com.ibm.crypto.fips.provider

Class ByteAdder

java.lang.Object

com.ibm.crypto.fips.provider.ByteAdder

public final class ByteAdder
extends java.lang.Object

Adds byte arrays, intended for unsigned/positive numbers only.

Since:

NIST SP 800-131 and HASH-DRBG support

Method Summary

Methods

Modifier and Type	Method and Description
static byte[]	add(int maxbytes, byte[]... arrays) Add a variable number of byte arrays of variable size.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

add

public static byte[] add(int maxbytes,
         byte[]... arrays)

Add a variable number of byte arrays of variable size. This is useful for operations involving positive numbers encoded as byte arrays, where the output is going to be modulo a power of two where the power is divisible by 8 (so 2**8, which is what can be rendered in hex in a byte). We are exploiting the fact that x modulo y, where x is positive and y is a power of two can reduce down to (x & (y-1)), and we are also avoiding BigInteger's nasty habit of putting unneeded sign bytes out when you ask it to do toByteArray() or you have to construct a BigInteger from bytes. We have no need of expensive BigInteger.mod operations for numbers that are powers of 2 that end up also being powers of 2**8. // V=(V+H+C+reseed_counter)mod2**440 BigInteger accumulator = new BigInteger(1, V); accumulator = accumulator.add(new BigInteger(1, H)); accumulator = accumulator.add(new BigInteger(1, C)); byte[] reseedB = new byte[4]; msbf4((int)reseed_counter, reseedB, 0); accumulator = accumulator.add(new BigInteger(1, reseedB)); accumulator = accumulator.mod(MOD2_440); byte[] vprime = stripOffSignByte(accumulator.toByteArray()); int vprimelen = vprime.length; if (vprimelen > MIN_SEED_BYTES) { System.arraycopy(vprime, vprimelen-MIN_SEED_BYTES, V, 0, V.length); vprime = null; } else V = vprime; becomes simply V = ByteAdder.add(55, V, H, C, reseedB);

Parameters:

maxbytes - the number of bytes desired in the output array

arrays - variable number of byte arrays of variable size

Returns:

a byte array of the specified length, with the sum of the input