GSChapter6UsingJavaCryptographyforAuthentication详解.pptVIP

csci5233 Computer Security GS: Chapter 6Using Java Cryptography for Authentication Topics Message digest (MD) Password authentication for MD Message Authentication Code (MAC) Digital signatures Identity authentication Digital certificates, X.509, certificate chaining Keystores Public Key Infrastructure (PKI) Dependencies Message Digests message digest: a fingerprint of a piece of data goal: data integrity (stored data, transmitted data, file copying, …) message ? hashing algorithm ? digest Java class: MessageDigest Methods: getInstance ( ), update ( ), digest ( ) Algorithms: MD5, SHA, SHA-1 Message Digests in Java java.security Class MessageDigest Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value. A MessageDigest object starts out initialized. The data is processed through it using the update methods. At any point reset can be called to reset the digest. Once all the data to be updated has been updated, one of the digest methods should be called to complete the hash computation. After digest has been called, the MessageDigest object is reset to its initialized state. Message Digests in Java byte[] digest () Completes the hash computation by performing final operations such as padding. byte[] digest (byte[]?input) Performs a final update on the digest using the specified array of bytes, then completes the digest computation. int digest (byte[]?buf, int?offset, int?len) Completes the hash computation by performing final operations such as padding. Message Digests in Java Computing a message digest on a file: DigestFile.java Size of the output digest SHA-1: 20 bytes MD5: 16 bytes Exercise: Change the content of the input data file and compare the output digests. Project: Write a program that gets a file, the MD algorithm, and the generated digest as the input, and then determine if the file has been corrupted. Message Digests in Java Alternative classes for computing a message digest on