question: public static MasterPrivateKey create ( byte [ ] seed ) throws HyperLedgerException { try { Mac mac = Mac . getInstance ( "HmacSHA512" , "BC" ) ; SecretKey seedkey = new SecretKeySpec ( BITCOIN_SEED , "HmacSHA512" ) ; mac . init ( seedkey ) ; byte [ ] lr = mac . doFinal ( seed ) ; byte [ ] l = Arrays . copyOfRange ( lr , 0 , 32 ) ; byte [ ] r = Arrays . copyOfRange ( lr , 32 , 64 ) ; BigInteger m = new BigInteger ( 1 , l ) ; if ( m . compareTo ( curve . getN ( ) ) >= 0 || m . compareTo ( BigInteger . ZERO ) == 0 ) { throw new HyperLedgerException ( "This is rather unlikely, but it did just happen" ) ; } PrivateKey keyPair = new PrivateKey ( m , true ) ; return new MasterPrivateKey ( keyPair , r , 0 , 0 , 0 ) ; } catch ( NoSuchAlgorithmException | InvalidKeyException | NoSuchProviderException e ) { throw new HyperLedgerException ( e ) ; } }
target:  Create a MasterPrivateKey from a plain text seed. The seed is stretched/resized to 64 bytes with HmacSHA512