Authenticated encryption schemes which resist misuse of nonce at some desired level of privacy ar... more Authenticated encryption schemes which resist misuse of nonce at some desired level of privacy are two-pass or Mac-then-Encrypt constructions (inherently inefficient but provide full privacy) and online constructions like McOE, sponge-type authenticated encryptions (such as duplex) and COPA. Only the last one is almost parallelizable except that for associated data processing, the final block-cipher call is sequential (it needs to wait for the encryption of all the previous ones). In this paper, we design a new online secure authenticated encryption, called ELmD or Encrypt-Linear mix-Decrypt, which is completely (two-stage) parallel (even in associated data) and fully pipeline implementable. It also provides full privacy when associated data is not repeated. Like COPA, our construction is based on EME, an Encrypt-Mix-Encrypt type SPRP construction (secure against chosen plaintext and ciphertext). But unlike EME, we have used an online computable efficient linear mixing instead of a non-linear mixing. We have also provided the hardware implementation of the construction and compare the performance with similar constructions like COPA and EME2.
In CRYPTO’21, Shen et al. proved that Two-Keyed-DbHtS construction is secure up to 22n/3 queries ... more In CRYPTO’21, Shen et al. proved that Two-Keyed-DbHtS construction is secure up to 22n/3 queries in the multi-user setting independent of the number of users. Here the underlying double-block hash function H of the construction realized as the concatenation of two independent n-bit keyed hash functions (HKh,1,HKh,2), and the security holds under the assumption that each of the n-bit keyed hash function is universal and regular. The authors have also demonstrated the applicability of their result to the key-reduced variants of DbHtS MACs, including 2K-SUM-ECBC, 2K-PMAC_Plus and 2K-LightMAC_Plus without requiring domain separation technique and proved 2n/3-bit multi-user security of these constructions in the ideal cipher model. Recently, Guo and Wang have invalidated the security claim of Shen et al.’s result by exhibiting three constructions, which are instantiations of the Two-Keyed-DbHtS framework, such that each of their n-bit keyed hash functions are O(2−n) universal and regular...
2019 32nd International Conference on VLSI Design and 2019 18th International Conference on Embedded Systems (VLSID)
In the era of lightweight cryptography, designing cryptographically good and power efficient 4 × ... more In the era of lightweight cryptography, designing cryptographically good and power efficient 4 × 4 S-boxes is a widely discussed problem. While the optimal cryptographic properties are easy to verify, it is not very straightforward to verify whether a S-box is power efficient or not. The traditional approach is to explicitly determine the dynamic power consumption using commercially available CAD tools and report accordingly based on a pre-defined threshold value. However, this procedure is highly time consuming, and the overhead becomes formidable while dealing with a set of S-boxes from a large space. This mandates development of an automation tool which should be able to quickly characterize the power efficiency from the Boolean function representation of an S-box. In this paper, we present a supervised machine learning (ML) assisted automated framework to resolve the problem for 4 × 4 S-boxes, which turns out to be approximately 14 times faster (using AND-OR-NOT gates) than the traditional approach. The key idea is to extrapolate the knowledge of the literal counts of various functional forms, AND-OR-NOT gate counts in the simplified SOP form of the underlying Boolean functions corresponding to the S-box to predict the dynamic power efficiency. We demonstrate the effectiveness of our framework by reporting a set of power efficient S-boxes from a large set of 4 × 4 optimal S-boxes. The experimental results and performance of our novel technique depicts its superiority with high efficiency and low time overhead.
The authenticated encryption scheme COLM is a third-round candidate in the CAESAR competition. Mu... more The authenticated encryption scheme COLM is a third-round candidate in the CAESAR competition. Much like its antecedents COPA, ELmE, and ELmD, COLM consists of two parallelizable encryption layers connected by a linear mixing function. While COPA uses plain XOR mixing, ELmE, ELmD, and COLM use a more involved invertible mixing function. In this work, we investigate the integrity of the COLM structure when unverified plaintext is released, and demonstrate that its security highly depends on the choice of mixing function. Our results are threefold. First, we discuss the practical nonce-respecting forgery by Andreeva et al. (ASIACRYPT 2014) against COPA’s XOR mixing. Then we present a noncemisusing forgery against arbitrary mixing functions with practical time complexity. Finally, by using significantly larger queries, we can extend the previous forgery to be nonce-respecting.
PHOTON-Beetle is an authenticated encryption and hash family, that uses a sponge-based mode Beetl... more PHOTON-Beetle is an authenticated encryption and hash family, that uses a sponge-based mode Beetle with the P256 (used for the hash function PHOTON) being the underlying permutation. This report updates software implementations of PHOTON-Beetle on 8-bit microcontrollers and that on general-purpose computers.
Authenticated encryption schemes are usually expected to offer confidentiality and authenticity. ... more Authenticated encryption schemes are usually expected to offer confidentiality and authenticity. In case of release of unverified plaintext (RUP), an adversary gets separated access to the decryption and verification functionality, and has more power in breaking the scheme. Andreeva et al. (ASIACRYPT 2014) formalized RUP security using plaintext awareness, informally meaning that the decryption functionality gives no extra power in breaking confidentiality, and INT-RUP security, covering authenticity in case of RUP. We describe a single, unified model, called AERUP security, that ties together these notions: we prove that an authenticated encryption scheme is AERUP secure if and only if it is conventionally secure, plaintext aware, and INT-RUP secure. We next present ANYDAE, a generalization of SUNDAE of Banik et al. (ToSC 2018/3). ANYDAE is a lightweight deterministic scheme that is based on a block cipher with block size n and arbitrary mixing functions that all operate on an n-bi...
Security, Privacy, and Applied Cryptography Engineering, 2022
This paper proposes a lightweight authenticated encryption (AE) scheme, called Light-OCB, which c... more This paper proposes a lightweight authenticated encryption (AE) scheme, called Light-OCB, which can be viewed as a lighter variant of the CAESAR winner OCB as well as a faster variant of the high profile NIST LWC competition submission LOCUS-AEAD. Light-OCB is structurally similar to LOCUS-AEAD and uses a nonce-based derived key that provides optimal security, and short-tweak tweakable blockcipher (tBC) for efficient domain separation. Light-OCB improves over LOCUS-AEAD by reducing the number of primitive calls, and thereby significantly optimizing the throughput. To establish our claim, we provide FPGA hardware implementation details and benchmark for Light-OCB against LOCUS-AEAD and several other well-known AEs. The implementation results depict that, when instantiated with the tBC TweGIFT64, Light-OCB achieves an extremely low hardware footprint-consuming only around 1128 LUTs and 307 slices (significantly lower than that for LOCUS-AEAD) while maintaining a throughput of 880 Mbps, which is almost twice that of LOCUS-AEAD. To the best of our knowledge, this figure is significantly better than all the known implementation results of other lightweight ciphers with parallel structures.
In the era of lightweight cryptography, designing cryptographically good and power efficient 4x4 ... more In the era of lightweight cryptography, designing cryptographically good and power efficient 4x4 S-boxes is a challenging problem. While the optimal cryptographic properties are easy to determine, verifying the power efficiency of an Sbox is non-trivial. The conventional approach of determining the power consumption using commercially available CAD-tools is highly time consuming, which becomes formidable while dealing with a large pool of S-boxes. This mandates development of an automation that should quickly characterize the power efficiency from the Boolean function representation of an Sbox. In this paper, we present a supervised machine learning assisted automated framework to resolve the problem for 4x4 S-boxes, which turns out to be 14 times faster than traditional approach. The key idea is to extrapolate the knowledge of literal counts, AND-OR-NOT gate counts in SOP form of the underlying Boolean functions to predict the dynamic power efficiency. The experimental results and ...
In this short note, we aim to give a structural classifcation of modes of operations for authenti... more In this short note, we aim to give a structural classifcation of modes of operations for authenticated encryption (AEAD). First, we briefy discuss various features that are desirable in an AEAD mode. Then, we classify AEAD modes according to their structure, understand their target area of applications, discuss their basic design goals and associated features. Finally, we give a brief description of each of the 32 second round candidates in NIST LwC project, distributing them in appropriate class based on their structure.
At CRYPTO 2015, Minaud and Seurin introduced and studied the iterated random permutation problem,... more At CRYPTO 2015, Minaud and Seurin introduced and studied the iterated random permutation problem, which is to distinguish the r-th iterate of a random permutation from a random permutation. In this paper, we study the closely related iterated random function problem, and prove the first almost-tight bound in the adaptive setting. More specifically, we prove that the advantage to distinguish the r-th iterate of a random function from a random function using q queries is bounded by \(O(q^2r(\log r)^3/N)\), where N is the size of the domain. In previous work, the best known bound was \(O(q^2r^2/N)\), obtained as a direct result of interpreting the iterated random function problem as a special case of CBC-MAC based on a random function. For the iterated random function problem, the best known attack has an advantage of \(\varOmega (q^2r/N)\), showing that our security bound is tight up to a factor of \((\log r)^3\).
In this short note, we propose two new designs for lightweight AE modes, called LOCUS and LOTUS, ... more In this short note, 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: achieving security against an adversary that can make close to 264 queries and 2128 computations, even when instantiated with a 64-bit primitive with 128-bit key. Both these modes are fully parallelizable and provide full INT-RUP security. We use TweGIFT-64, a tweakable variant of the GIFT block cipher, to instantiate our AE modes. TweGIFT-64-LOCUS and TweGIFT-64-LOTUS are signifcantly 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. We have also provided concrete security analysis both OCB...
Tweakable block cipher (TBC), a stronger notion than standard block ciphers, has wide-scale appli... more Tweakable block cipher (TBC), a stronger notion than standard block ciphers, has wide-scale applications in symmetric-key schemes. At a high level, it provides flexibility in design and (possibly) better security bounds. In multi-keyed applications, a TBC with short tweak values can be used to replace multiple keys. However, the existing TBC construction frameworks, including TWEAKEY and XEX, are designed for general purpose tweak sizes. Specifically, they are not optimized for short tweaks, which might render them inefficient for certain resource constrained applications. So a dedicated paradigm to construct shorttweak TBCs (tBC) is highly desirable. In this paper, we present a dedicated framework, called the Elastic-Tweak framework (ET in short), to convert any reasonably secure SPN block cipher into a secure tBC. We apply the ET framework on GIFT and AES to construct efficient tBCs, named TweGIFT and TweAES. We present hardware and software results to show that the performance ov...
NIST has recently initiated a standardization project for efficient lightweight authenticated enc... more NIST has recently initiated a standardization project for efficient lightweight authenticated encryption schemes. SUNDAE, a candidate in this project, achieves optimal state size which results in low circuit overhead on top of the underlying block cipher. In addition, SUNDAE provides security in nonce-misuse scenario as well. However, in addition to the block cipher circuit, SUNDAE also requires some additional circuitry for multiplication by a primitive element. Further, it requires an additional block cipher invocation to create the starting state. In this paper, we propose a new lightweight and low energy authenticated encryption family, called ESTATE, that significantly improves the design of SUNDAE in terms of implementation costs (both hardware area and energy) and efficient processing of short messages. In particular, ESTATE does not require an additional multiplication circuit, and it reduces the number of block cipher calls by one. Moreover, it provides integrity security e...
SUM-ECBC (Yasuda, CT-RSA 2010) is the first beyond birthday bound (BBB) secure block cipher based... more SUM-ECBC (Yasuda, CT-RSA 2010) is the first beyond birthday bound (BBB) secure block cipher based deterministic MAC. After this work, some more BBB secure deterministic MACs have been proposed, namely PMAC_Plus (Yasuda, CRYPTO 2011), 3kf9 (Zhang et al., ASIACRYPT 2012) and LightMAC_Plus (Naito, ASIACRYPT 2017). In this paper, we have abstracted out the inherent design principle of all these BBB secure MACs and present a generic design paradigm to construct a BBB secure pseudo random function, namely Double-block Hash-then- Sum or in short (DbHtS). A DbHtS construction, as the name implies, computes a double block hash on the message and then sum the encrypted output of the two hash blocks. Our result renders that if the underlying hash function meets certain security requirements (namely cover-free and block-wise universal advantage is low), DbHtS construction provides 2n/3-bit security. We demonstrate the applicability of our result by instantiating all the existing beyond birthday...
This work focuses on side-channel resilient design strategies for symmetrickey cryptographic prim... more This work focuses on side-channel resilient design strategies for symmetrickey cryptographic primitives targeting lightweight applications. In light of NIST’s lightweight cryptography project, design choices for block ciphers must consider not only security against traditional cryptanalysis, but also side-channel security, while adhering to low area and power requirements. In this paper, we explore design strategies for substitution-permutation network (SPN)-based block ciphers that make them amenable to low-cost threshold implementations (TI) - a provably secure strategy against side-channel attacks. The core building blocks for our strategy are cryptographically optimal 4×4 S-Boxes, implemented via repeated iterations of simple cellular automata (CA) rules. We present highly optimized TI circuits for such S-Boxes, that consume nearly 40% less area and power as compared to popular lightweight S-Boxes such as PRESENT and GIFT. We validate our claims via implementation results on ASI...
IACR Transactions on Cryptographic Hardware and Embedded Systems, 2018
This paper presents a lightweight, sponge-based authenticated encryption (AE) family called Beetl... more 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 s...
In CHES 2017, Chakraborti et al. proposed COFB, a rate-1 sequential block cipher-based authentica... more In CHES 2017, Chakraborti et al. proposed COFB, a rate-1 sequential block cipher-based authenticated encryption (AE) with only 1.5n-bit state, where n denotes the block size. They used a novel approach, the so-called combined feedback, where each block cipher input has a combined effect of the previous block cipher output and the current plaintext block. In this paper, we first study the security of a general rate-1 feedback-based AE scheme in terms of its overall internal state size. For a large class of feedback functions, we show that the overlying AE scheme can be attacked in 2r queries if the internal state size is n + r bits for some r ≥ 0. This automatically shows that a birthday bound (i.e. 2n/2 queries) secure AE scheme must have at least 1.5n-bit state, whence COFB is almost-optimal (use 1.5n-bit state and provides security up to 2n/2/n queries). We propose a new feedback function, called the hybrid feedback or HyFB, which is a hybrid composition of plaintext and ciphertex...
We present the first practically realizable side-channel assisted fault attack on any block-ciphe... more We present the first practically realizable side-channel assisted fault attack on any block-ciphers having bit-permutation with optimal diffusion, that can retrieve the round key efficiently using random nibble faults. The attack demonstrates how side-channel leakage can allow the adversary to precisely determine the fault mask resulting from a nibble fault injection instance. We first demonstrate the viability of such attack model via side-channel analysis experiments on top of a laser-based fault injection setup, targeting a PRESENT-80 and GIFT-128 (two popular block-ciphers based on bit-permutation having optimal diffusion) implementation on an ATmega328P microcontroller. Subsequently, we present a differential fault analysis (DFA) exploiting the knowledge of the output fault mask in the target round to recover multiple last round keys nibbles independently and in parallel. We show that the combined attack can recover the last round key of PRESENT-80 and GIFT-128 with 4 random nibble fault injections in the best case. In the average case, the number of random nibble faults required for PRESENT-80 and GIFT-128 are 9-18 and 6-9 respectively.
Authenticated encryption schemes which resist misuse of nonce at some desired level of privacy ar... more Authenticated encryption schemes which resist misuse of nonce at some desired level of privacy are two-pass or Mac-then-Encrypt constructions (inherently inefficient but provide full privacy) and online constructions like McOE, sponge-type authenticated encryptions (such as duplex) and COPA. Only the last one is almost parallelizable except that for associated data processing, the final block-cipher call is sequential (it needs to wait for the encryption of all the previous ones). In this paper, we design a new online secure authenticated encryption, called ELmD or Encrypt-Linear mix-Decrypt, which is completely (two-stage) parallel (even in associated data) and fully pipeline implementable. It also provides full privacy when associated data is not repeated. Like COPA, our construction is based on EME, an Encrypt-Mix-Encrypt type SPRP construction (secure against chosen plaintext and ciphertext). But unlike EME, we have used an online computable efficient linear mixing instead of a non-linear mixing. We have also provided the hardware implementation of the construction and compare the performance with similar constructions like COPA and EME2.
In CRYPTO’21, Shen et al. proved that Two-Keyed-DbHtS construction is secure up to 22n/3 queries ... more In CRYPTO’21, Shen et al. proved that Two-Keyed-DbHtS construction is secure up to 22n/3 queries in the multi-user setting independent of the number of users. Here the underlying double-block hash function H of the construction realized as the concatenation of two independent n-bit keyed hash functions (HKh,1,HKh,2), and the security holds under the assumption that each of the n-bit keyed hash function is universal and regular. The authors have also demonstrated the applicability of their result to the key-reduced variants of DbHtS MACs, including 2K-SUM-ECBC, 2K-PMAC_Plus and 2K-LightMAC_Plus without requiring domain separation technique and proved 2n/3-bit multi-user security of these constructions in the ideal cipher model. Recently, Guo and Wang have invalidated the security claim of Shen et al.’s result by exhibiting three constructions, which are instantiations of the Two-Keyed-DbHtS framework, such that each of their n-bit keyed hash functions are O(2−n) universal and regular...
2019 32nd International Conference on VLSI Design and 2019 18th International Conference on Embedded Systems (VLSID)
In the era of lightweight cryptography, designing cryptographically good and power efficient 4 × ... more In the era of lightweight cryptography, designing cryptographically good and power efficient 4 × 4 S-boxes is a widely discussed problem. While the optimal cryptographic properties are easy to verify, it is not very straightforward to verify whether a S-box is power efficient or not. The traditional approach is to explicitly determine the dynamic power consumption using commercially available CAD tools and report accordingly based on a pre-defined threshold value. However, this procedure is highly time consuming, and the overhead becomes formidable while dealing with a set of S-boxes from a large space. This mandates development of an automation tool which should be able to quickly characterize the power efficiency from the Boolean function representation of an S-box. In this paper, we present a supervised machine learning (ML) assisted automated framework to resolve the problem for 4 × 4 S-boxes, which turns out to be approximately 14 times faster (using AND-OR-NOT gates) than the traditional approach. The key idea is to extrapolate the knowledge of the literal counts of various functional forms, AND-OR-NOT gate counts in the simplified SOP form of the underlying Boolean functions corresponding to the S-box to predict the dynamic power efficiency. We demonstrate the effectiveness of our framework by reporting a set of power efficient S-boxes from a large set of 4 × 4 optimal S-boxes. The experimental results and performance of our novel technique depicts its superiority with high efficiency and low time overhead.
The authenticated encryption scheme COLM is a third-round candidate in the CAESAR competition. Mu... more The authenticated encryption scheme COLM is a third-round candidate in the CAESAR competition. Much like its antecedents COPA, ELmE, and ELmD, COLM consists of two parallelizable encryption layers connected by a linear mixing function. While COPA uses plain XOR mixing, ELmE, ELmD, and COLM use a more involved invertible mixing function. In this work, we investigate the integrity of the COLM structure when unverified plaintext is released, and demonstrate that its security highly depends on the choice of mixing function. Our results are threefold. First, we discuss the practical nonce-respecting forgery by Andreeva et al. (ASIACRYPT 2014) against COPA’s XOR mixing. Then we present a noncemisusing forgery against arbitrary mixing functions with practical time complexity. Finally, by using significantly larger queries, we can extend the previous forgery to be nonce-respecting.
PHOTON-Beetle is an authenticated encryption and hash family, that uses a sponge-based mode Beetl... more PHOTON-Beetle is an authenticated encryption and hash family, that uses a sponge-based mode Beetle with the P256 (used for the hash function PHOTON) being the underlying permutation. This report updates software implementations of PHOTON-Beetle on 8-bit microcontrollers and that on general-purpose computers.
Authenticated encryption schemes are usually expected to offer confidentiality and authenticity. ... more Authenticated encryption schemes are usually expected to offer confidentiality and authenticity. In case of release of unverified plaintext (RUP), an adversary gets separated access to the decryption and verification functionality, and has more power in breaking the scheme. Andreeva et al. (ASIACRYPT 2014) formalized RUP security using plaintext awareness, informally meaning that the decryption functionality gives no extra power in breaking confidentiality, and INT-RUP security, covering authenticity in case of RUP. We describe a single, unified model, called AERUP security, that ties together these notions: we prove that an authenticated encryption scheme is AERUP secure if and only if it is conventionally secure, plaintext aware, and INT-RUP secure. We next present ANYDAE, a generalization of SUNDAE of Banik et al. (ToSC 2018/3). ANYDAE is a lightweight deterministic scheme that is based on a block cipher with block size n and arbitrary mixing functions that all operate on an n-bi...
Security, Privacy, and Applied Cryptography Engineering, 2022
This paper proposes a lightweight authenticated encryption (AE) scheme, called Light-OCB, which c... more This paper proposes a lightweight authenticated encryption (AE) scheme, called Light-OCB, which can be viewed as a lighter variant of the CAESAR winner OCB as well as a faster variant of the high profile NIST LWC competition submission LOCUS-AEAD. Light-OCB is structurally similar to LOCUS-AEAD and uses a nonce-based derived key that provides optimal security, and short-tweak tweakable blockcipher (tBC) for efficient domain separation. Light-OCB improves over LOCUS-AEAD by reducing the number of primitive calls, and thereby significantly optimizing the throughput. To establish our claim, we provide FPGA hardware implementation details and benchmark for Light-OCB against LOCUS-AEAD and several other well-known AEs. The implementation results depict that, when instantiated with the tBC TweGIFT64, Light-OCB achieves an extremely low hardware footprint-consuming only around 1128 LUTs and 307 slices (significantly lower than that for LOCUS-AEAD) while maintaining a throughput of 880 Mbps, which is almost twice that of LOCUS-AEAD. To the best of our knowledge, this figure is significantly better than all the known implementation results of other lightweight ciphers with parallel structures.
In the era of lightweight cryptography, designing cryptographically good and power efficient 4x4 ... more In the era of lightweight cryptography, designing cryptographically good and power efficient 4x4 S-boxes is a challenging problem. While the optimal cryptographic properties are easy to determine, verifying the power efficiency of an Sbox is non-trivial. The conventional approach of determining the power consumption using commercially available CAD-tools is highly time consuming, which becomes formidable while dealing with a large pool of S-boxes. This mandates development of an automation that should quickly characterize the power efficiency from the Boolean function representation of an Sbox. In this paper, we present a supervised machine learning assisted automated framework to resolve the problem for 4x4 S-boxes, which turns out to be 14 times faster than traditional approach. The key idea is to extrapolate the knowledge of literal counts, AND-OR-NOT gate counts in SOP form of the underlying Boolean functions to predict the dynamic power efficiency. The experimental results and ...
In this short note, we aim to give a structural classifcation of modes of operations for authenti... more In this short note, we aim to give a structural classifcation of modes of operations for authenticated encryption (AEAD). First, we briefy discuss various features that are desirable in an AEAD mode. Then, we classify AEAD modes according to their structure, understand their target area of applications, discuss their basic design goals and associated features. Finally, we give a brief description of each of the 32 second round candidates in NIST LwC project, distributing them in appropriate class based on their structure.
At CRYPTO 2015, Minaud and Seurin introduced and studied the iterated random permutation problem,... more At CRYPTO 2015, Minaud and Seurin introduced and studied the iterated random permutation problem, which is to distinguish the r-th iterate of a random permutation from a random permutation. In this paper, we study the closely related iterated random function problem, and prove the first almost-tight bound in the adaptive setting. More specifically, we prove that the advantage to distinguish the r-th iterate of a random function from a random function using q queries is bounded by \(O(q^2r(\log r)^3/N)\), where N is the size of the domain. In previous work, the best known bound was \(O(q^2r^2/N)\), obtained as a direct result of interpreting the iterated random function problem as a special case of CBC-MAC based on a random function. For the iterated random function problem, the best known attack has an advantage of \(\varOmega (q^2r/N)\), showing that our security bound is tight up to a factor of \((\log r)^3\).
In this short note, we propose two new designs for lightweight AE modes, called LOCUS and LOTUS, ... more In this short note, 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: achieving security against an adversary that can make close to 264 queries and 2128 computations, even when instantiated with a 64-bit primitive with 128-bit key. Both these modes are fully parallelizable and provide full INT-RUP security. We use TweGIFT-64, a tweakable variant of the GIFT block cipher, to instantiate our AE modes. TweGIFT-64-LOCUS and TweGIFT-64-LOTUS are signifcantly 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. We have also provided concrete security analysis both OCB...
Tweakable block cipher (TBC), a stronger notion than standard block ciphers, has wide-scale appli... more Tweakable block cipher (TBC), a stronger notion than standard block ciphers, has wide-scale applications in symmetric-key schemes. At a high level, it provides flexibility in design and (possibly) better security bounds. In multi-keyed applications, a TBC with short tweak values can be used to replace multiple keys. However, the existing TBC construction frameworks, including TWEAKEY and XEX, are designed for general purpose tweak sizes. Specifically, they are not optimized for short tweaks, which might render them inefficient for certain resource constrained applications. So a dedicated paradigm to construct shorttweak TBCs (tBC) is highly desirable. In this paper, we present a dedicated framework, called the Elastic-Tweak framework (ET in short), to convert any reasonably secure SPN block cipher into a secure tBC. We apply the ET framework on GIFT and AES to construct efficient tBCs, named TweGIFT and TweAES. We present hardware and software results to show that the performance ov...
NIST has recently initiated a standardization project for efficient lightweight authenticated enc... more NIST has recently initiated a standardization project for efficient lightweight authenticated encryption schemes. SUNDAE, a candidate in this project, achieves optimal state size which results in low circuit overhead on top of the underlying block cipher. In addition, SUNDAE provides security in nonce-misuse scenario as well. However, in addition to the block cipher circuit, SUNDAE also requires some additional circuitry for multiplication by a primitive element. Further, it requires an additional block cipher invocation to create the starting state. In this paper, we propose a new lightweight and low energy authenticated encryption family, called ESTATE, that significantly improves the design of SUNDAE in terms of implementation costs (both hardware area and energy) and efficient processing of short messages. In particular, ESTATE does not require an additional multiplication circuit, and it reduces the number of block cipher calls by one. Moreover, it provides integrity security e...
SUM-ECBC (Yasuda, CT-RSA 2010) is the first beyond birthday bound (BBB) secure block cipher based... more SUM-ECBC (Yasuda, CT-RSA 2010) is the first beyond birthday bound (BBB) secure block cipher based deterministic MAC. After this work, some more BBB secure deterministic MACs have been proposed, namely PMAC_Plus (Yasuda, CRYPTO 2011), 3kf9 (Zhang et al., ASIACRYPT 2012) and LightMAC_Plus (Naito, ASIACRYPT 2017). In this paper, we have abstracted out the inherent design principle of all these BBB secure MACs and present a generic design paradigm to construct a BBB secure pseudo random function, namely Double-block Hash-then- Sum or in short (DbHtS). A DbHtS construction, as the name implies, computes a double block hash on the message and then sum the encrypted output of the two hash blocks. Our result renders that if the underlying hash function meets certain security requirements (namely cover-free and block-wise universal advantage is low), DbHtS construction provides 2n/3-bit security. We demonstrate the applicability of our result by instantiating all the existing beyond birthday...
This work focuses on side-channel resilient design strategies for symmetrickey cryptographic prim... more This work focuses on side-channel resilient design strategies for symmetrickey cryptographic primitives targeting lightweight applications. In light of NIST’s lightweight cryptography project, design choices for block ciphers must consider not only security against traditional cryptanalysis, but also side-channel security, while adhering to low area and power requirements. In this paper, we explore design strategies for substitution-permutation network (SPN)-based block ciphers that make them amenable to low-cost threshold implementations (TI) - a provably secure strategy against side-channel attacks. The core building blocks for our strategy are cryptographically optimal 4×4 S-Boxes, implemented via repeated iterations of simple cellular automata (CA) rules. We present highly optimized TI circuits for such S-Boxes, that consume nearly 40% less area and power as compared to popular lightweight S-Boxes such as PRESENT and GIFT. We validate our claims via implementation results on ASI...
IACR Transactions on Cryptographic Hardware and Embedded Systems, 2018
This paper presents a lightweight, sponge-based authenticated encryption (AE) family called Beetl... more 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 s...
In CHES 2017, Chakraborti et al. proposed COFB, a rate-1 sequential block cipher-based authentica... more In CHES 2017, Chakraborti et al. proposed COFB, a rate-1 sequential block cipher-based authenticated encryption (AE) with only 1.5n-bit state, where n denotes the block size. They used a novel approach, the so-called combined feedback, where each block cipher input has a combined effect of the previous block cipher output and the current plaintext block. In this paper, we first study the security of a general rate-1 feedback-based AE scheme in terms of its overall internal state size. For a large class of feedback functions, we show that the overlying AE scheme can be attacked in 2r queries if the internal state size is n + r bits for some r ≥ 0. This automatically shows that a birthday bound (i.e. 2n/2 queries) secure AE scheme must have at least 1.5n-bit state, whence COFB is almost-optimal (use 1.5n-bit state and provides security up to 2n/2/n queries). We propose a new feedback function, called the hybrid feedback or HyFB, which is a hybrid composition of plaintext and ciphertex...
We present the first practically realizable side-channel assisted fault attack on any block-ciphe... more We present the first practically realizable side-channel assisted fault attack on any block-ciphers having bit-permutation with optimal diffusion, that can retrieve the round key efficiently using random nibble faults. The attack demonstrates how side-channel leakage can allow the adversary to precisely determine the fault mask resulting from a nibble fault injection instance. We first demonstrate the viability of such attack model via side-channel analysis experiments on top of a laser-based fault injection setup, targeting a PRESENT-80 and GIFT-128 (two popular block-ciphers based on bit-permutation having optimal diffusion) implementation on an ATmega328P microcontroller. Subsequently, we present a differential fault analysis (DFA) exploiting the knowledge of the output fault mask in the target round to recover multiple last round keys nibbles independently and in parallel. We show that the combined attack can recover the last round key of PRESENT-80 and GIFT-128 with 4 random nibble fault injections in the best case. In the average case, the number of random nibble faults required for PRESENT-80 and GIFT-128 are 9-18 and 6-9 respectively.
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Papers by NILanjan Datta