Abstract
Cryptosystems have been developed over the years under the typical prevalent setting which assumes that the receiver’s key is kept secure from the adversary, and that the choice of the message to be sent is freely performed by the sender and is kept secure from the adversary as well. Under these fundamental and basic operational assumptions, modern Cryptography has flourished over the last half a century or so, with amazing achievements: New systems (including public-key Cryptography), beautiful and useful models (including security definitions such as semantic security), and new primitives (such as zero-knowledge proofs) have been developed. Furthermore, these fundamental achievements have been translated into actual working systems, and span many of the daily human activities over the Internet.
However, in recent years, there is an overgrowing pressure from many governments to allow the government itself access to keys and messages of encryption systems (under various names: escrow encryption, emergency access, communication decency acts, etc.). Numerous non-direct arguments against such policies have been raised, such as “the bad guys can utilize other encryption system” so all other cryptosystems have to be declared illegal, or that “allowing the government access is an ill-advised policy since it creates a natural weak systems security point, which may attract others (to masquerade as the government).” It has remained a fundamental open issue, though, to show directly that the above mentioned efforts by a government (called here “a dictator” for brevity) which mandate breaking of the basic operational assumption (and disallowing other cryptosystems), is, in fact, a futile exercise. This is a direct technical point which needs to be made and has not been made to date.
In this work, as a technical demonstration of the futility of the dictator’s demands, we invent the notion of “Anamorphic Encryption” which shows that even if the dictator gets the keys and the messages used in the system (before anything is sent) and no other system is allowed, there is a covert way within the context of well established public-key cryptosystems for an entity to immediately (with no latency) send piggybacked secure messages which are, in spite of the stringent dictator conditions, hidden from the dictator itself! We feel that this may be an important direct technical argument against the nature of governments’ attempts to police the use of strong cryptographic systems, and we hope to stimulate further works in this direction.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Notes
- 1.
This is masterly described in xkcd comic 538 (see https://xkcd.com/538).
- 2.
We do not use the term “law” to mark the conceptual difference from “law of Nature.”
- 3.
In “The Game-Players of Titan”, a novel by Philip K. Dick, randomness is the only weapon humans can use against silicon-based telepath aliens from Titan, called vugs.
- 4.
The adjective Anamorphic is used to denote a drawing with a distorted projection that appears normal when viewed from a particular point or with a suitable mirror or lens. Similarly, an anamorphic ciphertext will reveal a different plaintext when decrypted with a suitable key.
References
Abelson, H., et al.: The risks of key recovery, key escrow, and trusted third-party encryption (1997). https://doi.org/10.7916/D8GM8F2W
Abelson, H., et al.: Keys under doormats: mandating insecurity by requiring government access to all data and communications (2015). https://doi.org/10.7916/D8H41R9K
Alwen, J., Coretti, S., Dodis, Y.: The double ratchet: security notions, proofs, and modularization for the signal protocol. In: Ishai, Y., Rijmen, V. (eds.) EUROCRYPT 2019. LNCS, vol. 11476, pp. 129–158. Springer, Cham (2019). https://doi.org/10.1007/978-3-030-17653-2_5
Blaze, M.: Protocol failure in the escrowed encryption standard. In: CCS 1994, pp. 59–67 (1994)
Bellare, M., Paterson, K.G., Rogaway, P.: Security of symmetric encryption against mass surveillance. In: Garay, J.A., Gennaro, R. (eds.) CRYPTO 2014. LNCS, vol. 8616, pp. 1–19. Springer, Heidelberg (2014). https://doi.org/10.1007/978-3-662-44371-2_1
Canetti, R., Dwork, C., Naor, M., Ostrovsky, R.: Deniable encryption. In: Kaliski, B.S. (ed.) CRYPTO 1997. LNCS, vol. 1294, pp. 90–104. Springer, Heidelberg (1997). https://doi.org/10.1007/BFb0052229
Statement by the Press Secretary, The White House, 16 April 1993. Reprinted in David Banisar (ed.) Cryptography and Privacy Sourcebook (1994)
Checkoway, S., et al.: On the practical exploitability of dual EC in TLS implementations. In: USENIX Security Symposium, pp. 319–335 (2014)
Dakoff, H.S.: The clipper chip proposal: deciphering the unfounded fears that are wrongfully derailing its implementation. J. Marshall L. Rev. 29, 475 (1996)
Diffie, W., Hellman, M.E.: New directions in cryptography. IEEE Trans. Inf. Theory 22, 644–654 (1976)
Diffie, W., Landau, S.: Privacy on the Line. The Politics of Wiretapping and Encryption
Feistel, H.: Cryptography and computer privacy. Sci. Am. 228(5), 15–23 (1973)
Frankel, Y., Yung, M.: Escrow encryption systems visited: attacks, analysis and designs. In: Coppersmith, D. (ed.) CRYPTO 1995. LNCS, vol. 963, pp. 222–235. Springer, Heidelberg (1995). https://doi.org/10.1007/3-540-44750-4_18
Green, M., Kaptchuk, G., Van Laer, G.: Abuse resistant law enforcement access systems. In: Canteaut, A., Standaert, F.-X. (eds.) EUROCRYPT 2021. LNCS, vol. 12698, pp. 553–583. Springer, Cham (2021). https://doi.org/10.1007/978-3-030-77883-5_19
Goldwasser, S., Micali, S.: Probabilistic encryption. J. Comput. Syst. Sci. 2, 270–299 (1984)
Goldreich, O., Micali, S., Wigderson, A.: How to play any mental game. In: STOC 1987, pp. 218–229 (1987)
Gentry, C., Peikert, C., Vaikuntanathan, V.: Trapdoors for hard lattices and new cryptographic constructions. In: STOC 2008, pp. 197–206 (2008)
Horel, T., Park, S., Richelson, S., Vaikuntanathan, V.: How to subvert backdoored encryption: Security against adversaries that decrypt all ciphertexts. In: 10th ITCS, pp. 1–20 (2019)
Kerckhoffs, A.: La Cryptographie Militaire. Journal des sciences militaires (1883)
Micali, S.: Fair public-key cryptosystems. In: Brickell, E.F. (ed.) CRYPTO 1992. LNCS, vol. 740, pp. 113–138. Springer, Heidelberg (1993). https://doi.org/10.1007/3-540-48071-4_9
Marlinspike, M., Perrin, T.: The double ratchet algorithm, November 2016. https://whispersystems.org/docs/specifications/doubleratchet/doubleratchet.pdf
Naor, M., Yung, M.: Public-key cryptosystems provably secure against chosen ciphertext attacks. In: STOC 1990, pp. 427–437 (1990)
Regev, O.: On lattices, learning with errors, random linear codes, and cryptography. In: STOC 2005, pp. 84–93 (2005)
Rivest, R.L.: Chaffing and Winnowing: Confidentiality without Encryption. MIT Lab for Computer Science, 18 March 1998. http://people.csail.mit.edu/rivest/chaffing-980701.txt. Accessed 1 July 1998
Rogaway, P.: The Moral Character of Cryptographic Work. ePrint 2015/1162 (2015). https://ia.cr/2015/1162
Rivest, R.L., Shamir, A., Adleman, L.: A method for obtaining digital signatures and public-key cryptosystems. Commun. ACM 21 (1978)
Russell, A., Tang, Q., Yung, M., Zhou, H.-S.: Cliptography: clipping the power of kleptographic attacks. In: Cheon, J.H., Takagi, T. (eds.) ASIACRYPT 2016. LNCS, vol. 10032, pp. 34–64. Springer, Heidelberg (2016). https://doi.org/10.1007/978-3-662-53890-6_2
Russell, A., Tang, Q., Yung, M., Zhou, H.-S.: Generic semantic security against a kleptographic adversary. In: CCS 2017, pp. 907–922 (2017)
Sahai, A.: Non-malleable non-interactive zero knowledge and adaptive chosen-ciphertext security. In: FOCS 1999, p. 543 (1999)
Shannon, C.E.: Communication theory of secrecy systems. Bell Syst. Tech. J. 28(4), 656–715 (1949)
von Ahn, L., Hopper, N.J.: Public-key steganography. In: Cachin, C., Camenisch, J.L. (eds.) EUROCRYPT 2004. LNCS, vol. 3027, pp. 323–341. Springer, Heidelberg (2004). https://doi.org/10.1007/978-3-540-24676-3_20
WhatsApp. WhatsApp Encryption Overview, October 2020
Yao, A.C.-C.: How to generate and exchange secrets. In: FOCS 1986, pp. 162–167 (1986)
Young, A., Yung, M.: The dark side of “Black-Box’’ cryptography or: should we trust capstone? In: Koblitz, N. (ed.) CRYPTO 1996. LNCS, vol. 1109, pp. 89–103. Springer, Heidelberg (1996). https://doi.org/10.1007/3-540-68697-5_8
Young, A., Yung, M.: The prevalence of kleptographic attacks on discrete-log based cryptosystems. In: Kaliski, B.S. (ed.) CRYPTO 1997. LNCS, vol. 1294, pp. 264–276. Springer, Heidelberg (1997). https://doi.org/10.1007/BFb0052241
Young, A., Yung, M.: Kleptography: using cryptography against cryptography. In: Fumy, W. (ed.) EUROCRYPT 1997. LNCS, vol. 1233, pp. 62–74. Springer, Heidelberg (1997). https://doi.org/10.1007/3-540-69053-0_6
Young, A., Yung, M.: Auto-recoverable auto-certifiable cryptosystems. In: Nyberg, K. (ed.) EUROCRYPT 1998. LNCS, vol. 1403, pp. 17–31. Springer, Heidelberg (1998). https://doi.org/10.1007/BFb0054114
Acknowledgments
We thank all anonymous reviewers for insightful feedback. Duong Hieu Phan was partially supported by the ANR ALAMBIC (ANR16-CE39-0006). Part of this work was done while Giuseppe Persiano was visiting Google NY.
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2022 International Association for Cryptologic Research
About this paper
Cite this paper
Persiano, G., Phan, D.H., Yung, M. (2022). Anamorphic Encryption: Private Communication Against a Dictator. In: Dunkelman, O., Dziembowski, S. (eds) Advances in Cryptology – EUROCRYPT 2022. EUROCRYPT 2022. Lecture Notes in Computer Science, vol 13276. Springer, Cham. https://doi.org/10.1007/978-3-031-07085-3_2
Download citation
DOI: https://doi.org/10.1007/978-3-031-07085-3_2
Published:
Publisher Name: Springer, Cham
Print ISBN: 978-3-031-07084-6
Online ISBN: 978-3-031-07085-3
eBook Packages: Computer ScienceComputer Science (R0)