Paul Crowley, "Truncated differential cryptanalysis of five rounds
of Salsa20", pdf, submitted 2005-12-25. (An error in the paper was reported in the forum.)
Simon Fischer, Willi Meier, Côme Berbain, Jean-François Biasse, Matthew J. B. Robshaw, "Non-randomness in eSTREAM Candidates Salsa20 and TSC-4." Progress in Cryptology - INDOCRYPT 2006, LNCS 4329, pp. 2-16.
Yukiyasu Tsunoo, Teruo Saito, Hiroyasu Kubo,
Tomoyasu Suzaki and Hiroki Nakashima, "Differential Cryptanalysis of Salsa20/8", pdf, submitted 2007-01-02.