Digital Signature

I. Overview link

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flowchart LR
    A["Electronic\ndocument"] -- "Signed with sender's private key" --> B["Integrity and\nnon-repudiation secured"]
    style A fill:#f9f9f9,stroke:#333,stroke-width:3px
    style B fill:#e1f5fe,stroke:#01579b,stroke-width:3px

Definition: A technique in which the sender encrypts the hash value of an electronic document with their own private key and attaches it to the document, serving as an electronic equivalent of a personal seal.

Core Value:
( Integrity ) Proves that data has not been forged or altered in transit
( Authentication ) Confirms and guarantees the signer’s identity
( Non-repudiation ) Provides legal and technical evidence so the signer cannot later deny having signed

II. Mechanism & Components link

A. Digital Signature Generation and Verification Process link

sequenceDiagram
    participant Sender as "Sender"
    participant Receiver as "Receiver"

    Note over Sender: "1. Generate message hash (Hash A)"
    Note over Sender: "2. Encrypt hash with sender's private key (digital signature)"
    Sender->>Receiver: "Send original message + digital signature"
    Note over Receiver: "3. Decrypt signature with sender's public key (recover Hash A)"
    Note over Receiver: "4. Hash the original message directly (produce Hash B)"
    Note over Receiver: "5. Compare Hash A and Hash B to verify"

Detailed steps:

• Generate signature: The original message is reduced via a hash function, then encrypted with the sender’s private key to produce the signature
• Transmit: The original message and the digital signature are sent to the recipient together
• Verify signature: The recipient decrypts the signature with the sender’s public key to obtain hash value A, and independently hashes the original message to obtain hash value B
• Compare: If hash values A and B match, the signature is valid and the document has not been tampered with

B. Five Core Security Functions of a Digital Signature link

III. Advanced Topics & Comparison link