docs: crypto: convert asymmetric-keys.txt to ReST

This file is almost compatible with ReST. Just minor changes
were needed:

- Adjust document and titles markups;
- Adjust numbered list markups;
- Add a comments markup for the Contents section;
- Add markups for literal blocks.

Acked-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/c2275ea94e0507a01b020ab66dfa824d8b1c2545.1592203650.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 429 deletions

diff --git a/Documentation/crypto/asymmetric-keys.txt b/Documentation/crypto/asymmetric-keys.txt
deleted file mode 100644
index 8763866b11cf..000000000000
--- a/Documentation/crypto/asymmetric-keys.txt
+++ /dev/null
@@ -1,429 +0,0 @@
-		=============================================
-		ASYMMETRIC / PUBLIC-KEY CRYPTOGRAPHY KEY TYPE
-		=============================================
-
-Contents:
-
-  - Overview.
-  - Key identification.
-  - Accessing asymmetric keys.
-    - Signature verification.
-  - Asymmetric key subtypes.
-  - Instantiation data parsers.
-  - Keyring link restrictions.
-
-
-========
-OVERVIEW
-========
-
-The "asymmetric" key type is designed to be a container for the keys used in
-public-key cryptography, without imposing any particular restrictions on the
-form or mechanism of the cryptography or form of the key.
-
-The asymmetric key is given a subtype that defines what sort of data is
-associated with the key and provides operations to describe and destroy it.
-However, no requirement is made that the key data actually be stored in the
-key.
-
-A completely in-kernel key retention and operation subtype can be defined, but
-it would also be possible to provide access to cryptographic hardware (such as
-a TPM) that might be used to both retain the relevant key and perform
-operations using that key.  In such a case, the asymmetric key would then
-merely be an interface to the TPM driver.
-
-Also provided is the concept of a data parser.  Data parsers are responsible
-for extracting information from the blobs of data passed to the instantiation
-function.  The first data parser that recognises the blob gets to set the
-subtype of the key and define the operations that can be done on that key.
-
-A data parser may interpret the data blob as containing the bits representing a
-key, or it may interpret it as a reference to a key held somewhere else in the
-system (for example, a TPM).
-
-
-==================
-KEY IDENTIFICATION
-==================
-
-If a key is added with an empty name, the instantiation data parsers are given
-the opportunity to pre-parse a key and to determine the description the key
-should be given from the content of the key.
-
-This can then be used to refer to the key, either by complete match or by
-partial match.  The key type may also use other criteria to refer to a key.
-
-The asymmetric key type's match function can then perform a wider range of
-comparisons than just the straightforward comparison of the description with
-the criterion string:
-
- (1) If the criterion string is of the form "id:<hexdigits>" then the match
-     function will examine a key's fingerprint to see if the hex digits given
-     after the "id:" match the tail.  For instance:
-
-	keyctl search @s asymmetric id:5acc2142
-
-     will match a key with fingerprint:
-
-	1A00 2040 7601 7889 DE11  882C 3823 04AD 5ACC 2142
-
- (2) If the criterion string is of the form "<subtype>:<hexdigits>" then the
-     match will match the ID as in (1), but with the added restriction that
-     only keys of the specified subtype (e.g. tpm) will be matched.  For
-     instance:
-
-	keyctl search @s asymmetric tpm:5acc2142
-
-Looking in /proc/keys, the last 8 hex digits of the key fingerprint are
-displayed, along with the subtype:
-
-	1a39e171 I-----     1 perm 3f010000     0     0 asymmetric modsign.0: DSA 5acc2142 []
-
-
-=========================
-ACCESSING ASYMMETRIC KEYS
-=========================
-
-For general access to asymmetric keys from within the kernel, the following
-inclusion is required:
-
-	#include <crypto/public_key.h>
-
-This gives access to functions for dealing with asymmetric / public keys.
-Three enums are defined there for representing public-key cryptography
-algorithms:
-
-	enum pkey_algo
-
-digest algorithms used by those:
-
-	enum pkey_hash_algo
-
-and key identifier representations:
-
-	enum pkey_id_type
-
-Note that the key type representation types are required because key
-identifiers from different standards aren't necessarily compatible.  For
-instance, PGP generates key identifiers by hashing the key data plus some
-PGP-specific metadata, whereas X.509 has arbitrary certificate identifiers.
-
-The operations defined upon a key are:
-
- (1) Signature verification.
-
-Other operations are possible (such as encryption) with the same key data
-required for verification, but not currently supported, and others
-(eg. decryption and signature generation) require extra key data.
-
-
-SIGNATURE VERIFICATION
-----------------------
-
-An operation is provided to perform cryptographic signature verification, using
-an asymmetric key to provide or to provide access to the public key.
-
-	int verify_signature(const struct key *key,
-			     const struct public_key_signature *sig);
-
-The caller must have already obtained the key from some source and can then use
-it to check the signature.  The caller must have parsed the signature and
-transferred the relevant bits to the structure pointed to by sig.
-
-	struct public_key_signature {
-		u8 *digest;
-		u8 digest_size;
-		enum pkey_hash_algo pkey_hash_algo : 8;
-		u8 nr_mpi;
-		union {
-			MPI mpi[2];
-			...
-		};
-	};
-
-The algorithm used must be noted in sig->pkey_hash_algo, and all the MPIs that
-make up the actual signature must be stored in sig->mpi[] and the count of MPIs
-placed in sig->nr_mpi.
-
-In addition, the data must have been digested by the caller and the resulting
-hash must be pointed to by sig->digest and the size of the hash be placed in
-sig->digest_size.
-
-The function will return 0 upon success or -EKEYREJECTED if the signature
-doesn't match.
-
-The function may also return -ENOTSUPP if an unsupported public-key algorithm
-or public-key/hash algorithm combination is specified or the key doesn't
-support the operation; -EBADMSG or -ERANGE if some of the parameters have weird
-data; or -ENOMEM if an allocation can't be performed.  -EINVAL can be returned
-if the key argument is the wrong type or is incompletely set up.
-
-
-=======================
-ASYMMETRIC KEY SUBTYPES
-=======================
-
-Asymmetric keys have a subtype that defines the set of operations that can be
-performed on that key and that determines what data is attached as the key
-payload.  The payload format is entirely at the whim of the subtype.
-
-The subtype is selected by the key data parser and the parser must initialise
-the data required for it.  The asymmetric key retains a reference on the
-subtype module.
-
-The subtype definition structure can be found in:
-
-	#include <keys/asymmetric-subtype.h>
-
-and looks like the following:
-
-	struct asymmetric_key_subtype {
-		struct module		*owner;
-		const char		*name;
-
-		void (*describe)(const struct key *key, struct seq_file *m);
-		void (*destroy)(void *payload);
-		int (*query)(const struct kernel_pkey_params *params,
-			     struct kernel_pkey_query *info);
-		int (*eds_op)(struct kernel_pkey_params *params,
-			      const void *in, void *out);
-		int (*verify_signature)(const struct key *key,
-					const struct public_key_signature *sig);
-	};
-
-Asymmetric keys point to this with their payload[asym_subtype] member.
-
-The owner and name fields should be set to the owning module and the name of
-the subtype.  Currently, the name is only used for print statements.
-
-There are a number of operations defined by the subtype:
-
- (1) describe().
-
-     Mandatory.  This allows the subtype to display something in /proc/keys
-     against the key.  For instance the name of the public key algorithm type
-     could be displayed.  The key type will display the tail of the key
-     identity string after this.
-
- (2) destroy().
-
-     Mandatory.  This should free the memory associated with the key.  The
-     asymmetric key will look after freeing the fingerprint and releasing the
-     reference on the subtype module.
-
- (3) query().
-
-     Mandatory.  This is a function for querying the capabilities of a key.
-
- (4) eds_op().
-
-     Optional.  This is the entry point for the encryption, decryption and
-     signature creation operations (which are distinguished by the operation ID
-     in the parameter struct).  The subtype may do anything it likes to
-     implement an operation, including offloading to hardware.
-
- (5) verify_signature().
-
-     Optional.  This is the entry point for signature verification.  The
-     subtype may do anything it likes to implement an operation, including
-     offloading to hardware.
-
-
-==========================
-INSTANTIATION DATA PARSERS
-==========================
-
-The asymmetric key type doesn't generally want to store or to deal with a raw
-blob of data that holds the key data.  It would have to parse it and error
-check it each time it wanted to use it.  Further, the contents of the blob may
-have various checks that can be performed on it (eg. self-signatures, validity
-dates) and may contain useful data about the key (identifiers, capabilities).
-
-Also, the blob may represent a pointer to some hardware containing the key
-rather than the key itself.
-
-Examples of blob formats for which parsers could be implemented include:
-
- - OpenPGP packet stream [RFC 4880].
- - X.509 ASN.1 stream.
- - Pointer to TPM key.
- - Pointer to UEFI key.
- - PKCS#8 private key [RFC 5208].
- - PKCS#5 encrypted private key [RFC 2898].
-
-During key instantiation each parser in the list is tried until one doesn't
-return -EBADMSG.
-
-The parser definition structure can be found in:
-
-	#include <keys/asymmetric-parser.h>
-
-and looks like the following:
-
-	struct asymmetric_key_parser {
-		struct module	*owner;
-		const char	*name;
-
-		int (*parse)(struct key_preparsed_payload *prep);
-	};
-
-The owner and name fields should be set to the owning module and the name of
-the parser.
-
-There is currently only a single operation defined by the parser, and it is
-mandatory:
-
- (1) parse().
-
-     This is called to preparse the key from the key creation and update paths.
-     In particular, it is called during the key creation _before_ a key is
-     allocated, and as such, is permitted to provide the key's description in
-     the case that the caller declines to do so.
-
-     The caller passes a pointer to the following struct with all of the fields
-     cleared, except for data, datalen and quotalen [see
-     Documentation/security/keys/core.rst].
-
-	struct key_preparsed_payload {
-		char		*description;
-		void		*payload[4];
-		const void	*data;
-		size_t		datalen;
-		size_t		quotalen;
-	};
-
-     The instantiation data is in a blob pointed to by data and is datalen in
-     size.  The parse() function is not permitted to change these two values at
-     all, and shouldn't change any of the other values _unless_ they are
-     recognise the blob format and will not return -EBADMSG to indicate it is
-     not theirs.
-
-     If the parser is happy with the blob, it should propose a description for
-     the key and attach it to ->description, ->payload[asym_subtype] should be
-     set to point to the subtype to be used, ->payload[asym_crypto] should be
-     set to point to the initialised data for that subtype,
-     ->payload[asym_key_ids] should point to one or more hex fingerprints and
-     quotalen should be updated to indicate how much quota this key should
-     account for.
-
-     When clearing up, the data attached to ->payload[asym_key_ids] and
-     ->description will be kfree()'d and the data attached to
-     ->payload[asm_crypto] will be passed to the subtype's ->destroy() method
-     to be disposed of.  A module reference for the subtype pointed to by
-     ->payload[asym_subtype] will be put.
-
-
-     If the data format is not recognised, -EBADMSG should be returned.  If it
-     is recognised, but the key cannot for some reason be set up, some other
-     negative error code should be returned.  On success, 0 should be returned.
-
-     The key's fingerprint string may be partially matched upon.  For a
-     public-key algorithm such as RSA and DSA this will likely be a printable
-     hex version of the key's fingerprint.
-
-Functions are provided to register and unregister parsers:
-
-	int register_asymmetric_key_parser(struct asymmetric_key_parser *parser);
-	void unregister_asymmetric_key_parser(struct asymmetric_key_parser *subtype);
-
-Parsers may not have the same name.  The names are otherwise only used for
-displaying in debugging messages.
-
-
-=========================
-KEYRING LINK RESTRICTIONS
-=========================
-
-Keyrings created from userspace using add_key can be configured to check the
-signature of the key being linked.  Keys without a valid signature are not
-allowed to link.
-
-Several restriction methods are available:
-
- (1) Restrict using the kernel builtin trusted keyring
-
-     - Option string used with KEYCTL_RESTRICT_KEYRING:
-       - "builtin_trusted"
-
-     The kernel builtin trusted keyring will be searched for the signing key.
-     If the builtin trusted keyring is not configured, all links will be
-     rejected.  The ca_keys kernel parameter also affects which keys are used
-     for signature verification.
-
- (2) Restrict using the kernel builtin and secondary trusted keyrings
-
-     - Option string used with KEYCTL_RESTRICT_KEYRING:
-       - "builtin_and_secondary_trusted"
-
-     The kernel builtin and secondary trusted keyrings will be searched for the
-     signing key.  If the secondary trusted keyring is not configured, this
-     restriction will behave like the "builtin_trusted" option.  The ca_keys
-     kernel parameter also affects which keys are used for signature
-     verification.
-
- (3) Restrict using a separate key or keyring
-
-     - Option string used with KEYCTL_RESTRICT_KEYRING:
-       - "key_or_keyring:<key or keyring serial number>[:chain]"
-
-     Whenever a key link is requested, the link will only succeed if the key
-     being linked is signed by one of the designated keys.  This key may be
-     specified directly by providing a serial number for one asymmetric key, or
-     a group of keys may be searched for the signing key by providing the
-     serial number for a keyring.
-
-     When the "chain" option is provided at the end of the string, the keys
-     within the destination keyring will also be searched for signing keys.
-     This allows for verification of certificate chains by adding each
-     certificate in order (starting closest to the root) to a keyring.  For
-     instance, one keyring can be populated with links to a set of root
-     certificates, with a separate, restricted keyring set up for each
-     certificate chain to be validated:
-
-	# Create and populate a keyring for root certificates
-	root_id=`keyctl add keyring root-certs "" @s`
-	keyctl padd asymmetric "" $root_id < root1.cert
-	keyctl padd asymmetric "" $root_id < root2.cert
-
-	# Create and restrict a keyring for the certificate chain
-	chain_id=`keyctl add keyring chain "" @s`
-	keyctl restrict_keyring $chain_id asymmetric key_or_keyring:$root_id:chain
-
-	# Attempt to add each certificate in the chain, starting with the
-	# certificate closest to the root.
-	keyctl padd asymmetric "" $chain_id < intermediateA.cert
-	keyctl padd asymmetric "" $chain_id < intermediateB.cert
-	keyctl padd asymmetric "" $chain_id < end-entity.cert
-
-     If the final end-entity certificate is successfully added to the "chain"
-     keyring, we can be certain that it has a valid signing chain going back to
-     one of the root certificates.
-
-     A single keyring can be used to verify a chain of signatures by
-     restricting the keyring after linking the root certificate:
-
-	# Create a keyring for the certificate chain and add the root
-	chain2_id=`keyctl add keyring chain2 "" @s`
-	keyctl padd asymmetric "" $chain2_id < root1.cert
-
-	# Restrict the keyring that already has root1.cert linked.  The cert
-	# will remain linked by the keyring.
-	keyctl restrict_keyring $chain2_id asymmetric key_or_keyring:0:chain
-
-	# Attempt to add each certificate in the chain, starting with the
-	# certificate closest to the root.
-	keyctl padd asymmetric "" $chain2_id < intermediateA.cert
-	keyctl padd asymmetric "" $chain2_id < intermediateB.cert
-	keyctl padd asymmetric "" $chain2_id < end-entity.cert
-
-     If the final end-entity certificate is successfully added to the "chain2"
-     keyring, we can be certain that there is a valid signing chain going back
-     to the root certificate that was added before the keyring was restricted.
-
-
-In all of these cases, if the signing key is found the signature of the key to
-be linked will be verified using the signing key.  The requested key is added
-to the keyring only if the signature is successfully verified.  -ENOKEY is
-returned if the parent certificate could not be found, or -EKEYREJECTED is
-returned if the signature check fails or the key is blacklisted.  Other errors
-may be returned if the signature check could not be performed.