Defining Keys in Parmlib › Keys for Business Partners › How Business Partners Read Files Encrypted by Code Books › How the MDU Decrypts a B2B Tape

How the MDU Decrypts a B2B Tape

The MDU decrypts a B2B tape as outlined by the following points:

• The MDU accesses the z/OS standard labels file that was unloaded and extracts the following:
  • Information that identifies the code book
  • Information about how to rebuild the required symmetric key using the code book.
• The MDU selects the needed code book from books that have been stored on the local system by the import process.
• The MDU decrypts a special signature in the code book, using the passkey provided by the business partner who sent the tape. This verifies that the correct passkey has been supplied. If the signature is not verified, the passkey is not the correct key and the decryption process terminates with an error.
• The MDU decrypts the contents of the code book, using the passkey. Then it uses information in the z/OS standard header file to rebuild the symmetric key from the contents of the code book.
• The MDU uses the symmetric key to decrypt the encrypted data file on the local file system to create a plain-text copy of the file.