciphertext are dependent upon attributes. In such a system, the decryption of a ciphertext is possible only if the set of attributes of the user key matches the attributes of the ciphertext.

In cryptography, server-based signatures are digital signatures in which a publicly available server participates in the signature creation process. This is in contrast to conventional digital signatures that are based on public-key cryptography and public-key infrastructure. With that, they assume that signers use their personal trusted computing bases for generating signatures without any communication with servers.

Matthew Keith "Matt" Franklin is an American cryptographer, and a professor of computer science at the University of California, Davis.

The Sakai–Kasahara scheme, also known as the Sakai–Kasahara key encryption algorithm (SAKKE), is an identity-based encryption (IBE) system proposed by Ryuichi Sakai and Masao Kasahara in 2003. Alongside the Boneh–Franklin scheme, this is one of a small number of commercially implemented identity-based encryption schemes. It is an application of pairings over elliptic curves and finite fields. A security proof for the algorithm was produced in 2005 by Chen and Cheng. SAKKE is described in Internet Engineering Task Force (IETF) RFC 6508.

Identity-based conditional proxy re-encryption (IBCPRE) is a type of proxy re-encryption (PRE) scheme in the identity-based public key cryptographic setting. An IBCPRE scheme is a natural extension of proxy re-encryption on two aspects. The first aspect is to extend the proxy re-encryption notion to the identity-based public key cryptographic setting. The second aspect is to extend the feature set of proxy re-encryption to support conditional proxy re-encryption. By conditional proxy re-encryption, a proxy can use an IBCPRE scheme to re-encrypt a ciphertext but the ciphertext would only be well-formed for decryption if a condition applied onto the ciphertext together with the re-encryption key is satisfied. This allows fine-grained proxy re-encryption and can be useful for applications such as secure sharing over encrypted cloud data storage.

SM9 is a Chinese national cryptography standard for Identity Based Cryptography issued by the Chinese State Cryptographic Authority in March 2016. It is represented by the Chinese National Cryptography Standard (Guomi), GM/T 0044-2016 SM9. The standard contains the following components:

An oblivious pseudorandom function (OPRF) is a cryptographic function, similar to a keyed-hash function, but with the distinction that in an OPRF two parties cooperate to securely compute a pseudorandom function (PRF).

References

  1. Shamir, Adi (1985). "Identity-Based Cryptosystems and Signature Schemes" (PDF). In Blakley, George Robert; Chaum, David (eds.). Advances in Cryptology Proceedings of CRYPTO '84. Lecture Notes in Computer Science. Vol. 196 (1 ed.). Springer Berlin Heidelberg. pp. 47–53. doi: 10.1007/3-540-39568-7_5 . ISBN   978-3-540-39568-3. Archived (PDF) from the original on 26 July 2018. Retrieved 30 October 2024.
  2. Sakai, R; Ohgishi, K; Kasahara, M (2000). "Cryptosystems based on pairings". SICS. Symposium on cryptography and information security.
  3. Dan, Boneh; Matt, Franklin (2001). "Identity-based encryption from the Weil pairing". Advances in Cryptology – CRYPTO 2001. Lecture Notes in Computer Science. Vol. 2139/2001. Springer. pp. 213–229. CiteSeerX   10.1.1.66.1131 .
  4. Cocks, Cliff (2001). "An Identity Based Encryption Scheme Based on Quadratic Residues". Cryptography and Coding (PDF). Lecture Notes in Computer Science. Vol. 2260/2001. Springer. pp. 360–363. CiteSeerX   10.1.1.116.5477 . doi:10.1007/3-540-45325-3_32. ISBN   978-3-540-43026-1. Archived from the original (PDF) on 2007-02-06.
  5. "Dr Clifford Cocks CB, Honorary Doctor of Science". University of Bristol. Archived from the original on 2015-06-27.
  6. Okamoto, E. (1986). "Proposal for identity-based key distribution systems". Electronics Letters. 22 (24): 1283–1284. Bibcode:1986ElL....22.1283O. doi:10.1049/el:19860880. ISSN   0013-5194.
  7. McCullagh, Noel; Barreto, Paulo S. L. M. (2004). "A New Two-Party Identity-Based Authenticated Key Agreement". Topics in Cryptology – CT-RSA 2005. Lecture Notes in Computer Science. Vol. 3376.
  8. 1 2 Green, Matthew; Miers, Ian (17 May 2015). "Forward Secure Asynchronous Messaging from Puncturable Encryption". 2015 IEEE Symposium on Security and Privacy. ACM (published 20 July 2015). pp. 305–320. doi:10.1109/SP.2015.26. ISBN   978-1-4673-6949-7. S2CID   9171925. Archived from the original on 8 June 2021. Retrieved 8 June 2021.