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 ([Grif09], p. 22)_

 

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 Security 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>

_Listing 1: @CK_SLOT_INFO@ structure_

 

*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.

|_. @CFK_LOGIN_REQUIRED@ |_. @CFK_USER_PIN_INITIALIZED@ |_. Netscape Security Library assumes that: |

| @FALSE@                | @FALSE@                      | This is a general access device. The Netscape Security Library will use it without prompting the user for a PIN. |

| @TRUE@                 | @FALSE@                      | The device is uninitialized. The Netscape Security Library attempts to initialize the device only if it needs to generate a key or needs to set the user PIN. The Netscape Security Library calls @C_InitPIN@ to initialize the device and set the user PIN; if these calls are successful, the key is generated and at that point the @CFK_USER_PIN_INITIALIZED@ flag should change from @FALSE@ to @TRUE@. |

| @FALSE@                | @TRUE@                       | This is a general access device that can have a PIN set on it. Because it's a general access device, the Netscape Security Library never prompts for the PIN, even though it's possible to set a PIN with @C_SetPIN@. If the PIN is set successfully, the @CFK_LOGIN_REQUIRED@ flag should change to @TRUE@. The Netscape Security Library uses this combination of flags for its internal token when the key database password is @NULL@. These are not standard PKCS #11 semantics; they are intended for the Netscape Security Library's internal use only. |

| @TRUE@                 | @TRUE@                       | The device has been initialized and requires authentication. The Netscape Security Library checks whether the user is logged on, and if not prompts the user for a PIN. |

_Table 1: Interpretation of flags ([NSS-PKCS#11], Table 1.1)_

 

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>

_Listing 2: @CK_TOKEN_INFO@ structure ([PKCS#11(v2.3)], p. 37)_

 

*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>

_Listing 3: @CK_MECHANISM_INFO@ structure ([PKCS#11(v2.3)], p. 49)_

 

|_. Bit Flag              |_. Mask     |_. Meaning |

| @CKF_HW@                | 0x00000001 | True if the mechanism is performed by the device; false if the mechanism is performed in software   |

| @CKF_ENCRYPT@           | 0x00000100 | True if the mechanism can be used with @C_EncryptInit@                                              |

| @CKF_DECRYPT@           | 0x00000200 | True if the mechanism can be used with @C_DecryptInit@                                              |

| @CKF_DIGEST@            | 0x00000400 | True if the mechanism can be used with @C_DigestInit@                                               |

| @CKF_SIGN@              | 0x00000800 | True if the mechanism can be used with @C_SignInit@                                                 |

| @CKF_SIGN_RECOVER@      | 0x00001000 | True if the mechanism can be used with @C_SignRecoverInit@                                          |

| @CKF_VERIFY@            | 0x00002000 | True if the mechanism can be used with @C_VerifyInit@                                               |

| @CKF_VERIFY_RECOVER@    | 0x00004000 | True if the mechanism can be used with @C_VerifyRecoverInit@                                        |

| @CKF_GENERATE@          | 0x00008000 | True if the mechanism can be used with @C_GenerateKey@                                              |

| @CKF_GENERATE_KEY_PAIR@ | 0x00010000 | True if the mechanism can be used with @C_GenerateKeyPair@                                          |

| @CKF_WRAP@              | 0x00020000 | True if the mechanism can be used with @C_WrapKey@                                                  |

| @CKF_UNWRAP@            | 0x00040000 | True if the mechanism can be used with @C_UnwrapKey@                                                |

| @CKF_DERIVE@            | 0x00080000 | True if the mechanism can be used with @C_DeriveKey@                                                |

| @CKF_EXTENSION@         | 0x80000000 | True if there is an extension to the flags; false if no extensions. Must be false for this version. |

_Table 2: Mechanism Information Flags ([PKCS#11(v2.3)], p. 50)_

 

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 something 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 attributes 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

[PKCS#11(v2.3)]	RSA Laboratories: PKCS #11 Base Functionality v2.30: Cryptoki – Draft 4, 10 July 2009

h2. Additional links

PKCS11 FAQ

https://developer.mozilla.org/en-US/docs/PKCS11_FAQ

Using the PKCS #11 Module Logger

NSS Technical Note: 2

http://www.mozilla.org/projects/security/pki/nss/tech-notes/tn2.html