[Autocrypt] How to create the "raw key" part from an RSA key

[holger krekel]

Hi Bjoern,

i am not involved with openssl on the c-level but did you look into 
https://shanetully.com/2012/06/openssl-rsa-aes-and-c/ ? 

This also might help:
http://openssl.6102.n7.nabble.com/How-to-use-a-binary-public-key-td43325.html

And if you or someone finds out an openssl cmdline invocation which generates a proper Autocrypt RSA-2048 key we could add it to the docs.  

holger


On Tue, May 16, 2017 at 13:13 +0200, Bjoern wrote:
> Hi there,
> 
> I'm just about to add AutoCrypt to Delta Chat.
> 
> I'm creating the key pair using the following code:
> 
>     // generate key
>     BIGNUM*       e   = BN_new();
>     RSA*          rsa = RSA_new();
> 
>     BN_set_word(e, 65537);
>     if( RSA_generate_key_ex(rsa, 2024, e, 0) != 1 ) {
>         goto cleanup;
>     }
> 
>     //  convert RSA key to PUBLIC KEY
>     EVP_PKEY* pkey = EVP_PKEY_new();
>     EVP_PKEY_set1_RSA(pkey, rsa);
> 
> now I can get the keys as `-----BEGIN PUBLIC KEY----- ...` and
> `-----BEGIN RSA PRIVATE KEY----- ...` using
> 
> PEM_write_bio_PUBKEY(bio1, pkey);
> 
> and
> 
> PEM_write_bio_RSAPrivateKey(bio2, rsa, NULL, NULL, 0, NULL, NULL);
> 
> But how can I get the key in the "raw" form needed by Autocrypt?
> (base64 encoding itself is no problem)
> 
> (for various reasons, I cannont use libraries based upon GnuPG as PEP
> or GPGME and I wanted a portable C code)
> 
> Any help is wecome as this would saves me tons of time :-) (I am not
> expert in OpenSSL)
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