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In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor. For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users. Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often used in military messa

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Power Yoga: Variable-Stretch Security of CCM for Energy-Efficient Lightweight IoT

Emiljano Gjiriti, Reza Reyhanitabar, Damian Vizár

The currently ongoing NIST LWC project aims at identifying new standardization targets for lightweight authenticated encryption with associated data (AEAD) and (optionally) lightweight cryptographic hashing. NIST has deemed it important for performance and cost to be optimized on relevant platforms, especially for short messages. Reyhanitabar, Vaudenay and Vizar (Asiacrypt 2016) gave a formal treatment for security of nonce-based AEAD with variable stretch, i.e., when the length of the authentication tag is changed between encryptions without changing the key. They argued that AEAD supporting variable stretch is of practical interest for constrained applications, especially low-power devices operated by battery, due to the ability to flexibly trade communication overhead and level of integrity. In this work, we investigate this hypothesis with affirmative results. We present vCCM, a variable-stretch variant of the standard CCM and prove it is secure when used with variable stretch. We then experimentally measure the energy consumption of a real-world wireless sensor node when encrypting and sending messages with vCCM and CCM, respectively. Our projections show that the flexible trade of integrity level and ciphertext expansion can lead up to 21% overall energy consumption reduction in certain scenarios. As vCCM is obtained from the widely-used CCM by a black-box transformation, allowing any existing CCM implementations to be reused as-is, our results can be immediately put to use in practice. vCCM is all the more relevant because neither the NIST LWC project, nor any of the candidates give a consideration for the support of variable stretch and the related integrity-overhead trade-off.

RUHR-UNIV BOCHUM, HORST GORTZ INST IT-SICHERHEIT2021

Authenticated Encryption: Toward Next-Generation Algorithms

Reza Reyhanitabar

Ieee Computer Soc2014

Security of Full-State Keyed Sponge and Duplex: Applications to Authenticated Encryption

Reza Reyhanitabar, Damian Vizár

We provide a security analysis for full-state keyed Sponge and full-state Duplex constructions. Our results can be used for making a large class of Sponge-based authenticated encryption schemes more efficient by concurrent absorption of associated data and message blocks. In particular, we introduce and analyze a new variant of SpongeWrap with almost free authentication of associated data. The idea of using full-state message absorption for higher efficiency was first made explicit in the Donkey Sponge MAC construction, but without any formal security proof. Recently, Gaži, Pietrzak and Tessaro (CRYPTO 2015) have provided a proof for the fixed-output-length variant of Donkey Sponge. Yasuda and Sasaki (CT-RSA 2015) have considered partially full-state Sponge-based authenticated encryption schemes for efficient incorporation of associated data. In this work, we unify, simplify, and generalize these results about the security and applicability of full-state keyed Sponge and Duplex constructions; in particular, for designing more efficient authenticated encryption schemes. Compared to the proof of Gaži et al., our analysis directly targets the original Donkey Sponge construction as an arbitrary-output-length function. Our treatment is also more general than that of Yasuda and Sasaki, while yielding a more efficient authenticated encryption mode for the case that associated data might be longer than messages.

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