org.web3j.crypto

Class MnemonicUtils

java.lang.Object

org.web3j.crypto.MnemonicUtils

public class MnemonicUtils
extends java.lang.Object

Provides utility methods to generate random mnemonics and also generate seeds from mnemonics.

See Also:

Mnemonic code for generating deterministic keys

Constructor Summary

Constructors

Constructor and Description
MnemonicUtils()

Method Summary

Modifier and Type	Method and Description
static byte	calculateChecksum(byte[] initialEntropy)
static byte[]	generateEntropy(java.lang.String mnemonic) Create entropy from the mnemonic.
static java.lang.String	generateMnemonic(byte[] initialEntropy) The mnemonic must encode entropy in a multiple of 32 bits.
static byte[]	generateSeed(java.lang.String mnemonic, java.lang.String passphrase) To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt.
static java.util.List<java.lang.String>	getWords()
static boolean	validateMnemonic(java.lang.String mnemonic)

Methods inherited from class java.lang.Object

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

Constructor Detail

MnemonicUtils

public MnemonicUtils()

Method Detail

generateMnemonic

public static java.lang.String generateMnemonic(byte[] initialEntropy)

The mnemonic must encode entropy in a multiple of 32 bits. With more entropy security is improved but the sentence length increases. We refer to the initial entropy length as ENT. The allowed size of ENT is 128-256 bits.

Mnemonic generation algorithm

Given a randomly generated initial entropy of size ENT, first a checksum is generated by taking the first ENT / 32 bits of its SHA256 hash. This checksum is appended to the end of the initial entropy. Next, these concatenated bits are split into groups of 11 bits, each encoding a number from 0-2047, serving as an index into a wordlist. Finally, we convert these numbers into words and use the joined words as a mnemonic sentence.

Parameters:

initialEntropy - The initial entropy to generate mnemonic from

Returns:

The generated mnemonic

Throws:

java.lang.IllegalArgumentException - If the given entropy is invalid

java.lang.IllegalStateException - If the word list has not been loaded

generateEntropy

public static byte[] generateEntropy(java.lang.String mnemonic)

Create entropy from the mnemonic.

Parameters:

mnemonic - The input mnemonic which should be 128-160 bits in length containing only valid words

Returns:

Byte array representation of the entropy

getWords

public static java.util.List<java.lang.String> getWords()

generateSeed

public static byte[] generateSeed(java.lang.String mnemonic,
                                  java.lang.String passphrase)

To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes).

Parameters:

mnemonic - The input mnemonic which should be 128-160 bits in length containing only valid words

passphrase - The passphrase which will be used as part of salt for PBKDF2 function

Returns:

Byte array representation of the generated seed

validateMnemonic

public static boolean validateMnemonic(java.lang.String mnemonic)

calculateChecksum

public static byte calculateChecksum(byte[] initialEntropy)