JDK 1.4 supports the following message-digest algorithms:

• MD2 and MD5, which are 128-bit algorithms
• SHA-1, which is a 160-bit algorithm
• SHA-256, SHA-383, and SHA-512, which offer longer fingerprint sizes of 256, 383, and 512 bits, respectively

MD5 and SHA-1 are the most used algorithms.

The MessageDigest class manipulates message digests. The following methods are used in the Message digest code example:

• MessageDigest.getInstance("MD5"): Creates the message digest.
• .update(plaintext): Calculates the message digest with a plaintext string.
• .digest(): Reads the message digest.

If a key is used as part of the message-digest generation, the algorithm is known as a message-authentication code. JDK 1.4 supports the HMAC/SHA-1 and HMAC/MD5 message-authentication code algorithms.

The Mac class manipulates message-authentication codes using a key produced by the KeyGenerator class. The following methods are used in the Message authentication code example:

• KeyGenerator.getInstance("HmacMD5") and .generateKey(): Generates the key.
  
  
• Mac.getInstance("HmacMD5"): Creates a MAC object.
  
  
• .init(MD5key): Intializes the MAC object.
  
  
• .update(plaintext) and .doFinal(): Calculates the MAC object with a plaintext string.