In this paper, we give a fast attack against hash function——HAVAL-128.HAVAL was presented by Y. L. Zheng et al. at Auscrypto’92. It can be processed in 3, 4 or 5 passes, and produces 128, 160, 192, or 224-bit fingerprint. We break the HAVAL with 128-bit fingerprint. The conclusion is that, given any 1024-bit message m, we just make some modifications about m, and the modified message m can collide with another message m’ only with probability 1/27, where m’ = m + △m, in which Am is a fixed difference selected in advance. In addition, two collision examples for HAVAL-128 are given in this paper.
