Question about Blind Signature

Hi! I have some stupid question about how to implement blind signature. I Know it works as follows: If A wants B to sign X but donot know it is X, A can send X*PK(random) : PK is public key of B Then B signs on message: SK(X*PK(random)) ==> SK(X)*random Then A can obtain SK(X) by SK(X)*random/random My question is when I see how RSA encrypts using PKCS The PKCS block is like this 00 01 FF FF FF FF ... 00 input Then SK(00 01 FF FF FF .. 00 input) . If the input = X*PK(random) then SK(00 01 FF FF FF .. 00 X*PK(random)) will not produce SK(X)*random How to solve this?? Thanks!!