COSE-encoding a publickey

[Arun Sudhir]

I'm trying to build a FIDO2 client. As part of the FIDO2 registration process, I'm trying to generate the client payload to send to the FIDO2 server. For the authData structure,  https://medium.com/@herrjemand/verifying-fido2-responses-4691288c8770  has the split up of how it is populated, but has no details on the COSEencoded publickey. I have an RSA publickey. Can someone tell me how to coseencode it?

 

Should i make a CBOR map with fields "n" and "E" that stores the modulus and exponent respectively?

Thanks

Arun

[Alex Seigler]

There are some samples here:

https://tools.ietf.org/html/rfc8152#appendix-C.7

List of assignments can be found here:

https://www.iana.org/assignments/cose/cose.xhtml

-aseigler

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From: fido...@fidoalliance.org <fido...@fidoalliance.org> on behalf of Arun Sudhir <aruns...@gmail.com>
Sent: Monday, December 2, 2019 5:33:46 PM
To: FIDO Dev (fido-dev) <fido...@fidoalliance.org>
Subject: [FIDO-DEV] COSE-encoding a publickey

 

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[Arun Sudhir]

Thanks Alex. After looking those up my RSA public key would be cbor map that looks like:

"1" : "3"                                          //kty = 3 for RSA as per https://tools.ietf.org/html/rfc8152#page-34 for label and https://www.iana.org/assignments/cose/cose.xhtml#key-type for value

"3" : "-257"                                    //alg: RS256 as per  https://tools.ietf.org/html/rfc8152#page-34 for label and  https://www.iana.org/assignments/cose/cose.xhtml#algorithms for value

"-1" : <binary modulus value>      // as per https://www.iana.org/assignments/cose/cose.xhtml#key-type-parameters 

"-2" : <binary exponent value>    //again as per https://www.iana.org/assignments/cose/cose.xhtml#key-type-parameters 

Does this  make sense?

Thanks

Arun

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[Alex Seigler]

Looks about right to me, but typically displayed without the quotes.

-aseigler 

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From: Arun Sudhir <aruns...@gmail.com>
Sent: Monday, December 2, 2019, 7:07 PM
To: Alex Seigler
Cc: FIDO Dev (fido-dev)
Subject: Re: [FIDO-DEV] COSE-encoding a publickey

[Arun Sudhir]

Thanks Alex!