[strongSwan-dev] RSA-PSS-SHA256

Sahana Prasad sahana.prasad07 at gmail.com
Mon Feb 5 22:34:05 CET 2018

Thanks Andreas and Tobias for your reply.

Is there a reason why a new errata was not reported with the 2nd and 15th
byte changed (rightly done as in the current strongswan identifier/ASN.1
blob) from the rejected errata?

Just want to know which ASN.1 blob we should use to interop and maybe
standardise/generalise it since the RFC ASN.1 blob (72 byte long) and the
rejected errata are wrong.

Sahana Prasad

On Mon, Feb 5, 2018 at 11:19 AM, Tobias Brunner <tobias at strongswan.org>

> Hi Sahana,
> > Question 1 : Difference in OID bytes :
> >
> > The 67 bytes ASN.1 OID that should be sent as per the errata from 7427
> > (https://www.rfc-editor.org/errata_search.php?rfc=7427)  and the 67
> > bytes that I receive from strongswan are different.
> Please note that both of these erratas were rejected.  And as Andreas
> mentioned the second errata's ASN.1 encoding is incorrect.  While the
> ASCII length was changed the ASN.1 encoding was not.
> > Question 2 : Calculation of RSA signature
> >
> > To calculate the 128 byte signature, the 67 bytes OID plus the 32 bytes
> > hash (sha256)  is considered right?
> No, the signature is built as specified in RFC 7296, section 2.15.  The
> length and OID are just added in front of the signature value within the
> Authentication Data field of the Authentication payload.
> > Is there a way to see the hash that is generated? I have all logs
> > enabled, but do not see the hash value. I can only see the 128
> > byte rss-signature that gets added to the 204 byte long auth payload
> There are no log messages that print the value to be signed.
> Regards,
> Tobias
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