The DES modes are good for protecting a secret plaintext with a DES key, but in our case we have a short, known plaintext - the username, which is encrypted with the password (or with blocks of the password phrase). So we have a long key with a short plaintext, instead of a long plaintext with a short key. IBM has tried to sort of adapt the CBC mode to this scenario, but did not word out very well.
Costin On 3 Sep 2013, at 16:42, Paul Gilmartin <paulgboul...@aim.com> wrote: > On Tue, 3 Sep 2013 14:41:49 +0100, Costin Enache wrote: >> >>> The password phrase hash can be split into blocks of 8 bytes, and each of >>> them "cracked" independently, also in parallel. >> Sounds like a half-hearted implementation -- what would have been the >> additional cost of using larger blocks? > So I look at: > > http://en.wikipedia.org/wiki/Data_Encryption_Standard > > (Yah, I know; "Wikipedia"), which says: > > Like other block ciphers, DES by itself is not a secure means of encryption > but must instead be used in a mode of operation. FIPS-81 specifies several > modes for use with DES.[20] Further comments on the usage of DES are > contained in FIPS-74.[21] > > And from FIPS-81: > > http://www.itl.nist.gov/fipspubs/fip81.htm > > which seems to be rife with typos, confusing "zero" with "oscar" (not even > "Oscar"), it would appear that the passphrase handling is using the simplest > method, ECB, which is susceptible to paralleization. Other methods, CBC, > CFB, and OFB would seem to resist parallelization and to be stronger. > >> Not possible directly with DES, but there are many other alternatives >> which would be quite secure at no additional cost. I have no idea why >> the password phrase is encrypted in this way, considering the available >> modern technology already employed by RACF. > > I see. > > -- gil > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
