Encoding using SHA256 with RSA

Question

I'm attempting to authorize with the Google Data API as a service in a language for which there isn't any client library. The crux is in how to generate the signature. To do this I have to encode a string using "SHA256 with RSA".

I have it from here that it shouldn't be "terribly difficult" however I cannot find a description of the procedure? Anyone knows?

(The language does have a function to generate SHA256 hash codes.)

What language are you actually using? And, please also specify which auth procedure Google Data API uses. — Nickolay Olshevsky
– Nickolay Olshevsky, Commented Aug 31, 2013 at 16:41
Please provide a link to the spec of what you want to implement. RSA+SHA256 isn't enough to fully describe the scheme. — CodesInChaos
– CodesInChaos, Commented Aug 31, 2013 at 17:30
@CodesInChaos This is the description, is it enough? "Sign the UTF-8 representation of the input using SHA256withRSA (also known as RSASSA-PKCS1-V1_5-SIGN with the SHA-256 hash function) with the private key obtained from the API console." (I mean that PKC... part) — C. E.
– C. E., Commented Aug 31, 2013 at 17:39
@NickolayOlshevsky Mathematica. oAuth 2.0 with a service account: developers.google.com/accounts/docs/OAuth2ServiceAccount — C. E.
– C. E., Commented Aug 31, 2013 at 17:40

Nickolay Olshevsky · Accepted Answer · 2013-08-31 18:09:25Z

2

OAuth 2.0 requires RSASSA-PKCS1-V1_5-SIGN, which is described in RFC 3447. Just check section 9.2 of this RFC - you need just add some formatting to the hash of your message.

answered Aug 31, 2013 at 18:09

Nickolay Olshevsky

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