Re: [Qemu-devel] [PATCH v2 03/17] crypto: add support for PBKDF2 algorithm

From: "Daniel P. Berrange" <berrange@redhat.com>
To: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2 03/17] crypto: add support for PBKDF2 algorithm
Date: Thu, 21 Jan 2016 10:59:35 +0000	[thread overview]
Message-ID: <20160121105935.GF19835@redhat.com> (raw)
In-Reply-To: <20160121065924.GE31960@ad.usersys.redhat.com>

On Thu, Jan 21, 2016 at 02:59:24PM +0800, Fam Zheng wrote:
> On Wed, 01/20 17:38, Daniel P. Berrange wrote:
> > The LUKS data format includes use of PBKDF2 (Password-Based
> > Key Derivation Function). The Nettle library can provide
> > an implementation of this, but we don't want code directly
> > depending on a specific crypto library backend. Introduce
> > a include/crypto/pbkdf.h header which defines a QEMU
> > API for invoking PBKDK2. The initial implementations are
> > backed by nettle & gcrypt, which are commonly available
> > with distros shipping GNUTLS.
> > 
> > The test suite data is taken from the cryptsetup codebase
> > under the LGPLv2.1+ license. This merely aims to verify
> > that whatever backend we provide for this function in QEMU
> > will comply with the spec.
> > 
> > Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> > ---
> >  crypto/Makefile.objs      |   6 +-
> >  crypto/pbkdf-gcrypt.c     |  65 ++++++++
> >  crypto/pbkdf-nettle.c     |  64 ++++++++
> >  crypto/pbkdf-stub.c       |  41 +++++
> >  crypto/pbkdf.c            |  68 +++++++++
> >  include/crypto/pbkdf.h    | 152 +++++++++++++++++++
> >  tests/.gitignore          |   1 +
> >  tests/Makefile            |   2 +
> >  tests/test-crypto-pbkdf.c | 378 ++++++++++++++++++++++++++++++++++++++++++++++
> >  9 files changed, 776 insertions(+), 1 deletion(-)
> >  create mode 100644 crypto/pbkdf-gcrypt.c
> >  create mode 100644 crypto/pbkdf-nettle.c
> >  create mode 100644 crypto/pbkdf-stub.c
> >  create mode 100644 crypto/pbkdf.c
> >  create mode 100644 include/crypto/pbkdf.h
> >  create mode 100644 tests/test-crypto-pbkdf.c
> > 
> > +int qcrypto_pbkdf2(QCryptoHashAlgorithm hash,
> > +                   const uint8_t *key, size_t nkey,
> > +                   const uint8_t *salt, size_t nsalt,
> > +                   unsigned int iterations,
> > +                   uint8_t *out, size_t nout,
> > +                   Error **errp)
> > +{
> > +    static const int hash_map[QCRYPTO_HASH_ALG__MAX] = {
> > +        [QCRYPTO_HASH_ALG_MD5] = GCRY_MD_MD5,
> > +        [QCRYPTO_HASH_ALG_SHA1] = GCRY_MD_SHA1,
> > +        [QCRYPTO_HASH_ALG_SHA256] = GCRY_MD_SHA256,
> > +    };
> > +    int ret;
> > +
> > +    if (hash > G_N_ELEMENTS(hash_map)) {
> 
> Do you want ">="?

Yes.

> 
> > +        error_setg(errp, "Unexpected hash algorithm %d", hash);
> > +        return -1;
> > +    }
> > +
> > +    ret = gcry_kdf_derive(key, nkey, GCRY_KDF_PBKDF2,
> > +                          hash_map[hash],
> > +                          salt, nsalt, iterations,
> > +                          nout, out);
> 
> We go ahead with QCRYPTO_HASH_ALG_MD5 here, but we didn't accept it in
> qcrypto_pbkdf2_supports, is that a mistake?

Yes, I should have reported MD5 in the earlier function, since
gcrypt allows that.

> > diff --git a/crypto/pbkdf.c b/crypto/pbkdf.c
> > new file mode 100644
> > index 0000000..71f96cd
> > --- /dev/null
> > +++ b/crypto/pbkdf.c
> > @@ -0,0 +1,68 @@
> > +/*
> > + * QEMU Crypto PBKDF support (Password-Based Key Derivation Function)
> > + *
> > + * Copyright (c) 2015-2016 Red Hat, Inc.
> > + *
> > + * This library is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2 of the License, or (at your option) any later version.
> > + *
> > + * This library is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with this library; if not, see <http://www.gnu.org/licenses/>.
> > + *
> > + */
> > +
> > +#include "crypto/pbkdf.h"
> > +#include <sys/resource.h>
> > +
> > +
> > +int qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
> > +                               const uint8_t *key, size_t nkey,
> > +                               const uint8_t *salt, size_t nsalt,
> > +                               Error **errp)
> > +{
> > +    uint8_t out[32];
> > +    int iterations = (1 << 15);
> 
> To be safe from overflow, I'd use at least 64 bits to do the math, just in case
> that some machine is too good at computing this stuff. :)

Hmm, probably need to change the return type to be 64 bit too then

> 
> > +    struct rusage start, end;
> > +    unsigned long long delta;
> > +
> > +    while (1) {
> > +        if (getrusage(RUSAGE_THREAD, &start) < 0) {
> > +            error_setg_errno(errp, errno, "Unable to get thread CPU usage");
> > +            return -1;
> > +        }
> > +        if (qcrypto_pbkdf2(hash,
> > +                           key, nkey,
> > +                           salt, nsalt,
> > +                           iterations,
> > +                           out, sizeof(out),
> > +                           errp) < 0) {
> > +            return -1;
> > +        }
> > +        if (getrusage(RUSAGE_THREAD, &end) < 0) {
> > +            error_setg_errno(errp, errno, "Unable to get thread CPU usage");
> > +            return -1;
> > +        }
> > +
> > +        delta = (((end.ru_utime.tv_sec * 1000ll) +
> > +                  (end.ru_utime.tv_usec / 1000)) -
> > +                 ((start.ru_utime.tv_sec * 1000ll) +
> > +                  (start.ru_utime.tv_usec / 1000)));
> > +
> > +        if (delta > 500) {
> > +            break;
> > +        } else if (delta < 100) {
> > +            iterations = iterations * 10;
> > +        } else {
> > +            iterations = (iterations * 1000 / delta);
> > +        }
> > +    }
> > +
> > +    return iterations * 1000 / delta;
> > +}
> > +/**
> > + * This module provides an interface to the PBKDF2 algorithm
> > + *
> > + *   https://en.wikipedia.org/wiki/PBKDF2
> > + *
> > + * <example>
> > + *   <title>Generating a AES encryption key from a user password</title>
> 
> s/a AES/an AES/ ?

Yes

Regards,
Daniel
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