OpenPseudonymiser is a free, open source, standalone Windows application.
OpenPseudonymiser checks the validity of the NHS Number within a Comma Separated Variable (CSV) file, adds extra data to the NHS Number using an encrypted set of characters, known as a salt, followed by cryptographic hash functions using the internationally recognised Secure Hash Algorithm 2 (SHA-256) to produce a string of output characters, known as the digest.
It is the digest that will be used as the case identifier within REDCap. To learn how to use OpenPseudonymiser here:
Link to resource
Further details can be found in the OpenPseudonymiser Desktop User Guide and instructional video at https://www.openpseudonymiser.org/OpenPseudonymiser_Docs.aspx