A ScriptSig, an input script unlocking funds committing transaction output.

ScriptSig contains one(1) or more signatures with other data needed to satisfy spending condition defined in the output.

See also: ScriptPubKey

To understand how transactions work on basic technical level, check blog post Types of Bitcoin transactions: Part I, Part 2.

More detailed description can be found in Bitcoin Wiki or in Bitcoin.org Developer guide, MyCryptoPedia ScriptSig.

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