157 lines
6.2 KiB
Markdown
157 lines
6.2 KiB
Markdown
Passing AlgorithmIdentifier parameters to operations
|
|
====================================================
|
|
|
|
Quick background
|
|
----------------
|
|
|
|
We currently only support passing the AlgorithmIdentifier (`X509_ALGOR`)
|
|
parameter field to symmetric cipher provider implementations.
|
|
|
|
We do support passing them to legacy implementations of other types of
|
|
operation algorithms as well, but it's done in a way that can't be supported
|
|
with providers, because it involves sharing specific structures between
|
|
libcrypto and the backend implementation.
|
|
|
|
For a longer background and explanation, see
|
|
[Background / tl;dr](#background-tldr) at the end of this design.
|
|
|
|
Establish an OSSL_PARAM key that any algorithms may become aware of
|
|
-------------------------------------------------------------------
|
|
|
|
We already have a parameter key, but it's currently only specified for
|
|
`EVP_CIPHER`, in support of `EVP_CIPHER_param_to_asn1()` and
|
|
`EVP_CIPHER_asn1_to_param()`.
|
|
|
|
"alg_id_param", also known as the macro `OSSL_CIPHER_PARAM_ALGORITHM_ID_PARAMS`
|
|
|
|
This parameter can be used in the exact same manner with other operations,
|
|
with the value of the AlgorithmIdentifier parameter as an octet string, to
|
|
be interpreted by the implementations in whatever way they see fit.
|
|
|
|
Applications can choose to add these in an `OSSL_PARAM` array, to be passed
|
|
with the multitude of initialization functions that take such an array, or
|
|
using specific operation `OSSL_PARAM` setters and getters (such as
|
|
`EVP_PKEY_CTX_set_params`), or using other available convenience functions
|
|
(see below).
|
|
|
|
This parameter will have to be documented in the following files:
|
|
|
|
- `doc/man7/provider-asym_cipher.pod`
|
|
- `doc/man7/provider-cipher.pod`
|
|
- `doc/man7/provider-digest.pod`
|
|
- `doc/man7/provider-kdf.pod`
|
|
- `doc/man7/provider-kem.pod`
|
|
- `doc/man7/provider-keyexch.pod`
|
|
- `doc/man7/provider-mac.pod`
|
|
- `doc/man7/provider-signature.pod`
|
|
|
|
That should cover all algorithms that are, or should be possible to fetch by
|
|
AlgorithmIdentifier.algorithm, and for which there's potentially a relevant
|
|
AlgorithmIdentifier.parameters field.
|
|
|
|
We may arguably want to consider `doc/man7/provider-keymgmt.pod` too, but
|
|
an AlgorithmIdentifier that's attached directly to a key is usually part of
|
|
a PrivKeyInfo or SubjectPublicKeyInfo structure, and those are handled by
|
|
encoders and decoders as those see fit, and there's no tangible reason why
|
|
that would have to change.
|
|
|
|
Public convenience API
|
|
----------------------
|
|
|
|
For convenience, the following set of functions would be added to pass the
|
|
AlgorithmIdentifier parameter data to diverse operations, or to retrieve
|
|
such parameter data from them.
|
|
|
|
``` C
|
|
/*
|
|
* These two would essentially be aliases for EVP_CIPHER_param_to_asn1()
|
|
* and EVP_CIPHER_asn1_to_param().
|
|
*/
|
|
EVP_CIPHER_CTX_set_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
EVP_CIPHER_CTX_get_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
|
|
EVP_MD_CTX_set_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
EVP_MD_CTX_get_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
|
|
EVP_MAC_CTX_set_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
EVP_MAC_CTX_get_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
|
|
EVP_KDF_CTX_set_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
EVP_KDF_CTX_get_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
|
|
EVP_PKEY_CTX_set_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
EVP_PKEY_CTX_get_algor_param(EVP_PKEY_CTX *ctx, X509_ALGOR *alg);
|
|
```
|
|
|
|
Note that all might not need to be added immediately, depending on if they
|
|
are considered useful or not. For future proofing, however, they should
|
|
probably all be added.
|
|
|
|
Requirements on the providers
|
|
-----------------------------
|
|
|
|
Providers that implement ciphers or any operation that uses asymmetric keys
|
|
will have to implement support for passing AlgorithmIdentifier parameter
|
|
data, and will have to process that data in whatever manner that's necessary
|
|
to meet the standards for that operation.
|
|
|
|
Fallback strategies
|
|
-------------------
|
|
|
|
There are no possible fallback strategies, which is fine, considering that
|
|
current provider functionality doesn't support passing AlgorithmIdentifier
|
|
parameter data at all (except for `EVP_CIPHER`), and therefore do not work
|
|
at all when such parameter data needs to be passed.
|
|
|
|
-----
|
|
|
|
-----
|
|
|
|
Background / tl;dr
|
|
------------------
|
|
|
|
### AlgorithmIdenfier parameter and how it's used
|
|
|
|
OpenSSL has historically done a few tricks to not have to pass
|
|
AlgorithmIdenfier parameter data to the backend implementations of
|
|
cryptographic operations:
|
|
|
|
- In some cases, they were passed as part of the lower level key structure
|
|
(for example, the `RSA` structure can also carry RSA-PSS parameters).
|
|
- In the `EVP_CIPHER` case, there is functionality to pass the parameter
|
|
data specifically.
|
|
- For asymmetric key operations, PKCS#7 and CMS support was added as
|
|
`EVP_PKEY` ctrls.
|
|
|
|
With providers, some of that support was retained, but not others. Most
|
|
crucially, the `EVP_PKEY` ctrls for PKCS#7 and CMS were not retained,
|
|
because the way they were implemented violated the principle that provider
|
|
implementations *MUST NOT* share complex OpenSSL specific structures with
|
|
libcrypto.
|
|
|
|
### Usage examples
|
|
|
|
Quite a lot of the available examples today revolve around CMS, with a
|
|
number of RFCs that specify what parameters should be passed with certain
|
|
operations / algorithms. This list is not exhaustive, the reader is
|
|
encouraged to research further usages.
|
|
|
|
- [DSA](https://www.rfc-editor.org/rfc/rfc3370#section-3.1) signatures
|
|
typically have the domain parameters *p*, *q* and *g*.
|
|
- [RC2 key wrap](https://www.rfc-editor.org/rfc/rfc3370#section-4.3.2)
|
|
- [PBKDF2](https://www.rfc-editor.org/rfc/rfc3370#section-4.4.1)
|
|
- [3DES-CBC](https://www.rfc-editor.org/rfc/rfc3370#section-5.1)
|
|
- [RC2-CBC](https://www.rfc-editor.org/rfc/rfc3370#section-5.2)
|
|
|
|
- [GOST 28147-89](https://www.rfc-editor.org/rfc/rfc4490.html#section-5.1)
|
|
|
|
- [RSA-OAEP](https://www.rfc-editor.org/rfc/rfc8017#appendix-A.2.1)
|
|
- [RSA-PSS](https://www.rfc-editor.org/rfc/rfc8017#appendix-A.2.3)
|
|
|
|
- [XOR-MD5](https://www.rfc-editor.org/rfc/rfc6210.html) is experimental,
|
|
but it does demonstrate the possibility of a parametrized hash algorithm.
|
|
|
|
Some of it can be claimed to already have support in OpenSSL. However, this
|
|
is with old libcrypto code that has special knowledge of the algorithms that
|
|
are involved.
|