International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Avik Chakraborti

Affiliation: NTT Secure Platform Laboratories

Publications

Year
Venue
Title
2020
TOSC
INT-RUP Secure Lightweight Parallel AE Modes
Owing to the growing demand for lightweight cryptographic solutions, NIST has initiated a standardization process for lightweight cryptographic algorithms. Specific to authenticated encryption (AE), the NIST draft demands that the scheme should have one primary member that has key length of 128 bits, and it should be secure for at least 250 − 1 byte queries and 2112 computations. Popular (lightweight) modes, such as OCB, OTR, CLOC, SILC, JAMBU, COFB, SAEB, Beetle, SUNDAE etc., require at least 128-bit primitives to meet the NIST criteria, as all of them are just birthday bound secure. Furthermore, most of them are sequential, and they either use a two pass mode or they do not offer any security when the adversary has access to unverified plaintext (RUP model). In this paper, we propose two new designs for lightweight AE modes, called LOCUS and LOTUS, structurally similar to OCB and OTR, respectively. These modes achieve notably higher AE security bounds with lighter primitives (only a 64-bit tweakable block cipher). Especially, they satisfy the NIST requirements: secure as long as the data complexity is less than 264 bytes and time complexity is less than 2128, even when instantiated with a primitive with 64-bit block and 128-bit key. Both these modes are fully parallelizable and provide full integrity security under the RUP model. We use TweGIFT-64[4,16,16,4] (also referred as TweGIFT-64), a tweakable variant of the GIFT block cipher, to instantiate our AE modes. TweGIFT-64-LOCUS and TweGIFT-64-LOTUS are significantly light in hardware implementation. To justify, we provide our FPGA based implementation results, which demonstrate that TweGIFT-64-LOCUS consumes only 257 slices and 690 LUTs, while TweGIFT-64-LOTUS consumes only 255 slices and 664 LUTs.
2019
JOFC
Blockcipher-Based Authenticated Encryption: How Small Can We Go?
This paper presents a lightweight blockcipher-based authenticated encryption mode mainly focusing on minimizing the implementation size, i.e., hardware gates or working memory on software. The mode is called $$\textsf {COFB}$$COFB, for COmbined FeedBack. $$\textsf {COFB}$$COFB uses an n-bit blockcipher as the underlying primitive and relies on the use of a nonce for security. In addition to the state required for executing the underlying blockcipher, $$\textsf {COFB}$$COFB needs only n / 2 bits state as a mask. Till date, for all existing constructions in which masks have been applied, at least n bit masks have been used. Thus, we have shown the possibility of reducing the size of a mask without degrading the security level much. Moreover, it requires one blockcipher call to process one input block. We show $$\textsf {COFB}$$COFB is provably secure up to $$O(2^{n/2}/n)$$O(2n/2/n) queries which is almost up to the standard birthday bound. We first present an idealized mode $$\textsf {iCOFB}$$iCOFB along with the details of its provable security analysis. Next, we extend the construction to the practical mode COFB. We instantiate COFB with two 128-bit blockciphers, AES-128 and GIFT-128, and present their implementation results on FPGAs. We present two implementations, with and without CAESAR hardware API. When instantiated with AES-128 and implemented without CAESAR hardware API, COFB achieves only a few more than 1000 Look-Up-Tables (LUTs) while maintaining almost the same level of provable security as standard AES-based AE, such as GCM. When instantiated with GIFT-128, COFB performs much better in hardware area. It consumes less than 1000 LUTs while maintaining the same security level. However, when implemented with CAESAR hardware API, there are significant overheads both in hardware area and in throughput. COFB with AES-128 achieves about 1475 LUTs. COFB with GIFT-128 achieves a few more than 1000 LUTs. Though there are overheads, still both these figures show competitive implementation results compared to other authenticated encryption constructions.
2018
TCHES
Beetle Family of Lightweight and Secure Authenticated Encryption Ciphers 📺
This paper presents a lightweight, sponge-based authenticated encryption (AE) family called Beetle. When instantiated with the PHOTON permutation from CRYPTO 2011, Beetle achieves the smallest footprint—consuming only a few more than 600 LUTs on FPGA while maintaining 64-bit security. This figure is significantly smaller than all known lightweight AE candidates which consume more than 1,000 LUTs, including the latest COFB-AES from CHES 2017. In order to realize such small hardware implementation, we equip Beetle with an “extremely tight” bound of security. The trick is to use combined feedback to create a difference between the cipher text block and the rate part of the next feedback (in traditional sponge these two values are the same). Then we are able to show that Beetle is provably secure up to min{c − log r, b/2, r} bits, where b is the permutation size and r and c are parameters called rate and capacity, respectively. The tight security bound allows us to select the smallest security parameters, which in turn result in the smallest footprint.
2017
CHES
Blockcipher-Based Authenticated Encryption: How Small Can We Go?
This paper presents a design of authenticated encryption (AE) focusing on minimizing the implementation size, i.e., hardware gates or working memory on software. The scheme is called $$\textsf {COFB}$$, for COmbined FeedBack. $$\textsf {COFB}$$ uses an n-bit blockcipher as the underlying primitive, and relies on the use of a nonce for security. In addition to the state required for executing the underlying blockcipher, $$\textsf {COFB}$$ needs only n / 2 bits state as a mask. Till date, for all existing constructions in which masks have been applied, at least n bit masks have been used. Thus, we have shown the possibility of reducing the size of a mask without degrading the security level much. Moreover, it requires one blockcipher call to process one input block. We show $$\textsf {COFB}$$ is provably secure up to $$O(2^{n/2}/n)$$ queries which is almost up to the standard birthday bound. We also present our hardware implementation results. Experimental implementation results suggest that our proposal has a good performance and the smallest footprint among all known blockcipher-based AE.
2016
FSE
2015
EPRINT
2015
CHES