Hi Jay, Hi Brent, Sorry. It looks like I was not clear enough. My question was not related to the discussed MD5 strength that occurred during the last week. Public key is not needed very often, no need to pay attention to the speed of fingerprint generation. I was talking about Hash usage in many networking protocols, where it delays a network control plane message. Eduard -----Original Message----- From: Jay Acuna via NANOG <[email protected]> Sent: Friday, September 5, 2025 20:02 To: North American Network Operators Group <[email protected]> Cc: Jay Acuna <[email protected]> Subject: Re: MD5 is slow
On Fri, Sep 5, 2025 at 2:22 AM Vasilenko Eduard via NANOG <[email protected]> wrote: > I have a temptation to ask: why hash in the first place?!? (does not > matter MD5 or SHA-2) The purpose of a hashing is to create a space-efficient figure representing bytes of data. The hashing system is secure or cryptographic If it is intractible to perform specified manipulations, such as deriving bits that were hashed from the output hash (with or without knowing other data bits), creating or altering data given an existing hash and some data such that the output hash will be the same as a pre-chosen hash value, or the same hash value as a prior input, etc. > Any hash MUST be slow (by design) to withstand brute force. In the > network device case, it is about 5ms for SHA-2 (of course, MD5 and SHA-2 are not slow in this sense. They are not designed to withstand "brute force". They are designed with enough bit perturbations to accomplish the fundamental objectives of a secure hash above, but they are not slow enough to protect some small amount of text such as a password. A slow hash would be something like md5crypt, Poul-Henning Kemp's algorithm. PBKDF on SHA-2. Or 100,000 rounds of MD5 or SHA-2, rather than a single round. BCrypt, etc. Hashes designed for greater brute force resistance, but these can be more quickly obsoleted for this purpose than the underlying SHA-2, etc, which are not resistant to brute force. I think your latency figures have to do with a specific software implementation. These numbers vary depending on implementation and computing power. Most likely your latency calculation is for evaluating a single hash value, but brute force attacks would use unique customized implementations of the hashing algorithm designed to perform billions of Hash operations in parallel at a much greater volume of operations per second. For example, a Massively-multithreaded parallel implementation performing a billion simultaneous MD5 operations for brute force purposes Can take certain computations MD5 normally performs on each hash _one_ time, and copy the calculation result as the starting point across all the parallel hashing instances before MD5 computation unique to each attempt starts. Only a part of the implementation's equivalent to the final MD5Update() on the last block of input has to be repeated upon each parallel element. In reality parts of the MD5 algorithm may be further separable allowing for greater volume of processing in a parallel implementation Versus calculating a single hash value. -- -JA _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/SBAFN4EFNFLMZWMKOSMJGUT4IGOZ53PB/ _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/AA6KAA4XOLKSSR6XL7FKVYZCQRWIEWRI/
