lkml.org 
[lkml]   [2016]   [Jun]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v6 3/6] crypto: AF_ALG -- add asymmetric cipher interface
    Hi Stephan,

    On 16 June 2016 at 10:05, Stephan Mueller <smueller@chronox.de> wrote:
    > Am Dienstag, 14. Juni 2016, 09:42:34 schrieb Andrew Zaborowski:
    >
    > Hi Andrew,
    >
    >> >
    >> > I think we have agreed on dropping the length enforcement at the interface
    >> > level.
    >>
    >> Separately from this there's a problem with the user being unable to
    >> know if the algorithm is going to fail because of destination buffer
    >> size != key size (including kernel users). For RSA, the qat
    >> implementation will fail while the software implementation won't. For
    >> pkcs1pad(...) there's currently just one implementation but the user
    >> can't assume that.
    >
    > If I understand your issue correctly, my initial code requiring the caller to
    > provide sufficient memory would have covered the issue, right?

    This isn't an issue with AF_ALG, I should have changed the subject
    line perhaps. In this case it's an inconsistency between some
    implementations and the documentation (header comment). It affects
    users accessing the cipher through AF_ALG but also directly.

    > If so, we seem
    > to have implementations which can handle shorter buffer sizes and some which
    > do not. Should a caller really try to figure the right buffer size out? Why
    > not requiring a mandatory buffer size and be done with it? I.e. what is the
    > gain to allow shorter buffer sizes (as pointed out by Mat)?

    It's that client code doesn't need an intermediate layer with an
    additional buffer and a memcpy to provide a sensible API. If the code
    wants to decrypt a 32-byte Digest Info structure with a given key or a
    reference to a key it makes no sense, logically or in terms of
    performance, for it to provide a key-sized buffer.

    In the case of the userspace interface I think it's also rare for a
    recv() or read() on Linux to require a buffer larger than it's going
    to use, correct me if i'm wrong. (I.e. fail if given a 32-byte
    buffer, return 32 bytes of data anyway) Turning your questino around
    is there a gain from requiring larger buffers?

    Best regards

    \
     
     \ /
      Last update: 2016-06-16 17:41    [W:7.169 / U:0.064 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site