Java IO.pdf - Nguyen Dang Binh

Java I/O
algorithms. Depending on which service providers are installed, you may or may not have all
of these. The JDK 1.1 includes SHA-1 (which is the same as SHA) and MD5 but not MD2.
RSA's paywareCrypto-J cryptography library also supports MD2. (See
http://www.rsa.com/rsa/products/jsafe/.)
Name Algorithm
SHA-
1
Table 10.1. Message Digest Algorithms in Java 1.1
The Secure Hash Algorithm, as defined in Secure Hash Standard, NIST FIPS 180-1 (National Institute of
Standards and Technology Federal Information Processing Standards Publications 180-1); produces 20byte
digests; see http://www.itl.nist.gov/div897/pubs/fip180-1.htm
SHA Another name for SHA-1
RSA-MD2 as defined in RFC 1319 and RFC 1423 (RFC 1423 corrects a mistake in RFC 1319); produces
MD2 16-byte digests; suitable for use with digital signatures; see http://www.faqs.org/rfcs/rfc1319.html and
http://www.faqs.org/rfcs/rfc1423.html
RSA-MD5 as defined in RFC 1321; produces 16-byte digests; quite fast on 32-bit machines; see
MD5
http://www.faqs.org/rfcs/rfc1321.html
10.2.1 Calculating Message Digests
There are four steps to calculating a hash code for a file or other sequential set of bytes with a
MessageDigest object; Figure 10.1 shows a flow chart for this process.
1. Pass the name of the algorithm you want to use to the static
MessageDigest.getInstance() factory method to get a new MessageDigest object.
2. Feed bytes into the update() method.
3. If more data remains, repeat step 2.
4. Invoke a digest() method to complete computation of the digest and return it as an
array of bytes.
196