Analysis of the CAESAR Candidate Silver

Part of the Lecture Notes in Computer Science book series (LNCS, volume 9566)

Abstract

In this paper, we present the first third-party cryptanalysis against the authenticated encryption scheme Silver. In high-level, Silver builds a tweakable block cipher by tweaking AES-128 with a dedicated method and performs a similar computation as OCB3 to achieve 128-bit security for both of integrity and confidentiality in nonce-respecting model. Besides, by modifying the tag generation of OCB3, some robustness against nonce-repeating adversaries is claimed. We first present a forgery attack against 8 (out of 10) rounds with \(2^{111}\) blocks of queries in the nonce-respecting model. The attack exploits a weakness of the dedicated AES tweaking method of Silver. Then, we present several attacks in the nonce-repeating model. Those include (1) a forgery against full Silver with \(2^{49.46}\) blocks of queries which matches a conservative security claim by the designers, (2) a plaintext recovery against full Silver with a single query and (3) a key recovery against 8 rounds with \(2^{111}\) blocks of queries. In particular, the plaintext recovery breaks the security claim by the designers. Considering that the current best key recovery for plain AES-128 is up to seven rounds, Silver lowers the security margin of AES due to its tweaking method. The attacks have been partially implemented and experimentally verified.

Keywords

Silver CAESAR Authenticated encryption Forgery Plaintext recovery Key recovery 

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Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  1. 1.Nanyang Technological UniversitySingaporeSingapore
  2. 2.NTT Secure Platform LaboratoriesTokyoJapan
  3. 3.Shanghai Jiao Tong UniversityShanghaiChina

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