CCM-SIV: Single-PRF Nonce-Misuse-Resistant Authenticated Encryption

We propose a new nonce-misuse-resistant authenticated encryption scheme, which instantiates the SIV paradigm of Rogaway and Shrimpton. In contrast to the GCM-SIV approach proposed by Gueron and Lindell, we do only use a single type of cryptographic primitive, which can be advantageous in restricted embedded devices. Furthermore, we use three independent and fixed subkeys derived from a single master key. Similar to the CCM mode, our scheme uses a combination of the CTR mode for the symmetric encryption and a MAC based on the CBC construction and is therefore called CCM-SIV. We provide a detailed security proof for our scheme. Furthermore, we outline its extension to a nonce-based key derivation as the AES-GCM-SIV approach

GCM-SIV: Full Nonce Misuse-Resistant Authenticated Encryption at Under One Cycle per Byte

Authenticated encryption schemes guarantee both privacy and integrity, and have become the default level of encryption in modern protocols. One of the most popular authenticated encryption schemes today is AES-GCM due to its impressive speed. The current CAESAR competition is considering new modes for authenticated encryption that will improve on existing methods. One property of importance that is being considered more today -- due to multiple real-life cases of faulty sources of randomness -- is that repeating nonces and IVs can have disastrous effects on security. A (full) nonce misuse-resistant authenticated encryption scheme has the property that if the \emph{same} nonce is used to encrypt the \emph{same} message twice, then the same ciphertext is obtained and so the fact that the same message was encrypted is detected. Otherwise, \emph{full security} is obtained -- even if the same nonce is used for different messages. In this paper, we present a new fully nonce misuse-resistant authenticated encryption scheme that is based on carefully combining the GCM building blocks into the SIV paradigm of Rogaway and Shrimpton. We provide a full proof of security of our scheme, and an optimized implementation using the AES-NI and PCLMULQDQ instruction sets. We compare our performance to the highly optimized OpenSSL 1.0.2 implementation of GCM and show that our \emph{nonce misuse-resistant} scheme is only 14\% slower on Haswell architecture and 19\% slower on Broadwell architecture. On Broadwell, GCM-SIV encryption takes only {\em 0.92 cycles per byte}, and GCM-SIV decryption is exactly the same as GCM decryption taking only 0.77 cycles per byte. In addition, we compare to other optimized authenticated-encryption implementations carried out by Bogdanov et al., and conclude that our mode is very competitive. Beyond being very fast, our new mode of operation uses the same building blocks as GCM and so existing hardware and software can be utilized to easily deploy GCM-SIV. We conclude that GCM-SIV is a viable alternative to GCM, providing full nonce misuse-resistance at little cost

Daence: Salsa20 and ChaCha in Deterministic Authenticated Encryption with no noNCEnse

We present Daence, a deterministic authenticated cipher based on a pseudorandom function family and a universal hash family, similar to SIV. We recommend instances with Salsa20 or ChaCha, and Poly1305, for high performance, high security, and easy deployment

The Summation-Truncation Hybrid: Reusing Discarded Bits for Free

A well-established PRP-to-PRF conversion design is truncation: one evaluates an $n$-bit pseudorandom permutation on a certain input, and truncates the result to $a$ bits. The construction is known to achieve tight $2^{n-a/2}$ security. Truncation has gained popularity due to its appearance in the GCM-SIV key derivation function (ACM CCS 2015). This key derivation function makes four evaluations of AES, truncates the outputs to $n/2$ bits, and concatenates these to get a $2n$-bit subkey. In this work, we demonstrate that truncation is wasteful. In more detail, we present the Summation-Truncation Hybrid (STH). At a high level, the construction consists of two parallel evaluations of truncation, where the truncated $(n-a)$-bit chunks are not discarded but rather summed together and appended to the output. We prove that STH achieves a similar security level as truncation, and thus that the $n-a$ bits of extra output is rendered for free. In the application of GCM-SIV, the current key derivation can be used to output $3n$ bits of random material, or it can be reduced to three primitive evaluations. Both changes come with no security loss

Fast Parallelizable Misuse-Resistant Authenticated Encryption: Low Latency (Decryption-Fast) SIV

MRAE security is an important goal for many AEAD applications where the nonce uniqueness cannot be maintained and security risks are significant. However, MRAE schemes can be quite expensive. Two of the SoTA MRAE-secure schemes; Deoxys-II and AES-GCM-SIV rely on internal parallelism and special instructions to achieve competitive performance. However, they both suffer from the same bottleneck, they have at least one call to the underlying primitive that cannot be parallelized to any other call. Romulus-M and LMDAE are two other more recent MRAE secure schemes based on TBCs that target low area hardware. However, they are unparallelizable so they are slower than their counterparts. In this paper, we present two new AEAD modes and four instantiations based on Tweakable Block Ciphers. These new modes target equipping high-speed applications on parallel platforms with nonce misuse resistant AEAD (MRAE). The first mode, LLSIV, targets similar performance on single-core platforms to SCT-2, while eliminating the bottlenecks that make SCT-2 not fully parallelizable. The enhanced parallelism allows LLSIV to encrypt significantly more blocks on parallel platforms, compared to SCT-2, in the same amount of time. LLSIV is based on the NaT MAC, where each ciphertext block can itself be viewed as an instance of NaT when the plaintext is prepended with $0^n$. The trade-off is that LLSIV requires the inverse function of the TBC. However, the inverse function is used only once per message and we demonstrate that for parallel implementations it represents a very small overhead. We give an instantiation of LLSIV based on the SKINNY-128-384 TBC, and a pruned scheme, dubbed pLLSIV, which targets enhanced performance compared both SCT-2 and LLSIV on all platforms, while having reduced security claims. It relies on the recently popularized prove-then-prune methodology to take full advantage of the properties of LLSIV. This leads to a significant performance improvement, making pLLSIV even faster than online TBC-based schemes that are not MRAE-secure. Last but not least, we give an instantiation that uses the primitives used in AES-GCM-SIV: the PolyVal hash function and AES. Our instantiation is faster than AES-GCM-SIV on all platforms and have better bounds. On the other hand, it relies on the ideal cipher model as it uses the ICE TBC proposed as part of the Remus AEAD design. The second mode we describe is LLDFV. It uses ideas from LLSIV combined the Decryption-Fast SIV (DFV) framework proposed recently by Minematsu. The goal is to reduce the number of calls to the TBC by one, while making the scheme as parallelizable as LLSIV. This makes the scheme faster that DFV on all platforms

Toward a Fully Secure Authenticated Encryption Scheme From a Pseudorandom Permutation (Full Version)

In this paper, we propose a new block cipher-based authenticated encryption scheme, dubbed the Synthetic Counter with Masking~(SCM) mode. SCM follows the NSIV paradigm proposed by Peyrin and Seurin~(CRYPTO 2016), where a keyed hash function accepts a nonce N with associated data and a message, yielding an authentication tag T, and then the message is encrypted by a counter-like mode using both T and N. Here we move one step further by encrypting nonces; in the encryption part, the inputs to the block cipher are determined by T, counters, and an encrypted nonce, and all its outputs are also masked by an (additional) encrypted nonce, yielding keystream blocks. As a result, we obtain, for the first time, a block cipher-based authenticated encryption scheme of rate 1/2 that provides n-bit security with respect to the query complexity (ignoring the influence of message length) in the nonce-respecting setting, and at the same time guarantees graceful security degradation in the faulty nonce model, when the underlying n-bit block cipher is modeled as a secure pseudorandom permutation. Seen as a slight variant of GCM-SIV, SCM is also parallelizable and inverse-free, and its performance is still comparable to GCM-SIV

Masked Iterate-Fork-Iterate: A new Design Paradigm for Tweakable Expanding Pseudorandom Function

Many modes of operations for block ciphers or tweakable block ciphers do not require invertibility from their underlying primitive. In this work, we study fixed-length Tweakable Pseudorandom Function (TPRF) with large domain extension, a novel primitive that can bring high security and significant performance optimizations in symmetric schemes, such as (authenticated) encryption. Our first contribution is to introduce a new design paradigm, derived from the Iterate-Fork-Iterate construction, in order to build $n$-to-$\alpha n$-bit ($\alpha\geq2$), $n$-bit secure, domain expanding TPRF. We dub this new generic composition masked Iterate-Fork-Iterate (mIFI). We then propose a concrete TPRF instantiation ButterKnife that expands an $n$-bit input to $8n$-bit output via a public tweak and secret key. ButterKnife is built with high efficiency and security in mind. It is fully parallelizable and based on Deoxys-BC, the AES-based tweakable block cipher used in the authenticated encryption winner algorithm in the defense-in-depth category of the recent CAESAR competition. We analyze the resistance of ButterKnife to differential, linear, meet-in-the-middle, impossible differentials and rectangle attacks. A special care is taken to the attack scenarios made possible by the multiple branches. Our next contribution is to design and provably analyze two new TPRF-based deterministic authenticated encryption (DAE) schemes called SAFE and ZAFE that are highly efficient, parallelizable, and offer $(n+\min(n,t))/2$ bits of security, where $n,t$ denote respectively the input block and the tweak sizes of the underlying primitives. We further implement SAFE with ButterKnife to show that it achieves an encryption performance of 1.06 c/B for long messages on Skylake, which is 33-38% faster than the comparable Crypto\u2717 TBC-based ZAE DAE. Our second candidate ZAFE, which uses the same authentication pass as ZAE, is estimated to offer a similar level of speedup. Besides, we show that ButterKnife, when used in Counter Mode, is slightly faster than AES (0.50 c/B vs 0.56 c/B on Skylake)

Revisiting AES-GCM-SIV: Multi-user Security, Faster Key Derivation, and Better Bounds

This paper revisits the multi-user (mu) security of symmetric encryption, from the perspective of delivering an analysis of the AES-GCM-SIV AEAD scheme. Our end result shows that its mu security is comparable to that achieved in the single-user setting. In particular, even when instantiated with short keys (e.g., 128 bits), the security of AES-GCM-SIV is not impacted by the collisions of two user keys, as long as each individual nonce is not re-used by too many users. Our bounds also improve existing analyses in the single-user setting, in particular when messages of variable lengths are encrypted. We also validate security against a general class of key-derivation methods, including one that halves the complexity of the final proposal. As an intermediate step, we consider mu security in a setting where the data processed by every user is bounded, and where user keys are generated according to arbitrary, possibly correlated distributions. This viewpoint generalizes the currently adopted one in mu security, and can be used to analyze re-keying practices

Elastic-Tweak: A Framework for Short Tweak Tweakable Block Cipher

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 short-tweak TBCs (tBC) is highly desirable. In this paper, as a first contribution, 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. These short-tweak TBCs have already been employed in recent NIST lightweight competition candidates, LOTUS-LOCUS and ESTATE. As our second contribution, we show some concrete applications of ET-based tBCs, which are better than their block cipher counterparts in terms of key size, state size, number of block cipher calls, and short message processing. Some notable applications include, Twe-FCBC (reduces the key size of FCBC and gives better security than CMAC), Twe-LightMAC Plus (better rate than LightMAC Plus), Twe-CLOC, and Twe-SILC (reduces the number of block cipher calls and simplifies the design of CLOC and SILC)

Automated Analysis of Protocols that use Authenticated Encryption: How Subtle AEAD Differences can impact Protocol Security

Many modern security protocols such as TLS, WPA2, WireGuard, and Signal use a cryptographic primitive called Authenticated Encryption (optionally with Authenticated Data), also known as an AEAD scheme. AEAD is a variant of symmetric encryption that additionally provides authentication. While authentication may seem to be a straightforward additional requirement, it has in fact turned out to be complex: many different security notions for AEADs are still being proposed, and several recent protocol-level attacks exploit subtle behaviors that differ among real-world AEAD schemes. We provide the first automated analysis method for protocols that use AEADs that can systematically find attacks that exploit the subtleties of the specific type of AEAD used. This can then be used to analyze specific protocols with a fixed AEAD choice, or to provide guidance on which AEADs might be (in)sufficient to make a protocol design secure. We develop generic symbolic AEAD models, which we instantiate for the Tamarin prover. Our approach can automatically and efficiently discover protocol attacks that could previously only be found using manual inspection, such as the Salamander attack on Facebook’s message franking, and attacks on SFrame and YubiHSM. Furthermore, our analysis reveals undesirable behaviors of several other protocols