Public-key cryptography

Public-Key Cryptography Basics

– Unpredictable number used to generate key pair
– Anyone can encrypt messages with public key
– Only holder of private key can decrypt messages
– Security depends on secrecy of private key
– Diffie-Hellman key exchange allows shared secret computation

Public-Key Encryption

– Anyone with public key can encrypt message
– Only those with private key can decrypt ciphertext
– Journalist can publish public key for secret messages
– Public-key encryption does not conceal metadata
– Conceals content of message in ciphertext

Digital Signatures

– Sender uses private key to create a signature
– Anyone with corresponding public key can verify signature
– Software publisher can distribute updates with private key
– Computers can confirm genuine updates with public key
– Private key must be kept secret to maintain security

Applications of Public-Key Cryptography

– Public key encryption provides confidentiality
– Digital signatures ensure sender authentication
– Non-repudiation systems use digital signatures
– Further applications include digital cash and time-stamping services
– Public key cryptography underpins Internet standards

Hybrid Cryptosystems

– Asymmetric key algorithms are computationally intensive
– Hybrid cryptosystems combine symmetric and asymmetric encryption
– Asymmetric encryption used to securely exchange secret key
– Secret key then used for faster symmetric encryption
– Commonly used in modern cryptosystems like TLS and SSHSources: