## CryptoDB

### Phillip Rogaway

#### Publications

Year
Venue
Title
2019
ASIACRYPT
The customary formulation of authenticated encryption (AE) requires the decrypting party to supply the correct nonce with each ciphertext it decrypts. To enable this, the nonce is often sent in the clear alongside the ciphertext. But doing this can forfeit anonymity and degrade usability. Anonymity can also be lost by transmitting associated data (AD) or a session-ID (used to identify the operative key). To address these issues, we introduce anonymous AE, wherein ciphertexts must conceal their origin even when they are understood to encompass everything needed to decrypt (apart from the receiver’s secret state). We formalize a type of anonymous AE we call anAE, anonymous nonce-based AE, which generalizes and strengthens conventional nonce-based AE, nAE. We provide an efficient construction for anAE, NonceWrap, from an nAE scheme and a blockcipher. We prove NonceWrap secure. While anAE does not address privacy loss through traffic-flow analysis, it does ensure that ciphertexts, now more expansively construed, do not by themselves compromise privacy.
2018
JOFC
2018
CRYPTO
Often the simplest way of specifying game-based cryptographic definitions is apparently barred because the adversary would have some trivial win. Disallowing or invalidating these wins can lead to complex or unconvincing definitions. We suggest a generic way around this difficulty. We call it indistinguishability up to correctness, or IND$\vert$C. Given games ${{\text {G}}}$ and ${{\text {H}}}$ and a correctness condition ${{\text {C}}}$ we define an advantage measure ${\mathbf {Adv}_{{{\text {G}}},{{\text {H}}},{{\text {C}}}}^{{\text {indc}}}}$ wherein ${{{\text {G}}}}$/${{{\text {H}}}}$ distinguishing attacks are effaced to the extent that they are inevitable due to ${{\text {C}}}$. We formalize this in the language of oracle silencing, an alternative to exclusion-style and penalty-style definitions. We apply our ideas to a domain where game-based definitions have been cumbersome: stateful authenticated-encryption (sAE). We rework existing sAE notions and encompass new ones, like replay-free AE permitting a specified degree of out-of-order message delivery.
2016
CRYPTO
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
EUROCRYPT
2015
CRYPTO
2015
ASIACRYPT
2014
CRYPTO
2014
EUROCRYPT
2014
EUROCRYPT
2014
EPRINT
2014
EPRINT
2012
CRYPTO
2012
ASIACRYPT
2012
FSE
2011
FSE
2011
CRYPTO
2010
JOFC
2010
CRYPTO
2010
EPRINT
We prove beyond-birthday-bound security for the well-known types of generalized Feistel networks, including: (1) unbalanced Feistel networks, where the $n$-bit to $m$-bit round functions may have $n\ne m$; (2) alternating Feistel networks, where the round functions alternate between contracting and expanding; (3) type-1, type-2, and type-3 Feistel networks, where $n$-bit to $n$-bit round functions are used to encipher $kn$-bit strings for some $k\ge2$; and (4) numeric variants of any of the above, where one enciphers numbers in some given range rather than strings of some given size. Using a unified analytic framework we show that, in any of these settings, for any $\varepsilon>0$, with enough rounds, the subject scheme can tolerate CCA attacks of up to $q\sim N^{1-\varepsilon}$ adversarial queries, where $N$ is the size of the round functions' domain (the size of the larger domain for alternating Feistel). This is asymptotically optimal. Prior analyses for generalized Feistel networks established security to only $q\sim N^{0.5}$ adversarial queries.
2009
CRYPTO
2009
EUROCRYPT
2008
EUROCRYPT
2008
CRYPTO
2007
FSE
2007
EPRINT
Given (deterministic) ciphers $\calE$ and~$E$ that can encipher messages of $\el$ and $n$ bits, respectively, we construct a cipher~$\calE^*=XLS[\calE,E]$ that can encipher messages of $\el+s$ bits for any $s<n$. Enciphering such a string will take one call to~$\calE$ and two calls to~$E$. We prove that~$\calE^*$ is a strong pseudorandom permutation as long as~$\calE$ and~$E$ are. Our construction works even in the tweakable and VIL (variable-input-length) settings. It makes use of a multipermutation (a pair of orthogonal Latin squares), a combinatorial object not previously used to get a provable-security result.
2007
JOFC
2006
EUROCRYPT
2006
EUROCRYPT
2006
EPRINT
Standards bodies have been addressing the key-wrap problem, a cryptographic goal that has never received a provable-security treatment. In response, we provide one, giving definitions, constructions, and proofs. We suggest that key-wrapâs goal is security in the sense of deterministic authenticated-encryption (DAE), a notion that we put forward. We also provide an alternative notion, a pseudorandom injection (PRI), which we prove to be equivalent. We provide a DAE construction, SIV, analyze its concrete security, develop a blockcipher-based instantiation of it, and suggest that the method makes a desirable alternative to the schemes of the X9.102 draft standard. The construction incorporates a method to turn a PRF that operates on a string into an equally efficient PRF that operates on a vector of strings, a problem of independent interest. Finally, we consider IV-based authenticated- encryption (AE) schemes that are maximally forgiving of repeated IVs, a goal we formalize as misuse-resistant AE.We show that a DAE scheme with a vector-valued header, such as SIV, directly realizes this goal.
2006
EPRINT
There is a rarely mentioned foundational problem involving collision-resistant hash-functions: common constructions are keyless, but formal definitions are keyed. The discrepancy stems from the fact that a function H:{0,1}^* -> {0,1}^n always admits an efficient collision-finding algorithm, it's just that us human beings might be unable to write the program down. We explain a simple way to sidestep this difficulty that avoids having to key our hash functions. The idea is to state theorems in a way that prescribes an explicitly-given reduction, normally a black-box one. We illustrate this approach using well-known examples involving digital signatures, pseudorandom functions, and the Merkle-Damgard construction.
2006
EPRINT
We give a unified account of classical secret-sharing goals from a modern cryptographic vantage. Our treatment encompasses perfect, statistical, and computational secret sharing; static and dynamic adversaries; schemes with or without robustness; schemes where a participant recovers the secret and those where an external party does so. We then show that Krawczyk's 1993 protocol for robust computational secret sharing (RCSS) need not be secure, even in the random-oracle model and for threshold schemes, if the encryption primitive it uses satisfies only one-query indistinguishability (ind1), the only notion Krawczyk defines. Nonetheless, we show that the protocol is secure (in the random-oracle model, for threshold schemes) if the encryption scheme also satisfies one-query key-unrecoverability (key1). Since practical encryption schemes are ind1+key1 secure, our result effectively shows that Krawczyk's RCSS protocol is sound (in the random-oracle model, for threshold schemes). Finally, we prove the security for a variant of Krawczyk's protocol, in the standard model and for arbitrary access structures, assuming ind1 encryption and a statistically-hiding, weakly-binding commitment scheme.
2005
CRYPTO
2005
JOFC
2004
ASIACRYPT
2004
FSE
2004
FSE
2004
FSE
2004
EPRINT
We consider basic notions of security for cryptographic hash functions: collision resistance, preimage resistance, and second-preimage resistance. We give seven different definitions that correspond to these three underlying ideas, and then we work out all of the implications and separations among these seven definitions within the concrete-security, provable-security framework. Because our results are concrete, we can show two types of implications, "conventional" and "provisional", where the strength of the latter depends on the amount of compression achieved by the hash function. We also distinguish two types of separations, "conditional" and "unconditional". When constructing counterexamples for our separations, we are careful to preserve specified hash-function domains and ranges; this rules out some pathological counterexamples and makes the separations more meaningful in practice. Four of our definitions are standard while three appear to be new; some of our relations and separations have appeared, others have not. Here we give a modern treatment that acts to catalog, in one place and with carefully-considered nomenclature, the most basic security notions for cryptographic hash functions.
2004
EPRINT
The game-playing technique is a powerful tool for analyzing cryptographic constructions. We illustrate this by using games as the central tool for proving security of three-key triple-encryption, a long-standing open problem. Our result, which is in the ideal-cipher model, demonstrates that for DES parameters (56-bit keys and 64-bit plaintexts) an adversary's maximal advantage is small until it asks about $2^{78}$ queries. Beyond this application, we develop the foundations for game playing, formalizing a general framework for game-playing proofs and discussing techniques used within such proofs. To further exercise the game-playing framework we show how to use games to get simple proofs for the PRP/PRF Switching Lemma, the security of the basic CBC MAC, and the chosen-plaintext-attack security of OAEP.
2003
CRYPTO
2003
EPRINT
We propose a block-cipher mode of operation, called EAX, for authenticated-encryption with associated-data (AEAD). Given a nonce N, a message M, and a header H, the mode protects the privacy of M and the authenticity of both M and H. Strings N,M,H$are arbitrary, and the mode uses$2\lceil |M|/n \rceil + \lceil |H|/n\rceil + \lceil |N|/n\rceil$block-cipher calls when these strings are nonempty and n is the block length of the underlying block cipher. Among EAX's characteristics are that it is on-line (the length of a message isn't needed to begin processing it) and a fixed header can be pre-processed, effectively removing the per-message cost of binding it to the ciphertext. EAX is obtained by instantiating a simple generic-composition method, and then collapsing its two keys into one. EAX is provably secure under a standard complexity-theoretic assumption. EAX was designed in response to the expressed need of several standardization bodies, including NIST, IETF and IEEE 802.11, for a patent-free AEAD scheme. Such a scheme would have to be conventional, meaning it would make two passes, one aimed at achieving privacy and one aimed at achieving authenticity. EAX aims to fill this need by doing as well as possible within the space of conventional schemes with regard to issues of efficiency, simplicity, elegance, ease of correct use, and provable-security guarantees. EAX is an alternative to CCM. 2003 EPRINT CCM is a conventional authenticated-encryption scheme obtained from a 128-bit block cipher. The mechanism has been adopted as the mandatory encryption algorithm in an IEEE 802.11 draft standard [15], and its use has been proposed more broadly [16,17]. In this note we point out a number of limitations of CCM. A related note provides an alternative to CCM [5]. 2003 EPRINT We describe a block-cipher mode of operation, EME, that turns an n-bit block cipher into a tweakable enciphering scheme that acts on strings of mn bits, where m \in [1..n]. The mode is parallelizable, but as serial-efficient as the non-parallelizable mode CMC. EME can be used to solve the disk-sector encryption problem. The algorithm entails two layers of ECB encryption and a "lightweight mixing" in between. We prove EME secure, in the reduction-based sense of modern cryptography. We motivate some of the design choices in EME by showing that a few simple modifications of this mode are insecure. 2003 EPRINT We describe a block-cipher mode of operation, CMC, that turns an n-bit block cipher into a tweakable enciphering scheme that acts on strings of mn bits, where m>=2. When the underlying block cipher is secure in the sense of a strong pseudorandom permutation (PRP), our scheme is secure in the sense of tweakable, strong PRP. Such an object can be used to encipher the sectors of a disk, in-place, offering security as good as can be obtained in this setting. CMC makes a pass of CBC encryption, xors in a mask, and then makes a pass of CBC decryption; no universal hashing, nor any other non-trivial operation beyond the block-cipher calls, is employed. Besides proving the security of CMC we initiate a more general investigation of tweakable enciphering schemes, considering issues like the non-malleability of these objects. 2002 CRYPTO 2002 EUROCRYPT 2002 EPRINT Encryption that is only semantically secure should not be used on messages that depend on the underlying secret key; all bets are off when, for example,one encrypts using a shared key K the value K. Here we introduce a new notion of security, KDM security, appropriate for key-dependent messages. The notion makes sense in both the public-key and shared-key settings. For the latter we show that KDM security is easily achievable within the random-oracle model. By developing and achieving stronger notions of encryption-scheme security it is hoped that protocols which are proven secure under formal'' models of security can, in time, be safely realized by generically instantiating their primitives. 2002 EPRINT Preneel, Govaerts, and Vandewalle considered the 64 most basic ways to construct a hash function$H:\{0,1\}^*\rightarrow\{0,1\}^n$from a block cipher$E:\{0,1\}^n\times\{0,1\}^n\rightarrow\{0,1\}^n$. They regarded 12 of these 64 schemes as secure, though no proofs or formal claims were given. The remaining 52 schemes were shown to be subject to various attacks. Here we provide a formal and quantitative treatment of the 64 constructions considered by PGV. We prove that, in a black-box model, the 12 schemes that PGV singled out as secure really \textit{are} secure: we give tight upper and lower bounds on their collision resistance. Furthermore, by stepping outside of the Merkle-Damgard approach to analysis, we show that an additional 8 of the 64 schemes are just as collision resistant (up to a small constant) as the first group of schemes. Nonetheless, we are able to differentiate among the 20 collision-resistant schemes by bounding their security as one-way functions. We suggest that proving black-box bounds, of the style given here, is a feasible and useful step for understanding the security of any block-cipher-based hash-function construction. 2002 EPRINT We describe a block-cipher mode of operation, EMD, that builds a strong pseudorandom permutation (PRP) on$nm$bits ($m\ge2$) out of a strong PRP on$n$bits (i.e., a block cipher). The constructed PRP is also tweaked (in the sense of [LRW02]): to determine the$nm$-bit ciphertext block$C=\E_K^T(P)$one provides, besides the key$K$and the$nm$-bit plaintext block$P$, an$n$-bit tweak$T$. The mode uses$2m$block-cipher calls and no other complex or computationally expensive steps (such as universal hashing). Encryption and decryption are identical except that encryption uses the forward direction of the underlying block cipher and decryption uses the backwards direction. We suggest that EMD provides an attractive solution to the disk-sector encryption problem, where one wants to encipher the contents of an$nm$-bit disk sector in a way that depends on the sector index and is secure against chosen-plaintext/chosen-ciphertext attack. 2002 JOFC 2001 EPRINT We introduce the problem of enciphering members of a finite set$M$where$k=|M|$is arbitrary (in particular, it need not be a power of two). We want to achieve this goal starting from a block cipher (which requires a message space of size$N=2^n$, for some$n$). We look at a few solutions to this problem, focusing on the case when$M=[0, k-1]$. 2001 EPRINT This paper was prepared for NIST, which is considering new block-cipher modes of operation. It describes a parallelizable mode of operation that simultaneously provides both privacy and authenticity. "OCB mode" encrypts-and-authenticates an arbitrary message$M\in\bits^*$using only$\lceil |M|/n\rceil + 2$block-cipher invocations, where$n$is the block length of the underlying block cipher. Additional overhead is small. OCB refines a scheme, IAPM, suggested by Jutla [IACR-2000/39], who was the first to devise an authenticated-encryption mode with minimal overhead compared to standard modes. Desirable new properties of OCB include: very cheap offset calculations; operating on an arbitrary message$M\in\bits^*\$; producing ciphertexts of minimal length; using a single underlying cryptographic key; making a nearly optimal number of block-cipher calls; avoiding the need for a random IV; and rendering it infeasible for an adversary to find "pretag collisions". The paper provides a full proof of security for OCB.
2001
EPRINT
We define and analyze a simple and fully parallelizable block-cipher mode of operation for message authentication. Parallelizability does not come at the expense of serial efficiency: in a conventional, serial environment, the algorithm's speed is within a few percent of the (inherently sequential) CBC~MAC. The new mode, PMAC, is deterministic, resembles a standard mode of operation (and not a Carter-Wegman MAC), works for strings of any bit length, employs a single block-cipher key, and uses just max{1, ceiling(|M|/n)} block-cipher calls to MAC any string M using an n-bit block cipher. We prove PMAC secure, quantifying an adversary's forgery probability in terms of the quality of the block cipher as a pseudorandom permutation.
2001
JOFC
2000
ASIACRYPT
2000
CRYPTO
2000
EUROCRYPT
2000
EPRINT
This paper gives definitions and results about password-based protocols for authenticated key exchange (AKE), mutual authentication MA), and the combination of these goals (AKE, MA). Such protocols are designed to work despite interference by an active adversary and despite the use of passwords drawn from a space so small that an adversary might well enumerate, off line, a user's password. While several such password-based protocols have been suggested, the underlying theory has been lagging, and some of the protocols don't actually work. This is an area strongly in need of foundations, but definitions and theorems here can get overwhelmingly complex. To help manage this complexity we begin by defining a model, one rich enough to deal with password guessing, forward secrecy, server compromise, and loss of session keys. The one model can be used to define various goals. We take AKE (with implicit authentication---no one besides your intended partner could possibly get the key, though he may or may not actually get it) as the basic goal. Then we prove that any secure AKE protocol can be embellished (in a simple and generic way) to also provide for MA. This approach turns out to be simpler than trying to augment an MA protocol to also distribute a session key. Next we prove correctness for the idea at the center of the Encrypted Key-Exchange (EKE) protocol of Bellovin and Merritt: we prove (in an ideal-cipher model) that the two-flow protocol at the core of EKE is a secure AKE. Combining with the result above we have a simple 3-flow protocol for AKE,MA which is proven secure against dictionary attack.
1999
CRYPTO
1999
FSE
1999
EPRINT
scheme, DHAES. The scheme is as efficient as ElGamal encryption, but has stronger security properties. Furthermore, these security properties are proven to hold under appropriate assumptions on the underlying primitive. We show that DHAES has not only the basic'' property of secure encryption (namely privacy under a chosen-plaintext attack) but also achieves privacy under both non-adaptive and adaptive chosen-ciphertext attacks. (And hence it also achieves non-malleability.) DHAES is built in a generic way from lower-level primitives: a symmetric encryption scheme, a message authentication code, group operations in an arbitrary group, and a cryptographic hash function. In particular, the underlying group may be an elliptic-curve group or the multiplicative group of integers modulo a prime number. The proofs of security are based on appropriate assumptions about the hardness of the Diffie-Hellman problem and the assumption that the underlying symmetric primitives are secure. The assumptions are all standard in the sense that no random oracles are involved. We suggest that DHAES provides an attractive starting point for developing public-key encryption standards based on the Diffie-Hellman assumption.
1999
JOFC
1998
CRYPTO
1998
EUROCRYPT
1998
EPRINT
We compare the relative strengths of popular notions of security for public key encryption schemes. We consider the goals of indistinguishability and non-malleability, each under chosen plaintext attack and two kinds of chosen ciphertext attack. For each of the resulting pairs of definitions we prove either an implication (every scheme meeting one notion must meet the other) or a separation (there is a scheme meeting one notion but not the other, assuming the first notion can be met at all). We similarly treat plaintext awareness, a notion of security in the random oracle model. An additional contribution of this paper is a new definition of non-malleability which we believe is simpler than the previous one.
1998
JOFC
1997
CRYPTO
1997
JOFC
1996
CRYPTO
1996
EUROCRYPT
1995
CRYPTO
1995
CRYPTO
1994
CRYPTO
1994
EUROCRYPT
1993
CRYPTO
1993
FSE
1991
CRYPTO
1990
CRYPTO
1988
CRYPTO

#### Program Committees

TCC 2015
Eurocrypt 2013
Crypto 2011 (Program chair)
Eurocrypt 2010
Asiacrypt 2009
Asiacrypt 2008
Asiacrypt 2006
FSE 2006
Eurocrypt 2004
PKC 2002
Asiacrypt 2000
Crypto 2000
Crypto 1999
Crypto 1998