Cryptology ePrint Archive: Report 2006/036

Vector Stream Cipher Instant Key Recovery

Sean O'Neil

Abstract: Vector Stream Cipher (VSC) is a stream cipher designed by ChaosWare and patented by NICT (formerly CRL), Japanese patents 3030341 and 3455758, US patent 6,668,265. VSC is recommended by the Softbank Technology Corporation for use in high bandwidth and high security applications. In this paper we present a practical attack instantly recovering the entire secret key of the high-speed single-round VSC variants with only 4 known subsequent plaintext blocks showing how all single-round VSC variants can be trivially broken due to their simple algebraic nature. The algorithm presented in this paper cannot break the 8-round VSC, but it can be easily adapted to any particular high-speed single-round VSC variant and extended to break some of the multiple-round VSC variants with very little effort and it may help accelerate other attacks.

Category / Keywords: secret-key cryptography / cryptanalysis, key recovery

Date: received 31 Jan 2006

Contact author: ajevans at bigpond net au

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Version: 20060206:192448 (All versions of this report)

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