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NSS Shared DB

Revision as of 22:32, 8 May 2007 by Relyea (talk | contribs) (→‎Layering)

Shared Database Proposal

NSS has not updated it's database format since 199x. Over the years the restrictions created by the current database has become more accute. Of these restrictions, the lack of the ability for applications to share certificate and key database has been one of the more severe. As more applications use NSS, the need for each one to manage a database separately becomes unnecessary overhead.

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.

Besides the lack of shared database, other issues with the current NSS database scheme include:

  1. The need for a more flexible schema which can handle storing more meta information about certificates and keys, particular finer grain information about the trust of a certificate.
  2. The need to match the underlying certificate and key storage with it's reflection into NSS (that is PKCS #11).
  3. FIPS requires integrity checks on critical keys and trust objects. We need to be able to store that information in the database.

Where we are today

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

  • cert8.db - stores publicly accessible objects (certs, CRLs, S/MIME 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 (cert7.db, cert5.db, etc.) and build a new cert8.db if 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 its path and load it. This shared library is expected to implement a 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 from NSS. The library does not do any formatting of the data.

What we want to do

We want to move key3 and cert8 into new SQL databases called key4.db and cert9.db. These databases 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. Softoken will automatically identify any cert9.db which has an imbedded key store and open that key store up. By default a separate key4.db and cert9.db will be opened. In the first release there will be no way to create a combined cert/keydb.

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 PKCS #5 PBE in the same way the pkcs8 private and secret key data is 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 will be handled by storing a special value which means 'NULL' when writing a NULL record.
    • integrity will be maintained by a PBE based MAC on critical attributes.

Out of band data necessary for the proper operation of softoken, but not reflected back to NSS in general (currently this only applies to password entries), will be stored in separate tables in the database with their own schema.

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_TRUST_EXTENSION_OVERRIDE to trust objects to add or override existing certificate extensions).
  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*)

Softoken will be able to store the following objects and attributes.

< table Here >

Accessing the shared Database

In order to maintain binary compatibility, the following keywords will be understood and used by softoken.

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, the plain directory spec as the same as dbm:directory unless overridden with the NSS_DEFAULT_DATABASE environment variable. Applications will not need to change for this release of NSS. (particularly unfriendly applications that want to tweak with the actual database file). Users can force older applications to share the database with the environment variable. The environment variable only affects non-tagged directories.

When accessing the dbm: and multiaccess: directories, external shared library will be loaded which 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 directory with separate flat files containing text files of the format specified in the PKCS #11 working group, but not yet included in any spec. This directory will be opened, locked, used, then closed (much like the current secmod.db). The directory will live as a sub directory of the directory that holds cert9.db/key4.db. As a directory of flat files it would not use the sqlite database to access these records. The file name should become pkcs11.

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

Review Input Requested: 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.

Upgrade itself is an issue. Do we want to support automatic upgrade (as we do today for older cert db types), or do we want to supply the application with an upgrade tool. The complication comes when we need to upgrade multiple old databases into a new one.

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 (not the database adapter layer) will manage canonicalizing any CK_ULONGs, encrypting or decrypting private data blobs, checking integrity and deciding what attributes an object should have and setting the appropriate defaults if necessary.

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

The database layer must be multi-thread safe. If the underlying database is not thread safe, sdb_ layer must implement the appropriate locking.

s_open

The database API consists of an initialization call, which returns an SDB data structure (defined below). 

CK_RV
s_open(const char *directory, int cert_version,
       int key_version, int flags, SDB **certdb, SDB **keydb)

The sdb_init function takes:

  • directory full path to where the database lives.
  • cert_version current version is the current database version
  • key_version is the current key database version
  • flags are:
    • FORCE
    • READONLY
    • READ/WRITE/CREATE
  • certdb is the returned cert SDB structure
  • keydb is the returned key SDB structure

(NOTE: the signature of this function is likely to change. Comments on how to change it would be appreciated.

Issues include:

  1. Should cert and key versions be part of the API, or should they be part of the underlying database?
  2. The cert and key prefix values are missing and should be added.
  3. Do we need separate create flag or is the combined READ/WRITE/CREATE sufficient?
  4. Do we need a way to supply the list of know attributes so old DB's can be updated and initialized properly?

The returned SDB structure has the following format: 

typedef struct SDBStr SDB;

struct SDBStr {
   void *private;
   int  sdb_type;
   int  sdb_flags;
   int  sdb_version;
   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:

  • private is a pointer to opaque private data specific to the Shared DB implementation.
  • sdb_type is the type of database (key [aka private] or cert [aka public]).
  • sdb_flags specifies how the database was opened (ReadOnly, Create, etc).
  • sdb_version specifies the version of the underlying sdb structure. This allows us to handle future expansion of the sdb data structure safely.
  • The rest are function pointers to database primitives described next.
sdb_FindObjectsInit
CK_RV (*sdb_FindObjectsInit)(SDB *sdb, const CK_ATTRIBUTE *template,
                                int count, SDBFind **find);

This function is the equivalent of PKCS #11 C_FindObjectsInit(). It returns a SDBFind context with is opaque to the caller. The caller must call sdb_FindObjectsFinal with this context if sdb_FindobjectsInit succeeds.

sdb_FindObjects
CK_RV (*sdb_FindObjects)(SDB *sdb, SDBFind *find, CK_OBJECT_HANDLE *ids,
                               int arraySize, int *count);

This function is the equivalent of PKCS #11 C_FindObjects(). It takes a SDBFind context returned by sdb_FindObjectsInit. This function has the same semantics as C_FindObjects with respect to handling how many objects are returned in a single call.

sdb_FindObjectsFinal
CK_RV (*sdb_FindObjectsFinal)(SDB *sdb, SDBFind *find);

This function is the equivalent of PKCS #11 C_FindObjectsFinal(). It frees any resources associated with SDBFIND.

sdb_GetAttributeValue
CK_RV (*sdb_GetAttributeValue)(SDB *sdb, CK_OBJECT_HANDLE object,
                               CK_ATTRIBUTE *template, int count);

This function is the equivalent of PKCS #11 C_GetAttributeValue(). It has the same memory allocation and error code semantics of the PKCS #11 call. The attributes passed to sdb_GetAttributeValues are already transformed from their native representations in the following ways:

  1. CKU_LONG values are stored as 32-bit values in network byte order.
  2. Private attributes will be encrypted.
sdb_SetAttributeValue
CK_RV (*sdb_SetAttributeValue)(SDB *sdb, CK_OBJECT_HANDLE object,
                               const CK_ATTRIBUTE *template, int count);

This function is the equivalent of PKCS #11 C_SetAttributeValue(). The attributes returned to sdb_SetAttributeValues are transformed from their native representations in the following ways:

  1. CKU_LONG values returned 32-bit values in network byte order.
  2. Private attributes returned encrypted.
sdb_CreateObject
CK_RV (*sdb_CreateObject)(SDB *sdb, CK_OBJECT_HANDLE *object,
                               const CK_ATTRIBUTE *template, int count);

This function is the equivalent of PKCS #11 C_CreateObject(). The value of 'object' is chosen by the implementer of sdb_CreateObject. This value must be unique for this sdb instance. It should be no more than 30 bits long.

sdb_DestroyObject
CK_RV (*sdb_DestroyObject)(SDB *sdb, CK_OBJECT_HANDLE object);

This function is the equivalent of PKCS #11 C_Destroy object(). It removed the object from the database.

sdb_GetPWEntry
CK_RV (*sdb_GetPWEntry)(SDB *sdb, SDBPasswordEntry *entry);

Get the password entry. This only applies to the private database.

Review input needed: Would it be better to define a 'metadata' operation where we call the database to fetch data that is not reflected through the PKCS #11 interface?

sdb_PutPWEntry
CK_RV (*sdb_PutPWEntry)(SDB *sdb, SDBPasswordEntry *entry);

Write the password entry. This only applies to the private database. Writing a password entry will overwrite the old entry.

Would it be better to define a 'metadata' operation where we call the database to put data that is not reflected through the PKCS #11 interface?

sdb_Begin
CK_RV (*sdb_Begin)(SDB *sdb);

Begin a transaction. Any write to the database (sdb_CreateObject, sdb_DestroyObject, sdb_SetAttributeValue) must be accomplished while holding a transaction. Transactions are completed by calling sdb_Commit to commit the change, or sdb_Abort to discard the change. More than one write operation may be made while holding a transaction. Aborting the transaction will discard all writes made while in the transaction.

sdb_Commit
CK_RV (*sdb_Commit)(SDB *sdb);

Commit a transaction. Any write to the database (sdb_CreateObject, sdb_DestroyObject, sdb_SetAttributeValue) must be accomplished while holding a transaction. Transactions are completed by calling sdb_Commit to commit the change, or sdb_Abort to discard the change. More than one write operation may be made while holding a transaction.

sdb_Abort
CK_RV (*sdb_Abort)(SDB *sdb);

Abort a transaction. Any write to the database (sdb_CreateObject, sdb_DestroyObject, sdb_SetAttributeValue) must be accomplished while holding a transaction. Transactions are completed by calling sdb_Commit to commit the change, or sdb_Abort to discard the change. More than one write operation may be made while holding a transaction. Aborting the transaction will discard all writes made while in the transaction.

sdb_Close
CK_RV (*sdb_Close)(SDB *sdb);

Close the SDB and free up any resources associated with it.

legacy DB support

The old dbm code can be supported with the above SDB structure with the following exceptions:

  1. The old db code cannot be extensible (can't dynamically handle new types).
  2. A private interface may be needed to unwrap the private keys, or provide a handle to the password so the keys can be presented in the attribute format.

This code would live in its own shared library. Most of the low level cert, CRL, key handling, and translation to PKCS #11 objects and attributes that was part of softoken will moved to this legacy shared library. It will be loaded whenever access to old databases is required.

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