linux-kernel - Re: [PATCH 01/19] User-space API definition

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Message-ID: <4C8558FD.2010107@gmail.com>
Date:	Mon, 06 Sep 2010 23:11:25 +0200
From:	Nikos Mavrogiannopoulos <n.mavrogiannopoulos@...il.com>
To:	Kyle Moffett <kyle@...fetthome.net>
CC:	Miloslav Trmac <mitr@...hat.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	linux-crypto@...r.kernel.org, Neil Horman <nhorman@...hat.com>,
	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 01/19] User-space API definition

On 09/06/2010 10:42 PM, Kyle Moffett wrote:

>>> The problem with the approach you're proposing is that we then have
>>> two entirely separate classes of keys.  First we have the existing
>>> keyring class, which can be securely and revokably passed between
>>> different processes with limited rights, but cannot be handed up to
>>> the kernel's cryptoapi.
>>
>> I don't think this is the case. The NCR does not store any keys nor
>> retrieves them. It does delegate the burden of that to userspace
>> application. NCR exports a wrapped version of the key and the userspace
>> application stores it. It could use the keyring to store the keys or
>> could directly store them in the filesystem.
> 
> Hmm, I'm confused.  You say "The NCR does not store any keys nor
> retrieves them", but ~75% of your API is specifically related to
> storing keys into kernel memory or retrieving them out of kernel
> memory.
> Specifically, putting keys into and out of the kernel and
> passing them around between processes is the *whole point* of the
> keyring API.

I suppose you mean the reference to the internal representation of the
key. This might be valid for few seconds until the required operation is
over.
This is not really what I would call storage. The storage and retrieval
of keys is being done using two ioctl() the STORAGE_WRAP and STORAGE_UNWRAP.

An example of how NCR works:
1. A Process generates an RSA key pair
2. Stores the (encrypted) pair using the STORAGE_WRAP to a file.

3. Another process loads the file, unwraps it using STORAGE_UNWRAP and
gets a reference to the key
4. Does an RSA decryption using the key
5. Discards the reference to the key

Consider the reference as a file descriptor after you have opened a file
(a wrapped key).

How do you see keyring being involved in a setup like this?

> So let me ask for some clarification:
> You talk a lot in the patches about the API itself, but what is the
> intended *use-case* for NCR?

In short: cryptographic operations.

> Is it to provide a back-end for code such as enhanced-security OpenSSL
> libraries?  For example, a privileged process would loads a key from
> disk into the kernel, then fork the unprivileged SSL server process?

An unprivileged process will load a key from disk to kernel and use it.
The keys leave the NCR framework only encrypted and authenticated.

> Is it just a canonical interface for userspace to encrypt or decrypt
> data using the kernel's CryptoAPI?

I don't understand what do you mean by canonical, but this API can be
used to perform crypto operations. It uses the internal linux API where
possible.

regards,
Nikos
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