encrypted value storage

I have a varchar column that I would like to encrypt and store within
the same column. Encryption functions return binary. I would change
the column datatype , but certain parties will not change the datatype
to varbinary. I can store the value after explicitly converting the
binary to varchar...[ convert(varchar(), EncryptByKey(...)) ]. It
seems to work. Will this break one day? The data is normally
accessed through an abstracting UDF. Will this scheme survive?

Thanks,
Bill
.