On 11 July 2014 08:30, Andy Polyakov via RT <r...@openssl.org> wrote: >>> openssl enc command with -aes-xxx-xts doesnt work if an IV is specified >> >> When you say it "doesn't work", what do you mean? Do you get an error? If so >> what is it? > > If only it was the actual problem. The thing is that *if* one wants to > make enc work with XTS, it has to be treated specially, i.e. not as any > other cipher. See http://marc.info/?t=136844751600003&r=1&w=2 for > additional info. Another alternative to custom header mentioned in > referred thread can be to adhere to pre-defined fixed block size and > read 16 bytes ahead, so that when one hits end of file, and finds that > total_size%fixed_block_size<16, one can expand last block with > total_size%fixed_block_size. I mean last block would be variable size > from 16 up to fixed_block_size + 15 bytes, so that one doesn't have to > make up padding scheme. > >>> as below: >>> openssl enc -engine af_alg -aes-256-xts -in <plaintext_file> -out >>> <output_encrypted_file> -K >>> 0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef -iv >>> 00000000000000000000000000000000 >> >> I notice you have installed a custom engine. Does it advertise XTS support? >> What happens if you do not use the engine? > > I'm not saying that it's the case here, but it should be noted that in > this case engine can impose own behaviour on enc. Most notably it can > trick enc to treating whole file as one single sector [which is not > necessarily cryptographically sound]. > > Bottom line [still] is that enc is not the place to perform XTS, > *unless* it's treated specially. In other words question should not be > about setting IV, but about *if* XTS should be supported by enc, and if > so, how exactly.
It seems to me this is why jamming modes like XTS into standard EVP as if they were like other modes is a less than great idea. ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List openssl-dev@openssl.org Automated List Manager majord...@openssl.org
