PKC 2003 was the Sixth International Workshop on Practice and Theory in Public Key Cryptography and was sponsored by IACR, the International As- ciation for Cryptologic Research (www.iacr.org). This year the workshop was organized in cooperation with the Department of Computer Science, Florida State University. The General Chair, Mike Burmester was responsible for local organization, registration, etc. There were 105 submitted papers which were considered by the Program Committee. This is an increase of 52% compared to PKC 2002, which took place in Paris, France, February 2002, and which was incorrectly identified on the cover of the proceedings as being the fourth workshop. Due to the large number of submissions, some papers that contained new ideas had to be rejected. Priority was given to novel papers. Of the 105 submissions, 26 were selected for the proceedings. These contain the revised versions of the accepted papers. Each paper was sent to at least 3 members of the program committee for comments. Revisions were not checked for correctness of their scientific aspects and the authors bear full responsibility for the contents of their papers. Some authors will write final versions of their papers for publication in refereed journals. I am very grateful to the members of the Program Committee for their hard work in the difficult task of selecting roughly 1 out of 4 of the submitted papers.