Method KDF

security/src/main/java/pro/tools/security/sm/SM2.java:159–179

密钥派生函数 @param Z @param klen 生成klen字节数长度的密钥 @return

(byte[] Z, int klen)

     * @return
     */
    private static byte[] KDF(byte[] Z, int klen) {
        int ct = 1;
        int end = (int) Math.ceil(klen * 1.0 / 32);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            for (int i = 1; i < end; i++) {
                baos.write(sm3hash(Z, SM3.toByteArray(ct)));
                ct++;
            }
            byte[] last = sm3hash(Z, SM3.toByteArray(ct));
            if (klen % 32 == 0) {
                baos.write(last);
            } else {
                baos.write(last, 0, klen % 32);
            }
            return baos.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 判断字节数组是否全0