When A sends a signed transaction to B, is the data operation visible in the transaction ? Are the details of the transaction visible to B ? We are planning to put some key value pairs in the transaction , and we don't want B to be able to see that data, but B can submit that transaction for execution.
All transaction details are always visible to anyone. It's one of the pillars of public blockchains.
Besides that, a transaction can hold only a relatively small amount of additional data (see memo field), so it won't be enough for you. However, you can store the data on your server, hash it and attach the hash value to a transaction as
You might want to use IPFS to extend the case further and make the data storage fully decentralized.