But if you're offline (and no blockchain access), how can it get the UTXO?
It can't in that case, thats why it has an optional scriptpubkey argument. 
Topic: How does signrawtransaction know which private key to use? (Read 633 times)
hash and vout index refer to a UTXO record containing a spend script. the spend script refers to a public address, upon which a private key can be matched.
But if you're offline (and no blockchain access), how can it get the UTXO? 
hash and vout index refer to a UTXO record containing a spend script. the spend script refers to a public address, upon which a private key can be matched.
It only has a previous output (hash and vout index) but nothing to tell it which address that output was for, so how can it choose the correct private key to sign the transaction?
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