digsig.txt: standardize document format

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- comment the internal index;
- use the proper markups for titles;
- mark literal blocks.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/digsig.txt

+==================================
 Digital Signature Verification API
+==================================
 
-CONTENTS
+:Author: Dmitry Kasatkin
+:Date: 06.10.2011
 
-1. Introduction
-2. API
-3. User-space utilities
 
+.. CONTENTS
 
-1. Introduction
+   1. Introduction
+   2. API
+   3. User-space utilities
+
+
+Introduction
+============
 
 Digital signature verification API provides a method to verify digital signature.
 Currently digital signatures are used by the IMA/EVM integrity protection subsystem.
@@ -17,17 +24,17 @@ GnuPG multi-precision integers (MPI) library. The kernel port provides
 memory allocation errors handling, has been refactored according to kernel
 coding style, and checkpatch.pl reported errors and warnings have been fixed.
 
-Public key and signature consist of header and MPIs.
+Public key and signature consist of header and MPIs::
 
-struct pubkey_hdr {
+	struct pubkey_hdr {
 		uint8_t		version;	/* key format version */
 		time_t		timestamp;	/* key made, always 0 for now */
 		uint8_t		algo;
 		uint8_t		nmpi;
 		char		mpi[0];
-} __packed;
+	} __packed;
 
-struct signature_hdr {
+	struct signature_hdr {
 		uint8_t		version;	/* signature format version */
 		time_t		timestamp;	/* signature made */
 		uint8_t		algo;
@@ -35,7 +42,7 @@ struct signature_hdr {
 		uint8_t		keyid[8];
 		uint8_t		nmpi;
 		char		mpi[0];
-} __packed;
+	} __packed;
 
 keyid equals to SHA1[12-19] over the total key content.
 Signature header is used as an input to generate a signature.
@@ -43,14 +50,15 @@ Such approach insures that key or signature header could not be changed.
 It protects timestamp from been changed and can be used for rollback
 protection.
 
-2. API
+API
+===
 
-API currently includes only 1 function:
+API currently includes only 1 function::
 
 	digsig_verify() - digital signature verification with public key
 
 
-/**
+	/**
 	* digsig_verify() - digital signature verification with public key
 	* @keyring:	keyring to search key in
 	* @sig:	digital signature
@@ -64,10 +72,11 @@ API currently includes only 1 function:
 	* Normally hash of the content is used as a data for this function.
 	*
 	*/
-int digsig_verify(struct key *keyring, const char *sig, int siglen,
+	int digsig_verify(struct key *keyring, const char *sig, int siglen,
 			  const char *data, int datalen);
 
-3. User-space utilities
+User-space utilities
+====================
 
 The signing and key management utilities evm-utils provide functionality
 to generate signatures, to load keys into the kernel keyring.
@@ -75,22 +84,18 @@ Keys can be in PEM or converted to the kernel format.
 When the key is added to the kernel keyring, the keyid defines the name
 of the key: 5D2B05FC633EE3E8 in the example bellow.
 
-Here is example output of the keyctl utility.
+Here is example output of the keyctl utility::
 
-$ keyctl show
-Session Keyring
+	$ keyctl show
+	Session Keyring
 	-3 --alswrv      0     0  keyring: _ses
-603976250 --alswrv      0    -1   \_ keyring: _uid.0
-817777377 --alswrv      0     0       \_ user: kmk
-891974900 --alswrv      0     0       \_ encrypted: evm-key
-170323636 --alswrv      0     0       \_ keyring: _module
-548221616 --alswrv      0     0       \_ keyring: _ima
-128198054 --alswrv      0     0       \_ keyring: _evm
-
-$ keyctl list 128198054
-1 key in keyring:
-620789745: --alswrv     0     0 user: 5D2B05FC633EE3E8
-
-
-Dmitry Kasatkin
-06.10.2011
+	603976250 --alswrv      0    -1   \_ keyring: _uid.0
+	817777377 --alswrv      0     0       \_ user: kmk
+	891974900 --alswrv      0     0       \_ encrypted: evm-key
+	170323636 --alswrv      0     0       \_ keyring: _module
+	548221616 --alswrv      0     0       \_ keyring: _ima
+	128198054 --alswrv      0     0       \_ keyring: _evm
+
+	$ keyctl list 128198054
+	1 key in keyring:
+	620789745: --alswrv     0     0 user: 5D2B05FC633EE3E8