[erlang-questions] crypto ECDSA private key -> public

[Andreas Schultz]

Hi,

----- On 27 Oct, 2014, at 23:24, semmit mondo semmitmondo@REDACTED wrote:

> Yes and no.
> According to the source of the crypto module generate_key/3
> does accept a private key only for a few encryption method types.
> This is the only function head that matches ecdh:
> generate_key(ecdh, Curve, undefined) -> ...
> There's no definition for ecdh with a 3rd param that is not
> undefined. ...and generate_key/2 calls the above one:
> generate_key(Type, Params) ->
> generate_key(Type, Params, undefined).
> It would be the function I'm after...

The function you are looking for is ec_key_new in lib/crypto/c_src/crypto.c. That
function is not exported to the Erlang world (originally it was in some faschion,
but the crypto API restructuring un-exported it).

Andreas

> 
> Ingela Andin <ingela.andin@REDACTED> írta:
> 
> 
> Hi!
> There is also a function crypto:generate_key/3 that takes a private key as third
> argument, maybe that is what you want?
> Regards Ingela Erlang/OTP team - Ericsson AB
> 2014-10-21 17:00 GMT+02:00 semmit mondo < semmitmondo@REDACTED > :
> 
> 
> Hi,
> How can I generate an ECDSA public key from the private one using crypto?
> All I can do with it is to generate a public and private key pair at once:
> {Pub, Priv} = crypto:generate_key(ecdh, prime239v3).
> but can't calculate the public key if the private key was known beforehand.
> (prime239v3 isn't important, it could be any EC curve...)
> 
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Dipl. Inform.
Andreas Schultz

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