Package org.bitcoinj.base

Class Sha256Hash

java.lang.Object

org.bitcoinj.base.Sha256Hash

All Implemented Interfaces:

java.lang.Comparable<Sha256Hash>

public class Sha256Hash
extends java.lang.Object
implements java.lang.Comparable<Sha256Hash>

A Sha256Hash wraps a byte[] so that equals(java.lang.Object) and hashCode() work correctly, allowing it to be used as a key in a map. It also checks that the length is correct (equal to LENGTH) and provides a bit more type safety.

Given that Sha256Hash instances can be created using wrapReversed(byte[]) or twiceOf(byte[]) or by wrapping raw bytes, there is no guarantee that if two Sha256Hash instances are found equal (via equals(Object)) that their preimages would be the same (even in the absence of a hash collision.)

Field Summary

Fields

Modifier and Type	Field	Description
static int	LENGTH
static Sha256Hash	ZERO_HASH

Method Summary

Modifier and Type	Method	Description
int	compareTo(Sha256Hash other)
boolean	equals(java.lang.Object o)
byte[]	getBytes()	Returns the internal byte array, without defensively copying.
static byte[]	hash(byte[] input)	Calculates the SHA-256 hash of the given bytes.
static byte[]	hash(byte[] input, int offset, int length)	Calculates the SHA-256 hash of the given byte range.
int	hashCode()	Returns the last four bytes of the wrapped hash.
static byte[]	hashTwice(byte[] input)	Calculates the SHA-256 hash of the given bytes, and then hashes the resulting hash again.
static byte[]	hashTwice(byte[] input1, byte[] input2)	Calculates the hash of hash on the given chunks of bytes.
static byte[]	hashTwice(byte[] input, int offset, int length)	Calculates the SHA-256 hash of the given byte range, and then hashes the resulting hash again.
static byte[]	hashTwice(byte[] input1, int offset1, int length1, byte[] input2, int offset2, int length2)	Calculates the hash of hash on the given byte ranges.
static java.security.MessageDigest	newDigest()	Returns a new SHA-256 MessageDigest instance.
static Sha256Hash	of(byte[] contents)	Creates a new instance containing the calculated (one-time) hash of the given bytes.
static Sha256Hash	of(java.io.File file)	Creates a new instance containing the calculated (one-time) hash of the given file's contents.
static Sha256Hash	read(java.nio.ByteBuffer buf)	Create a new instance by reading from the given buffer.
byte[]	serialize()	Allocates a byte array and writes the hash into it, in reversed order.
java.math.BigInteger	toBigInteger()	Returns the bytes interpreted as a positive integer.
java.lang.String	toString()
static Sha256Hash	twiceOf(byte[] contents)	Creates a new instance containing the hash of the calculated hash of the given bytes.
static Sha256Hash	twiceOf(byte[] content1, byte[] content2)	Creates a new instance containing the hash of the calculated hash of the given bytes.
static Sha256Hash	wrap(byte[] rawHashBytes)	Creates a new instance that wraps the given hash value.
static Sha256Hash	wrap(java.lang.String hexString)	Creates a new instance that wraps the given hash value (represented as a hex string).
static Sha256Hash	wrapReversed(byte[] rawHashBytes)	Creates a new instance that wraps the given hash value, but with byte order reversed.
java.nio.ByteBuffer	write(java.nio.ByteBuffer buf)	Write hash into the given buffer.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

LENGTH

public static final int LENGTH

See Also:

Constant Field Values

ZERO_HASH

public static final Sha256Hash ZERO_HASH

Method Detail

wrap

public static Sha256Hash wrap(byte[] rawHashBytes)

Creates a new instance that wraps the given hash value.

Parameters:

rawHashBytes - the raw hash bytes to wrap

Returns:

a new instance

Throws:

java.lang.IllegalArgumentException - if the given array length is not exactly 32

wrap

public static Sha256Hash wrap(java.lang.String hexString)

Creates a new instance that wraps the given hash value (represented as a hex string).

Parameters:

hexString - a hash value represented as a hex string

Returns:

a new instance

Throws:

java.lang.IllegalArgumentException - if the given string is not a valid hex string, or if it does not represent exactly 32 bytes

wrapReversed

public static Sha256Hash wrapReversed(byte[] rawHashBytes)

Creates a new instance that wraps the given hash value, but with byte order reversed.

Parameters:

rawHashBytes - the raw hash bytes to wrap

Returns:

a new instance

Throws:

java.lang.IllegalArgumentException - if the given array length is not exactly 32

read

public static Sha256Hash read(java.nio.ByteBuffer buf)
                       throws java.nio.BufferUnderflowException

Create a new instance by reading from the given buffer.

Parameters:

buf - buffer to read from

Returns:

a new instance

Throws:

java.nio.BufferUnderflowException - if the read hash extends beyond the remaining bytes of the buffer

of

public static Sha256Hash of(byte[] contents)

Creates a new instance containing the calculated (one-time) hash of the given bytes.

Parameters:

contents - the bytes on which the hash value is calculated

Returns:

a new instance containing the calculated (one-time) hash

twiceOf

public static Sha256Hash twiceOf(byte[] contents)

Creates a new instance containing the hash of the calculated hash of the given bytes.

Parameters:

contents - the bytes on which the hash value is calculated

Returns:

a new instance containing the calculated (two-time) hash

twiceOf

public static Sha256Hash twiceOf(byte[] content1,
                                 byte[] content2)

Creates a new instance containing the hash of the calculated hash of the given bytes.

Parameters:

content1 - first bytes on which the hash value is calculated

content2 - second bytes on which the hash value is calculated

Returns:

a new instance containing the calculated (two-time) hash

of

public static Sha256Hash of(java.io.File file)
                     throws java.io.IOException

Creates a new instance containing the calculated (one-time) hash of the given file's contents. The file contents are read fully into memory, so this method should only be used with small files.

Parameters:

file - the file on which the hash value is calculated

Returns:

a new instance containing the calculated (one-time) hash

Throws:

java.io.IOException - if an error occurs while reading the file

newDigest

public static java.security.MessageDigest newDigest()

Returns a new SHA-256 MessageDigest instance. This is a convenience method which wraps the checked exception that can never occur with a RuntimeException.

Returns:

a new SHA-256 MessageDigest instance

hash

public static byte[] hash(byte[] input)

Calculates the SHA-256 hash of the given bytes.

Parameters:

input - the bytes to hash

Returns:

the hash (in big-endian order)

hash

public static byte[] hash(byte[] input,
                          int offset,
                          int length)

Calculates the SHA-256 hash of the given byte range.

Parameters:

input - the array containing the bytes to hash

offset - the offset within the array of the bytes to hash

length - the number of bytes to hash

Returns:

the hash (in big-endian order)

hashTwice

public static byte[] hashTwice(byte[] input)

Calculates the SHA-256 hash of the given bytes, and then hashes the resulting hash again.

Parameters:

input - the bytes to hash

Returns:

the double-hash (in big-endian order)

hashTwice

public static byte[] hashTwice(byte[] input1,
                               byte[] input2)

Calculates the hash of hash on the given chunks of bytes. This is equivalent to concatenating the two chunks and then passing the result to hashTwice(byte[]).

hashTwice

public static byte[] hashTwice(byte[] input,
                               int offset,
                               int length)

Calculates the SHA-256 hash of the given byte range, and then hashes the resulting hash again.

Parameters:

input - the array containing the bytes to hash

offset - the offset within the array of the bytes to hash

length - the number of bytes to hash

Returns:

the double-hash (in big-endian order)

hashTwice

public static byte[] hashTwice(byte[] input1,
                               int offset1,
                               int length1,
                               byte[] input2,
                               int offset2,
                               int length2)

Calculates the hash of hash on the given byte ranges. This is equivalent to concatenating the two ranges and then passing the result to hashTwice(byte[]).

equals

public boolean equals(java.lang.Object o)

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Returns the last four bytes of the wrapped hash. This should be unique enough to be a suitable hash code even for blocks, where the goal is to try and get the first bytes to be zeros (i.e. the value as a big integer lower than the target value).

Overrides:

hashCode in class java.lang.Object

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

toBigInteger

public java.math.BigInteger toBigInteger()

Returns the bytes interpreted as a positive integer.

getBytes

public byte[] getBytes()

Returns the internal byte array, without defensively copying. Therefore do NOT modify the returned array.

serialize

public byte[] serialize()

Allocates a byte array and writes the hash into it, in reversed order.

Returns:

byte array containing the hash

write

public java.nio.ByteBuffer write(java.nio.ByteBuffer buf)
                          throws java.nio.BufferOverflowException

Write hash into the given buffer.

Parameters:

buf - buffer to write into

Returns:

the buffer

Throws:

java.nio.BufferOverflowException - if the hash doesn't fit the remaining buffer

compareTo

public int compareTo(Sha256Hash other)

Specified by:

compareTo in interface java.lang.Comparable<Sha256Hash>