How SegWit Fixed Bitcoin's Transaction Malleability Problem and Boosted Capacity

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Bitcoin transactions historically included a scriptSig field containing the digital signature, which accounted for roughly 60% of total blockchain size. This signature data could be subtly altered by malicious actors to produce a different transaction ID while keeping the signature technically valid, a flaw known as the transaction malleability problem. The vulnerability caused issues when confirmed transaction IDs differed from their originals, and it also hindered the Lightning Network, which relies on spending unconfirmed transactions. Segregated Witness, or SegWit, addressed this by moving signature data into a separate witness field that is excluded from transaction ID calculation, making IDs tamper-resistant. This architectural change simultaneously reduced effective transaction size, increasing Bitcoin's throughput capacity without a direct block size increase.

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