Understanding Digital Signatures

Digital signatures ensure data integrity, authenticity, and non-repudiation. They use asymmetric cryptography, where the private key creates the signature, and the corresponding public key validates it. Surprisingly, they can be more secure than handwritten signatures.

When you 'sign' a document digitally, a mathematical algorithm generates a unique hash of the data. The private key encrypts this hash, creating the signature. The process is complex, ensuring high security.

Digital certificates bind a public key to an entity's identity. Certificate authorities (CAs) issue certificates after verifying the entity's identity, akin to a digital passport. The X.509 standard governs their structure, which isn't widely known.

When you visit a secure website, its digital certificate helps establish a secure session. The browser checks the certificate's validity with the issuing CA. This happens seamlessly, often without your direct awareness.

Certificates can be revoked or expire, just like passports. CAs maintain revocation lists, and browsers check these to ensure a certificate is still trustworthy. Notably, certificate expiry played a role in the 2020 Kazakhstan internet outage.

Several algorithms exist for digital signatures, including RSA, DSA, and ECDSA. ECDSA, based on elliptic curve cryptography, is gaining popularity for its strong security with shorter key lengths, which was once a debate in the cryptographic community.

Quantum computing poses a future threat to digital signatures, potentially breaking current cryptographic methods. Post-quantum cryptography is in development to counter this, with new algorithms already being tested in the field.