Re: Combining certificate and key in PEM format into a P12 file without knowing the key password?

[Frank Migge <fm@xxxxxxxxxxxx>]

Hi Toby,

>> the question remains: Is there a way to reuse an already-encrypted privkey?

I'd say yes it *could* work, but not with OpenSSL API functions. You'd have to roll your own code for the PKCS12 creation.

OpenSSL's PKCS12_create() function expects an unencrypted EVP_PKEY object.  But, internally, that key is turned into a encrypted PKCS8 structure, as expected by the PKCS8ShroudedKeyBag type defined in RFC-7292.

Thats why I think it may be possible to experiment and modify code such as in crypto/pkcs12/p12_crt.c, trying to pass-through that already encrypted PKCS8 key "as-is" straight into the pkcs8ShroudedKeyBag object. If your key is a file in PEM format, you'd need to get that into an internal structure first (more coding), I don't think there is a simple API import (without decryption).

If you manage to successfully built that PKCS12, you'd run into trouble for decoding, which probably fails for all known software. They all expect to be able to read the private key, when in your case it needs saving to a file somewhere for further handling, or for entering that second key-specific password.  You'd again have to code your own PKCS12 unpack program, just for this specific use case.

I may be wrong but to me it looks doable, just a *lot* of work.

Frank

Tobias Dussa (SCC)

Tuesday, February 20, 2018 9:15 PM

Hi,

On Tue, Feb 20, 2018 at 12:23:14PM +0100, Jakob Bohm wrote:

Googling does not reveal much useful information, unfortunately, and so far we
have been unsuccessfully diving into PKCS12/8/5 specs.  I don't really see a
reason why it should not be possible, but of course that doesn't mean it is. :)

In the commonly accepted variants of PKCS#12, private key and all the
certificates are encrypted with the same password.  PKCS#12 with
different password for private key and certificates is not widely
supported.

I see.

In the concatenated PEM format, only the private key is encrypted, but
not the certificates.

Yep.

So to convert from concatenated PEM format to PKCS#12, even if the
encrypted private key could be kept without decrypting the private
key, the password for the private key is still needed to encrypt
the certificates with the same password.

... iff you need to retain wide-spread compatibility.  So if that is not
necessary, the question remains: Is there a way to reuse an already-encrypted
privkey?

THX & Cheers,
Toby.

Jakob Bohm

Tuesday, February 20, 2018 8:23 PM

In the commonly accepted variants of PKCS#12, private key and all the
certificates are encrypted with the same password.  PKCS#12 with
different password for private key and certificates is not widely
supported.

In the concatenated PEM format, only the private key is encrypted, but
not the certificates.

So to convert from concatenated PEM format to PKCS#12, even if the
encrypted private key could be kept without decrypting the private
key, the password for the private key is still needed to encrypt
the certificates with the same password.


Enjoy

Jakob

Tobias Dussa (SCC)

Tuesday, February 20, 2018 7:04 PM

Hi,

I was wondering whether it was possible somehow to take a certificate and an
enciphered private key, both in .pem format, and combine them into a PKCS12
structure without knowing the key passphrase?

Googling does not reveal much useful information, unfortunately, and so far we
have been unsuccessfully diving into PKCS12/8/5 specs. I don't really see a
reason why it should not be possible, but of course that doesn't mean it is. :)

THX & Cheers,
Toby.

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