[openssl-users] engine interface for genrsa

[William Roberts]

On Thu, Apr 19, 2018 at 7:45 PM, Scott Wisniewski
<swisniewski at salesforce.com> wrote:
> FYI:
>
> If you provide an genrsa implementation in your engine that doesn't include
> the private parameters, even if it's marked with RSA_FLAG_EXT_PKEY, the
> openssl executable will not handle it correctly.
>
> That's because genrsa_main assumes that the object that comes back is an rsa
> private key. So it will attempt to save a PEM encoded RSA private key even
> though it doesn't have the private key fields and openssl won't be able to
> open the saved file.
>
> So, if you want to enable use of the openssl executable with genrsa being
> supported by your engine, you will actually need to modify apps/genrsa.c So
> that genrsa_main does:
>
> if (RSA_test_flags(rsa, RSA_FLAG_EXT_PKEY) == RSA_FLAG_EXT_PKEY) {
>
>     if (! PEM_write_bio_RSA_PUBKEY(out, rsa))
>
>         goto end;
>
> }
>
> else {
>
>     if (!PEM_write_bio_RSAPrivateKey(out, rsa, enc, NULL, 0,
>
>                                      (pem_password_cb *)password_callback,
>
>                                      &cb_data))
>
>         goto end;
>
> }
>
>
> instead of:
>
> if (!PEM_write_bio_RSAPrivateKey(out, rsa, enc, NULL, 0,
>
>                                     (pem_password_cb *)password_callback,
>
>                                     &cb_data))
>
>        goto end;
>
>
> And then it will save the key you generated in public key pem format. which
> will allow openssl to read it.

Good to know, thanks for the detail.

>
> One thing to note:
>
> None of the open source engines I checked (neither the PCKS11 engine, the
> NCipher engine, nor the CAPI engine) implement the genrsa hook. If you are
> looking for wide compatibility you may wish to ask your clients to do key
> generation using an external utility (as that's how almost everyone else
> does it).

I have only looked at the PKCS11 module, and it's quite limited in
functionality.
I've been extending it submitting patches as they make sense. I just added
random support.


>
> On Fri, Apr 13, 2018 at 5:28 PM, William Roberts <bill.c.roberts at gmail.com>
> wrote:
>>
>> On Fri, Apr 13, 2018 at 2:55 PM, Richard Levitte <levitte at openssl.org>
>> wrote:
>> > In message
>> > <CAFftDdqWPXq1+Mo9_6J0EzhZ4uwg5QC=R5fx8N1j=QYchA8+YQ at mail.gmail.com> on Fri,
>> > 13 Apr 2018 09:17:28 -0700, William Roberts <bill.c.roberts at gmail.com> said:
>> >
>> > bill.c.roberts> I am currently working on writing an openssl engine
>> > bill.c.roberts> to interface with a piece of hardware.
>> > bill.c.roberts>
>> > bill.c.roberts> I am trying to understand how to implement
>> > bill.c.roberts> rsa key generation, where the private key
>> > bill.c.roberts> bytes would not be available.
>> > bill.c.roberts>
>> > bill.c.roberts> I am currently invoking the
>> > bill.c.roberts> command:
>> > bill.c.roberts>
>> > bill.c.roberts> openssl genrsa -engine foo
>> > bill.c.roberts>
>> > bill.c.roberts> Which is calling my callback for RSA keygen, registered
>> > via ENGINE_set_RSA()
>> > bill.c.roberts> and I set the flags: RSA_FLAG_EXT_PKEY.
>> > bill.c.roberts>
>> > bill.c.roberts> However, genrsa app seems to want rsa->e set here:
>> > bill.c.roberts>
>> > https://github.com/openssl/openssl/blob/OpenSSL_1_0_2g/apps/genrsa.c#L291
>> > bill.c.roberts>
>> > bill.c.roberts> I can't find documentation on how to handle the keygen
>> > interface
>> > bill.c.roberts> for RSA.
>> > bill.c.roberts>
>> > bill.c.roberts> Can someone point me in the right direction?
>> >
>> > e and n are public components of any RSA key pair (and RSA structure
>> > in OpenSSL).  You *must* make them available.  The rest of the numbers
>> > are private and do not need to be part of the RSA structure that
>> > OpenSSL handles.
>>
>> Thanks. I went and read the RSA page on Wikipedia, and sure enough it
>> has what common meanings of what all the single letter variables
>> are in the RSA struct.
>> https://en.wikipedia.org/wiki/RSA_(cryptosystem)
>>
>> >
>> > Cheers,
>> > Richard
>> >
>> > --
>> > Richard Levitte         levitte at openssl.org
>> > OpenSSL Project         http://www.openssl.org/~levitte/
>> > --
>> > openssl-users mailing list
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>
>
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