### Abstract

We introduce a new cryptographic primitive we call concealment, which is related, but quite different from the notion of commitment. A concealment is a publicly known randomized transformation, which, on input m, outputs a hider h and a binder b. Together, h and b allow one to recover m, but separately, (1) the hider h reveals "no information" about m, while (2) the binder b can be "meaningfully opened" by at most one hider h. While setting b = m, h = ∅ is a trivial concealment, the challenge is to make |b| ≪ |m|, which we call a "non-trivial" concealment. We show that non-trivial concealments are equivalent to the existence of collision-resistant hash functions. Moreover, our construction of concealments is extremely simple, optimal, and yet very general, giving rise to a multitude of efficient implementations. We show that concealments have natural and important applications in the area of authenticated encryption. Specifically, let Aε be an authenticated encryption scheme (either public- or symmetric-key) designed to work on short messages. We show that concealments are exactly the right abstraction allowing one to use Aε for encrypting long messages. Namely, to encrypt "long" m, one uses a concealment scheme to get h and b, and outputs authenticated ciphertext 〈Aε(b), h〉. More surprisingly, the above paradigm leads to a very simple and general solution to the problem of remotely keyed (authenticated) encryption (RKAE) [12,13]. In this problem, one wishes to split the task of high-bandwidth authenticated encryption between a secure, but low-bandwidth/computationally limited device, and an insecure, but computationally powerful host. We give formal definitions for RKAE, which we believe are simpler and more natural than all the previous definitions. We then show that our composition paradigm satisfies our (very strong) definition. Namely, for authenticated encryption, the host simply sends a short value b to the device (which stores the actual secret key for Aε), gets back Aε(b), and outputs 〈Aε(b), h〉 (authenticated decryption is similar). Finally, we also observe that the particular schemes of [13,17] are all special examples of our general paradigm.

Original language | English (US) |
---|---|

Pages (from-to) | 312-329 |

Number of pages | 18 |

Journal | Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) |

Volume | 2656 |

State | Published - 2003 |

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### ASJC Scopus subject areas

- Computer Science(all)
- Biochemistry, Genetics and Molecular Biology(all)
- Theoretical Computer Science

### Cite this

**Concealment and its applications to authenticated encryption.** / Dodis, Yevgeniy; An, Jee Hea.

Research output: Contribution to journal › Article

}

TY - JOUR

T1 - Concealment and its applications to authenticated encryption

AU - Dodis, Yevgeniy

AU - An, Jee Hea

PY - 2003

Y1 - 2003

N2 - We introduce a new cryptographic primitive we call concealment, which is related, but quite different from the notion of commitment. A concealment is a publicly known randomized transformation, which, on input m, outputs a hider h and a binder b. Together, h and b allow one to recover m, but separately, (1) the hider h reveals "no information" about m, while (2) the binder b can be "meaningfully opened" by at most one hider h. While setting b = m, h = ∅ is a trivial concealment, the challenge is to make |b| ≪ |m|, which we call a "non-trivial" concealment. We show that non-trivial concealments are equivalent to the existence of collision-resistant hash functions. Moreover, our construction of concealments is extremely simple, optimal, and yet very general, giving rise to a multitude of efficient implementations. We show that concealments have natural and important applications in the area of authenticated encryption. Specifically, let Aε be an authenticated encryption scheme (either public- or symmetric-key) designed to work on short messages. We show that concealments are exactly the right abstraction allowing one to use Aε for encrypting long messages. Namely, to encrypt "long" m, one uses a concealment scheme to get h and b, and outputs authenticated ciphertext 〈Aε(b), h〉. More surprisingly, the above paradigm leads to a very simple and general solution to the problem of remotely keyed (authenticated) encryption (RKAE) [12,13]. In this problem, one wishes to split the task of high-bandwidth authenticated encryption between a secure, but low-bandwidth/computationally limited device, and an insecure, but computationally powerful host. We give formal definitions for RKAE, which we believe are simpler and more natural than all the previous definitions. We then show that our composition paradigm satisfies our (very strong) definition. Namely, for authenticated encryption, the host simply sends a short value b to the device (which stores the actual secret key for Aε), gets back Aε(b), and outputs 〈Aε(b), h〉 (authenticated decryption is similar). Finally, we also observe that the particular schemes of [13,17] are all special examples of our general paradigm.

AB - We introduce a new cryptographic primitive we call concealment, which is related, but quite different from the notion of commitment. A concealment is a publicly known randomized transformation, which, on input m, outputs a hider h and a binder b. Together, h and b allow one to recover m, but separately, (1) the hider h reveals "no information" about m, while (2) the binder b can be "meaningfully opened" by at most one hider h. While setting b = m, h = ∅ is a trivial concealment, the challenge is to make |b| ≪ |m|, which we call a "non-trivial" concealment. We show that non-trivial concealments are equivalent to the existence of collision-resistant hash functions. Moreover, our construction of concealments is extremely simple, optimal, and yet very general, giving rise to a multitude of efficient implementations. We show that concealments have natural and important applications in the area of authenticated encryption. Specifically, let Aε be an authenticated encryption scheme (either public- or symmetric-key) designed to work on short messages. We show that concealments are exactly the right abstraction allowing one to use Aε for encrypting long messages. Namely, to encrypt "long" m, one uses a concealment scheme to get h and b, and outputs authenticated ciphertext 〈Aε(b), h〉. More surprisingly, the above paradigm leads to a very simple and general solution to the problem of remotely keyed (authenticated) encryption (RKAE) [12,13]. In this problem, one wishes to split the task of high-bandwidth authenticated encryption between a secure, but low-bandwidth/computationally limited device, and an insecure, but computationally powerful host. We give formal definitions for RKAE, which we believe are simpler and more natural than all the previous definitions. We then show that our composition paradigm satisfies our (very strong) definition. Namely, for authenticated encryption, the host simply sends a short value b to the device (which stores the actual secret key for Aε), gets back Aε(b), and outputs 〈Aε(b), h〉 (authenticated decryption is similar). Finally, we also observe that the particular schemes of [13,17] are all special examples of our general paradigm.

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M3 - Article

VL - 2656

SP - 312

EP - 329

JO - Lecture Notes in Computer Science

JF - Lecture Notes in Computer Science

SN - 0302-9743

ER -