VE 07KeyMgmt

This is a draft document

Key Management

1. Our private key and certificate databases are hash (DBM) indexed flat files (regular files).
2. Private keys and secret keys are stored in the private key database. At Security Level 1, the operating system is restricted to a single operator mode of operation, which protects against unauthorized disclosure, modification, and substitution of the private keys and secret keys stored in the private key database. At Security Level 2, we use the discretionary access control mechanism of the operating system on the private key database to protect against unauthorized disclosure, modification, and substitution of the private keys and secret keys stored in the private key database.
   The private keys and secret keys stored in the private key database are actually encrypted using three-key Triple DES in CBC mode (DES-EDE3-CBC) to provide additional protection against unauthorized disclosure, modification, and substitution. Although Triple DES is an Approved security function, the key encrypting key is derived from the user's password using an extension of the PKCS #5 PBKDF1 key derivation function (see the nsspkcs5_PBKDF1Extended function) with an iteration count of 1 and SHA-1 as the underlying hash function. Since password-based encryption such as PKCS #5 is not FIPS Approved, the private and secret keys in the private key database are considered in plaintext form by FIPS 140-2 (see FIPS 140-2 Section 4.7 and FIPS 140-2 IG 7.1). For more information on how the secret and private keys in the private key database are password-encrypted, see the nsspkcs5_CipherData function.
3. When the secret keys and private keys reside in memory, they are protected by the OS from unauthorized disclosure, modification, and substitution.
4. Public keys are stored in two ways.
   • Public keys in public/private key pairs (owned by the operator) are stored as attributes of the associated private keys in the private key database.
     Attributes of private keys are also password-encrypted as explained in the note above.
   • X.509 v3 certificates containing public keys are stored DER encoded in the certificate database. The certificates are not encrypted, but are digitally signed by the Certification Authority (CA) that created them.
   • At Security Level 1, the operating system is restricted to a single operator mode of operation, which protects against unauthorized modification and substitution of the public keys and certificates stored in the private key and certificate databases. At Security Level 2, we use the discretionary access control mechanism of the operating system on the private key and certificate databases to protect against unauthorized modification and substitution of the public keys and certificates stored in the private key and certificate databases.
5. When the public keys reside in memory, they are protected by the OS from unauthorized modification and substitution.
6. The NSS cryptographic module uses the following cryptographic keys, cryptographic key components, and CSPs in the FIPS Approved mode of operation:
   • AES secret keys
   • Triple DES secret keys
   • HMAC secret keys
   • DSA public keys and private keys
   • RSA public keys and private keys (used for key transport and digital signatures)
   • ECDSA public keys and private keys
   • Diffie-Hellman public keys and private keys (used for key agreement)
   • EC Diffie-Hellman public keys and private keys (used for key agreement)
   • seed keys (for the Approved RNG)
   • TLS premaster secret (used in deriving the TLS master secret)
   • TLS master secret (used in the generation of symmetric cipher keys, IVs, and MAC keys for TLS)
   • authentication data (passwords).
7. The NSS cryptographic module uses the following cryptographic keys internally. These keys are not visible to the operator.
   • The Triple DES key derived from the user's password, used to encrypt the secret keys and private keys stored in the private key database.
   • The 1024-bit DSA public keys for the software/firmware integrity test are stored along with the DSA signatures in the .chk files for the softoken (PKCS #11) and freebl shared libraries/DLLs. The DSA domain parameters (prime p, subprime q, base g) and public key (y) are stored in a straight binary format (i.e., not DER encoded).
8. PKCS #12 (or previously known as PFX) defines a protocol for wrapping (encrypting) and unwrapping (decrypting) private key material and related certificates for import/export.
9. The exported private key is encrypted with a DES-EDE3 (Triple DES) key derived from a user provided password -- see PKCS #5 below.
10. No passwords (e.g., the export password for PKCS #12, or the private key database password) are stored on disk in plaintext.
11. PKCS #5 is used to convert a user's password to a DES-EDE3 (Triple DES) key that is used to encrypt a known plaintext to determine if it matches the password stored in the database, or in the case of exported private key.
12. Prior to exiting the Cryptographic Module, all passwords entered by users and private key (stored on disk) are zeroized from memory.
13. PKCS #12 can be used to archive a wrapped (encrypted) private key for recovery purposes.
14. Our use of DES and DES-EDE3, as called out in PKCS #12, are FIPS 46-3 validated.
15. The NSS cryptographic module's Triple DES implementation conforms to FIPS 46-3. ( TripleDES)
16. The NSS cryptographic module's SHA-1 implementation conforms to FIPS 180-2. See SHS.
17. The NSS cryptographic module's DSA implementation conforms to FIPS 186-2. (DSA)

Key Generation

The FC_GenerateKey and FC_GenerateKeyPair functions of the NSS cryptographic module perform key generation. FC_GenerateKey generates secret keys and domain parameters, and FC_GenerateKeyPair generates public/private key pairs.

Approved key generation method: The NSS cryptographic module uses the Approved RNG specified as Algorithm 1 of FIPS 186-2 Change Notice 1 to generate cryptographic keys used by the Approved and non-Approved security functions. The validation certificate for the Approved RNG is Cert# 208.

Secret keys for symmetric key algorithms and HMAC are generated using the output of the Approved RNG.

DSA public and private keys are generated using the method specified in FIPS 186-2 with Change Notice 1.

RSA public and private keys are generated using the method specified in PKCS #1.

The prime numbers that are generated for both RSA and DSA are tested using Miller-Rabin test (FIPS 186-2 Appendix 2.1. A Probabilistic Primality Test).

ECDSA public and private keys are generated using the method specified in ANSI X9.62-1998.

Security of key generation method: The seed key of the Approved RNG is 256 bits. The keys generated by the NSS cryptographic module have at most 256 bits of security. (See NIST Special Publication (SP) 800-57 Part 1, Table 2 in Section 5.6.1 on page 63.) Therefore, compromising the security of the key generation method (e.g., guessing the seed value to initialize the Approved RNG) requires at least as many operations as determining the value of the generated key.

Key Establishment Techniques

The NSS cryptographic module uses the following asymmetric key establishment techniques listed in FIPS 140-2 Implementation Guidance Section 7.1, which FIPS 140-2 Annex D says are allowed in a FIPS Approved mode of operation:

• Diffie-Hellman (key agreement). The module supports Diffie-Hellman public key sizes of 1024-2236 bits, corresponding to 80-112 bits of security.
• EC Diffie-Hellman (key agreement). The module supports elliptic curve key sizes of 163-571 bits, corresponding to 80-256 bits of security.
• Key Wrapping using RSA keys (PKCS #1, key wrapping). The module supports RSA key sizes of 1024-8192 bits, corresponding to 80-192 bits of security.
  Note: The Cryptographic Algorithm Validation Program (CAVP) can only validate RSA key sizes up to 4096 bits, so our RSA algorithm implementation has only been validated for RSA key sizes of 1024-4096 bits.

The strengths of security of the asymmetric key establishment techniques are obtained from Table 2 of Section 5.6.1, NIST SP 800-57 Part 1.

Caveats:

Since the NSS cryptographic module allows a key establishment method to establish a cryptographic key that is stronger than the key establishment method, the following caveats are required by FIPS 140-2 IG 7.5:

• Diffie-Hellman (key agreement, key establishment methodology provides between 80 bits and 112 bits of encryption strength)
• EC Diffie-Hellman (key agreement, key establishment methodology provides between 80 bits and 256 bits of encryption strength)
• RSA (PKCS #1, key wrapping, key establishment methodology provides between 80 bits and 192 bits of encryption strength)

The Security Policy is also annotated with these caveats.

The NSS cryptographic module does not implement the Over-The-Air-Rekeying (OTAR) Protocol.

Entity Association Assurance

Each instance of the NSS cryptographic module is owned by a single operator (the module owner).

By definition, all the secret and private keys in the NSS cryptographic module are associated with the module owner.

The public and private keys are correlated based on their PKCS #11 CKA_ID attribute. The public and private keys in a key pair have the same CKA_ID value. In the NSS cryptographic module, the CKA_ID attribute of a public key or private key is the SHA-1 hash of (a component of) the (associated) public key.

If a public key's CKA_ID value is the same as that of a private key in the NSS cryptographic module, the public key is associated with the module owner. Otherwise, the public key is associated with an entity other than the module owner. Such a public key is usually extracted from a public key certificate, which contains the name of the entity associated with the public key, and imported into the NSS cryptographic module. The operator of the NSS cryptographic module is responsible for associating such a public key with the right entity. The NSS cryptographic module only knows such a public key doesn't belong to the module owner because it doesn't have the associated private key.

The NSS cryptographic module returns unique PKCS #11 object handles (CK_OBJECT_HANDLE) for the stored or imported cryptographic keys. With the object handles as unique identifiers, the operator can associate the keys with the correct entity (self or another entity).

Key Entry and Output Methods

The NSS cryptographic module does not employ either manual or electronic key entry and output methods.

The NSS cryptographic module does not support entry of the seed key during key generation.

The NSS cryptographic module uses automated key transport methods, so the cryptographic key being transported needs to meet the key entry/output requirements (in Section 4.7.4 of FIPS 140-2). Automated key transport methods use the FC_UnwrapKey and FC_WrapKey functions.

• The FC_UnwrapKey function enters an encrypted secret or private key into the NSS cryptographic module.
• The FC_WrapKey function outputs an encrypted secret or private key from the NSS cryptographic module.

For example, in a TLS handshake with RSA key exchange, the NSS SSL library (outside the cryptographic module boundary) calls FC_WrapKey to output the premaster secret (encrypted with the server's RSA public key) from the cryptographic module on the client side, sends it to the server in the ClientKeyExchange message, and calls FC_UnwrapKey to enter the RSA-encrypted premaster secret into the cryptographic module on the server side.

Encrypted secret and private keys, entered into or output from the NSS cryptographic module and used in the FIPS Approved mode of operation, are encrypted using one of the following Approved algorithms:

• Key Wrapping using RSA keys
• AES
• Triple DES

Note: If the AES or Triple DES key is derived from a password, the encrypted secret or private key is considered to be in plaintext form because password-based encryption is not FIPS Approved.

In the FIPS Approved mode of operation, secret and private keys established using automated methods (e.g., key transport protocols such as Key Wrapping using RSA keys) can only be entered into or output from the NSS cryptographic module in encrypted form (using FC_UnwrapKey and FC_WrapKey).

Random Number Generator

There are three random number generators (RNGs) used in the NSS cryptographic module.

The first RNG is the Standard C Library function rand() (declared in the header file <stdlib.h>). The rand() function is a non-Approved RNG and used within the NSS cryptographic module only for probabilistic algorithms such as the Miller-Rabin primality test.

The second RNG (on Unix and Unix-like platforms only) is the special device /dev/urandom. It is a non-Approved RNG and used only once during the library initialization of the NSS cryptographic module for generating (1024 bytes) seeds for the Approved RNG, described next.

The third RNG is an Approved RNG, implementing Algorithm 1 of FIPS 186-2 Change Notice 1. (The RNG validation certificate is Cert# 208.) The Approved RNG is used within the NSS cryptographic module for all cryptographic purposes, including the generation of cryptographic keys used by an Approved security function.

If the seed and seed key input to the Approved RNG have the same value, the Approved RNG returns a failure status code and doesn't produce any output. The check is done by the memcmp function call in the function FIPS186Change_GenerateX:

           if (memcmp(XKEY_old, XSEEDj, BSIZE) == 0) {
               /* Should we add the error code SEC_ERROR_BAD_RNG_SEED? */
               PORT_SetError(SEC_ERROR_INVALID_ARGS);
               rv = SECFailure;
               goto done;
           }

Key Zeroization

The NSS cryptographic module takes a number of explicit zeroization steps to clear the memory region previously occupied by a secret or private key or password. In summary, secret and private keys are always stored in encrypted form. Any key material that has been unwrapped (decrypted) for use is zeroized once the use is complete. The function used to zeroize memory used by private key material is the Standard C library function memset() or its synonym PORT_Memset():

 #define PORT_Memset     memset

If the memory used by private key material is allocated from the heap, the PORT_ZFree() function can be used to both zeroize and free memory:

 void
 PORT_ZFree(void *ptr, size_t len)
 {
     if (ptr) {
         memset(ptr, 0, len);
         PR_Free(ptr);
     }
 }

(PR_Free() calls the Standard C library function free() to free memory allocated from the heap.)

A plaintext secret or private key is zeroized when it is deleted.

All plaintext secret and private keys are zeroized when

• the NSS cryptographic module is shut down (with a FC_Finalize call),
• the NSS cryptographic module is reinitialized (with a FC_InitToken call), or
• the NSS cryptographic module switches between the FIPS and non-FIPS modes.

Passwords are automatically zeroized immediately after use.

The memset() function is extremely fast. Zeroization can be performed in a time that is not sufficient to compromise plaintext secret and private keys and passwords.