Modification Detection Code (MDC)

Files encrypted by PGP or GPG include a Modification Detection Code (MDC) that confirms the integrity of the file.

In current versions of PGP and GPG (version 7 onwards), the MDC is included by default. Older versions (version 6 and earlier) did not include the MDC by default, but allowed it to be optionally added.

When you receive a PGP or GPG encrypted file that does not include the MDC, the logs and site alert emails show the following error message:

File is gpg encrypted but is missing modification detection code (MDC): path/to/folder/encrypted_file.txt.pgp

This error means that the integrity of the file cannot be confirmed. That is a cause for concern when data security matters to you.

To accept GPG files whose integrity cannot be checked, enable the Ignore MDC integrity check option for file decryption to bypass this check.

You can also contact your counterparty and ask them to include the MDC when encrypting files. If your counterparty is using GPG to encrypt the file, ask them to use version 7 or later, which includes the MDC by default, or to use the --force-mdc flag with older GPG versions to enforce inclusion of the MDC.