It is probably a 512 bit decryption key. It is a string of 128 hexadecimal characters. Each hexadecimal character can represent a decimal value between 0 and 16. It requires 4 bits to store a hexadecimal character. Since the string is 128 characters in length, it is a 512 bit key (128 characters * 4 bits per character). A 512 bit key is considered strong. >>> len("86d53c1315f42ea48caa0dc1b82a1c61e988b1035db897e90c2303c05d8721648ca816eada320c950b75985575b495a12c06d0a0ba77b9e23ccbd7d31b5bd035") 128 >>> 128*4 512