Hi,
MD5 was marked incompliant with FIPS in 2009:
a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
But hibernation_e820_save() is still using MD5, and fails in FIPS mode
due to the 2018 patch:
749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
As a result, hibernation doesn't work when FIPS is on.
Do you think if hibernation_e820_save() should be changed to use a
FIPS-compliant algorithm like SHA-1?
PS, currently it looks like FIPS mode is broken in the mainline:
https://www.mail-archive.com/[email protected]/msg49414.html
Thanks,
-- Dexuan
On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
>
> Hi,
> MD5 was marked incompliant with FIPS in 2009:
> a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
>
> But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> due to the 2018 patch:
> 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
>
> As a result, hibernation doesn't work when FIPS is on.
>
> Do you think if hibernation_e820_save() should be changed to use a
> FIPS-compliant algorithm like SHA-1?
I would say yes, it should.
> PS, currently it looks like FIPS mode is broken in the mainline:
> https://www.mail-archive.com/[email protected]/msg49414.html
On 3/30/21 10:46 AM, Rafael J. Wysocki wrote:
> On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
>> Hi,
>> MD5 was marked incompliant with FIPS in 2009:
>> a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
>> a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
>>
>> But hibernation_e820_save() is still using MD5, and fails in FIPS mode
>> due to the 2018 patch:
>> 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
>>
>> As a result, hibernation doesn't work when FIPS is on.
>>
>> Do you think if hibernation_e820_save() should be changed to use a
>> FIPS-compliant algorithm like SHA-1?
> I would say yes, it should.
If we're not actually encrypting anything, shouldn't something like
ghash work as well?
>
>> PS, currently it looks like FIPS mode is broken in the mainline:
>> https://www.mail-archive.com/[email protected]/msg49414.html
On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > Hi,
> > MD5 was marked incompliant with FIPS in 2009:
> > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> >
> > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > due to the 2018 patch:
> > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> >
> > As a result, hibernation doesn't work when FIPS is on.
> >
> > Do you think if hibernation_e820_save() should be changed to use a
> > FIPS-compliant algorithm like SHA-1?
>
> I would say yes, it should.
>
> > PS, currently it looks like FIPS mode is broken in the mainline:
> > https://www.mail-archive.com/[email protected]/msg49414.html
FYI, SHA-1 is not a good choice, it is only permitted in HMAC
constructions and only for specified uses. If you need to change
algorithm you should go straight to SHA-2 or SHA-3 based hashes.
HTH,
Simo.
--
Simo Sorce
RHEL Crypto Team
Red Hat, Inc
On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
>
> On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > Hi,
> > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > >
> > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > due to the 2018 patch:
> > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > >
> > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > >
> > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > FIPS-compliant algorithm like SHA-1?
> > > >
> > > > I would say yes, it should.
> > > >
> > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > >
> > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > constructions and only for specified uses. If you need to change
> > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > >
> >
> > What is the reason for using a [broken] cryptographic hash here? if
> > this is just an integrity check, better use CRC32
>
> If the integrity check is used exclusively to verify there were no
> accidental changes and is not used as a security measure, by all means
> I agree that using crc32 is a better idea.
>
Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
this, it is only a best effort check which is simply omitted if md5
happens to be unavailable, so there is definitely no need for crypto
here.
On Thu, 2021-04-01 at 18:31 +0200, Rafael J. Wysocki wrote:
> On Thu, Apr 1, 2021 at 6:22 PM Simo Sorce <[email protected]> wrote:
> > On Thu, 2021-04-01 at 18:02 +0200, Rafael J. Wysocki wrote:
> > > On Thu, Apr 1, 2021 at 3:54 PM Ard Biesheuvel <[email protected]> wrote:
> > > > On Thu, 1 Apr 2021 at 15:38, Rafael J. Wysocki <[email protected]> wrote:
> > > > > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> > > > > > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> > > > > > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > > > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > > > > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > > > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > > > > > > Hi,
> > > > > > > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > > > > > > >
> > > > > > > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > > > > > > due to the 2018 patch:
> > > > > > > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > > > > > > >
> > > > > > > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > > > > > > >
> > > > > > > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > > > > > > FIPS-compliant algorithm like SHA-1?
> > > > > > > > > >
> > > > > > > > > > I would say yes, it should.
> > > > > > > > > >
> > > > > > > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > > > > > > >
> > > > > > > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > > > > > > constructions and only for specified uses. If you need to change
> > > > > > > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > > > > > > >
> > > > > > > >
> > > > > > > > What is the reason for using a [broken] cryptographic hash here? if
> > > > > > > > this is just an integrity check, better use CRC32
> > > > >
> > > > > Not really.
> > > > >
> > > > > CRC32 is not really sufficient for integrity checking here AFAICS. It
> > > > > might be made a fallback option if MD5 is not available, but making it
> > > > > the default would be somewhat over the top IMO.
> > > > >
> > > > > > > If the integrity check is used exclusively to verify there were no
> > > > > > > accidental changes and is not used as a security measure, by all means
> > > > > > > I agree that using crc32 is a better idea.
> > > > > > >
> > > > > >
> > > > > > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > > > > > this, it is only a best effort check which is simply omitted if md5
> > > > > > happens to be unavailable, so there is definitely no need for crypto
> > > > > > here.
> > > > >
> > > > > Yes, it is about integrity checking only. No, CRC32 is not equivalent
> > > > > to MD5 in that respect AFAICS.
> > > > >
> > > >
> > > > There are two possibilities:
> > > > - we care about an adversary attempting to forge a collision, in which
> > > > case you need a cryptographic hash which is not broken;
> > > > - we only care about integrity, in which case crypto is overkill, and
> > > > CRC32 is sufficient. (Note that the likelihood of an honest,
> > > > inadvertent modification not being caught by CRC32 is 1 in 4 billion)
> > >
> > > That depends on how you count.
> > >
> > > Surely, there are modifications caught by MD5 that will not be caught by CRC32.
> >
> > This is a technically correct statement, but does it matter in this
> > context? (Hint, probably not)
> >
> > > > MD5 does not meet either requirement, given that it is known to be
> > > > broken, and overkill for simple integrity checks. MD5 should be phased
> > > > out and removed, and moving this code onto the correct abstraction
> > > > would be a reasonable step towards that goal.
> > >
> > > This clearly is a matter of opinion.
> >
> > Sorry, but this is not a matter of opinion.
> > The only reason to use a cryptographic hash is that you want to protect
> > from active tampering, rather than from accidental changes. And if you
> > need to protect from active tampering then you cannot use a known
> > broken hash, there is no point.
> >
> > OTOH if you do not care for active tampering but only to catch
> > transmission/storage errors then all you care for is error checking. In
> > that case a cryptographic hash is overkill because it entails a lot
> > more computation than is needed.
>
> But the amount of data in question is not huge in this case.
>
> > > I'm not religious about it though. If there is a general consensus
> > > that CRC32 is sufficient for error detection in hibernation files,
> > > then it can be used. So is there such a consensus and if so, can you
> > > give me a pointer to some research that it is based on?
> >
> > CRC32 is an industry standard to check for accidental modifications of
> > a bit stream. The chances of missing an accidental change are 1 in 4
> > billion.
>
> This is not about accidental change which basically is my point.
>
> The BIOSes in question change the memory map over hibernation/resume,
> because they think that the memory layout is now different, so this is
> about detecting a sort of intentional change. Definitely not random,
> though.
Ok, not random, but also not intentional, it is just "accidental".
> But as stated elsewhere, it is just about failing more gracefully at
> least in some cases, so let's just go ahead with using CRC32 here
> (worst case, it will not fail more gracefully in super-corner cases).
Sounds good.
Simo.
--
Simo Sorce
RHEL Crypto Team
Red Hat, Inc
On 4/1/21 9:38 AM, Rafael J. Wysocki wrote:
> On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
>> On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
>>> On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
>>>> On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
>>>>> On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
>>>>>> On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
>>>>>>> Hi,
>>>>>>> MD5 was marked incompliant with FIPS in 2009:
>>>>>>> a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
>>>>>>> a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
>>>>>>>
>>>>>>> But hibernation_e820_save() is still using MD5, and fails in FIPS mode
>>>>>>> due to the 2018 patch:
>>>>>>> 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
>>>>>>>
>>>>>>> As a result, hibernation doesn't work when FIPS is on.
>>>>>>>
>>>>>>> Do you think if hibernation_e820_save() should be changed to use a
>>>>>>> FIPS-compliant algorithm like SHA-1?
>>>>>> I would say yes, it should.
>>>>>>
>>>>>>> PS, currently it looks like FIPS mode is broken in the mainline:
>>>>>>> https://www.mail-archive.com/[email protected]/msg49414.html
>>>>> FYI, SHA-1 is not a good choice, it is only permitted in HMAC
>>>>> constructions and only for specified uses. If you need to change
>>>>> algorithm you should go straight to SHA-2 or SHA-3 based hashes.
>>>>>
>>>> What is the reason for using a [broken] cryptographic hash here? if
>>>> this is just an integrity check, better use CRC32
> Not really.
>
> CRC32 is not really sufficient for integrity checking here AFAICS. It
> might be made a fallback option if MD5 is not available, but making it
> the default would be somewhat over the top IMO.
Would ghash be a better choice? It produces the same size digest as md5.
Does anyone have any other suggestions of algorithms to try?
Thanks,
Chris
>
>>> If the integrity check is used exclusively to verify there were no
>>> accidental changes and is not used as a security measure, by all means
>>> I agree that using crc32 is a better idea.
>>>
>> Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
>> this, it is only a best effort check which is simply omitted if md5
>> happens to be unavailable, so there is definitely no need for crypto
>> here.
> Yes, it is about integrity checking only. No, CRC32 is not equivalent
> to MD5 in that respect AFAICS.
>
> Thanks!
>
On Thu, Apr 1, 2021 at 6:22 PM Simo Sorce <[email protected]> wrote:
>
> On Thu, 2021-04-01 at 18:02 +0200, Rafael J. Wysocki wrote:
> > On Thu, Apr 1, 2021 at 3:54 PM Ard Biesheuvel <[email protected]> wrote:
> > > On Thu, 1 Apr 2021 at 15:38, Rafael J. Wysocki <[email protected]> wrote:
> > > > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> > > > > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> > > > > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > > > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > > > > > Hi,
> > > > > > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > > > > > >
> > > > > > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > > > > > due to the 2018 patch:
> > > > > > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > > > > > >
> > > > > > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > > > > > >
> > > > > > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > > > > > FIPS-compliant algorithm like SHA-1?
> > > > > > > > >
> > > > > > > > > I would say yes, it should.
> > > > > > > > >
> > > > > > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > > > > > >
> > > > > > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > > > > > constructions and only for specified uses. If you need to change
> > > > > > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > > > > > >
> > > > > > >
> > > > > > > What is the reason for using a [broken] cryptographic hash here? if
> > > > > > > this is just an integrity check, better use CRC32
> > > >
> > > > Not really.
> > > >
> > > > CRC32 is not really sufficient for integrity checking here AFAICS. It
> > > > might be made a fallback option if MD5 is not available, but making it
> > > > the default would be somewhat over the top IMO.
> > > >
> > > > > > If the integrity check is used exclusively to verify there were no
> > > > > > accidental changes and is not used as a security measure, by all means
> > > > > > I agree that using crc32 is a better idea.
> > > > > >
> > > > >
> > > > > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > > > > this, it is only a best effort check which is simply omitted if md5
> > > > > happens to be unavailable, so there is definitely no need for crypto
> > > > > here.
> > > >
> > > > Yes, it is about integrity checking only. No, CRC32 is not equivalent
> > > > to MD5 in that respect AFAICS.
> > > >
> > >
> > > There are two possibilities:
> > > - we care about an adversary attempting to forge a collision, in which
> > > case you need a cryptographic hash which is not broken;
> > > - we only care about integrity, in which case crypto is overkill, and
> > > CRC32 is sufficient. (Note that the likelihood of an honest,
> > > inadvertent modification not being caught by CRC32 is 1 in 4 billion)
> >
> > That depends on how you count.
> >
> > Surely, there are modifications caught by MD5 that will not be caught by CRC32.
>
> This is a technically correct statement, but does it matter in this
> context? (Hint, probably not)
>
> > > MD5 does not meet either requirement, given that it is known to be
> > > broken, and overkill for simple integrity checks. MD5 should be phased
> > > out and removed, and moving this code onto the correct abstraction
> > > would be a reasonable step towards that goal.
> >
> > This clearly is a matter of opinion.
>
> Sorry, but this is not a matter of opinion.
> The only reason to use a cryptographic hash is that you want to protect
> from active tampering, rather than from accidental changes. And if you
> need to protect from active tampering then you cannot use a known
> broken hash, there is no point.
>
> OTOH if you do not care for active tampering but only to catch
> transmission/storage errors then all you care for is error checking. In
> that case a cryptographic hash is overkill because it entails a lot
> more computation than is needed.
But the amount of data in question is not huge in this case.
> > I'm not religious about it though. If there is a general consensus
> > that CRC32 is sufficient for error detection in hibernation files,
> > then it can be used. So is there such a consensus and if so, can you
> > give me a pointer to some research that it is based on?
>
> CRC32 is an industry standard to check for accidental modifications of
> a bit stream. The chances of missing an accidental change are 1 in 4
> billion.
This is not about accidental change which basically is my point.
The BIOSes in question change the memory map over hibernation/resume,
because they think that the memory layout is now different, so this is
about detecting a sort of intentional change. Definitely not random,
though.
But as stated elsewhere, it is just about failing more gracefully at
least in some cases, so let's just go ahead with using CRC32 here
(worst case, it will not fail more gracefully in super-corner cases).
On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
>
> On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> >
> > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > Hi,
> > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > >
> > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > due to the 2018 patch:
> > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > >
> > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > >
> > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > FIPS-compliant algorithm like SHA-1?
> > > > >
> > > > > I would say yes, it should.
> > > > >
> > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > >
> > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > constructions and only for specified uses. If you need to change
> > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > >
> > >
> > > What is the reason for using a [broken] cryptographic hash here? if
> > > this is just an integrity check, better use CRC32
Not really.
CRC32 is not really sufficient for integrity checking here AFAICS. It
might be made a fallback option if MD5 is not available, but making it
the default would be somewhat over the top IMO.
> > If the integrity check is used exclusively to verify there were no
> > accidental changes and is not used as a security measure, by all means
> > I agree that using crc32 is a better idea.
> >
>
> Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> this, it is only a best effort check which is simply omitted if md5
> happens to be unavailable, so there is definitely no need for crypto
> here.
Yes, it is about integrity checking only. No, CRC32 is not equivalent
to MD5 in that respect AFAICS.
Thanks!
On Thu, Apr 01, 2021 at 09:54:21AM -0400, Chris von Recklinghausen wrote:
> On 4/1/21 9:38 AM, Rafael J. Wysocki wrote:
> > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> > > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> > > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > > > Hi,
> > > > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > > > >
> > > > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > > > due to the 2018 patch:
> > > > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > > > >
> > > > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > > > >
> > > > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > > > FIPS-compliant algorithm like SHA-1?
> > > > > > > I would say yes, it should.
> > > > > > >
> > > > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > > > constructions and only for specified uses. If you need to change
> > > > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > > > >
> > > > > What is the reason for using a [broken] cryptographic hash here? if
> > > > > this is just an integrity check, better use CRC32
> > Not really.
> >
> > CRC32 is not really sufficient for integrity checking here AFAICS. It
> > might be made a fallback option if MD5 is not available, but making it
> > the default would be somewhat over the top IMO.
>
>
> Would ghash be a better choice? It produces the same size digest as md5.
>
> Does anyone have any other suggestions of algorithms to try?
>
> Thanks,
>
> Chris
>
> >
> > > > If the integrity check is used exclusively to verify there were no
> > > > accidental changes and is not used as a security measure, by all means
> > > > I agree that using crc32 is a better idea.
> > > >
> > > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > > this, it is only a best effort check which is simply omitted if md5
> > > happens to be unavailable, so there is definitely no need for crypto
> > > here.
> > Yes, it is about integrity checking only. No, CRC32 is not equivalent
> > to MD5 in that respect AFAICS.
> >
If you need to detect intentional changes (ensure authenticity, not just
integrity) then you need a cryptographic MAC, such as HMAC-SHA256.
If you only need to detect accidental changes (ensure integrity-only), then a
checksum such as CRC-32 or xxHash64 is sufficient. A cryptographic hash
function such as SHA-256 would also be sufficient, though much slower. Using a
broken cryptographic hash function such as MD5 doesn't make sense because it is
broken (so doesn't actually provide cryptographic security), and is much slower
than a checksum.
If the 1 in 4 billion collision rate of a CRC-32 isn't sufficient, then use
CRC-64 or xxHash64 for a 1 in 2^64 collision rate.
Don't use GHASH, as it is neither a checksum nor a cryptographic hash function.
- Eric
On Thu, 2021-04-01 at 18:02 +0200, Rafael J. Wysocki wrote:
> On Thu, Apr 1, 2021 at 3:54 PM Ard Biesheuvel <[email protected]> wrote:
> > On Thu, 1 Apr 2021 at 15:38, Rafael J. Wysocki <[email protected]> wrote:
> > > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> > > > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> > > > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > > > > Hi,
> > > > > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > > > > >
> > > > > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > > > > due to the 2018 patch:
> > > > > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > > > > >
> > > > > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > > > > >
> > > > > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > > > > FIPS-compliant algorithm like SHA-1?
> > > > > > > >
> > > > > > > > I would say yes, it should.
> > > > > > > >
> > > > > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > > > > >
> > > > > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > > > > constructions and only for specified uses. If you need to change
> > > > > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > > > > >
> > > > > >
> > > > > > What is the reason for using a [broken] cryptographic hash here? if
> > > > > > this is just an integrity check, better use CRC32
> > >
> > > Not really.
> > >
> > > CRC32 is not really sufficient for integrity checking here AFAICS. It
> > > might be made a fallback option if MD5 is not available, but making it
> > > the default would be somewhat over the top IMO.
> > >
> > > > > If the integrity check is used exclusively to verify there were no
> > > > > accidental changes and is not used as a security measure, by all means
> > > > > I agree that using crc32 is a better idea.
> > > > >
> > > >
> > > > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > > > this, it is only a best effort check which is simply omitted if md5
> > > > happens to be unavailable, so there is definitely no need for crypto
> > > > here.
> > >
> > > Yes, it is about integrity checking only. No, CRC32 is not equivalent
> > > to MD5 in that respect AFAICS.
> > >
> >
> > There are two possibilities:
> > - we care about an adversary attempting to forge a collision, in which
> > case you need a cryptographic hash which is not broken;
> > - we only care about integrity, in which case crypto is overkill, and
> > CRC32 is sufficient. (Note that the likelihood of an honest,
> > inadvertent modification not being caught by CRC32 is 1 in 4 billion)
>
> That depends on how you count.
>
> Surely, there are modifications caught by MD5 that will not be caught by CRC32.
This is a technically correct statement, but does it matter in this
context? (Hint, probably not)
> > MD5 does not meet either requirement, given that it is known to be
> > broken, and overkill for simple integrity checks. MD5 should be phased
> > out and removed, and moving this code onto the correct abstraction
> > would be a reasonable step towards that goal.
>
> This clearly is a matter of opinion.
Sorry, but this is not a matter of opinion.
The only reason to use a cryptographic hash is that you want to protect
from active tampering, rather than from accidental changes. And if you
need to protect from active tampering then you cannot use a known
broken hash, there is no point.
OTOH if you do not care for active tampering but only to catch
transmission/storage errors then all you care for is error checking. In
that case a cryptographic hash is overkill because it entails a lot
more computation than is needed.
> I'm not religious about it though. If there is a general consensus
> that CRC32 is sufficient for error detection in hibernation files,
> then it can be used. So is there such a consensus and if so, can you
> give me a pointer to some research that it is based on?
CRC32 is an industry standard to check for accidental modifications of
a bit stream. The chances of missing an accidental change are 1 in 4
billion.
Does your application require a higher threshold? If so you should
justify why you think your case is not fulfilled by an industry
standard.
HTH,
Simo.
--
Simo Sorce
RHEL Crypto Team
Red Hat, Inc
On Thu, Apr 1, 2021 at 3:54 PM Ard Biesheuvel <[email protected]> wrote:
>
> On Thu, 1 Apr 2021 at 15:38, Rafael J. Wysocki <[email protected]> wrote:
> >
> > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> > >
> > > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> > > >
> > > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > > > Hi,
> > > > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > > > >
> > > > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > > > due to the 2018 patch:
> > > > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > > > >
> > > > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > > > >
> > > > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > > > FIPS-compliant algorithm like SHA-1?
> > > > > > >
> > > > > > > I would say yes, it should.
> > > > > > >
> > > > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > > > >
> > > > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > > > constructions and only for specified uses. If you need to change
> > > > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > > > >
> > > > >
> > > > > What is the reason for using a [broken] cryptographic hash here? if
> > > > > this is just an integrity check, better use CRC32
> >
> > Not really.
> >
> > CRC32 is not really sufficient for integrity checking here AFAICS. It
> > might be made a fallback option if MD5 is not available, but making it
> > the default would be somewhat over the top IMO.
> >
> > > > If the integrity check is used exclusively to verify there were no
> > > > accidental changes and is not used as a security measure, by all means
> > > > I agree that using crc32 is a better idea.
> > > >
> > >
> > > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > > this, it is only a best effort check which is simply omitted if md5
> > > happens to be unavailable, so there is definitely no need for crypto
> > > here.
> >
> > Yes, it is about integrity checking only. No, CRC32 is not equivalent
> > to MD5 in that respect AFAICS.
> >
>
> There are two possibilities:
> - we care about an adversary attempting to forge a collision, in which
> case you need a cryptographic hash which is not broken;
> - we only care about integrity, in which case crypto is overkill, and
> CRC32 is sufficient. (Note that the likelihood of an honest,
> inadvertent modification not being caught by CRC32 is 1 in 4 billion)
That depends on how you count.
Surely, there are modifications caught by MD5 that will not be caught by CRC32.
> MD5 does not meet either requirement, given that it is known to be
> broken, and overkill for simple integrity checks. MD5 should be phased
> out and removed, and moving this code onto the correct abstraction
> would be a reasonable step towards that goal.
This clearly is a matter of opinion.
I'm not religious about it though. If there is a general consensus
that CRC32 is sufficient for error detection in hibernation files,
then it can be used. So is there such a consensus and if so, can you
give me a pointer to some research that it is based on?
On Thu, 1 Apr 2021 at 15:38, Rafael J. Wysocki <[email protected]> wrote:
>
> On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> >
> > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> > >
> > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> > > > > On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> > > > > > On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> > > > > > > Hi,
> > > > > > > MD5 was marked incompliant with FIPS in 2009:
> > > > > > > a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> > > > > > > a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> > > > > > >
> > > > > > > But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> > > > > > > due to the 2018 patch:
> > > > > > > 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> > > > > > >
> > > > > > > As a result, hibernation doesn't work when FIPS is on.
> > > > > > >
> > > > > > > Do you think if hibernation_e820_save() should be changed to use a
> > > > > > > FIPS-compliant algorithm like SHA-1?
> > > > > >
> > > > > > I would say yes, it should.
> > > > > >
> > > > > > > PS, currently it looks like FIPS mode is broken in the mainline:
> > > > > > > https://www.mail-archive.com/[email protected]/msg49414.html
> > > > >
> > > > > FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> > > > > constructions and only for specified uses. If you need to change
> > > > > algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> > > > >
> > > >
> > > > What is the reason for using a [broken] cryptographic hash here? if
> > > > this is just an integrity check, better use CRC32
>
> Not really.
>
> CRC32 is not really sufficient for integrity checking here AFAICS. It
> might be made a fallback option if MD5 is not available, but making it
> the default would be somewhat over the top IMO.
>
> > > If the integrity check is used exclusively to verify there were no
> > > accidental changes and is not used as a security measure, by all means
> > > I agree that using crc32 is a better idea.
> > >
> >
> > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > this, it is only a best effort check which is simply omitted if md5
> > happens to be unavailable, so there is definitely no need for crypto
> > here.
>
> Yes, it is about integrity checking only. No, CRC32 is not equivalent
> to MD5 in that respect AFAICS.
>
There are two possibilities:
- we care about an adversary attempting to forge a collision, in which
case you need a cryptographic hash which is not broken;
- we only care about integrity, in which case crypto is overkill, and
CRC32 is sufficient. (Note that the likelihood of an honest,
inadvertent modification not being caught by CRC32 is 1 in 4 billion)
MD5 does not meet either requirement, given that it is known to be
broken, and overkill for simple integrity checks. MD5 should be phased
out and removed, and moving this code onto the correct abstraction
would be a reasonable step towards that goal.
On Thu, 1 Apr 2021 at 15:54, Chris von Recklinghausen
<[email protected]> wrote:
>
> On 4/1/21 9:38 AM, Rafael J. Wysocki wrote:
> > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <[email protected]> wrote:
> >> On Tue, 30 Mar 2021 at 21:56, Simo Sorce <[email protected]> wrote:
> >>> On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> >>>> On Tue, 30 Mar 2021 at 20:05, Simo Sorce <[email protected]> wrote:
> >>>>> On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> >>>>>> On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <[email protected]> wrote:
> >>>>>>> Hi,
> >>>>>>> MD5 was marked incompliant with FIPS in 2009:
> >>>>>>> a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> >>>>>>> a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> >>>>>>>
> >>>>>>> But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> >>>>>>> due to the 2018 patch:
> >>>>>>> 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> >>>>>>>
> >>>>>>> As a result, hibernation doesn't work when FIPS is on.
> >>>>>>>
> >>>>>>> Do you think if hibernation_e820_save() should be changed to use a
> >>>>>>> FIPS-compliant algorithm like SHA-1?
> >>>>>> I would say yes, it should.
> >>>>>>
> >>>>>>> PS, currently it looks like FIPS mode is broken in the mainline:
> >>>>>>> https://www.mail-archive.com/[email protected]/msg49414.html
> >>>>> FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> >>>>> constructions and only for specified uses. If you need to change
> >>>>> algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> >>>>>
> >>>> What is the reason for using a [broken] cryptographic hash here? if
> >>>> this is just an integrity check, better use CRC32
> > Not really.
> >
> > CRC32 is not really sufficient for integrity checking here AFAICS. It
> > might be made a fallback option if MD5 is not available, but making it
> > the default would be somewhat over the top IMO.
>
>
> Would ghash be a better choice? It produces the same size digest as md5.
>
No, ghash is a MAC not a hash. It should only ever be used with GCM
and nowhere else.
> Does anyone have any other suggestions of algorithms to try?
>
Just use crc32