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| Block ciphers | |
|---|---|
| Name | Block ciphers |
| Type | Symmetric-key cipher |
| Introduced | 1970s |
| Designers | IBM, National Security Agency, NIST |
| Key size | variable |
| Block size | variable |
| Structure | substitution–permutation network, Feistel network |
| Related | Stream cipher, Public-key cryptography, Hash function |
Block ciphers are symmetric-key NIST-oriented cryptographic primitives used to transform fixed-size plaintext blocks into ciphertext blocks under a secret key. They underpin many protocols and standards developed by IBM, NSA, IETF, ISO, and ENISA for secure communication, storage, and authentication. Designs draw on principles from pioneering work at Bell Labs, research by Claude Shannon, systematization by Horst Feistel, and formal analysis influenced by researchers at MIT, Stanford University, University of California, Berkeley, and Princeton University.
Block ciphers operate on fixed-size blocks (commonly 64 or 128 bits) and use a symmetric key schedule to produce reversible transformations; examples historically include algorithms from IBM proposals, government-driven designs by NSA, and academic ciphers from RSA Laboratories, EPFL, and Technische Universität Darmstadt. Their development intersected with milestones like the release of public standards by NIST and the advent of protocols standardized by the IETF and industry consortia such as the IEEE and ITU. Implementations are embedded in products from companies like Microsoft Corporation, Cisco Systems, Amazon Web Services, and Google LLC and are referenced in regulatory frameworks promulgated by institutions such as the European Commission, Federal Trade Commission, and U.S. Department of Commerce.
Designs use structural paradigms such as the Feistel network (rooted in work by Horst Feistel at IBM) and substitution–permutation networks exemplified in proposals evaluated by NIST during competitions. Security goals are formalized using models advanced by researchers at Stanford University, MIT, University of Cambridge, and ETH Zurich; criteria include confusion and diffusion inspired by Claude Shannon and provable bounds developed in academic labs like Bell Labs and Columbia University. Key schedule construction, S-box design, linear and differential cryptanalysis resistance were explored in collaborations among cryptographers at Royal Holloway, University of London, ENS, University of Waterloo, and Aarhus University. Design trade-offs balance throughput requirements emphasized by Intel Corporation, ARM Holdings, and NVIDIA against side-channel resistance topics investigated at University of Luxembourg, Radboud University Nijmegen, and Saarland University.
Modes are standardized methods to apply block ciphers for variable-length data, developed and ratified by bodies like NIST, ISO, and the IETF (through RFCs). Commonly used modes specified by these organizations include techniques facilitating confidentiality, integrity, and authenticated encryption in protocols by TLS WG and document formats from OASIS and IETF. Implementers at firms such as OpenSSL Project, Mozilla Foundation, Apple Inc., Oracle Corporation, and Dropbox, Inc. use modes to meet requirements from regulators including European Banking Authority and Financial Conduct Authority. Mode selection has been influenced by cryptanalytic results from researchers at ECRYPT, IRTF, and laboratories at NIST.
Security proofs and attacks emerged from collaborations involving NIST, academic centers like Princeton University, Cornell University, École Polytechnique, and research groups at Google Research and Microsoft Research. Classical attack categories—differential and linear cryptanalysis—were discovered and refined by teams at Politecnico di Torino, EPFL, and University of Bristol. Later techniques such as integral attacks, related-key analysis, and algebraic cryptanalysis were developed by scholars at Technische Universität München, University of Amsterdam, Royal Holloway, and KTH Royal Institute of Technology. Evaluations often occur in contests and workshops hosted by CRYPTO Conference, EUROCRYPT Conference, ASIACRYPT Conference, and RSA Conference where proposals are vetted by panels including experts from NSA, NIST, and academic institutions.
High-performance implementations are produced by vendors like Intel Corporation (instruction-set extensions), ARM Holdings (embedded cores), and Qualcomm (mobile SoCs) while open-source projects such as the OpenSSL Project, LibreSSL, and BoringSSL provide software libraries used by Apache Software Foundation, Mozilla Foundation, and Canonical Ltd.. Hardware implementations are integrated in products by Xilinx, Broadcom, and Samsung Electronics and evaluated in contexts like cloud services from Amazon Web Services, Google Cloud Platform, and Microsoft Azure. Side-channel countermeasures and constant-time implementations are researched at TÜBİTAK BİLGEM, INRIA, and Graz University of Technology to mitigate attacks disclosed in papers from USENIX Security Symposium and ACM CCS.
Standards and algorithms have been promulgated by NIST, ISO, IETF, and national bodies including the NSA and NIST. Notable algorithm designs and competitions involved entities such as RSA Laboratories, MIT, École Polytechnique, IBM, Siemens AG, and independent researchers from Queens University Belfast. Evaluation and adoption activities took place in forums run by NIST, IETF, and conferences like CFRG.
Block ciphers are embedded in protocols and products used by IETF-standardized suites like TLS and IPsec, document and archive formats standardized by ISO and supported by companies such as Adobe Systems, Microsoft Corporation, and Oracle Corporation. They secure network appliances from Cisco Systems, cloud platforms from Amazon Web Services and Microsoft Azure, payment systems regulated by PCI Security Standards Council, and storage encryption in consumer devices by Apple Inc. and Samsung Electronics. Block ciphers also support cryptographic constructions in authentication frameworks developed by OASIS, identity providers such as Okta, Inc., and federated services used across enterprises including Salesforce and ServiceNow.