关于PKCS5Padding与PKCS7Padding的区别

NoPadding No padding. ISO10126Padding This padding for block ciphers is described in 5.2 Block Encryption Algorithms in the W3C's "XML Encryption Syntax and Processing" document. OAEPPadding, OAEPWith<digest>And<mgf>Padding Optimal Asymmetric Encryption Padding scheme defined in PKCS1, where <digest> should be replaced by the message digest and <mgf> by the mask generation function. Examples: OAEPWithMD5AndMGF1Padding and OAEPWithSHA-512AndMGF1Padding.

If OAEPPadding is used, Cipher objects are initialized with a javax.crypto.spec.OAEPParameterSpec object to suppply values needed for OAEPPadding. PKCS1Padding The padding scheme described in PKCS1, used with the RSA algorithm. PKCS5Padding The padding scheme described in RSA Laboratories, "PKCS5: 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):

    block-ciphered struct {
	opaque content[SSLCompressed.length];
	opaque MAC[CipherSpec.hash_size];
	uint8 padding[
	    GenericBlockCipher.padding_length];
	uint8 padding_length;
    } GenericBlockCipher;

The size of an instance of a GenericBlockCipher must be a multiple of the block cipher's block length.

The padding length, which is always present, contributes to the padding, which implies that if:

    sizeof(content) + sizeof(MAC) % block_length = 0, 

padding has to be (block_length - 1) bytes long, because of the existence of padding_length.

This make the padding scheme similar (but not quite) to PKCS5Padding, where the padding length is encoded in the padding (and ranges from 1 to block_length). With the SSL scheme, the sizeof(padding) is encoded in the always present padding_length and therefore ranges from 0 to block_length-1.