On Monday, May 11, 2015 12:04:19 PM Douglas Otis wrote: > On 5/11/15 10:06 AM, Scott Kitterman wrote: > > RFC 6376 (which I think is the latest) includes: > >> 3.3.3. Key Sizes > >> > >> Selecting appropriate key sizes is a trade-off between cost, > >> performance, and risk. Since short RSA keys more easily succumb to > >> off-line attacks, Signers MUST use RSA keys of at least 1024 bits for > >> long-lived keys. Verifiers MUST be able to validate signatures with > >> keys ranging from 512 bits to 2048 bits, and they MAY be able to > >> validate signatures with larger keys. Verifier policies may use the > >> length of the signing key as one metric for determining whether a > >> signature is acceptable. > > > > Since receivers have no good way of knowing what keys are long-lived, > > there's no way on the receiver side to reliably determine if a key > > shorter than 1024 bits is being appropriately used or not. I think it's > > time to kill keys shorter than 1024 bits dead. It's not like the risks > > associated with them are new [1]. > > > > I propose a short draft that updates 6376 to say MUST use at least 1024 > > bits and setting that as the minimum size verifiers must be able to > > validate. I'm volunteering to write it if people agree it's appropriate. > > > > Scott K > > > > > > [1] http://www.wired.com/2012/10/dkim-vulnerability-widespread/ > > Dear Scott, > > Signatures normally offer options not easily supported by > DKIM. One being use of a binary keys, rather than base64. > Indeed shorter keys were a mistake. What other mistakes > should be corrected? I can name a few.
I'm not particularly interested in a comprehensive update to DKIM. Time has passed. Moore's Law has operated. It's time to change the minimum key size (past time, IMO). I'd much rather get that done as I don't think it will be controversial rather than get into a broader debate that might get bogged down. Scott K _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html
