Nxt transaction has the following format:
64 bytes of the header
64 bytes of the signature
X bytes of the attachment
Before signing it looks:
64 bytes of the header
64 zeros
X bytes of the attachment
All [64+64+X] bytes r signed and the signature is placed instead of the zeros.
PS: Ordinary payment is the only transaction that doesn't have an attachment.
Then unless the signature can have more than one equivalent representation I don't see why we actually *have* a malleability problem?
Care to enlighten me?
Sorry, was somehow confused by thinking of blocks.