What does a valid digital signature prove in Bitcoin?
Correct answer
Answer C: That the spending was authorized with the appropriate key.
Quick explanation
The signature shows that the spending was authorized without revealing the private key. The network can verify the signature without needing to know that secret.
Detailed explanation
A Bitcoin output specifies the conditions under which it may later be spent. For many common output types, these include a cryptographic signature. The wallet creates the signature with a private key over specified parts of the new transaction. Full nodes then use the corresponding public key and script rules to check whether the signature is valid.
This check does not establish a person's legal identity. Nor does it show that the signer is the owner according to a government register. Technically, it proves that someone could use the secret key information matching the spending condition and that the signed transaction data were not changed undetected.
The private key never needs to be sent to the network for this. Only the signature and, where needed, the public key or other required proof data are published. Bitcoin uses different signature methods and script rules depending on output type, including ECDSA and Schnorr signatures for Taproot. For beginners, the central point is independent of the method: the secret key authorizes, public verification checks, and the secret key stays secret.
Key takeaway
Signatures authorize spending without revealing the private key.
Common misconception
Beginners often confuse digital signatures with signing a name or believe the private key is sent along. Neither is true.
What the sources support
NIST describes digital signatures generally as mechanisms for detecting unauthorized modification and authenticating a signatory. In Bitcoin, a signature is used specifically to authorize spending with the appropriate key; it does not automatically prove a person’s real-world identity.