ISO10126PADDING, minor optimizations and random question

[Bernd Eckenfels]

Hello,

while looking at ISO10126Padding I noticed a few minor optimizations
are possible:

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/8u40-b25/com/sun/crypto/provider/ISO10126Padding.java?av=f

unpad() - there is already a int cast done to this value:
104        int start = off + len - ((int)lastByte & 0x0ff);

can be changed into "int start = off + len - padValue;"


padWithLen() - we can request one byte less from PRNG and copy one less:
71         byte[] padding = new byte[len];
72         SunJCE.getRandom().nextBytes(padding);
73         padding[len-1] = paddingOctet;
74         System.arraycopy(padding, 0, in, off, len);

byte[] padding = new byte[len-1];
SunJCE.getRandom().nextBytes(padding);
System.arraycopy(padding, 0, in, off, len-1);
in[off+len-1] = paddingOctet;


BTW: the JCA Standards Names documentation refer to W3C XML Encryption
Standard 5.2 which does not mandate or suggest to use random padding.
It allows any value. So a possible optimization would be to not use
random bytes. If you think random bytes (and therefore non
deterministic padding) is a desireable property I would suggest to
actually document it in the SunJCE documentation. "This implements
padding as defined by the JCA Standard Names using random padding bytes.

Greetings
Bernd