Hashing functions include one-way hash generation and modification detection code (MDC) processing.

One-Way Hash Generate Callable Service (CSNBOWH or CSNBOWH1 and CSNEOWH or CSNEOWH1)

This service hashes a supplied message. Supported hashing methods include:

• SHA-1¹
• SHA-224
• SHA-256
• RIPEMD-160
• MD5

MDC Generation Callable Service (CSNBMDG or CSNBMDG1 and CSNEMDG or CSNEMDG1)

The modification detection code (MDC) provides a form of support for data integrity. The MDC allows you to verify that data was not altered during transmission or while in storage. The originator of the data ensures that the MDC is transmitted with integrity to the intended receiver of the data. For instance, the MDC could be published in a reliable source of public information. When the receiver gets the data, an application program can generate an MDC, and compare it with the original MDC value. If the MDC values are equal, the data is accepted as unaltered. If the MDC values differ the data is assumed to be bogus.

Supported hashing methods through the MDC generation callable service are:

• MDC-2
• MDC-4
• PADMDC-2
• PADMDC-4

In a similar manner, MDCs can be used to ensure the integrity of data stored on the system or on removable media, such as tape.

When data is sent, an application program can generate a modification detection code for it using the MDC generation callable service. The callable service computes the modification detection code by encrypting the data using a publicly-known cryptographic one-way function. The MDC is a 128-bit value that is easy to compute for specific data, yet it is hard to find data that will result in a given MDC.

Once an MDC has been established for a file, the MDC generate service can be run at any other time on the file. The resulting MDC can then be compared with the previously established MDC to detect deliberate or inadvertent modification.