With the latest runtime libraries on macOS 15.3.1 it seems to work, the crash cannot be reproduced anymore, using the same test code as about one year ago.

I was using the SecTransforms created by SecEncryptTransformCreate and SecDecryptTransformCreate, just for encryption and decryption of certain binary data with a symmetric cipher. Judging from the documentation I found CryptoKit should be powerful enough to do the same. Thanks, Jakob