To calculate an MDC in one call, specify the ONLY keyword for segmenting control in the rule_array parameter. For more than one call, specify the FIRST keyword for the first input block, the MIDDLE keyword for any intermediate blocks, and the LAST keyword for the last block. For a given text string, the resulting MDC is the same whether the text is segmented or not.

The two versions of MDC calculation (with two or four encipherments per 8 bytes of input text) allow the caller to trade a performance improvement for a decrease in security. Since 2 encipherments create results different from the results of 4 encipherments, ensure that you use the same number of encipherments to verify the MDC value.

The following table lists the required cryptographic hardware for each server type and describes restrictions for this callable service.

Table 154. MDC generate required hardware

Server	Required cryptographic hardware	Restrictions
IBM zSeries 900	Cryptographic Coprocessor Feature
IBM zSeries 990 IBM zSeries 890	CP Assist for Cryptographic Functions
IBM System z9 EC IBM System z9 BC	CP Assist for Cryptographic Functions