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Cyber Security Academy · Lesson

Digital Signatures and Certificates

Understand how digital signatures prove authenticity and how X.509 certificates bind identity to keys.

What are Digital Signatures?

A digital signature proves that a document or message was created by a specific private key holder and has not been modified. Unlike a handwritten signature, it is mathematically bound to the content — any change invalidates the signature.

How Signing Works

Signing process:

  1. Hash the document: H = SHA256(document)
  2. Encrypt the hash with the private key: sig = RSA_encrypt(H, private_key)
  3. Attach the signature to the document

Verification: decrypt sig with public key, recompute hash, compare.

All lessons in this course

  1. Symmetric Encryption: AES and Stream Ciphers
  2. Asymmetric Encryption: RSA and Elliptic Curves
  3. Hash Functions: SHA-256 and Beyond
  4. Digital Signatures and Certificates
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