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diff --git a/Documentation/s390/crypto/crypto-API.txt b/Documentation/s390/crypto/crypto-API.txt new file mode 100644 index 000000000000..78a77624a716 --- /dev/null +++ b/Documentation/s390/crypto/crypto-API.txt @@ -0,0 +1,83 @@ +crypto-API support for z990 Message Security Assist (MSA) instructions +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +AUTHOR: Thomas Spatzier (tspat@de.ibm.com) + + +1. Introduction crypto-API +~~~~~~~~~~~~~~~~~~~~~~~~~~ +See Documentation/crypto/api-intro.txt for an introduction/description of the +kernel crypto API. +According to api-intro.txt support for z990 crypto instructions has been added +in the algorithm api layer of the crypto API. Several files containing z990 +optimized implementations of crypto algorithms are placed in the +arch/s390/crypto directory. + + +2. Probing for availability of MSA +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It should be possible to use Kernels with the z990 crypto implementations both +on machines with MSA available an on those without MSA (pre z990 or z990 +without MSA). Therefore a simple probing mechanisms has been implemented: +In the init function of each crypto module the availability of MSA and of the +respective crypto algorithm in particular will be tested. If the algorithm is +available the module will load and register its algorithm with the crypto API. + +If the respective crypto algorithm is not available, the init function will +return -ENOSYS. In that case a fallback to the standard software implementation +of the crypto algorithm must be taken ( -> the standard crypto modules are +also build when compiling the kernel). + + +3. Ensuring z990 crypto module preference +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If z990 crypto instructions are available the optimized modules should be +preferred instead of standard modules. + +3.1. compiled-in modules +~~~~~~~~~~~~~~~~~~~~~~~~ +For compiled-in modules it has to be ensured that the z990 modules are linked +before the standard crypto modules. Then, on system startup the init functions +of z990 crypto modules will be called first and query for availability of z990 +crypto instructions. If instruction is available, the z990 module will register +its crypto algorithm implementation -> the load of the standard module will fail +since the algorithm is already registered. +If z990 crypto instruction is not available the load of the z990 module will +fail -> the standard module will load and register its algorithm. + +3.2. dynamic modules +~~~~~~~~~~~~~~~~~~~~ +A system administrator has to take care of giving preference to z990 crypto +modules. If MSA is available appropriate lines have to be added to +/etc/modprobe.conf. + +Example: z990 crypto instruction for SHA1 algorithm is available + + add the following line to /etc/modprobe.conf (assuming the + z990 crypto modules for SHA1 is called sha1_z990): + + alias sha1 sha1_z990 + + -> when the sha1 algorithm is requested through the crypto API + (which has a module autoloader) the z990 module will be loaded. + +TBD: a userspace module probin mechanism + something like 'probe sha1 sha1_z990 sha1' in modprobe.conf + -> try module sha1_z990, if it fails to load load standard module sha1 + the 'probe' statement is currently not supported in modprobe.conf + + +4. Currently implemented z990 crypto algorithms +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The following crypto algorithms with z990 MSA support are currently implemented. +The name of each algorithm under which it is registered in crypto API and the +name of the respective module is given in square brackets. + +- SHA1 Digest Algorithm [sha1 -> sha1_z990] +- DES Encrypt/Decrypt Algorithm (64bit key) [des -> des_z990] +- Tripple DES Encrypt/Decrypt Algorithm (128bit key) [des3_ede128 -> des_z990] +- Tripple DES Encrypt/Decrypt Algorithm (192bit key) [des3_ede -> des_z990] + +In order to load, for example, the sha1_z990 module when the sha1 algorithm is +requested (see 3.2.) add 'alias sha1 sha1_z990' to /etc/modprobe.conf. + |