FIPS Mode (The Libgcrypt Reference Manual)

Appendix B Description of the FIPS Mode

This appendix gives detailed information pertaining to the FIPS mode. In particular, the changes to the standard mode and the finite state machine are described. The self-tests required in this mode are described in the appendix on self-tests.

Restrictions in FIPS Mode
FIPS Finite State Machine
FIPS Miscellaneous Information

B.1 Restrictions in FIPS Mode

If Libgcrypt is used in FIPS mode, these restrictions are effective:

The cryptographic algorithms are restricted to this list:

GCRY_CIPHER_AES128

AES 128 bit symmetric encryption.

GCRY_CIPHER_AES192

AES 192 bit symmetric encryption.

GCRY_CIPHER_AES256

AES 256 bit symmetric encryption.

GCRY_MD_SHA1

SHA-1 message digest.

GCRY_MD_SHA224

SHA-224 message digest.

GCRY_MD_SHA256

SHA-256 message digest.

GCRY_MD_SHA384

SHA-384 message digest.

GCRY_MD_SHA512

SHA-512 message digest.

GCRY_MD_SHA3_224

SHA3-224 message digest.

GCRY_MD_SHA3_256

SHA3-256 message digest.

GCRY_MD_SHA3_384

SHA3-384 message digest.

GCRY_MD_SHA3_512

SHA3-512 message digest.

GCRY_MD_SHA1,GCRY_MD_FLAG_HMAC

HMAC using a SHA-1 message digest.

GCRY_MD_SHA224,GCRY_MD_FLAG_HMAC

HMAC using a SHA-224 message digest.

GCRY_MD_SHA256,GCRY_MD_FLAG_HMAC

HMAC using a SHA-256 message digest.

GCRY_MD_SHA384,GCRY_MD_FLAG_HMAC

HMAC using a SHA-384 message digest.

GCRY_MD_SHA512,GCRY_MD_FLAG_HMAC

HMAC using a SHA-512 message digest.

GCRY_MD_SHA3_224,GCRY_MD_FLAG_HMAC

HMAC using a SHA3-224 message digest.

GCRY_MD_SHA3_256,GCRY_MD_FLAG_HMAC

HMAC using a SHA3-256 message digest.

GCRY_MD_SHA3_384,GCRY_MD_FLAG_HMAC

HMAC using a SHA3-384 message digest.

GCRY_MD_SHA3_512,GCRY_MD_FLAG_HMAC

HMAC using a SHA3-512 message digest.

GCRY_MAC_CMAC_AES

CMAC using a AES key.

GCRY_PK_RSA

RSA encryption and signing.

GCRY_PK_ECC

ECC encryption and signing.

Note that the CRC algorithms are not considered cryptographic algorithms and thus are in addition available.
RSA key generation refuses to create and use a key with a keysize of less than 2048 bits.
The transient-key flag for RSA key generation is ignored.
Support for the VIA Padlock engine is disabled.
FIPS mode may only be used on systems with a /dev/random device or with a getentropy syscall. Switching into FIPS mode on other systems will fail at runtime.
Saving and loading a random seed file is ignored.
The DRBG style random number generator is used in place of the large-pool-CSPRNG generator.
The command GCRYCTL_ENABLE_QUICK_RANDOM is ignored.
Message digest debugging is disabled.
All debug output related to cryptographic data is suppressed.
On-the-fly self-tests are not performed, instead self-tests are run before entering operational state.
The function gcry_set_allocation_handler may not be used. In FIPS mode this function does not have any effect, because FIPS has requirements for memory zeroization.
The digest algorithm MD5 may not be used.
The signatures using SHA-1 digest algorithm may not be used.
In FIPS mode the command GCRYCTL_DISABLE_SECMEM is ignored.
A handler set by gcry_set_outofcore_handler is ignored.
A handler set by gcry_set_fatalerror_handler is ignored.

Note that when we speak about disabling FIPS mode, it merely means that the function gcry_fips_mode_active returns false; it does not mean that any non FIPS algorithms are allowed.

B.2 FIPS Finite State Machine

The FIPS mode of Libgcrypt implements a finite state machine (FSM) using 8 states (see Table B.1) and checks at runtime that only valid transitions (see Table B.2) may happen.

Figure B.1: FIPS mode state diagram

States used by the FIPS FSM:

Power-Off: Libgcrypt is not runtime linked to another application. This usually means that the library is not loaded into main memory. This state is documentation only.
Power-On: Libgcrypt is loaded into memory and API calls may be made. Compiler introduced constructor functions may be run. Note that Libgcrypt does not implement any arbitrary constructor functions to be called by the operating system
Init: The Libgcrypt initialization functions are performed and the library has not yet run any self-test.
Self-Test: Libgcrypt is performing self-tests.
Operational: Libgcrypt is in the operational state and all interfaces may be used.
Error: Libgrypt is in the error state. When calling any FIPS relevant interfaces they either return an error (GPG_ERR_NOT_OPERATIONAL) or put Libgcrypt into the Fatal-Error state and won’t return.
Fatal-Error: Libgcrypt is in a non-recoverable error state and will automatically transit into the Shutdown state.
Shutdown: Libgcrypt is about to be terminated and removed from the memory. The application may at this point still run cleanup handlers.

Table B.1: FIPS mode states

The valid state transitions (see Figure B.1) are:

1: Power-Off to Power-On is implicitly done by the OS loading Libgcrypt as a shared library and having it linked to an application.
2: Power-On to Init is triggered by the application calling the Libgcrypt initialization function gcry_check_version.
3: Init to Self-Test is either triggered by a dedicated API call or implicit by invoking a Libgrypt service controlled by the FSM.
4: Self-Test to Operational is triggered after all self-tests passed successfully.
5: Operational to Shutdown is an artificial state without any direct action in Libgcrypt. When reaching the Shutdown state the library is deinitialized and can’t return to any other state again.
6: Shutdown to Power-Off is the process of removing Libgcrypt from the computer’s memory. For obvious reasons the Power-Off state can’t be represented within Libgcrypt and thus this transition is for documentation only.
7: Operational to Error is triggered if Libgcrypt detected an application error which can’t be returned to the caller but still allows Libgcrypt to properly run. In the Error state all FIPS relevant interfaces return an error code.
8: Error to Shutdown is similar to the Operational to Shutdown transition (5).
9: Error to Fatal-Error is triggered if Libgrypt detects an fatal error while already being in Error state.
10: Fatal-Error to Shutdown is automatically entered by Libgcrypt after having reported the error.
11: Power-On to Shutdown is an artificial state to document that Libgcrypt has not yet been initialized but the process is about to terminate.
12: Power-On to Fatal-Error will be triggered if certain Libgcrypt functions are used without having reached the Init state.
13: Self-Test to Fatal-Error is triggered by severe errors in Libgcrypt while running self-tests.
14: Self-Test to Error is triggered by a failed self-test.
15: Operational to Fatal-Error is triggered if Libcrypt encountered a non-recoverable error.
16: Operational to Self-Test is triggered if the application requested to run the self-tests again.
17: Error to Self-Test is triggered if the application has requested to run self-tests to get back into operational state after an error.
18: Init to Error is triggered by errors in the initialization code.
19: Init to Fatal-Error is triggered by non-recoverable errors in the initialization code.
20: Error to Error is triggered by errors while already in the Error state.

Table B.2: FIPS mode state transitions

B.3 FIPS Miscellaneous Information

Libgcrypt does not do any key management on itself; the application needs to care about it. Keys which are passed to Libgcrypt should be allocated in secure memory as available with the functions gcry_malloc_secure and gcry_calloc_secure. By calling gcry_free on this memory, the memory and thus the keys are overwritten with zero bytes before releasing the memory.

For use with the random number generator, Libgcrypt generates 3 internal keys which are stored in the encryption contexts used by the RNG. These keys are stored in secure memory for the lifetime of the process. Application are required to use GCRYCTL_TERM_SECMEM before process termination. This will zero out the entire secure memory and thus also the encryption contexts with these keys.