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1crypto-API support for z990 Message Security Assist (MSA) instructions
2~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3
4AUTHOR: Thomas Spatzier (tspat@de.ibm.com)
5
6
71. Introduction crypto-API
8~~~~~~~~~~~~~~~~~~~~~~~~~~
9See Documentation/crypto/api-intro.txt for an introduction/description of the
10kernel crypto API.
11According to api-intro.txt support for z990 crypto instructions has been added
12in the algorithm api layer of the crypto API. Several files containing z990
13optimized implementations of crypto algorithms are placed in the
14arch/s390/crypto directory.
15
16
172. Probing for availability of MSA
18~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
19It should be possible to use Kernels with the z990 crypto implementations both
20on machines with MSA available an on those without MSA (pre z990 or z990
21without MSA). Therefore a simple probing mechanisms has been implemented:
22In the init function of each crypto module the availability of MSA and of the
23respective crypto algorithm in particular will be tested. If the algorithm is
24available the module will load and register its algorithm with the crypto API.
25
26If the respective crypto algorithm is not available, the init function will
27return -ENOSYS. In that case a fallback to the standard software implementation
28of the crypto algorithm must be taken ( -> the standard crypto modules are
29also build when compiling the kernel).
30
31
323. Ensuring z990 crypto module preference
33~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
34If z990 crypto instructions are available the optimized modules should be
35preferred instead of standard modules.
36
373.1. compiled-in modules
38~~~~~~~~~~~~~~~~~~~~~~~~
39For compiled-in modules it has to be ensured that the z990 modules are linked
40before the standard crypto modules. Then, on system startup the init functions
41of z990 crypto modules will be called first and query for availability of z990
42crypto instructions. If instruction is available, the z990 module will register
43its crypto algorithm implementation -> the load of the standard module will fail
44since the algorithm is already registered.
45If z990 crypto instruction is not available the load of the z990 module will
46fail -> the standard module will load and register its algorithm.
47
483.2. dynamic modules
49~~~~~~~~~~~~~~~~~~~~
50A system administrator has to take care of giving preference to z990 crypto
51modules. If MSA is available appropriate lines have to be added to
52/etc/modprobe.conf.
53
54Example: z990 crypto instruction for SHA1 algorithm is available
55
56 add the following line to /etc/modprobe.conf (assuming the
57 z990 crypto modules for SHA1 is called sha1_z990):
58
59 alias sha1 sha1_z990
60
61 -> when the sha1 algorithm is requested through the crypto API
62 (which has a module autoloader) the z990 module will be loaded.
63
64TBD: a userspace module probin mechanism
65 something like 'probe sha1 sha1_z990 sha1' in modprobe.conf
66 -> try module sha1_z990, if it fails to load load standard module sha1
67 the 'probe' statement is currently not supported in modprobe.conf
68
69
704. Currently implemented z990 crypto algorithms
71~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
72The following crypto algorithms with z990 MSA support are currently implemented.
73The name of each algorithm under which it is registered in crypto API and the
74name of the respective module is given in square brackets.
75
76- SHA1 Digest Algorithm [sha1 -> sha1_z990]
77- DES Encrypt/Decrypt Algorithm (64bit key) [des -> des_z990]
78- Tripple DES Encrypt/Decrypt Algorithm (128bit key) [des3_ede128 -> des_z990]
79- Tripple DES Encrypt/Decrypt Algorithm (192bit key) [des3_ede -> des_z990]
80
81In order to load, for example, the sha1_z990 module when the sha1 algorithm is
82requested (see 3.2.) add 'alias sha1 sha1_z990' to /etc/modprobe.conf.
83