[Openid-specs-fapi] Question regarding JWS alg in FAPI part 2, read and write security profile

[Brian Campbell]

I know that there's a general push to move away from RSASSA-PKCS1-v1_5 but
is it accurate to say it's unsafe? I see things like this, for example,
https://crypto.stackexchange.com/questions/34558/is-ssl-
sign-safe-as-it-is-using-openssl-pkcs1-padding

On Thu, Jul 20, 2017 at 10:47 AM, Nat Sakimura via Openid-specs-fapi <
openid-specs-fapi at lists.openid.net> wrote:

> Hi Sascha,
>
> This came up during the WG calls as well.
>
> The short answer is that there are several attacks identified for
> RSASSA-PKCS1-v1_5 while PSS padding is safe. Cryptographer's opinion is
> that RSASSA-PKCS1-v1_5 should be retired.
>
> We agreed in the WG call to add RS256 as a permissible algorithm when HSM
> is used and the HSM in place does not support PS256 or ES256 in the final
> but has to be done in the way that it does not raise a red flag from the
> cryptographers. Please see https://bitbucket.org/openid/f
> api/issues/101/jws-signature-algorithms-for-rw.
>
> Best,
>
> ---
> Nat Sakimura
> Research Fellow, Nomura Research Institute
> Chairman of the Board, OpenID Foundation
>
>
> On 2017-07-20 15:20, Preibisch, Sascha H via Openid-specs-fapi wrote:
>
>> Hi all!
>>
>> I just read through the spec. and in section 8.6
>> (http://openid.net/specs/openid-financial-api-part-2.html#
>> jws-algorithm-con
>> siderations) we recommend to use PS256 or ES256 as signing algorithms.
>>
>> Here
>> "https://tools.ietf.org/html/draft-ietf-jose-json-web-algori
>> thms-14#section
>> -3.1" PS256 is marked as OPTIONAL.
>>
>> I would like to understand why we recommend PS256 rather than RS256, which
>> is RECOMMENDED and widely used.
>>
>> I saw that issue #92 spoke about this topic but I did not really
>> understood it I believe.
>>
>>
>> Thanks,
>> Sascha
>>
>>
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