More on Bitcoin Transactions

To understand why digital signatures are integral to Bitcoin transactions, you'll need to learn a bit about the structure of Bitcoin transactions. This chapter will introduce you to what's happening "Behind the Scenes" in these transactions. We'll discuss this more in Unit 5.

Transactions in Detail

Transactions – Behind the Scenes

Behind the scenes, an actual transaction looks very different from a transaction provided by a typical block explorer. In fact, most of the high-level constructs we see in the various bitcoin application user interfaces do not actually exist in the bitcoin system.

We can use Bitcoin Core's command-line interface (getrawtransaction and decoderawtransaction) to retrieve Alice's "raw" transaction, decode it, and see what it contains. The result looks like this:

Alice's transaction decoded:

  "version": 1,
  "locktime": 0,
  "vin": [
      "txid": "7957a35fe64f80d234d76d83a2a8f1a0d8149a41d81de548f0a65a8a999f6f18",
      "vout": 0,
      "scriptSig" : "3045022100884d142d86652a3f47ba4746ec719bbfbd040a570b
      "sequence": 4294967295
  "vout": [
      "value": 0.01500000,
      "scriptPubKey": "OP_DUP OP_HASH160 
      ab68025513c3dbd2f7b92a94e0581f5d50f654e7 OP_EQUALVERIFY OP_CHECKSIG"
      "value": 0.08450000,
      "scriptPubKey": "OP_DUP OP_HASH160 
      7f9b1a7fb68d60c536c2fd8aeaa53a8f3cc025a8 OP_EQUALVERIFY OP_CHECKSIG",


You may notice a few things about this transaction, mostly the things that are missing! Where is Alice's address? Where is Bob's address? Where is the 0.1 input "sent" by Alice? In bitcoin, there are no coins, no senders, no recipients, no balances, no accounts, and no addresses. All those things are constructed at a higher level for the benefit of the user, to make things easier to understand.

You may also notice a lot of strange and indecipherable fields and hexadecimal strings. Don't worry, we will explain each field shown here in detail in this chapter.