there is no "Char" use, but there is a function called "FillChar" that may be causing problems. I don't know how to replace and Embarcadero tips don't work.
I'm currently reviewing for the 100th time all the code and found out that the Decrypt routine does not use FillChar, so it should be safe. The problems may arise in the Initialisation of the Key or in the Creation of the Cipher (Cipher:= TDCP_rc6.Create(nil); Cipher.InitStr(KeyStr,TDCP_sha1)
so I'm investigating this way...
UPDATE1: Cipher:= TDCP_rc6.Create(nil); does nothing else than filling KeyData (which is an array of DWord) with $FF and IV and CV (which are array of byte) again with $FF. So unless there is something else wrong, it shouldn't be the culprit...