org.bitcoinj.crypto.ChildNumber Maven / Gradle / Ivy
/*
* Copyright 2013 Matija Mazi.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.bitcoinj.crypto;
import java.util.List;
import java.util.Locale;
/**
* This is just a wrapper for the i (child number) as per BIP 32 with a boolean getter for the most significant bit
* and a getter for the actual 0-based child number. A {@link List} of these forms a path through a
* {@link DeterministicHierarchy}. This class is immutable.
*/
public class ChildNumber implements Comparable {
/**
* The bit that's set in the child number to indicate whether this key is "hardened". Given a hardened key, it is
* not possible to derive a child public key if you know only the hardened public key. With a non-hardened key this
* is possible, so you can derive trees of public keys given only a public parent, but the downside is that it's
* possible to leak private keys if you disclose a parent public key and a child private key (elliptic curve maths
* allows you to work upwards).
*/
public static final int HARDENED_BIT = 0x80000000;
public static final ChildNumber ZERO = new ChildNumber(0);
public static final ChildNumber ZERO_HARDENED = new ChildNumber(0, true);
public static final ChildNumber ONE = new ChildNumber(1);
public static final ChildNumber ONE_HARDENED = new ChildNumber(1, true);
public static final ChildNumber FIVE_HARDENED = new ChildNumber(5, true);
public static final ChildNumber NINE_HARDENED = new ChildNumber(9, true);
/** Integer i as per BIP 32 spec, including the MSB denoting derivation type (0 = public, 1 = private) **/
private final int i;
private final boolean simple;
public ChildNumber(int childNumber, boolean isHardened) {
if (hasHardenedBit(childNumber))
throw new IllegalArgumentException("Most significant bit is reserved and shouldn't be set: " + childNumber);
i = isHardened ? (childNumber | HARDENED_BIT) : childNumber;
simple = true;
}
public ChildNumber(int i) {
this.i = i;
simple = true;
}
public ChildNumber(boolean simple) {
this.i = -1;
this.simple = simple;
}
/** Returns the uint32 encoded form of the path element, including the most significant bit. */
public int getI() {
return i;
}
/** Returns the uint32 encoded form of the path element, including the most significant bit. */
public int i() { return i; }
public boolean isHardened() {
return hasHardenedBit(i);
}
private static boolean hasHardenedBit(int a) {
return (a & HARDENED_BIT) != 0;
}
/** Returns the child number without the hardening bit set (i.e. index in that part of the tree). */
public int num() {
return i & (~HARDENED_BIT);
}
public boolean isSimple() { return simple; }
@Override
public String toString() {
return String.format(Locale.US, "%d%s", num(), isHardened() ? "H" : "");
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
return i == ((ChildNumber)o).i;
}
@Override
public int hashCode() {
return i;
}
@Override
public int compareTo(ChildNumber other) {
// note that in this implementation compareTo() is not consistent with equals()
return Integer.compare(this.num(), other.num());
}
}