Re: Proposal for adding setpubkey callback to akcipher_alg
Hi Herbert, We already have an interface that can handle asymmetric keys and it is easy to extend with new key formats and key types. So lets use that. I can clearly see that after RSA, we get DSA, ECDH etc. So having a simple way to handle these key formats is a good idea. That infrastructure is already in place and easy to extend if needed. Especially with the background that some keys might be actually in hardware or compiled into the kernel, the current asymmetric key interface has the right abstraction. It is also the right abstraction to deal with crypto hardware like TPM or even UEFI. The crypto API akcipher interface is never going to be used for TPM or UEFI. This is a purely algorithmic interface intended for hardware acceleration devices. If your key is embedded into the hardware or otherwise hidden then this is not the interface for you. I think it actually is the correct interface. And it will still stay a purely algorithmic interface. It is just that the algorithm is bound to specific hardware with a specific key. I really do not understand your distinction here. Seriously where is the difference. Lets say you have AES-CCM offload in one PCI card and AES-ECB offload in another PCI card. The main job of skcipher here is to pick the right engine. So RSA-key1 in one PCI card compared to RSA-key2 in another PCI card is pretty much the same concept. So really explain to me where you are deriving your difference from. If the hardware can offload the operation for you, then that is what it is doing. Not everything is about speed. Some things are actually about security. And treating akcipher the same as skcipher is not going to work. They are two different concepts and they are used differently. Why would you advocate that we duplicate akcipher abstraction once for hardware acceleration and once for security key storage operation. At the end of the day it is the same abstraction. As I mentioned before, for skcipher the acceleration aspects are clear first and foremost. However just extending that reasoning blindly to akcipher is short sighted. I think we have a great opportunity to create a really powerful and simple API for asymmetric cryptography and hardware assisted asymmetric cryptography. And if you think about how RSA for example is used these days, you spent more time loading the certificate and the keys, then you actually spent in the cipher operation. It is just the stepping stone for creating the session key that you are using with skcipher like AES. So I do not want to waste time setting up my keys over and over again for a single RSA operation. I want to set them up quickly and then run my RSA cipher operation. I also want to set them up securely where my private key is protect and not copied for every single instance. Regards Marcel -- To unsubscribe from this list: send the line unsubscribe linux-crypto in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Proposal for adding setpubkey callback to akcipher_alg
On Tue, Aug 04, 2015 at 09:33:27PM -0700, Marcel Holtmann wrote: I think it actually is the correct interface. And it will still stay a purely algorithmic interface. It is just that the algorithm is bound to specific hardware with a specific key. I really do not understand your distinction here. The crypto API provides a platform where you can provide hardware accelerated implementations for pure software algorithms. Hardware keys are fundamentally incompatible with that as you cannot do it in software. Cheers, -- Email: Herbert Xu herb...@gondor.apana.org.au Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line unsubscribe linux-crypto in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Proposal for adding setpubkey callback to akcipher_alg
On Mon, Aug 03, 2015 at 12:25:31AM -0700, Marcel Holtmann wrote: RSA Private Key is n + e + d (including 6 other fields). RSA Public Key is n + e (no other fields). So for RSA you would make setkey to take RSA Private Key and setpubkey to take RSA Public Key. Meaning you only have to use one of them since if you have the private key, you always have the public key. This real difference here is that you can provide the key in two different key formats. As explained RSA uses two different format. I don't have a problem with a setpubkey/setprivkey split interface. However, I'm totally against importing MPI keys which is just silly. The BER-encoded keys are just raw integers. Most of the hardware out there take raw integers. So it makes no sense to have our interface take MPIs instead of raw integers, as this would mean converting into MPIs and then straight back into raw integers for hardware devices. Cheers, -- Email: Herbert Xu herb...@gondor.apana.org.au Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line unsubscribe linux-crypto in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Proposal for adding setpubkey callback to akcipher_alg
Hi Herbert, RSA Private Key is n + e + d (including 6 other fields). RSA Public Key is n + e (no other fields). So for RSA you would make setkey to take RSA Private Key and setpubkey to take RSA Public Key. Meaning you only have to use one of them since if you have the private key, you always have the public key. This real difference here is that you can provide the key in two different key formats. As explained RSA uses two different format. I don't have a problem with a setpubkey/setprivkey split interface. However, I'm totally against importing MPI keys which is just silly. The BER-encoded keys are just raw integers. Most of the hardware out there take raw integers. So it makes no sense to have our interface take MPIs instead of raw integers, as this would mean converting into MPIs and then straight back into raw integers for hardware devices. after looking further into this, the whole akcipher setkey should not operate on BER-encoded key blobs nor MPIs. Instead it should take a struct key as input and reference it. For skcipher the key as binary blob thing works nicely, but for akcipher this is not a good interface. I prefer to have one interface for loading public/private keys and not have 2 or more different ways of loading and parsing these keys. That will get messy really quick. They are just magnitude more complicated than skcipher keys since they come in more complicated packaging. We already have an interface that can handle asymmetric keys and it is easy to extend with new key formats and key types. So lets use that. I can clearly see that after RSA, we get DSA, ECDH etc. So having a simple way to handle these key formats is a good idea. That infrastructure is already in place and easy to extend if needed. Especially with the background that some keys might be actually in hardware or compiled into the kernel, the current asymmetric key interface has the right abstraction. It is also the right abstraction to deal with crypto hardware like TPM or even UEFI. The nice advantage is that keys do not have to be copied around. The struct key supports referencing keys and it also ties nicely into process and user permissions. So essentially you reference your key for akcipher by struct key or from userspace indirectly via key_serial_t. No need to duplicate the key for each instance of the akcipher. There is only a single key. Especially when handling private keys, I prefer to keep them nicely in one place and not spread copies around kernel memory. Duplicating sensitive key material is a bad security practice. It also avoids having to duplicate the ASN.1 parsing over and over again (I found 3 places that parse RSA keys at the moment). Have the asymmetric key interface parse the key once and stop duplicating this on every single attempt. This is especially helpful if your key comes in form of a certificate. We can validate the certificate and provide a key reference. More important we can also validate it against the kernel system keyring or a hardware provided keyring or certificate. I really want to avoid that we are getting into the business of converting from format a to format b to format c because everybody invents their own ones. That is a bad API for me. And lets face it, when it comes to public key cryptography, there are standards we should follow. If the Linux kernel starts making up yet another format and interface, then we are doing a pretty bad job. With the support for different sub-keytypes, we can really easily optimize the handling of struct key for the actual hardware in question. So instead of using an interim BER format or MPI or whatever, the keys can be parsed right into the correct format of the hardware that will eventually run the offload. This will be done once and we can avoid all the extra work. Further more the important part for me is that when keys are actually bound to hardware, meaning we will never see the actual private key in kernel memory, we can still reference them. The selection of a hardware provided private key with a RSA cipher then can automatically select the right implementation for usage of that key. No point in trying a software RSA cipher if the key is only in hardware. If the hardware supports RSA offload and has a private key storage of its own, why should that be treated any different than AES hardware engine. It is just that its usage is limited to its keys. However the interface of akcipher should handle this. If it does not, then we boxed ourselves into a corner and end up inventing new interfaces for these kinds of hardware. TPM and UEFI are such devices / services already out there. For me they are no different than skcipher offload. It is just that they are bound to a key and not just an instruction or hardware block. The keys subsystem with the asymmetric key type should be responsible for loading and managing the keys. The crypto subsystem with akcipher
Re: Proposal for adding setpubkey callback to akcipher_alg
Am Sonntag, 2. August 2015, 22:28:33 schrieb Marcel Holtmann:
Hi Marcel,
Hi Tadeusz,
I think we need to split the akcipher_alg setkey callback into a setkey and
setpubkey.
diff --git a/include/crypto/akcipher.h b/include/crypto/akcipher.h
index 69d163e39101..ca93952b6d19 100644
--- a/include/crypto/akcipher.h
+++ b/include/crypto/akcipher.h
@@ -91,6 +91,8 @@ struct akcipher_alg {
int (*decrypt)(struct akcipher_request *req);
int (*setkey)(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen);
+ int (*setpubkey)(struct crypto_akcipher *tfm, const void *key,
+unsigned int keylen);
int (*init)(struct crypto_akcipher *tfm);
void (*exit)(struct crypto_akcipher *tfm);
If the cipher actually uses two different formats for the public + private
The public key is n + e.
The private key is n + d.
Both are encoded in the BER structure the current API requires. It is
perfectly valid to provide only n + e when you do public key operations.
Please see in the testmgr.h for the 2048 bit key test vector (i.e. the one
with public_key_vec = true). The BER structure has nice comments from Tadeusz
to indicate it only contains n and e without d.
Thus, I do not currently understand your request. May I ask you to give more
explanation why the use of BER is insufficient?
Ciao
Stephan
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Re: Proposal for adding setpubkey callback to akcipher_alg
Hi Stephan,
I think we need to split the akcipher_alg setkey callback into a setkey
and
setpubkey.
diff --git a/include/crypto/akcipher.h b/include/crypto/akcipher.h
index 69d163e39101..ca93952b6d19 100644
--- a/include/crypto/akcipher.h
+++ b/include/crypto/akcipher.h
@@ -91,6 +91,8 @@ struct akcipher_alg {
int (*decrypt)(struct akcipher_request *req);
int (*setkey)(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen);
+ int (*setpubkey)(struct crypto_akcipher *tfm, const void *key,
+unsigned int keylen);
int (*init)(struct crypto_akcipher *tfm);
void (*exit)(struct crypto_akcipher *tfm);
If the cipher actually uses two different formats for the public +
private
The public key is n + e.
The private key is n + d.
for RSA Public Key it is just n and e. However for RSA Private Key it is n
and e and d and also version, primes etc. So the RSA Public Key contains a
sequence of 2 integers and the RSA Private Key contains a sequence of 9
integers.
Both are encoded in the BER structure the current API requires. It is
perfectly valid to provide only n + e when you do public key operations.
And from an API perspective that is fully wrong from my point of view. We
just invented another format that is not in any standard. The two standard
key formats for RSA are RSA Private Key and RSA Public Key. These are the
ones we should support.
The format with n plus e and optionally d is total Linux invention as far as
I can tell. And I do not want this exposed to userspace.
For a clean separation I think splitting this into setkey for the RSA
Private Key and setpubkey for the RSA Public Key is pretty obvious choice.
Please define exactly what your pubkey and your privkey contains. Even when I
think of the DER keys from OpenSSL, we once have n+e and once n+e+d (see
asn1dump), no?
RSA Private Key is n + e + d (including 6 other fields). RSA Public Key is n +
e (no other fields).
So for RSA you would make setkey to take RSA Private Key and setpubkey to take
RSA Public Key. Meaning you only have to use one of them since if you have the
private key, you always have the public key.
This real difference here is that you can provide the key in two different key
formats. As explained RSA uses two different format.
Please see in the testmgr.h for the 2048 bit key test vector (i.e. the one
with public_key_vec = true). The BER structure has nice comments from
Tadeusz to indicate it only contains n and e without d.
And it is totally made up format. Why would you force conversion of a RSA
BER is a made up implementation? I do not think so:
https://en.wikipedia.org/wiki/Basic_Encoding_Rules
Or do you say that the kernel's implementation of BER is broken?
BER is an encoding format. It does NOT define a key format. You can use BER to
define a key format, but that still means that our defined format that is
currently used for setkey with RSA is made up. It is Linux specific.
The standards for key formats for RSA are RSA Public Key and RSA Private Key.
Public Key or RSA Private Key in DER format into this format. This Linux
only input format makes it just complicated for no reason. It is also not
documented anywhere as I can tell. I had to dig this out of the code and
rsakey.asn1.
As mentioned above, splitting this into two functions makes this simpler.
For all intense and purposes this is akcipher so we always either have
public/private key pair or we just have the public key. And at least with
RSA they are defined as two independent formats.
I can see that user space (e.g. libkcapi) has such two functions. But
currently I do not see such distinction necessary in the kernel as mentioned
above.
Then how do you tell the two key formats apart? Try one, fail, try the other? I
do not like these things. Just tell the kernel clearly what format you have.
Simple and easy.
Since the parsing of the key data is not a generic handling, I do not see a
good enough reason to invent new formats. Use the format the cipher you
implement already has defined.
Thus, I do not currently understand your request. May I ask you to give
more explanation why the use of BER is insufficient?
Tell me how you create this Linux specific BER encoded key. I would like
someone to provide the magic OpenSSL conversion command line to get this.
Again: there is no DER to BER converter that I am aware of. Agreed, that
should be there. But currently I do not see that the kernel should do that.
For all intense and purposes DER is valid BER. Why are discussing this?
Hand crafting such keys when there is a standard format for RSA Private Key
and RSA Public Key makes no sense whatsoever.
Fully agreed. Thus, a BER encoder is on my agenda for libkcapi.
You are missing my point here. You should not need such a thing. The RSA keys
are already provided in two well defined DER
Re: Proposal for adding setpubkey callback to akcipher_alg
Hi Stephan,
I think we need to split the akcipher_alg setkey callback into a setkey and
setpubkey.
diff --git a/include/crypto/akcipher.h b/include/crypto/akcipher.h
index 69d163e39101..ca93952b6d19 100644
--- a/include/crypto/akcipher.h
+++ b/include/crypto/akcipher.h
@@ -91,6 +91,8 @@ struct akcipher_alg {
int (*decrypt)(struct akcipher_request *req);
int (*setkey)(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen);
+ int (*setpubkey)(struct crypto_akcipher *tfm, const void *key,
+unsigned int keylen);
int (*init)(struct crypto_akcipher *tfm);
void (*exit)(struct crypto_akcipher *tfm);
If the cipher actually uses two different formats for the public + private
The public key is n + e.
The private key is n + d.
for RSA Public Key it is just n and e. However for RSA Private Key it is n and
e and d and also version, primes etc. So the RSA Public Key contains a sequence
of 2 integers and the RSA Private Key contains a sequence of 9 integers.
Both are encoded in the BER structure the current API requires. It is
perfectly valid to provide only n + e when you do public key operations.
And from an API perspective that is fully wrong from my point of view. We just
invented another format that is not in any standard. The two standard key
formats for RSA are RSA Private Key and RSA Public Key. These are the ones we
should support.
The format with n plus e and optionally d is total Linux invention as far as I
can tell. And I do not want this exposed to userspace.
For a clean separation I think splitting this into setkey for the RSA Private
Key and setpubkey for the RSA Public Key is pretty obvious choice.
Please see in the testmgr.h for the 2048 bit key test vector (i.e. the one
with public_key_vec = true). The BER structure has nice comments from Tadeusz
to indicate it only contains n and e without d.
And it is totally made up format. Why would you force conversion of a RSA
Public Key or RSA Private Key in DER format into this format. This Linux only
input format makes it just complicated for no reason. It is also not documented
anywhere as I can tell. I had to dig this out of the code and rsakey.asn1.
As mentioned above, splitting this into two functions makes this simpler. For
all intense and purposes this is akcipher so we always either have
public/private key pair or we just have the public key. And at least with RSA
they are defined as two independent formats.
Since the parsing of the key data is not a generic handling, I do not see a
good enough reason to invent new formats. Use the format the cipher you
implement already has defined.
Thus, I do not currently understand your request. May I ask you to give more
explanation why the use of BER is insufficient?
Tell me how you create this Linux specific BER encoded key. I would like
someone to provide the magic OpenSSL conversion command line to get this. Hand
crafting such keys when there is a standard format for RSA Private Key and RSA
Public Key makes no sense whatsoever.
Regards
Marcel
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Re: Proposal for adding setpubkey callback to akcipher_alg
Am Montag, 3. August 2015, 00:03:03 schrieb Marcel Holtmann:
Hi Marcel,
Hi Stephan,
I think we need to split the akcipher_alg setkey callback into a setkey
and
setpubkey.
diff --git a/include/crypto/akcipher.h b/include/crypto/akcipher.h
index 69d163e39101..ca93952b6d19 100644
--- a/include/crypto/akcipher.h
+++ b/include/crypto/akcipher.h
@@ -91,6 +91,8 @@ struct akcipher_alg {
int (*decrypt)(struct akcipher_request *req);
int (*setkey)(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen);
+ int (*setpubkey)(struct crypto_akcipher *tfm, const void *key,
+unsigned int keylen);
int (*init)(struct crypto_akcipher *tfm);
void (*exit)(struct crypto_akcipher *tfm);
If the cipher actually uses two different formats for the public +
private
The public key is n + e.
The private key is n + d.
for RSA Public Key it is just n and e. However for RSA Private Key it is n
and e and d and also version, primes etc. So the RSA Public Key contains a
sequence of 2 integers and the RSA Private Key contains a sequence of 9
integers.
Both are encoded in the BER structure the current API requires. It is
perfectly valid to provide only n + e when you do public key operations.
And from an API perspective that is fully wrong from my point of view. We
just invented another format that is not in any standard. The two standard
key formats for RSA are RSA Private Key and RSA Public Key. These are the
ones we should support.
The format with n plus e and optionally d is total Linux invention as far as
I can tell. And I do not want this exposed to userspace.
For a clean separation I think splitting this into setkey for the RSA
Private Key and setpubkey for the RSA Public Key is pretty obvious choice.
Please define exactly what your pubkey and your privkey contains. Even when I
think of the DER keys from OpenSSL, we once have n+e and once n+e+d (see
asn1dump), no?
Please see in the testmgr.h for the 2048 bit key test vector (i.e. the one
with public_key_vec = true). The BER structure has nice comments from
Tadeusz to indicate it only contains n and e without d.
And it is totally made up format. Why would you force conversion of a RSA
BER is a made up implementation? I do not think so:
https://en.wikipedia.org/wiki/Basic_Encoding_Rules
Or do you say that the kernel's implementation of BER is broken?
Public Key or RSA Private Key in DER format into this format. This Linux
only input format makes it just complicated for no reason. It is also not
documented anywhere as I can tell. I had to dig this out of the code and
rsakey.asn1.
As mentioned above, splitting this into two functions makes this simpler.
For all intense and purposes this is akcipher so we always either have
public/private key pair or we just have the public key. And at least with
RSA they are defined as two independent formats.
I can see that user space (e.g. libkcapi) has such two functions. But
currently I do not see such distinction necessary in the kernel as mentioned
above.
Since the parsing of the key data is not a generic handling, I do not see a
good enough reason to invent new formats. Use the format the cipher you
implement already has defined.
Thus, I do not currently understand your request. May I ask you to give
more explanation why the use of BER is insufficient?
Tell me how you create this Linux specific BER encoded key. I would like
someone to provide the magic OpenSSL conversion command line to get this.
Again: there is no DER to BER converter that I am aware of. Agreed, that
should be there. But currently I do not see that the kernel should do that.
Hand crafting such keys when there is a standard format for RSA Private Key
and RSA Public Key makes no sense whatsoever.
Fully agreed. Thus, a BER encoder is on my agenda for libkcapi.
--
Ciao
Stephan
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