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OCB: A BlockCipher Mode of Operation for Efficient Authenticated Encryption
, 2001
"... We describe a parallelizable blockcipher mode of operation that simultaneously provides privacy and authenticity. OCB encryptsandauthenticates a nonempty string M # {0, 1} # using #M /n# + 2 blockcipher invocations, where n is the block length of the underlying block cipher. Additional ov ..."
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Cited by 154 (23 self)
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We describe a parallelizable blockcipher mode of operation that simultaneously provides privacy and authenticity. OCB encryptsandauthenticates a nonempty string M # {0, 1} # using #M /n# + 2 blockcipher invocations, where n is the block length of the underlying block cipher. Additional overhead is small. OCB refines a scheme, IAPM, suggested by Jutla [20]. Desirable properties of OCB include: the ability to encrypt a bit string of arbitrary length into a ciphertext of minimal length; cheap o#set calculations; cheap session setup, a single underlying cryptographic key; no extendedprecision addition; a nearly optimal number of blockcipher calls; and no requirement for a random IV. We prove OCB secure, quantifying the adversary's ability to violate privacy or authenticity in terms of the quality of the block cipher as a pseudorandom permutation (PRP) or as a strong PRP, respectively. Keywords: AES, authenticity, block ciphers, cryptography, encryption, integrity, modes of operation, provable security, standards . # Department of Computer Science, Eng. II Building, University of California at Davis, Davis, California 95616 USA; and Department of Computer Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200 Thailand. email: rogaway@cs.ucdavis.edu web: www.cs.ucdavis.edu/~rogaway + Department of Computer Science & Engineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093 USA. email: mihir@cs.ucsd.edu web: wwwcse.ucsd.edu/users/mihir # Department of Computer Science, University of Nevada, Reno, Nevada 89557 USA. email: jrb@cs.unr.edu web: www.cs.unr.edu/~jrb Digital Fountain, 600 Alabama Street, San Francisco, CA 94110 USA. email: tdk@acm.org 1
The order of encryption and authentication for protecting communications (or: how Secure is SSL?)
, 2001
"... We study the question of how to generically compose symmetric encryption and authentication when building “secure channels” for the protection of communications over insecure networks. We show that any secure channels protocol designed to work with any combination of secure encryption (against chose ..."
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Cited by 138 (5 self)
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We study the question of how to generically compose symmetric encryption and authentication when building “secure channels” for the protection of communications over insecure networks. We show that any secure channels protocol designed to work with any combination of secure encryption (against chosen plaintext attacks) and secure MAC must use the encryptthenauthenticate method. We demonstrate this by showing that the other common methods of composing encryption and authentication, including the authenticatethenencrypt method used in SSL, are not generically secure. We show an example of an encryption function that provides (Shannon’s) perfect secrecy but when combined with any MAC function under the authenticatethenencrypt method yields a totally insecure protocol (for example, finding passwords or credit card numbers transmitted under the protection of such protocol becomes an easy task for an active attacker). The same applies to the encryptandauthenticate method used in SSH. On the positive side we show that the authenticatethenencrypt method is secure if the encryption method in use is either CBC mode (with an underlying secure block cipher) or a stream cipher (that xor the data with a random or pseudorandom pad). Thus, while we show the generic security of SSL to be broken, the current practical implementations of the protocol that use the above modes of encryption are safe.
Encodethenencipher encryption: How to exploit nonces or redundancy in plaintexts for efficient cryptography
"... We investigate the following approach to symmetric encryption: first encode the message via some keyless transform, and then encipher the encoded message, meaning apply a permutation FK based on a shared key K. We provide conditions on the encoding functions and the cipher which ensure that the resu ..."
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Cited by 67 (26 self)
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We investigate the following approach to symmetric encryption: first encode the message via some keyless transform, and then encipher the encoded message, meaning apply a permutation FK based on a shared key K. We provide conditions on the encoding functions and the cipher which ensure that the resulting encryption scheme meets strong privacy (eg. semantic security) and/or authenticity goals. The encoding can either be implemented in a simple way (eg. prepend a counter and append a checksum) or viewed as modeling existing redundancy or entropy already present in the messages, whereby encodethenencipher encryption provides a way to exploit structured message spaces to achieve compact ciphertexts.
CircularSecure Encryption from Decision DiffieHellman
, 2008
"... Let E be a publickey encryption system and let (pk i, ski) be public/private key pairs for E for i = 0,..., n. A natural question is whether E remains secure once an adversary obtains an encryption cycle, which consists of the encryption of ski under pk (i mod n)+1 for all i = 1,..., n. Surprisingl ..."
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Cited by 53 (7 self)
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Let E be a publickey encryption system and let (pk i, ski) be public/private key pairs for E for i = 0,..., n. A natural question is whether E remains secure once an adversary obtains an encryption cycle, which consists of the encryption of ski under pk (i mod n)+1 for all i = 1,..., n. Surprisingly, even strong notions of security such as chosenciphertext security appear to be insufficient for proving security in these settings. Since encryption cycles come up naturally in several applications, it is desirable to construct systems that remain secure in the presence of such cycles. Until now, all known constructions have only be proved secure in the random oracle model. We construct an encryption system that is circularsecure under the Decision DiffieHellman assumption, without relying on random oracles. Our proof of security holds even if the adversary obtains an encryption clique, that is, encryptions of ski under pk j for all 0 ≤ i, j ≤ n. We also construct a circular counterexample: a oneway secure encryption scheme that becomes completely insecure if an encryption cycle of length 2 is published. 1
A provablesecurity treatment of the keywrap problem
 EUROCRYPT 2006, LNCS 4004
, 2006
"... Abstract. We give a provablesecurity treatment for the keywrap problem, providing definitions, constructions, and proofs. We suggest that keywrap’s goal is security in the sense of deterministic authenticatedencryption (DAE), a notion that we put forward. We also provide an alternative notion, a ..."
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Cited by 31 (5 self)
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Abstract. We give a provablesecurity treatment for the keywrap problem, providing definitions, constructions, and proofs. We suggest that keywrap’s goal is security in the sense of deterministic authenticatedencryption (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 blockcipherbased 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 IVbased authenticatedencryption (AE) schemes that are maximally forgiving of repeated IVs, a goal we formalize as misuseresistant AE. We show that a DAE scheme with a vectorvalued header, such as SIV, directly realizes this goal. 1
The Security of AllorNothing Encryption: Protecting against Exhaustive Key Search
 In Advances in Cryptology – CRYPTO ’00 (2000
, 2000
"... Abstract. We investigate the allornothing encryption paradigm which was introduced by Rivest as a new mode of operation for block ciphers. The paradigm involves composing an allornothing transform (AONT) with an ordinary encryption mode. The goal is to have secure encryption modes with the addit ..."
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Cited by 23 (0 self)
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Abstract. We investigate the allornothing encryption paradigm which was introduced by Rivest as a new mode of operation for block ciphers. The paradigm involves composing an allornothing transform (AONT) with an ordinary encryption mode. The goal is to have secure encryption modes with the additional property that exhaustive keysearch attacks on them are slowed down by a factor equal to the number of blocks in the ciphertext. We give a new notion concerned with the privacy of keys that provably captures this keysearch resistance property. We suggest a new characterization of AONTs and establish that the resulting allornothing encryption paradigm yields secure encryption modes that also meet this notion of key privacy. A consequence of our new characterization is that we get more efficient ways of instantiating the allornothing encryption paradigm. We describe a simple blockcipherbased AONT and prove it secure in the Shannon Model of a block cipher. We also give attacks against alternate paradigms that were believed to have the above keysearch resistance property. 1
Authenticated Encryption in the PublicKey Setting: Security Notions and Analyses
 http://eprint.iacr.org/2001/079
, 2001
"... This paper addresses the security of authenticated encryption schemes in the public key setting. We present two new notions of authenticity that are stronger than the integrity notions given in the symmetric setting [5]. We also show that chosenciphertext attack security (INDCCA) in the public key ..."
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Cited by 16 (0 self)
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This paper addresses the security of authenticated encryption schemes in the public key setting. We present two new notions of authenticity that are stronger than the integrity notions given in the symmetric setting [5]. We also show that chosenciphertext attack security (INDCCA) in the public key setting is not obtained in general from the combination of chosenplaintext security (INDCPA) and integrity of ciphertext (INTCTXT), which is in contrast to the results shown in the symmetric setting [13, 5]. We provide security analyses of authenticated encryption schemes constructed by combining a given public key encryption scheme and a given digital signature scheme in a \generic" manner namely, EncryptandSign, SignthenEncrypt, and EncryptthenSign and show that none of them, in general, provide security under all notions dened in this paper. We then present a scheme called ESSR that meets all security notions dened here. We also give security analyses on an ecient DieHellman based scheme called DHETM, which can be thought of as a transform of the encryption scheme \DHIES" [1] into an authenticated encryption scheme in the public key setting. Keywords: Public key setting, Authenticated encryption, Privacy, Authenticity, Unforgeability. Dept. of Computer Science, & Engineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA. Email: jeehea@cs.ucsd.edu. URL: http://wwwcse.ucsd.edu/~jeehea. Supported in part by Mihir Bellare's NSF CAREER Award CCR9624439 and a 1996 Packard Foundation Fellowship in Science and Engineering. Contents 1
Does Encryption with Redundancy Provide Authenticity?
 IN ADVANCES IN CRYPTOLOGY — EUROCRYPT 2001, B. PFITZMANN, ED. LECTURE NOTES IN COMPUTER SCIENCE
, 2001
"... A popular paradigm for achieving privacy plus authenticity is to append some “redundancy” to the data before encrypting. We investigate the security of this paradigm at both a general and a specific level. We consider various possible notions of privacy for the base encryption scheme, and for each s ..."
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Cited by 16 (5 self)
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A popular paradigm for achieving privacy plus authenticity is to append some “redundancy” to the data before encrypting. We investigate the security of this paradigm at both a general and a specific level. We consider various possible notions of privacy for the base encryption scheme, and for each such notion we provide a condition on the redundancy function that is necessary and sufficient to ensure authenticity of the encryptionwithredundancy scheme. We then consider the case where the base encryption scheme is a variant of CBC called NCBC, and find sufficient conditions on the redundancy functions for NCBC encryptionwithredundancy to provide authenticity. Our results highlight an important distinction between public redundancy functions, meaning those that the adversary can compute, and secret ones, meaning those that depend on the shared key between the legitimate parties.
The Software Performance of AuthenticatedEncryption Modes
, 2011
"... We study the software performance of authenticatedencryption modes CCM, GCM, and OCB. Across a variety of platforms, we find OCB to be substantially faster than either alternative. For example, on an Intel i5 (“Clarkdale”) processor, good implementations of CCM, GCM, and OCB encrypt at around 4.2 c ..."
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Cited by 12 (1 self)
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We study the software performance of authenticatedencryption modes CCM, GCM, and OCB. Across a variety of platforms, we find OCB to be substantially faster than either alternative. For example, on an Intel i5 (“Clarkdale”) processor, good implementations of CCM, GCM, and OCB encrypt at around 4.2 cpb, 3.7 cpb, and 1.5 cpb, while CTR mode requires about 1.3 cpb. Still we find room for algorithmic improvements to OCB, showing how to trim one blockcipher call (most of the time, assuming a counterbased nonce) and reduce latency. Our findings contrast with those of McGrew and Viega (2004), who claimed similar performance for GCM and OCB. Key words: authenticated encryption, cryptographic standards, encryption speed, modes of
New paradigms for constructing symmetric encryption schemes secure against chosen ciphertext attack
 Advances in Cryptology  CRYPTO 2000
, 2000
"... Abstract. The paradigms currently used to realize symmetric encryption schemes secure against adaptive chosen ciphertext attack (CCA) try to make it infeasible for an attacker to forge “valid ” ciphertexts. This is achieved by either encoding the plaintext with some redundancy before encrypting or b ..."
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Cited by 10 (0 self)
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Abstract. The paradigms currently used to realize symmetric encryption schemes secure against adaptive chosen ciphertext attack (CCA) try to make it infeasible for an attacker to forge “valid ” ciphertexts. This is achieved by either encoding the plaintext with some redundancy before encrypting or by appending a MAC to the ciphertext. We suggest schemes which are provably secure against CCA, and yet every string is a “valid ” ciphertext. Consequently, our schemes have a smaller ciphertext expansion than any other scheme known to be secure against CCA. Our most efficient scheme is based on a novel use of “variablelength ” pseudorandom functions and can be efficiently implemented using block ciphers. We relate the difficulty of breaking our schemes to that of breaking the underlying primitives in a precise and quantitative way. 1