Rijndael specification allows 32-byte block size (AES standard doesn't), don't know about Rijndael Crypto++ implementation (since in general this block size is supported by the library, see no reason why not).
If CFB mode is used, it is not recommended to use less than the full block feedback for cryptographic reasons. I recall that PGP used to have a weird modification of CFB back when. To the Original Poster: you can't do what you want with AES, period. If you can't reconfigure that server to use a standard algorithm - you're stuck with Rijndael, which is supported by Crypto ++. -- Regards, Mouse On Dec 23, 2012 1:45 AM, "Jeffrey Walton" <[email protected]> wrote: > > > On Dec 22, 9:02 pm, Jamaal Scarlett <[email protected]> wrote: > > I wrote a test program and the output for the mcrypt function > > : mcrypt_module_get_algo_block_size(MCRYPT_RIJNDAEL_256, NULL) is 32. > The > > key lengths from all three libraries is 32. > No. The key length is 32 byte in the case of AES-256. Its 24 bytes > with AES-192, and 16 bytes with AES-128. The block size is always 16 > bytes. csrc.nist.gov/publications/fips/fips197/fips-197.pdf. > > Rijndael may allow for a 32 byte block size. I don't know about > additional configurations because I don't use it in non-NIST > configurations. > > mcrypt has a unique feedback size, if I recall correctly. It has had > interop problems since the time I can remember. > http://www.google.com/#q=cryptopp+mcryptt+feedback+size. > > Jeff > > On Saturday, December 22, 2012 8:47:15 PM UTC-5, Mouse wrote: > > > > > The simple answer for AES is you can't. AES allows three key lengths > (128, > > > 192, 256 bits), but only one block size (128 bits). AES prototype > Rijndael > > > allowed three block sizes as well. > > > > > Perhaps by Rijndael-256 they meant only the key length? In that case I > > > would check the encryption mode, padding, etc. match what that server > is > > > set up with. > > > -- > > > Regards, > > > Mouse > > > On Dec 22, 2012 8:30 PM, "Jamaal Scarlett" <[email protected] > <javascript:>> > > > wrote: > > > > >> I need to use AES, the server I am communicating with is using > > >> mcrypt with the encryption mode set to RIJNDAEL_256. From what I have > > >> found online, this is a non-standard algorithm. I have tried both > crypto++ > > >> and OpenSSL's crypto library and while their encrypted outputs match, > I > > >> cannot get either to match the output from mcrypt. I would use > mcrypt, but > > >> there is a memory leak in the init function of the version I am > > >> using(2.5.7) and I am unable to find the lib(libmcrypt.lib) file for > any > > >> more recent version of the mcrypt library. > > > > >> Thanks for the help, > > >> Jamaal > > > > >> On Saturday, December 22, 2012 4:05:32 PM UTC-5, Jeffrey Walton wrote: > > > > >>> On Dec 22, 12:27 pm, Jamaal Scarlett <[email protected]> > > >>> wrote: > > >>> > Thank you for the reply. Upon further reading, it looks like the > 256 > > >>> in > > >>> > mcrypts RIJNDAEL_256 refers to the block cipher size. Does > cryptopp > > >>> aes > > >>> > support a 32-bit block cipher size? > > >>> No, AES is a 16 byte block size. SHACAL2 has a larger block size if > > >>> you need it. > > > > >>> I believe Zooko (correct me here) needed a cipher with a larger block > > >>> size and used SHACAL2 for Tahoe-LFS (http://en.wikipedia.org/wiki/ > > >>> Tahoe-LAFS <http://en.wikipedia.org/wiki/Tahoe-LAFS>). > > > > >>> Jeff > > > > >>> > On Saturday, December 22, 2012 4:11:58 AM UTC-5, Jeffrey Walton > wrote: > > > > >>> > > On Dec 22, 2:21 am, Jamaal Scarlett <[email protected]> > > >>> wrote: > > >>> > > > Is it possible to change key lengths. On the wiki it states > that > > >>> > > 16,24&32 byte keys are supported in aes but I cannot find any > > >>> documentation > > >>> > > on changing itbftomvthe default of 16. I am attempting to > > >>> encrypt/decrypt > > >>> > > data to communicate with a server using mcrypt rijndael 256, > > >>> however there > > >>> > > is a memory leak in the version of mcrypt we are using. Is 256 > bit > > >>> > > supported? > > > > >>> > > Yes. All relevant objects take a key and key size. See, for > example, > > >>> > >http://www.cryptopp.com/wiki/**CBC_mode< > http://www.cryptopp.com/wiki/CBC_mode>. > > > > >> -- > > >> You received this message because you are subscribed to the "Crypto++ > > >> Users" Google Group. > > >> To unsubscribe, send an email to [email protected] > <javascript:> > > >> . > > >> More information about Crypto++ and this group is available at > > >>http://www.cryptopp.com. > > -- > You received this message because you are subscribed to the "Crypto++ > Users" Google Group. > To unsubscribe, send an email to > [email protected]. > More information about Crypto++ and this group is available at > http://www.cryptopp.com. > -- You received this message because you are subscribed to the "Crypto++ Users" Google Group. To unsubscribe, send an email to [email protected]. More information about Crypto++ and this group is available at http://www.cryptopp.com.
