Open eCard

h1. PKCS11

The main goal of the PKCS#11-interface of the Open eCard App is to provide the functionality, which is required by Mozilla’s Firefox browser.

Mozilla’s overall crypto architecture as taken from [Grif09] is depicted in Figure 1.

!mozilla-crypto-architecture.jpg!

_Figure 1: Mozilla's Cryptographic Architecture_

The important part is the usage of the PKCS#11-interface by the “Core Crypto Code” within the “Network Security Services” as explained in [NSS-PKCS#11]. 

As this browser is a successor of Netscape’s Communicator it is expected that the PKCS#11-usage in today’s Firefox is similar to the PKCS#11-usage explained in [NSS-PKCS#11]. 

h2. Required Functions

h3. General-Purpose Functions

Among the general-purpose functions defined in Section 11.4 of [NSS-PKCS#11] the following functions need to be supported:

* C_Initialize

* C_Finalize

* C_GetFunctionList

* C_GetInfo

*C_Initialize*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_Initialize on startup or when it loads a new module. The Netscape Security Library always passes NULL, as required by the PKCS #11 specification, in the single C_Initialize parameter pReserved. This function will use the IFD-function EstablishContext to initialize the IFD-module.

*C_Finalize*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_Finalize on shutdown and whenever it unloads a module.

This function will use the IFD-function ReleaseContext to initialize the IFD-module.

*C_GetInfo*

The Netscape Security Library calls C_GetInfo on startup or when it loads a new module. The version numbers, manufacturer IDs, and so on are displayed when the user views the information. The supplied library names are used as the default library names; currently, these names should not include any double quotation marks. 

This function will only return static information and does not involve any IFD-function.

*C_GetFunctionList*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_GetFunctionList on startup or when it loads a new module. In [NSS-PKCS#11] it is recommended that for a not implemented function there should at least be a stub that returns CKR_FUNCTION_NOT_SUPPORTED. 

This function will only return static information and does not involve any IFD-function.

h3. Slot and Token Management

*C_GetSlotList*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_GetSlotList on startup or when it loads a new module, requests all the module's slots, and keeps track of the list from that point on. The slots are expected to remain static: that is, the module never has more slots or fewer slots than the number on the original list. This means that the function C_WaitForSlotEvent is not used by the Netscape Se-curity Library. 

This function uses the following IFD-functions:

* ListIFDs

* GetIFDCapabilities

* GetStatus

*C_GetSlotInfo*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_GetSlotInfo on startup or when it loads a new module and reads in the information that can be viewed on the slot information page. If the CKF_REMOVABLE_DEVICE flag is set, the Netscape Security Library also calls C_GetSlotInfo whenever it looks up slots to make sure the token is present. If the CKF_REMOVABLE_DEVICE flag is not set, the Netscape Security Library uses that token information without checking again.

If the CKF_REMOVABLE_DEVICE flag is not set, the CKF_TOKEN_PRESENT flag must be set, or else the Netscape Security Library marks the slot as bad and will never use it.

The Netscape Security Library doesn't currently use the CKF_HW_SLOT flag.

For a particular slot this function returns the following structure:

<pre><code class="c">

typedef struct CK_SLOT_INFO {

    CK_UTF8CHAR slotDescription[64];

    CK_UTF8CHAR manufacturerID[32];

    CK_FLAGS flags;

    CK_VERSION hardwareVersion;

    CK_VERSION firmwareVersion;

} CK_SLOT_INFO;

</code></pre>

*C_GetTokenInfo*

If a token is a permanent device (that is, if the CKF_REMOVABLE_DEVICE flag is not set), the Netscape Security Library calls C_GetTokenInfo only on startup or when it loads a new module. If the token is a removable device, the Netscape Security Library may call C_GetTokenInfo anytime it's looking for a new token to check whether the token is write protected, whether it can generate random numbers, and so on.

The Netscape Security Library expects CK_TOKEN_INFO.label to contain the name of the token.

If the CKF_WRITE_PROTECTED flag is set, the Netscape Security Library won't use the token to generate keys.

The Netscape Security Library interprets the combination of the CKF_LOGIN_REQUIRED and CKF_USER_PIN_INITIALIZED flags as shown in the following table.

TODO: insert table

For a typical signature card in operational mode the two flags are TRUE. On the other side the two flags for the private key on the eGK, which is used for card2card-authentication, are both FALSE.

This function returns the CK_TOKEN_INFO struct for a specific token.

<pre><code class="c">

typedef struct CK_TOKEN_INFO {

    CK_UTF8CHAR label[32];

    CK_UTF8CHAR manufacturerID[32];

    CK_UTF8CHAR model[16];

    CK_CHAR serialNumber[16];

    CK_FLAGS flags;

    CK_ULONG ulMaxSessionCount;

    CK_ULONG ulSessionCount;

    CK_ULONG ulMaxRwSessionCount;

    CK_ULONG ulRwSessionCount;

    CK_ULONG ulMaxPinLen;

    CK_ULONG ulMinPinLen;

    CK_ULONG ulTotalPublicMemory;

    CK_ULONG ulFreePublicMemory;

    CK_ULONG ulTotalPrivateMemory;

    CK_ULONG ulFreePrivateMemory;

    CK_VERSION hardwareVersion;

    CK_VERSION firmwareVersion;

    CK_CHAR utcTime[16];

} CK_TOKEN_INFO;

</code></pre>

*C_GetMechanismList*

As explained in [NSS-PKCS#11], the Netscape Security Library calls C_GetMechanismList fairly frequently to identify the mechanisms supported by a token.

This function returns the CK_MECHANISM_INFO struct for a specific token.

<pre><code class="c">

typedef struct CK_MECHANISM_INFO {

    CK_ULONG ulMinKeySize;

    CK_ULONG ulMaxKeySize;

    CK_FLAGS flags;

} CK_MECHANISM_INFO;

</code></pre>

TODO: insert table

h3. Session Management

*C_OpenSession*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_OpenSession whenever it initializes a token and keeps the session open as long as possible. The Netscape Security Library almost never closes a session after it finishes doing some-thing with a token. It uses a single session for all single-part RSA operations such as logging in, logging out, signing, verifying, generating keys, wrapping keys, and so on.

The Netscape Security Library opens a separate session for each part of a multipart encryption (bulk encryption). If it runs out of sessions, it uses the initial session for saves and restores.

This function will use the IFD-function Connect to open a session to the token.

*C_CloseSession*

As explained in [NSS-PKCS#11] the Netscape Security Library calls C_CloseSession to close sessions created for bulk encryption.

This function will use the IFD-function Disconnect to close a session to the token.

*C_CloseAllSessions*

As explained in [NSS-PKCS#11] the Netscape Security Library may call C_CloseAllSessions when it closes down a slot.

*C_GetSessionInfo*

The Netscape Security Library calls C_GetSessionInfo frequently.

If a token has been removed during a session, C_GetSessionInfo should return either CKR_SESSION_CLOSED or CKR_SESSION_HANDLE_INVALID. If a token has been removed and then the same or another token is inserted, C_GetSessionInfo should return CKR_SESSION_HANDLE_INVALID.

*C_Login*

The Netscape Security Library calls C_Login on a token's initial session whenever CKF_LOGIN_REQUIRED is TRUE and the user state indicates that the user isn't logged in.

This function will use the IFD-function VerifyUser to perform the authentication of a user.

*C_Logout*

The Netscape Security Library calls C_Logout on a token's initial session

* when the password is timed out

* when performing any kind of private key operation if "ask always" is turned on

* when changing a password

* when the user logs out

h3. Object Management

In the scope of a TLS-handshake the client needs to read the certificate from the card and send it to the server. This functionality is most likely  performed using the following two functions.

*C_GetAttributeValue*

The Netscape Security Library calls C_GetAttributeValue to get the value of attrib-utes for both single objects and multiple objects. This is useful for extracting public keys, nonsecret bulk keys, and so on.

*C_FindObjectsInit, C_FindObjects, C_FindFinal*

The Netscape Security Library calls these functions frequently to look up objects by CKA_ID or CKA_LABEL. These values must match the equivalent values for related keys and certificates and must be unique among key pairs on a given token.

The Netscape Security Library also looks up certificates by CK_ISSUER and CK_SERIAL. If those fields aren't set on the token, S/MIME won't work.

h3. Cryptographic Operations

In the scope of a TLS-handshake the client needs to sign data, which is constructed based on previously exchanged messages in the handshake. This signature is most likely  created using the functions C_SignInit, C_Sign and C_SignFinal.

h2. References

[Grif09] R. Griffin: Encryption and Key Management Tutorials, Part II: PKCS #11 – Enhancements and Opportunities, Talk at RSA 2009, ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-11/v2-30/TUT-M51_Griffin_PKCS11.pdf

[NSS-PKCS#11] Implementing PKCS #11 for the Netscape Security Library, http://docs.oracle.com/cd/E19957-01/816-6150-10/pkcs.htm