code: public static ECKey signatureToKey(byte[] messageHash, String signatureBase64) throws SignatureException {
          final byte[] keyBytes = signatureToKeyBytes(messageHash, signatureBase64);
          return ECKey.fromPublicOnly(keyBytes);
      }
docs: Compute the key that signed the given signature.
  
  @param messageHash
  32-byte hash of message
  @param signatureBase64
  Base-64 encoded signature
  @return ECKey
  @throws SignatureException
  SignatureException