加密里面的padding

在使用加密模块的时候，比如javax.crypto.Cipher，会碰到padding不同的形式。在java里面规定了如下几种padding:

NoPadding: No padding.

 

OAEPWith<digest></digest>And<mgf></mgf>Padding: Optimal Asymmetric Encryption Padding scheme defined in PKCS #1, where <digest></digest>should be replaced by the message digest and <mgf></mgf>by the mask generation function. Example: OAEPWithMD5AndMGF1Padding.

 

PKCS5Padding: The padding scheme described in: RSA Laboratories, "PKCS #5: Password-Based Encryption Standard," version 1.5, November 1993.

 

SSL3Padding: The padding scheme defined in the SSL Protocol Version 3.0, November 18, 1996, section 5.2.3.2 (CBC block cipher)

通过google查到这篇描述padding的文章讲的比较清楚：

http://www.di-mgt.com.au/cryptopad.html

不同的padding方式如下：

1. Pad with bytes all of the same value as the number of padding bytes （pkcs#5）
2. Pad with 0x80 followed by zero bytes
3. Pad with zeroes except make the last byte equal to the number of padding bytes
4. Pad with zero (null) characters
5. Pad with space characters