PKC2004wasthe7thInternationalWorkshoponPracticeandTheoryinPublic Key Cryptography and was sponsored by IACR, the International Association for Cryptologic Research (www. iacr. org). This year the workshop was organized 2 in cooperation with the Institute for Infocomm Research (I R), Singapore. There were 106 paper submissions from 19 countries to PKC 2004. That is the highest submission number in PKC history. Due to the large number of submissionsandthehighqualityofthe submittedpapers,notallthepapersthat contained new ideas were accepted. Of the 106 submissions, 32 were selected for the proceedings. Each paper was sent to at least 3 members of the Program Committee for comments. The revised versions of the accepted papers were not checked for correctness of their scienti?c aspects and the authors bear the full responsibility for the contents of their papers. Some authors will write ?nal 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 di?cult task of selecting fewer than 1 in 3 of the submitted papers, as well as the following external referees who helped the Program Committee: Nuttapong Attrapadung,RobertoMariaAvanzi,GildasAvoine,JoonsangBaek, Qingjun Cai, Jae Choon Cha, Chien-Ning Chen, Liqun Chen, Xiaofeng Chen, Koji Chida, Nicolas T. Courtois, Yang Cui, Jean-Franco , is Dhem, Louis Goubin, Louis Granboulan, Rob Granger, Jens Groth, Yumiko Hanaoka, Darrel Hank- son,Chao-ChihHsu,TetsutaroKobayashi,YuichiKomano,HidenoriKuwakado, TanjaLange,PeterLeadbitter,ByoungcheonLee,Chun-KoLee,HenryC. J. Lee, JohnMaloneLee,YongLi,Beno ?tLibert,Hsi-ChungLin,YiLu,JeanMonnerat, Anderson C. A. Nascimento, C.

Table of Contents:
A Generalized Wiener Attack on RSA.- Cryptanalysis of a Public-Key Encryption Scheme Based on the Polynomial Reconstruction Problem.- Faster Scalar Multiplication on Koblitz Curves Combining Point Halving with the Frobenius Endomorphism.- Application of Montgomery’s Trick to Scalar Multiplication for Elliptic and Hyperelliptic Curves Using a Fixed Base Point.- Fast Arithmetic on Jacobians of Picard Curves.- Undeniable Signatures Based on Characters: How to Sign with One Bit.- Efficient Extension of Standard Schnorr/RSA Signatures into Universal Designated-Verifier Signatures.- Constructing Committed Signatures from Strong-RSA Assumption in the Standard Complexity Model.- Constant Round Authenticated Group Key Agreement via Distributed Computation.- Efficient ID-based Group Key Agreement with Bilinear Maps.- New Security Results on Encrypted Key Exchange.- New Results on the Hardness of Diffie-Hellman Bits.- Short Exponent Diffie-Hellman Problems.- Efficient Signcryption with Key Privacy from Gap Diffie-Hellman Groups.- Algebraic Attacks over GF(2 k ), Application to HFE Challenge 2 and Sflash-v2.- Secret Exponent Attacks on RSA-type Schemes with Moduli N=p r q.- General Group Authentication Codes and Their Relation to “Unconditionally-Secure Signatures”.- From Digital Signature to ID-based Identification/Signature.- Identity-Based Threshold Decryption.- An Efficient Signature Scheme from Bilinear Pairings and Its Applications.- An RSA Family of Trap-Door Permutations with a Common Domain and Its Applications.- A New Variant of the Matsumoto-Imai Cryptosystem through Perturbation.- Efficient, Verifiable Shuffle Decryption and Its Requirement of Unlinkability.- A Point Compression Method for Elliptic Curves Defined over GF(2 n ).- On the Optimal Parameter Choicefor Elliptic Curve Cryptosystems Using Isogeny.- On the Security of Multiple Encryption or CCA-security+CCA-security=CCA-security?.- QuasiModo: Efficient Certificate Validation and Revocation.- A Distributed Online Certificate Status Protocol with a Single Public Key.- A First Approach to Provide Anonymity in Attribute Certificates.- A Nonuniform Algorithm for the Hidden Number Problem in Subgroups.- Cryptographic Randomized Response Techniques.- A Correct, Private, and Efficient Mix Network.