# Properties of Digital Signatures

In addition to the two properties of **conventional signatures** (identity linkage and uniqueness), digital signatures provide several **extra properties** that make them more secure and reliable.

***

### Integrity

A **digital signature** is directly tied to the **message content (x)**.

* If the message changes, the signature (**y**) also changes.
* Verification will then return **false**, making tampering easy to detect.
* By contrast, physical signatures can remain intact even if the document text is altered. 

 

<figure><img src="/files/WnyCRkiAHfUnnnDPhqrQ" alt=""><figcaption></figcaption></figure>

### Message Authentication

Because only **Alice** knows her **private key (k**<sub>**pr**</sub>**)**:

* The digital signature proves the message really came from Alice.
* This ensures the **authenticity of the sender**.
* Bob (or any receiver) can trust that the message was created by the claimed source.

***

### Sender Non-Repudiation

Since **k**<sub>**pr**</sub> is known only to Alice:

* She cannot later deny that she signed the message.
* This prevents dishonest senders from **repudiating** (denying) their actions.
* In case of disputes, a **neutral third party (e.g., a court)** can use the link between Alice and her private key as evidence.

***

### Key Takeaway

Digital signatures offer **integrity, authentication, and non-repudiation** — properties that go beyond conventional paper signatures. These guarantees make digital communication more secure, reliable, and legally enforceable.


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