NSS Shared DB

Shared Database Proposal

Applications have been chaffing at the restrictions of the current NSS database for quite some time now. In 2001 we built some tools to work around those restrictions so certain applications could share the database if they supplied their own shared database implementation, and configured NSS to use that implementation. Today we have a process level, ACID, open source, and widely available database called SQLite. In addition, there is a strong desire to make NSS the system security service for Linux. I am proposing how we could leverage this database to give all of our applications Shared Database access.

Where we are today

At initialization time, NSS currently takes an argument which points to some directory the application uses to store it's private configuration data. NSS uses 3 libdbm files in that directory:

• cert8.db - stores publicly accessible objects (certs, crls, smime records).
• key3.db - stores the private keys.
• secmod.db - stores the pkcs #11 module configuration.

In addition:

• NSS may also use a directory called cert8.dir to store very large blobs (typically large CRLs).
• NSS may read from from previous certificate database and build a new cert8.db it it doesn't exist.

These files are all accessed through the softoken, making libsoftokn3.so the only NSS library that needs to link with libdbm.

If the directory argument passed to NSS starts with the string 'multiaccess:', NSS does not use it as a directory path. Instead, NSS parses the string out as follows:

multiaccess:appName[:directory]

Where:
multicaccess is a keyword.
appName is a unique string for each group of applications which share the database.
directory is an optional parameter pointing to an NSS non-shared database which NSS will use to update the shared database from on loading.

NSS will find librdb.so (rdb.dll on windows) in it's patch and load it. This shared library is expected to implement a small superset of the standard libdbm interface. The main entry point is rdbopen, which will pass the appName, database name, and open flags. The rdb shared library will pick a location or method to store the database (it may not necessarily be a file), then handle the raw db records form NSS. The library does not do any formatting of the data.

What we want to do

We want to move key3 and cert8 into a new SQL databases called key4.db and cert9.db. This database will store the PKCS #11 objects currently stored or implied in cert8 and key3.

Optionally the databases could be combined into a single database, cert9.db, where private and public objects are stored in separate tables.

schema

The schema for the database will be simple.

• Each row will represent an object.
• The row schema will contain the the Object ID and the list of known Attribute Types.
• Newer versions of NSS may add new attribute types on the fly as necessary (extending the schema).
• The Attribute values will be stored as binary blobs.
  • Attributes that represent CK_ULONG values will be stored as 32-bit values in network byte order.
  • All other objects, byte order is already specified by PKCS #11.
  • Private attributes will be encrypted with a pkcs5 PBE in the same way private and secret keys are encrypted today.
  • Softoken will only set those attributes appropriate for the given object. If The attribute is not appropriate it will be left blank. (Note that sqlite does not distinguish between a NULL attribute and an empty one. This can be handled in the following ways:
    1. add a 'record' value around each attribute, where meta-data can be stored in the record. one of the meta-data values is that the record is empty.
    2. don't try to distinguish between a NULL attribute and a non-existant one.
    3. store a special value which means 'NULL' when writing a NULL record. (This is the current proposal).

Database extension is accomplished in 2 ways:

1. New attributes are added to the list known attributes and to already defined PKCS #11 objects. Older database objects can be detected because they will have 'invalid' values for these attributes (example, could add CKA_ONLY_FOR_URL to trust objects).
2. Add new PKCS #11 objects to hold the data (example, could add a new SSL_DATA record to store mappings to various certificates to different cipher suites and host name*)

NOTE: * I'm not suggesting this be the design for handling the SSL mapping problem, only as an example for the kind of thing that can be added to the database even after this deployment.

Accessing the shared Database

In order to maintain binary compatibility, I propose extending the keyword usage in NSS as follows:

multiaccess:appName[:directory] works as it does today, including using the cert8/key3 record version.
dbm:directory opens an existing non-shared libdbm version 8 database.
sql:directory1[:directory2] opens a shared database, cert9.db (& key4.db) in directory1 if cert9.db does exist. If the database does not exist, then directory2 is searched for a libdbm cert8.db and key3.db. If directory2 is not supplied, directory1 is searched.
extern:directory open a sql-like database by loading an external module, a. la. rdb and multiaccess:. This option would not be implemented in the initial release, but the extern: keyword would be reserved for future use.

Plain directory spec. For binary compatibility, we can treat the plain directory spec as the same as dbm:directory. In this case applications will not need to change for this release of NSS. (particularly unfriendly applications that want to tweak with the actual database file). Alternatively, we could treat it as sql:directory. In this case existing applications will get the benefits of shared databases immediately, though we risk breaking those aforementioned applications.

When accessing the dbm: and multiaccess: directories, external shared library will be loaded with knows how to handle these legacy databases. This allows us to move much of the current mapping code into this shared library.

Secmod.db

In the dbm: and multiaccess: cases, there will be no changes to secmod.db.

In the sql: case, a new flat text file of the format specified in the PKCS #11 working group, but not yet included in any spec. This file will be opened, locked, used, then closed (much like the current secmod.db). The file will live in the same directory as cert9.db/key4.db. As a flat file it would not use the sqlite database to access these records. The file name should become pkcs11.txt or secmod.txt

User App Initialization and System App Initialization

One of the goals of making a shared database version of NSS is to create a 'system crypto library' in which applications will automatically share database and configuration settings. In order for this to work, applications need to be able to open NSS databases from standard locations.

This design assumes that new NSS init functions will be defined for applications wanting to do 'standard user initialization', rather than building special knowledge into softoken or the database model. Note: This is different from the 2001 design, or and earlier prototype shared database, where the database code knew the location of the shared database.

Other issues

Question, should we 'mark' old cert8/key3 databases as having been used to upgrade the shared database? The issue here is applications that were once separated, but now combined. It would be nice if the keys and certs in each of these databases were properly merged into the overall shared database.

Layering

In order to keep clean separation between the data and database operations, we will continue to maintain an layer between the actual data handling and interpretation and the database itself. The database code will not need to understand:

1. What objects are actually stored in it.
2. The types of the attributes.
3. The meaning of the stored data.

Softoken itself will manage cannonicalizing any CK_ULONGS, encrypting or decrypting private data blobs, and deciding what attributes an object should have and setting the appropriate defaults if necessary.

Since softoken deals with PKCS #11 templates internally, It's interface to the database will be in terms of those templates.

The database API would look like:

struct SDBStr {
   void *private;
   int  sdb_type;
   int  sdb_flags;
   CK_RV (*sdb_FindObjectsInit)(SDB *sdb, const CK_ATTRIBUTE *template,
                                int count, SDBFind **find);
   CK_RV (*sdb_FindObjects)(SDB *sdb, SDBFind *find, CK_OBJECT_HANDLE *ids,
                               int arraySize, int *count);
   CK_RV (*sdb_FindObjectsFinal)(SDB *sdb, SDBFind *find);
   CK_RV (*sdb_GetAttributeValue)(SDB *sdb, CK_OBJECT_HANDLE object,
                               CK_ATTRIBUTE *template, int count);
   CK_RV (*sdb_SetAttributeValue)(SDB *sdb, CK_OBJECT_HANDLE object,
                               const CK_ATTRIBUTE *template, int count);
   CK_RV (*sdb_CreateObject)(SDB *sdb, CK_OBJECT_HANDLE *object,
                               const CK_ATTRIBUTE *template, int count);
   CK_RV (*sdb_DestroyObject)(SDB *sdb, CK_OBJECT_HANDLE object);
   CK_RV (*sdb_GetPWEntry)(SDB *sdb, SDBPasswordEntry *entry);
   CK_RV (*sdb_PutPWEntry)(SDB *sdb, SDBPasswordEntry *entry);
   CK_RV (*sdb_Begin)(SDB *sdb);
   CK_RV (*sdb_Commit)(SDB *sdb);
   CK_RV (*sdb_Abort)(SDB *sdb);
   CK_RV (*sdb_Close)(SDB *sdb);
};

where:

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