up:: [[Cryptology]] # Digital Signatures Digital signatures are a cryptographic mechanism used to verify the authenticity and integrity of digital messages or documents. A digital signature confirms that a document or message was sent by the verified sender and has not been altered in transit. ## How It Works Digital signatures utilize [[Asymmetric Encryption|asymmetric cryptography]]. The process involves: 1. **Creating a Hash of the Message:** The original message is hashed using a [[Hash Function|cryptographic hash function]], producing a fixed-size string of bytes. 2. **Signing the Hash:** The hash is encrypted with the sender's [[private key]]. This encrypted hash, along with the hashing algorithm, constitutes the digital signature. 3. **Verification:** The recipient decrypts the signature using the sender’s [[public key]], which should reveal the original hash if unchanged. The recipient then hashes the received message using the same [[hash function]] and compares this hash to the decrypted hash. If they match, it confirms both the integrity and authenticity of the message. ## Key Features - **Authenticity:** Ensures that the message or document comes from the declared source. - **Integrity:** Verifies that the content has not been changed since it was signed. - **Non-repudiation:** Prevents the sender from denying the authorship or sending of the message. ## Problem Addressed Digital signatures address the challenge of tampering and impersonation in digital communications, ensuring that the contents of a message or document can be trusted and are legally binding. ## Implications The use of digital signatures is crucial for electronic documents and transactions that require high levels of trust and security, such as legal contracts, financial transactions, and software distribution. ## Impact Digital signatures significantly enhance the security of electronic transactions by providing a reliable method of confirming the legitimacy of digital communications. They are essential for electronic commerce and the legal validity of digital documents. ## Defense Mechanisms - **Certificate Authorities (CA):** A trusted third party that issues digital certificates used to create digital signatures, which contain the [[public key]] and the identity of the holder. - **Timestamping:** Ensures that digital signatures are valid even if the signing key is compromised or expired after the time of signing. ## Exploitable Mechanisms/Weaknesses Digital signatures are generally secure, but their strength depends on the underlying [[encryption]] algorithm and key size. Weak or compromised private keys, poor implementation, and insecure certificate authorities can undermine the security of digital signatures. ## Common Tools/Software - **Adobe Sign:** Allows users to securely sign and manage documents electronically. - **DocuSign:** A platform that provides electronic signature technology and digital transaction management. - **Microsoft Envelope:** Integrates digital signatures into Microsoft Office documents. ## Related Cybersecurity Policies - **eIDAS Regulation (EU):** Establishes standards for electronic identification and trust services for electronic transactions in the European Union, including digital signatures. - **Electronic Signatures in Global and National Commerce Act (ESIGN, U.S.):** Provides legal recognition of electronic signatures in interstate and international commerce. - **NIST Special Publications:** Provide guidelines for implementing digital signature algorithms, such as [[NIST Special Publication 800-63|NIST SP 800-63]]. ## Best Practices - Use strong, up-to-date cryptographic algorithms and sufficiently long keys. - Secure the [[private key]] using hardware security modules (HSMs) or other secure storage mechanisms. - Ensure certificates are obtained from a reputable certificate authority. - Regularly update and review the security policies related to digital signatures and their management. ## Current Status Digital signatures continue to evolve with advances in [[cryptography]] and security practices. The development of [[Post-Quantum Cryptography (PQC)]] aims to prepare digital signature algorithms for the era of [[quantum computing]]. ## Revision History - **2024-04-14:** Entry created.