How does signrawtransaction know which private key to use?

[ned.ryerson]

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?

[piotr_n]

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.

[ned.ryerson]

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?

[gmaxwell]

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.