we're using XOR method on ring oram

store block on server as EncBlock || Sign_client(EncBlock)
store buckets on server with a bucket merkle tree

verification tree is augmented with bucket hashes, as before

we also have freshness tree

to ReadPath:
   client sends server a requested path with offsets
   server sends client all the requested blocks along path XORd together = PathXORBlock || PathXORSignature
   client reconstructs dummy encryptions and signatures
   client XORs away on PathXORBlock and PathXORSignature to retrieve real block and signature

   client verifies signature on block
   client verifies freshness of block
      if either fail, call CheckBucket on every bucket in path

   security note:
      if server changes any bit along the path, it'll sign wrong
         assumes signatures are guaranteed to not be homomorphic; ie, Sign(a) + Sign(b) !!= Sign(a + b)



to ReadBucket:
   client gets the bucket, verifies the signatures in the bucket
      if signatures are bad, call CheckBucket
      if freshnesses are bad, call CheckBucket
      if signatures are good, server gives merkle proof up to verification tree root


to WriteBucket:
   client writes bucket, gets signature from server of the root of the bucket tree
   updates freshness tree