On Tuesday, February 12, 2019, Wes Turner <wes.tur...@gmail.com> wrote:

>
>
> On Tuesday, February 12, 2019, Jeremy Stanley <fu...@yuggoth.org> wrote:
>
>> On 2019-02-12 13:37:20 -0500 (-0500), Wes Turner wrote:
>> > MD5 is no longer suitable for verifying package integrity.
>> >
>> > https://en.wikipedia.org/wiki/MD5#Security
>> >
>> > > The security of the MD5 hash function is severely compromised. A
>> > > collision attack exists [...] there is also a chosen-prefix
>> > > collision attack
>> [...]
>>
>> The difference between collision (or chosen-prefix collision) and
>> preimage (or second preimage) attacks is still very relevant. With
>> MD5 you can't trust that someone who provided you with an input and
>> a hash of that input hasn't carefully crafted that input so that
>> there is also a second input which results in the same hash. Or in
>> package terms, you can't trust that the package you've received
>> wasn't part of a contrived scheme on the part of someone you've
>> already decided to trust. You can still rest assured (for now
>> anyway) that the package you receive is the same one the person or
>> system providing the MD5 checksum intended for you to receive.
>
>
> It is possible to find a nonce value that causes an arbitrary package to
> have the same MD5 hash as the actual package.
>

e.g. browsers MUST NOT rely upon MD5 for x.509 certificate SSL/TLS/HTTPS
fingerprints for exactly this reason.



>
>
>>
>> But because trying to explain this nuance to people is considerably
>> harder than just saying "MD5 bad" it's simply not worth trying to
>> have the discussion most of the time, and so easier instead to
>> replace it with a more modern alternative and move on with your
>> life.
>> --
>> Jeremy Stanley
>>
>
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