Traditional cryptography methods
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Symmetric Encryption
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Known as secret key encryption, hold a common key, and use the same cryptographic algorithm to encrypt and decrypt the transmission message or data.
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Ciphertext stream is usually a complex combination of blocks of the plaintext, the secret common key, and the encrypted text.
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The assumption is that hackers or whoever is interested in the data have zero knowledge of the common key, otherwise, anyone who holds the secret key can read the message or data.
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Public-key Encryption
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Known as asymmetric encryption, it uses two types of keys, a public key known by everyone and a private key known by only the sender and the receiver.
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To encrypt a message from sender S to receive R, both S and R have to create their own key pairs and exchange the public key, when S sends a message M to R, A uses R's public key to encrypt M. R and the only R has the private key to encrypt the message M or data, as long as the private key is not compromised, the message M is secured.
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It ensures data confidentiality.
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This key architecture also ensures data integrity.
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Hash Function
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A mathematical function that takes an input message M with a given length and creates a unique fixed-length output code usually is a 128-bit or 160-bit stream, referred to as a hash.
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A one-way hash function creates a signature or fingerprint-like message.
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This hash function compresses the message to a fixed-length hash value.
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The function ensures that different messages have a different hash.
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Digital Signatures
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In addition to the private key of the sender, it appends a document to authenticate the message, as the written signature appended on the document.
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More like a combination of public-key encryption and hash function.
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Use a hash function to generate a message authentication code (MAC).
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Encrypt the MAC with public-key, private key encryption, attach the encrypted MAC as a message digital signature.
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