RE: MD5 is slow

[nanog--- via NANOG <nanog () lists nanog org>]

That's your fault for using a dumb password and the hash doesn't help you with that.

On 9 September 2025 10:09:56 CEST, Vasilenko Eduard via NANOG <nanog () lists nanog org> wrote:
> The problem is smaller: the attacker needs to predict only the password; some packets are predictable for 100%.
> The password is the thing that you put at the end of a command: "ip ospf message-digest-key 1 md5 c1$c0"
> How long could the password be? 10-12 letters are considered to be a good password (if upper case, lower case, special 
> letters, numbers), but people typically use just words (only 100k words are typically well-known).
> Then some APTs have billions of typical passwords in the database (prioritized for probability). They could just try 
> them all on a good GPU.
> It is needed for hash to be slow. Hence, for example, SHA-2 consists of "And, Xor, Or, Rot, Shr, Add (mod 2^32)" in 64 
> or 80 rounds! (for every block of 512bits).
> Hence, a few milliseconds twice per every hop for a rather small control plane message.
>
> It is strange for me that nobody cares about this latency.
> Eduard
> -----Original Message-----
> From: Jay Acuna <mysidia () gmail com> 
> Sent: Monday, September 8, 2025 22:26
> To: North American Network Operators Group <nanog () lists nanog org>
> Cc: Saku Ytti <saku () ytti fi>; Dan Collins <dcollinsn () gmail com>; Vasilenko Eduard <vasilenko.eduard () huawei 
> com>
> Subject: Re: MD5 is slow
>
> On Mon, Sep 8, 2025 at 3:00 AM Vasilenko Eduard via NANOG <nanog () lists nanog org> wrote:
>
> > Your comments on the performance are very important.
> > I still believe that any Hash must be slow enough, because if it were 
> > fast, then the attacker could take a big GPU and brute force it  only the password is not known, but could be tested 
> > from the dictionary).
>
> They do not require high latency.  0.1ms per call is still just fine.
> And the concept of brute force a hashing algorithm should resist involves many orders of magnitude more possibilities 
> than contained in a password.
>
> Put it this way:  MD5 has a block size of 512 bit.
> The MD5 algorithm has not failed in its security purpose for a hashing algorithm: If one is able to reverse an input 
> by directly trying every possible input that contains a number of unpredictable bits 447 or less.  Exactly the same 
> way as it's not a MD5 problem if you have a 1-byte password, and someone tried all 255 possibilities.
>
> You really need a bare minimum of least a block of input; if not more to properly use
> MD5 and similar secure hashing algorithms. Predictable bits also don't help against guessing, so you should consider 
> this as 512 bits of entropy on the input or more to safely use a hashing procedure calculated on 512-bit blocks.
> I also read MD5 input shorter than 512 must be padded congruent to 448 modulo 512.
>
> SHA-2 is similar. You need more bits than a typical password would contain.
>
> Standard secure hashing algorithms are not designed to save you in case your input contains fewer random bits.
>
> You have the option of using a key-stretching algorithm instead of a straight hash. PBKDF2, as mentioned before.  
> Multiple rounds of hashing chained in a certain manner can cause delays for brute force guessing.
>
> A dictionary word contains about 4-bits worth of entropy.  If the 512 bits are not filled, the input is to be padded 
> with bits in front of your password, which are predictable, so they don't count.  That is far from enough 
> unpredictable bits to directly use MD5.
>
> From a randomized password; you get approximately 6 to 7 bits worth of entropy per character, so a good password 
> length input for MD5 would be at about 85 random characters.
>
> --
> -JA
> _______________________________________________
> NANOG mailing list 
> https://lists.nanog.org/archives/list/nanog () lists nanog org/message/4LFVVQ7VGFM76EPKKFRSEAAXHKBGCREV/
_______________________________________________
NANOG mailing list 
https://lists.nanog.org/archives/list/nanog () lists nanog org/message/BNJWFADODFXFOURBOKXOAW2FQW2R5L5W/