Learn in the textbookApplying Encryption and Digital Signatures
DefinitionA digital signature (デジタル署名) is a signature made with a private key (秘密鍵) that only the sender holds and attached to electronic data, so the receiver can confirm who created it and whether it was altered.
ExplanationThe hash value (ハッシュ値) used in the comparison is always the same for the same data, and the original data cannot be worked out from it. Because the hash value is computed from the whole data rather than part of it, rewriting any part makes the values disagree.
AnalogyIt is like sealing a summary of a document with a stamp only you own. The imprint shows whose seal it is, and if the summary no longer matches the document, the rewrite is exposed.